Mobility of boron from coal ash in an aqueous system
by Anne Shirley Halligan
A thesis submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE
in Chemistry
Montana State University
© Copyright by Anne Shirley Halligan (1980)
Abstract:
An investigation of boron Teachability and adsorption by coal ash under a variety of conditions was
undertaken. Boron leachability was studied as a function of pH, time, ash type, particle size, and ash
concentration. Total available boron, aluminum, and iron were determined. Ash retention of boron was
calculated. The adsorption of boron by ash that was water conditioned and ash that was acid
conditioned was studied. A releaching of adsorption samples was pursued to determine changes in the
ash after adsorption had taken place. STATEMENT OF PERMISSION TO COPY
In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l l m e n t
o f t h e r e q u i r e m e n t s f o r an advanced degree a t Montana S t a t e
U n i v e r s i t y , I a gre e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l ­
able fo r in sp ectio n .
I f u r t h e r a g re e t h a t pe rm is si on f o r e x t e n s i v e
copying o f t h i s t h e s i s f o r s c h o l a r l y purposes may be g r a n t e d
/
by my major p r o f e s s o r , o r , in h i s a b s e n c e , by t h e D i r e c t o r o f
L ibraries.
I t i s u n de rs to od t h a t any copying o r p u b l i c a t i o n o f
t h i s t h e s i s f o r f i n a n c i a l gain s h a l l n o t be allowed w i t h o u t
my w r i t t e n p e r m i s s i o n .
Signature
M o b i l i t y o f Boron from Coal Ash i n an Aqueous System
by
rTtane S h i r l e y H a ll ig a n
A t h e s i s s u b m it te d in p a r t i a l f u l f i l l m e n t
o f t h e r e q u ir e m e n ts f o r t h e degree
of
MASTER OF SCIENCE
'
in
Chemistry
MONTANA STATE UNIVERSITY
Bozeman, Montana
J u l y , 1980
ACKNOWLEDGEMENT
Anne e x p r e s s e s a deep a p p r e c i a t i o n and thanks t o h e r a d v i s o r ,
Gordon K. Pagenkopf f o r h i s a d v ic e and a s s i s t a n c e which l e d t o t h e
achievement o f t h i s degre e and t h e s i s .
Thanks a l s o t o a l l th o s e
o t h e r s who r o u t i n e l y p a r t i c i p a t e d in d i s c u s s i o n s and s u p p o r t o f
t h i s work.
And a s p e c i a l tha nks t o George H. Thompson f o r t h e
s u p p o r t and u n d e r s t a n d i n g he i n v e s t e d th r o u g h o u t t h e work o f
th is project.
And o f c o u r s e , a g r a t e f u l th a nk s t o t h e p a t i e n t
t y p i s t o f t h i s t h e s i s , Peggie R il e y .
iv
TABLE OF CONTENTS
Page
LIST OF TABLES........................................................................................ ..
v
LIST OF FIGURES ................................................. ............... ................. .............
vii
ABSTRACT ................................................. . . . . . ; ................................................
viii
INTRODUCTION .......................................................
I
STATEMENT OF THE PROBLEM'AND RESEARCH OBJECTIVES .......................
Tl
EXPERIMENTAL SECTION ............................................
13
RESULTS AND DISCUSSION ...........
20
SUMMARY AND CONCLUSIONS..............................................................................
73
LITERATURE CITED ..............................................................................................
76
LIST OF TABLES
Table
Page
T.
D e s c r i p t i o n o f Ash Samples ..................
14
2.
A n a l y t i c a l P r oce dures ..............................................................................
18
3.
Chemical Analyses o f Ash Leachate- S o l u t i o n s ...............................
21
4.
S u c c e s s i v e Leaches w i t h R e s e r v o i r W a t e r .......................................
23
5.
pH o f Ash S l u r r y w it h Time ..........................................
27
6.
Rel ease o f Boron w it h Time .....................................
30
7.
Rel ease o f Boron as a Function o f
pH ...........................................
34
8.
Acid t e a c h a b l e Components o f Ash ......................................................
35
9.
Acid t e a c h a b l e Iron an,d Aluminum ......................................................
37
10.
Boron Leach with I M HCl and I M HNOg ...........................................
38
1.1. P a r r Bomb Acid D ig e s t i o n s ......................................................................
39
12.
D e te rm in at io n o f Ash Homogeneity ......................................................
40
13.
I n f l u e n c e o f P a r t i c l e Size on t h e A v a i l a b i l i t y o f Boron,
Sodium, Magnesium, and Calcium................................................................
14.
42
I n f l u e n c e o f P a r t i c l e S iz e oh t h e A v a i l a b i l i t y o f Bo ro n,
Sodium, Magnesium, and Calcium.,- Composite ..................................
......................................
43
15.
P a r t i c l e S i z e S tu dy , 4 Siz e S e p a r a t i o n s
16.
S e p a r a t i o n o f Ash by Mesh S iz e ............................................................ 45
17.
I n f l u e n c e o f Ash C o n c e n t r a t i o n on t e a c h a b i l i t y i n R e s e r v o ir
W a t e r ....................................................................................................................
18.
Rel ease o f Boron as a Function o f Ash C o n c e n t r a t i o n .............
19.
Summary: Re le a se o f Boron as a Fu nc tio n o f Ash
C o n c e n t r a t i o n ..................................................................................................
44
47
48
53
Vl
Tabl e
Page
20.
Boron Released and Re ta in e d a t Various Leaching R a t io s . . .
54
21.
Rel ease o f Re ta in e d
Boron ....................................................................
57
22.
A ds or pt io n o f
Boron onto Water Con dition ed Ash .......................
60
23.
A ds or pt io n o f
Boron on Acid Washed Ash ........................................
62
24.
A ds or pt io n o f
Boron as a Function o f Boron in S o l u t i o n . . .
66
25.
Acid Releaches o f Ad so rp tio n Samples .......................................... ..
k
'I
S u c c e s s iv e Washes with Acid (I M HCl) , D o u b l y - D i s t i l l e d
Water and Base (I M NaOH) .................. ..................................................
26.
68
70
vii
LIST OF FIGURES
Fig ur e
Page
1.
Schematic o f Water Flow a t a Power P l a n t ...................
2
2.
Schematic o f an Ash Pond .........................................
4
3.
S ta nda rd Curve f o r Boron Analyses ......................
19
4.
pH o f Leachate S o l u t i o n s with Time ...............................................
26
5.
Rel ease o f Boron from Ash as a Fun ction o f Time ...................
29
6.
Rel ease o f Boron from Ash as a Function o f pH, I g / 1 --------
32
7.
Rel ease o f Boron from Ash as a Fun ction o f p H , . 5 .5 g/1 . . .
33
8.
Rel ease o f Boron from Ash as a Fun ction o f C o n c e n t r a t i o n
52 •
9.
Boron Re ta in e d by Ash as a Function o f Boron
C o n c e n t r a t i o n .............................................................................................
56
10.
Ad so rp tio n o f Boron by Water C ond iti oned Ash ...........................
59
11.
A ds or pt io n o f Boron by HCl C ond iti oned Ash ...............
64
12.
Ad so rp tio n o f Boron as a Fu nc tio n o f S o l u t i o n
C o n c e n t r a t i on ............................. ; ...................................... ......................
65
viii
ABSTRACT
An i n v e s t i g a t i o n o f boron T e a c h a b i l i t y and a d s o r p t i o n by
coal ash under a v a r i e t y o f c o n d i t i o n s was u n d e r t a k e n . Boron
T e a c h a b i l i t y was s t u d i e d as a f u n c t i o n o f pH, t i m e , ash t y p e ,
p a r t i c l e s i z e , and ash c o n c e n t r a t i o n . Tot al a v a i l a b l e b o ro n , aluminum,
and i r o n were d e te r m in e d . Ash r e t e n t i o n o f boron was c a l c u l a t e d . The
a d s o r p t i o n o f boron by ash t h a t was w a t e r c o n d i t i o n e d and ash t h a t was
a c i d c o n d i t i o n e d was s t u d i e d . A r e l e a c h i n g o f a d s o r p t i o n samples was
pursued t o de te r m in e changes i n t h e ash a f t e r a d s o r p t i o n had ta ken
place.
INTRODUCTION
The combustion o f coal as a fu e l has become an i m p o r t a n t a l t e r n a ­
t i v e power s our c e in ou r modern s o c i e t y .
Coal i s among t h e f o s s i l
f u e l s which a r e r e a d i l y a v a i l a b l e , c o n v e n i e n t , and p r a c t i c a l f o r use.
Coal combustion,
lik e a ll other large scale in d u s tria l processes,
does n o t come w i t h o u t i t s t e c h n i c a l and en vironm ental c o n s i d e r a t i o n s .
As a mined r e s o u r c e , coal has n a t u r a l v a r i a b i l i t y in i t s composition
and i t s p r o p e r t i e s .
For i n s t a n c e , n o t a l l c o a l s burn c o n s i s t e n t l y
h o t depending on when and where t h e y were mined.
The s o l i d and gaseous
w a s t e s r e s u l t i n g from coal combustion p r e s e n t an i n c r e a s i n g c h a l l e n g e
in t h e i r d i s p o s a l .
S o l i d coal w a st e s a r e commonly r e f e r r e d t o as a sh .
methods o f ash d i s p o s a l a r e c u r r e n t l y in u s e .
i n v o l v e s s l u i c i n g in la g o o n s .
Several
One p o p u la r method
In d e ve lo pi ng ou r u n d e r s t a n d i n g o f th e
aqueous b e h a v i o r o f a s l u i c i n g p o n d , i t i s h e l p f u l t o e n v i s i o n a s ch e m a ti c o f a power p l a n t ope ra ti o n ..
Fig ur e I i s a s ch e m a ti c o r i g i n a t e d
by Dreesen ( I ) and i t r e p r e s e n t s w a t e r flow a t a power p l a n t .
The coal
i s burned in t h e p l a n t t o h e a t w a t e r t o produce steam which d r i v e s the
g e n e r a t o r s and produces e l e c t r i c i t y .
The f u n c t i o n o f t h e c o o l i n g pond
i s t o a ll o w t h e s u p e r h e a t e d w a t e r t o cool b e f o r e r e t u r n i n g t o t h e
river.
The ash pond i s i n v o lv e d in an e n t i r e l y s e g r e g a t e d c y c le o f
water.
Water i s spr ay ed i n t o t h e s t a c k s .
This proce dure c l e a n s t h e
ash o u t o f t h e s t a c k s and keeps l a r g e amounts o f p a r t i c u l a t e m a t t e r
Fi gure I
Schematic o f Water Flow a t a Power P l a n t ,
Dreesen and coworkers ( I ) .
—
San Juan River
----------- < ; --------
Ephemeral Str eam, Chaco River
V Aqueduct
y\
O u t l e t Channel
Cooling Lake
Dam
i\
Discharge
A
Canal
----------- ^ ----------
Decant Channel
Ash Pond
---------- < —
Ash S l u r r y
Channel
.In tak e
v Canal
Power
Plant
3
from e s c a p i n g o u t o f t h e s t a c k s i n t o t h e atmosphere and i n c r e a s i n g
a i r pollution.
The s l u r r y o f w a t e r and ash i s then chan ne le d i n t o
t h e ash pond.
The e n g i n e e r i n g o f t h i s pond i s s c h e m a t i c a l l y shown
in Fig ur e 2.
.
During t h e . h o l d i n g time in t h i s pond, t h e s o l i d p a r t i c l e s
i n t h e s l u r r y s e t t l e t o t h e bottom and t h e aqueous p o r t i o n i s then
allowed to s p i l l , back i n t o t h e n a t u r a l w a t e r system o f t h e a r e a .
Western coal o f t e n c o n t a i n s s i z a b l e q u a n t i t i e s o f a l k a l i and
a l k a l i n e e a r t h oxid es which upon c o n t a c t with w a t e r pro v id e b a s i c
solutions.
T a l b o t and coworkers (2) s t u d i e d t h e pH change o f s e v e r a l
suspended ash s l u r r i e s w it h t i m e .
and c l o s e d t o t h e atmos phere .
They looked a t systems both open
They note d t h a t in t h e open system
t h e r e was a d r a m a t i c i n i t i a l i n c r e a s e in pH, with hopper a s h ' e x h i b i t i n g
t h e most change.
A f t e r one week t h e i r s l u r r i e s e q u i l i b r a t e d a t a pH
o f a p p ro x im a te ly 8 . 5 .
With t h e c l o s e d sy stem th e y r e p o r t e d t h e same
pH i n c r e a s e b u t i t took s e v e r a l weeks t o d e c l i n e .
Green.and Manahan
(3) d i s s o l v e d ash in mineral a c i d , a ll o w in g t h e ash t o e q u i l i b r a t e
o v e r n i g h t and then b a c k - t i t r a t e d with NaOH.
ash d i s s o l v e d in d i s c r e t e
They r e p o r t e d t h e f l y
steps o f increasing a c id i ty , indicating
t h e p resen ce o f s p e c i f i c f r a c t i o n s in t h e m a t e r i a l .
The a u t h o r s a l s o
s t a t e d t h a t s c a t t e r o f d a t a t y p i f i e d in t h e i r p l o t s was due t o sample
inhomogeneity and u n c e r t a i n pH r e a d i n g s in t h e f l y ash s u s p e n s i o n s .
Compensation was made by t a k i n g l a r g e numbers of d a t a p o i n t s .
G e n e r a l l y , t h e n a t u r e o f coal ash i s n o n v o l a t i l e , i n o r g a n i c m a t t e r
4
Figure 2
Schematic o f an Ash Pond.
dam
Z'
X s p i l l pipe
pond
5
In 1977 Dreesen and coworkers (T) a n al yz e d and found some components
o f a s h , i n c l u d i n g such t o x i c el em ent s as b o r o n , a r s e n i c , f l u o r i n e ,
molybdenum, and s e l e n i u m , t o be le a c h e d w it h w a te r .
They proved
t h i s by sampling t h e e f f l u e n t w a te r s o f t h e Los Alamos, New Mexico
power p l a n t and comparing t h e r e s u l t s ' w i t h samples o f t h e i n f l u e n t
w aters.
They found e l e v a t i o n o f t h e s e el ements in t h e e f f l u e n t s .
For example, i n t a k e r i v e r w a t e r c o n t a i n e d l e s s than 0.1 yg/ml o f
boron bu t ash pond e f f l u e n t s c o n t a i n e d 12.0 yg/ml and c o o l i n g la ke
e f f l u e n t s c o n t a i n e d 0.95 yg/ml b o r o n .
Analyses o f ash c o n t e n t have been e x t e n s i v e l y r e p o r t e d and
compared usi ng a v a r i e t y o f a n a l y s e s te c h n i q u e s ( 4 - 7 ) .
Ash and its.
p a r e n t coal vary g r e a t l y in e x a c t c o n t e n t from sample t o Sample, b u t
t h e major components can be summarized from t h e r e p o r t s o f a n a l y s e s in
the l i t e r a t u r e .
The. major component a n a l y s e s condenses t o : s i l i c a ,
c al c iu m , aluminum, magnesium, i r o n , . p o ta s s iu m , and sodium.
Many t r a c e
a n a l y s e s a r e a l s o r e p o r t e d in t h e s e p a p e r s .
O th e r i n t e r e s t i n g i n t e r p r e t a t i o n s o f ash c o n t e n t have been added
t o t h e l i t e r a t u r e through t h e use o f e l e c t r o n m i c ro g ra p h s .
By r a d i ­
a t i n g a t s e l e c t e d wavelengths t h e ma jor component c o n c e n t r a t i o n s can
be photographed ( 4 , 5 ) .
In a unique s t u d y , Furr and o t h e r s (7) grew c a b b a g e s . i n s o i l
amended w it h seven p e r c e n t coal ash from tewnty-one coal burning
power p l a n t s .
They measured uptake o f t h e t o x i c el em en ts by th e
6
cabbages.
The c o n c e n t r a t i o n s in t h e cabbages o f a r s e n i c , b o ro n,
molybdenum, s e le n iu m , and s t r o n t i u m showed high c o r r e l a t i o n with t h o s e
in t h e a s h .
This s t u d y i n v o l v e s one t r a c e component o f coal a s h , boron.
. I n t e r e s t in boron comes from t h e f a c t t h a t , alth ough i t i s an
e s s e n t i a l t r a c e n u t r i e n t f o r p l a n t s ( 8 ) , i t becomes t o x i c a t con­
c e n t r a t i o n s g r e a t e r th a n one p a r t p e r m i l l i o n ( 9 , 1 0 ) .
Boron i s a r a r e e lem ent in t h e e a r t h ' s c r u s t and i s most abundant
I y a s s o c i a t e d w it h f o s s i l f u e l s such as o i l and coal w it h geothermal
waters (11).
s y st e m s .
Boron i s always found in t r a c e amounts in n a t u r a l w a te r
Most n a t u r a l w a te r s c o n t a i n l e s s than one h a l f o f a p a r t
pe r m i l l i o n w i t h s l i g h t l y h i g h e r c o n c e n t r a t i o n s found in geothermal ■waters and waterways thr ou gh coal r i c h a r e a s ( 1 2 ) .
Few a u t h o r s have looked s p e c i f i c a l l y a t t h e r e l a t i o n s h i p o f boron
l e a c h i n g in aqueous 'systems.
r e l e a s e d from coal a s h .
e m is sio n s p e c t r o m e t r y .
Cox and o t h e r s (13) looked a t boron
They det ermi ned t o t a l boron by d c - a r c
Over a s i x t y second span t h e y measured boron
r e l e a s e d a t pH 4.55 and pH 7.4 0 .
They r e p o r t e d f i f t y p e r c e n t o f t o t a l
b o r o n , which could be as high as 1900 ppm, was le ac he d i n t o w a t e r .
They a l s o r e p o r t e d t h e q u a n t i t y o f boron leache d was inde pen de nt o f pH
ove r t h e range o f 6 t o 8 b u t a v a i l a b i l i t y was g r e a t e r i n a c i d .
Also
in t h i s p a p er , t h e y s u g g e s t t h a t thermal f i x a t i o n o f t h e boron i n t o
an i n s o l u b l e chemical s t a t e could be o b t a i n e d by t r e a t i n g t h e ash a t
7
12.00°C f o r t h i r t y m in u te s .
Choi and Cheh (14) r e p o r t e d t h e amount o f boron l e a c h e d from f o u r
common a d s o r b e n t s ; hydro D arco, E i T t r a s o r b , a c t i v a t e d b a u x i t e , and
a c t i v a t e d a lu m in a , as a f u n c t i o n o f pH.
t h e amount o f boron le a c h e d a t .25 9/1
For a l l but one a d s o r b e n t
i n c r e a s e d as pH d e c r e a s e d below
pH 6 wit h boron le a c h e d remaining a pp ro x im a te ly c o n s t a n t above pH 6.
!
P a r t o f t h e v a r i a b i l i t y in a n a l y s e s o f ash can be improved by
f r a c tio n a tio n of pari c l e s iz e .
There i s a r e l a t i o n s h i p between th e
s i z e o f t h e ash p a r t i c l e s and t h e i r e le m en ta l c o m p o s i ti o n .
Electron
micrographs done by Smith (15) and Campbell (4) showed ash t o be
an amorphous, f r a g i l e m a t e r i a l composed o f many p a r t i c l e s i z e s ,
shapes;
and
densities.
Two s e p a r a t e r e p o r t s (1 6,1 7) group the
ash i n t o t h r e e m a s s - s i z e d i s t r i b u t i o n s .
Those elem ent s a s s o c i a t e d
w it h l a r g e p a r t i c l e s (>20.0 ym) a r e d e p l e t e d r e l a t i v e t o t h e o r i g i n a l
coal c o m p o s i ti o n ; a second group o f el em ent s in t h e i n t e r m e d i a t e
s i z e f r a c t i o n ( 2 0 . 0 - 6 . 0 ym) have, s i m i l a r c o n c e n t r a t i o n s in ash and
p a r e n t c o a l ; and a t h i r d f r a c t i o n o f small p a r t i c l e s ( 6 . 0 - 2 . 5 ym)
c o n t a i n el em en ts i n c l u d i n g boro n, which have e n r i c h e d c o n c e n t r a t i o n s
in ash .
Another group (18) which s t u d i e d s i z e f r a c t i o n a t i o n d e f i n e d
se v e n te e n s i z e f r a c t i o n s in ash ra n g in g from 10 ym th ro u g h submicron
in s i z e .
T h e i r r e s u l t s showed t h a t v o l a t i l e t r a c e el em en ts i n c r e a s e d
i n c o n c e n t r a t i o n w it h d e c r e a s i n g p a r t i c l e s i z e above one mic ron ; b u t .
8
f o r submicron p a r t i c l e s t h e c o n c e n t r a t i o n becomes in de p en d e n t o f
p a rtic le size.
These a r e s i g n i f i c a n t f i n d i n g s
s i n c e small p a r t i c l e s
a r e most e a s i l y suspended in w a t e r and t h e e n r i c h e d boron c o n t e n t i s
e asily released.
.
. ..
The a d s o r p t i o n c h a r a c t e r i s t i c s o f boron onto s o i l s has been
extensively studied.
In a s e r i e s o f p a p e r s , Harder (19- 21) s t u d i e d
boron in s edi m ent s and a s s o c i a t e d i t with t h e c l a y m i n e r a l , i l l i t e .
His prim ary concern in t h e s e s t u d i e s was o f a g r i c u l t u r a l s i g n i f i c a n c e ■
so pH and te m p e r a t u r e were n o t m onit or ed .
He did however, note t h a t
boron uptake was r a p i d a t f i r s t and then gradual a f t e r a few hours.
In 1964 Hingston ( 2 2 ) , a l s o i n t e r e s t e d in t h e s t u d y o f n a t u r a l
s e d i m e n t s , i n v e s t i g a t e d boron a d s o r p t i o n o nto i l l i t e , k a o l i n i t e , and
!
montmoriII o n i t e . He s t u d i e d boron uptake as a f u n c t i o n o f pH over
t h e range o f 3 . 8 t o 10.5 and as a f u n c t i o n o f c o n c e n t r a t i o n .
He was
t h e f i r s t t o s u g g e s t t h a t boron a d s o r p t i o n e x h i b i t e d Langmuir be h a v io r .
Couch and Grim (23) a l s o s t u d y i n g t h e c l a y s ; i l l i t e , k a o l i n i t e , and
montmori11o n i t e ,
d e te r m in e d t h a t t h e i n i t i a l boron c o n c e n t r a t i o n s and
t e m p e r a t u r e had a d i r e c t r e l a t i o n s h i p on boron upta ke.
Metwally (24) s t u d i e d boron a d s o r p t i o n onto f r e s h l y p r e c i p i t a t e d
aluminum hydrox ide as a f u n c t i o n o f pH.
Sims and Bingham (25)
foll ow ed t h i s proce dur e b u t a l s o r e p o r t e d an i n v e r s e r e l a t i o n s h i p
between boron uptake and aging o f t h e p r e c i p i t a t e .
McPhail and o t h e r s (26) confirmed Sims' r e s u l t s .
A s i m i l a r paper by
9
Co ncu rr en t w it h t h e s e s t u d i e s , s e v e r a l i n v e s t i g a t o r s w h il e lookin g
a t v o l c a n i c s o i l s in C h i l e , Hawaii, and Mexico'(27-29)
correlated a
hig h boron a d s o r p t i o n by t h e s e s o i l s w i t h high c o n c e n t r a t i o n s o f
aluminum in them.
...............
In a d d i t i o n t o aluminum h y d r o x i d e , f r e s h l y p r e c i p i t a t e d i r o n hy­
d r o x i d e was s t u d i e d f o r boron a d s o r p t i o n by Metwally (24) and by Sims
(25,30,31).
Iron i s a l s o c a p a b le o f p a r t i c i p a t i n g in t h e a d s o r p t i o n o f
boron b u t has 200 tim e s l e s s c a p a c i t y f o r a d s o r p t i o n th a n does aluminum.
Bingham and Page (32) r e p o r t e d t h a t s u l f u r and phosphorous e x h i b i t ­
ed no i n f l u e n c e upon t h e a d s o r p t i o n o f boron by an a l l o p h a n i c s o i l .
Choi and Chen (14) r e p o r t e d t h a t c alc ium ( I I ) ions and magnesium ( I I )
i o n s showed an e f f e c t on boron a d s o r p t i o n w it h some a d s o r b e n t s .
An i n c r e a s e in t h e c o n c e n t r a t i o n o f calciu m ( I I ) i o n s t o a c e r t a i n
v a l u e r e s u l t e d in a d e c r e a s e in t h e removal o f boron f o r a l l a d s o r b e n ts
studied.
The v a l u e was dependent upon t h e a d s o r b e n t used .
L i t t l e or
no a d d i t i o n a l e f f e c t was found with f u r t h e r i n c r e a s e in t h e concen­
t r a t i o n o f c alc ium ( I I ) above t h e v a l u e .
For example, F i l t r a s o r b
removed boron l e s s e f f i c i e n t l y in t h e pre s e n c e o f c alc ium ( I I ) ions up
t o a c o n c e n t r a t i o n o f 100 mg/1 b u t showed no f u r t h e r i n f l u e n c e with
i n c r e a s i n g calciu m ( I I ) c o n c e n t r a t i o n .
Magnesium ( I I ) io n s e f f e c t e d
boron removal only when F i l t r a s o r b was t h e a d s o r b e n t .
S i l i c a has been
s u g g e s t e d i n s e v e r a l pa per s ( 2 , 2 9 , 3 2 ) t o e x h i b i t a c o m p e t i t i v e e f f e c t
w it h boron f o r t h e a d s o r p t i o n s i t e s .
T he is and Wirth (33) s u g g e s te d
10
t h a t some s p e c i e s o f manganese may p l a y a r o l e in t h e a d s o r p t i o n of,
boron .
Choi and Chen (14) examined t h e e f f e c t s o f pH upon l e a c h i n g o f
boron from t h e a d s o r b e n t s and c o n v e r s e l y t h e pH e f f e c t s upon a d s o r p t i o n
o f boron ont o t h e a d s o r b e n t s .
They r e p o r t e d i n c r e a s i n g boron leache d
below pH 6 and a p p ro x im a te ly c o n s t a n t amounts o f boron le a c h e d f o r a l l
a d s o r b e n t s between pH 6 and 9.
They r e p o r t e d t h e optimum pH f o r
a d s o r p t i o n o f boron was dependent upon t h e a d s o r b e n t p r e s e n t and upon
t h e c o n c e n t r a t i o n o f boron in s o l u t i o n .
In t h e same p a p e r , t h e y
r e p o r t e d t h a t s a l i n i t y e f f e c t e d removal e f f i c i e n c y o f boron.
Removal
e f f i c i e n c y , d e c r e a s e d s h a r p l y and t h e pH a t which removal i s most e f ­
f i c i e n t , i n c r e a s e d s h a r p l y w it h i n c r e a s i n g s a l i n i t y up t o 8% f o r hydro
Darco, 5% f o r F i l t r a s o r b , 8% f o r a c t i v a t e d b a u x i t e , and 10% f o r
a c t i v a t e d al umina.
Above t h e s e c o n c e n t r a t i o n s no f u r t h e r d e c r e a s e in
removal e f f i c i e n c y and i n c r e a s e in pH was no te d .
All o f t h e p re v io u s a d s o r p t i o n s t u d i e s . u s e d s o i l o r some w e l l c h a r a c t e r i z e d s u r f a c e as t h e a d s o r b e n t .
In t h i s s tu d y t h e ash was
examined as a p a r t i c i p a n t in t h e a d s o r p t i o n p r o c e s s .
The m o b i l i t y o f
boron in an aqueous system has been shown t o be i n f l u e n c e d b y MpH,
t e m p e r a t u r e , ty p e and amount o f a d s o r b i n g s o l i d s , t h e shape
d e n s i t y o f t h e . a s h , and o t h e r chemical s p e c i e s p r e s e n t .
and
STATEMENT OF THE PROBLEM-AND RESEARCH OBJECTIVES
Boron i s one o f t h e t o x i c el ements in coal ash which i s r e a d i l y
Teachable i n t o an aqueous system.
The d e t e r m i n a t i o n o f t h e mechanism
o f boron m o b i l i t y in a n a t u r a l system i n v o l v e s many f a c t o r s .
A
mechanism has been s u g g e s t e d t o i n v o l v e t h e a d s o r p t i o n and d e s o r p t i o n
o f boron s p e c i e s from s o l i d s u r f a c e s .
such a p ro c e s s and
Many c o n d i t i o n s can i n f l u e n c e
need t o be s t u d i e d s p e c i f i c a l l y .
What ty p e of
s o i l o r ash a r e p r e s e n t and does t o t a l c o n c e n t r a t i o n o f t h e s e e f f e c t
t h e e f f i c i e n c y o f t h e system?
What i s t h e s p e c i e s o f boron involved
and what i s i t s s o l u b i l i t y in w a te r ?
t h e a d s o r p t i o n and d e s o r p t i o n ?
What a r e t h e maximum l i m i t s o f
And i t must be det ermi ned i f t h e
p ro c e s s i s simple r e v e r s i b l e o f i f some pa rame te rs such as pH, t i m e ,
and te m p e r a t u r e e f f e c t t h e forward and r e v e r s e sequences d i f f e r e n t l y .
Boron a d s o r p t i o n and d e s o r p t i o n from s o i l s has been s t u d i e d by
many w or ke rs .
ash.
Few people have looked a t t h e r o l e o f boron from coal
In t h i s s t u d y , i n v e s t i g a t i o n s were unde rtaken t o de te r m in e t h e
i n f l u e n c e o f pH, t i m e , and ash typ e upon boron T e a c h a b i l i t y .
The
i n f l u e n c e o f p a r t i c l e s i z e upon a v a r i e t y o f components was s t u d i e d .
Ash c o n c e n t r a t i o n was v a r i e d and was det ermi ne d t o have a s i g n i f i c a n t
e f f e c t upon t h e amount o f boron r e l e a s e d .
The boron r e t a i n e d was
c a l c u l a t e d and t o t a l a v a i l a b i l i t y o f boron was the n e x p e r i m e n t a l l y
determined.
Based upon t h e enhanced T e a c h a b i l i t y o f a v a r i e t y of
12. "
major components with a c i d , a n a l y s e s o f t o t a l a v a i l a b i l i t y o f t h e s e
components was made.
Iron and aluminum were s p e c i f i c a l l y s t u d i e d .
F u r t h e r i n v e s t i g a t i o n o f r e t a i n e d boron l e a d t o a d s o r p t i o n
experiments.
Ad sor pti on was s t u d i e d by w a t e r c o n d i t i o n e d ash and a c i d
c o n d i t i o n e d a sh .
de te r m in e d .
The e f f e c t s o f pH upon t h e pro ce ss were a l s o
A d d i t i o n a l l y , r e l e a c h i n g o f . t h e a d s o r p t i o n samples was
i n v e s t i g a t e d t o de te rm in e changes in t h e ash a f t e r a d s o r p t i o n had
ta k e n p l a c e .
EXPERIMENTAL SECTION '
Ash samples were o b t a i n e d from t h e Boundry Dam Power S t a t i o n
n e a r E s t e v a n , Saskatchewan, Canada, and from a t e s t burn o f coal to
be used a t t h e P o p la r R ive r Power P r o j e c t in so u th er n Saskatchewan.
A d e s c r i p t i o n o f t h e ash samples i s p r e s e n t e d in Table I .
The ash
samples were passe d thr ou gh 100 mesh s c r e e n p r i o r t o l e a c h i n g ;
P a r t i c l e s were manually f r a c t i o n a t e d w ith t h e use o f c o n c e n t r i c s i e v e s
■
■
'
-
'
The s i e v e s i z e s were 100, 140, 200, and 325 mesh.
s i z e s co rr e sp o n d t o Openings
respectively.
The mesh
o f 15p urn, 125 ym, 75 pm and 45 pm,
All a d s o r p t i o n s t u d i e s were done on ash which passed
thr oug h t h e 325 mesh s i e v e .
Whenever p o s s i b l e a l l pro c e d u re s w ere c a r r i e d o u t in p o l y ­
pro py le ne o r t e f l o n c o n t a i n e r s t o avoid any p o s s i b i l i t y o f l e a c h i n g
boron from g l a s s w a r e , e s p e c i a l l y a t extreme pH v a lu es o r e l e v a t e d
temperatures.
The l e a c h i n g s t u d i e s in v o lv e d mixing 50.0 ml o f l e a c h a t e w a t e r ,
d i s t i l l e d o r n a t u r a l , w it h t h e d e s i r e d amount o f a s h .
The s o l u t i o n s
were k e p t in p o l ypr opy l en e be ak e rs cover ed by watch g l a s s e s .
pro vid ed f o r exchange o f carbon d i o x i d e .
This
Water, l o s t by e v a p o r a t i o n
was r e p l a c e d thro ugh t h e r e g u l a r a d d i t i o n o f d o u b l y - d i s t i l l e d w a t e r .
At t h e d e s i r e d time i n t e r v a l , an a l i q u o t o f l e a c h a t e s o l u t i o n was
withdrawn and a n a ly z e d .
A P a r r , t e f l o n - l i n e d bomb: was u t i l i z e d t o
d i g e s t t h e ash samples when e l e v a t e d te m p e r a t u r e s and HF were used .
14
Table I
D e s c r i p t i o n o f Ash. Samples.
Sample
Description
Al
Bottom Ash— Pop la r River
A2
Upper A s h - - P o p l a r River
AS
Dust A s h - - P o p l a r River
A4
Upper Ash, 5-day co m posi te , Boundry Dam
AS.
Bottom Ash, 5-day c o m p o si te , Boundry Dam
AG
Composite:
Al (23.5%), A2 (4.7%),
AS (71 .8% ), Poplar River
A7
Composite:
A4 (58%), AS (42%),
Boundry Dam
15
/
Ad so rp tio n e xpe ri m en ts inv ol ved suspending th e ash samples in
s o l u t i o n s o f known boron c o n c e n t r a t i o n and measuring t h e d e c r e a s e in
s o l u t i o n boron c o n c e n t r a t i o n a f t e r f o r t y e i g h t ho u rs .
Ash was c o n d i t i o n e d f o r t h e a d s o r p t i o n e xper im ent s by l e a c h i n g
25 grams with t h r e e l i t e r s o f d o u b l y - d i s t i l l e d w a t e r .
This was done in
t h r e e c o n s e c u t i v e l i t e r p o r t i o n s f o r one and one h a l f , hours each .
ash was f i l t e r e d and a i r d r i e d .
The
The a c i d c o n d i t i o n e d ash p re pa re d by
t h e same pr oc e dur e was mixed with one molar HCl o r HNOg and
immediately f i l t e r e d and d r i e d .
Ad so rp tio n ex per im en ts were c a r r i e d
o u t i n covered pol y p ro p y l e n e b o t t l e s t o minimize e v a p o r a t i o n .
b o r a t e was used as t h e s t a n d a r d b o r o n . r e f e r e n c e .
Sodium
Ad so rp tio n e x p e r i ­
ments were allowed t o e q u i l i b r a t e f o r two days b e f o r e measurement.
The a d s o r p t i o n ex pe ri m en ts were done a t f i f t y f i v e grams o f a sh per
T i t e r and in 10 ml p o r t i o n s .
T h e r e l e a c h i n g s o f t h e a d s o r b e n t were
in 5 ml p o r t i o n s .
Ash was s u c c e s i v e l y washed f o r a d e t e r m i n a t i o n o f t o t a l r e l e a s e
o f components t o l e a c h a t e s .
One gram o f ash was s u b j e c t e d to
washes in one l i t e r o f I M HNOg, I M-NaOH
water.
and d o u b l y - d i s t i l l e d
Samples were th e n shaken on. a mechanical s h a k e r f o r twenty
f o u r h o u r s , c e n t r i f u g e d f o r twenty mi nute s a t nin e th o u s a n d rpms, and
decanted.
T hi s pro c e du re was r e p e a t e d f o r a t o t a l o f t h r e e washings.
The n i n e l e a c h a t e s were a n al yz e d s e p a r a t e l y .
S o l u t i o n pH was a d j u s t e d wit h a d d i t i o n s o f v a r i a b l e c o n c e n t r a t i o n s
16
o f NaOH o r HNO^ f o r t h e l e a c h i n g e x p e r im e n t s .
ex pe ri m en ts b u f f e r s were used.
For t h e a dso r ptio n,
The b u f f e r s used w ere: Trizma base
[ T r i s (hydr oxy methyl ) amino .methane], phosphate b u f f e r , ammonia b u f f e r ,
and a c e t a t e b u f f e r .
All r e a g e n t s o l u t i o n s were p r e p a r e d usi ng d o u b l y - d i s t i l l e d w a te r .
Unless o t h e r w i s e s p e c i f i e d , a l l ex p er im en t al s o l u t i o n s were a l s o made
with d o u b l y - d i s t i l l e d w a t e r .
All n a t u r a l w a te r samples were f i l t e r e d through
f i l t e r s p r i o r t o us e.
0.45 micron
The n a t u r a l w a te r o b t a i n e d from t h e Boundry Dam
P r o j e c t had t h e f o l l o w i n g c h a r a c t e r i s t i c s :
pH = 8 . 2 5 , s p e c i f i c con­
d u c ta nc e = 740 jimhos/cm, HCOg = 2 . 4 mg/1, SO^ = 210 mg/1, Cl = 10.3 mg/1,
Ca = 4 . 4 mg/1, Mg = 22.3 mg/1, K = 11.2 mg/1, Na = 92.2 m g / 1 , . B = 0.343
mg/1.
The n a t u r a l w a t e r o b t a i n e d from t h e P opla r R ive r had t h e f o l l o w ­
ing c h a r a c t e r i s t i c s :
pH = 8 . 3 0 , s p e c i f i c conductance = 986 umhos/cm,
HCOg = 406 mg/1, SO4 = 189 mg/1, Cl. = 6 . 0 mg/1, Ca = 33.0 mg/1, Mg =
33 .9 mg/1, K = 9 . 8 mg/1, Na = 140 mg/1, B = 0.820 mg/1.
Boron c o n c e n t r a t i o n s were e v a l u a t e d by t h e curcumin method u t i l ­
i z i n g d ry in g a t 7 5 . 0°C.
The s e n s i t i v i t y o f t h e a d s o r p t i o n ex periments
l e a d t o an ex am in at io n o f n i t r a t e i n t e r f e r e n c e .
N i t r a t e was determined
t o y i e l d e r r o n e o u s l y high r e s u l t s which a r e s i g n i f i c a n t when working in
t h e lower l i m i t s o f s e n s i t i v i t y o f t h e curcumin method o f boron a n a l y ­
ses.
H yd ro c h lo ri c a c i d was u t i l i z e d f o r a l l a c i d r e l a t e d p o r t i o n s o f
the adsorption experiments.
Atomic a d s o r p t i o n s p e c t r o p h o t o m e t r y , with
17
a p p r o p r i a t e r a d i a t i o n b u f f e r s , was used t o deter mine sodium,
p o t a s s i u m , c a lc iu m , magnesium, aluminum, cadmium, chromium, co pper,
manganese, l e a d , and i r o n .
B ic a rb o n a te was determine d by HCl
t i t r a t i o n , and pH was monito red by a Radiometer M-26 pH mete r using
glass-SCE e l e c t r o d e s .
S u l f a t e was d et ermi ned by c o l o r i m e t r i c t i t r a t i o n
(38) and c h l o r i d e by i r o n - t h i o c y a n a t e pro c e d u re .
summary o f t h e s e p r o c e d u r e s .
Table 2 c o n t a i n s a
The s t a n d a r d curve f o r t h e boron
a n a l y s e s , curcumin method i s p r e s e n t e d in Figure 3.
18
Table 2
Analytical Procedures.
S p e c i f i c Conductance
Determined by s t a n d a r d i z e d probe
and c o r r e c t e d t o 25°C.
PH
Measured by s t a n d a r d i z e d e l e c t r o d e s ,
g l a s s and SCE r e f e r e n c e .
HCO3 , CO3 , OH
These a r e determine d p o t e n t i o m e t r i c a l l y (pH) by t i t r a t i o n with
standard acid.
s°4
T i t r a t i o n with s t a n d a r d barium u s in g
n i t r o s u Ifazo II I i n d ic a to r for
equivalence point d e te c tio n .
Cl
S p e c t r o p h o t o m e t r i c usi ng Hg(SCN)2
and Ir o n ( I I I ) .
NO3
Brucinic s u lf a te and/or sp ectrop h o to m e tr ic method.
Na, K, Ca, Mg
Determined by atomic a b s o r p t i o n
s p e c t r o p h o t o m e t r y u s in g a p p r o p r i a t e
radiation buffers.
SiO2
S p e c t r o p h o t o m e t r i c us in g molybdos i I i c a t e pro c e d u re .
Boron
Curcumin method, s p e c t r o p h o t o m e t r i c
w it h c o l o r development a t 75°C.
A l , Cd, Cr, Cu, Fe, Mn, Pb, Zn
Determined by atomic a b s o r p t i o n
spectrophotometry.
19
Figure 3
Sta ndard Curve f o r Boron A na ly se s ,
(o v e r 12 d i f f e r e n t e x p e r im e n t s ).
Boron C o n c e n tr a ti o n (mg B/ml)
RESULTS. AND DISCUSSION
Ash Composition
■
Four ash samples were le ach ed with d o u b l y - d i s t i l l e d w a t e r to
a s c e r t a i n w a t e r Teachable components.
in Table 3.
The r e s u l t s a r e summarized
The major w a t e r Teachable components o f t h e s e ashes a re
sodium, p o t a s s i u m , c a l c i u m , magnesium, s u l f a t e , c a r b o n a t e , i r o n ,
and aluminum.
The i m p o r t a n t w a t e r Teachable t r a c e m e ta ls a r e s t r o n t i u m ,
vanadium, boron, c o p p e r , and z i n c .
The d a t a i n d i c a t e s t h a t some
ash components, i n c l u d i n g b o r o n , a r e r e a d i l y Teachable i n t o w a t e r .
Component a n a l y s e s o f ash from d i f f e r e n t p a r e n t c o a l s can n o t be com­
pared d i r e c t l y because o f t h e v a r i a b i l i t y o f mined n a t u r a l resources'.
I t i s r e a s o n a b l e t o n o te t h a t t h e ash samples an aly ze d show major
components s i m i l a r to t h o s e r e p o r t e d by o t h e r a u t h o r s ( 4 - 7 ) .
Three samples o f A2 were le a c h e d w it h r e s e r v o i r w a t e r as shown in
Table 4.
In one sample t h e w a t e r was c o n c e n t r a t e d , in one sample t h e
ash was h e a t e d .
in Table 4.
The a n a l y s i s o f t h e r e s e r v o i r w a te r i s a l s o in c lu de d
The he at e d ash composite was pre p a re d from bottom ash
t h a t had been h e a te d t o 2000°F f o r Jg h o u r , and upper and d u s t . a s h t h a t
had been h e a t e d t o 350°F f o r I hour.
The c o n c e n t r a t e d r e s e r v o i r w a te r
was p re p a re d by slow e v a p o r a t i o n o f t h e r e s e r v o i r w a te r as r e c e i v e d .
Four a l i q u o t s o f . l e a c h a t e were withdrawn a t 168 hour i n t e r v a l s
f o r time a n a l y s e s .
I t can be note d t h a t time i s a f a c t o r in th e
T e a c h a b i l i t y o f t h e components.
Boron le ac he d with r e s e r v o i r w a te r
TABLE 3
Chemical Analyses o f Ash Leachate S o l u t i o n s .
A l, A2, A3, A6, I g / 1 , open t o at mo sp here, 166 h o u r s .
Major Component Leached from Fly Ash Samples.
Sample
HCO~
COj
s£
C l'
m i
Na+
£
Ca++
Mq++
Values a r e mg/g Ash
A2
42.31
3.44
5.49
<1.00
<>.00
.349
.204
12.33
1.54
A3
40.16
18.95
6.49
<1.00
<1.00
.602
.077
20.47
1.72
Al
25.49
2.19
2.50
<1.00
<1.00
.192
.127
7.11
1.68
A6
36.42
15.22
5.79
<1.00
<1.00
.508
.164
17.45
1.56
'
Measured Parameters f o r Ash Leachates.
Sample
EU
S.C.
mmhos/cm
zcation
meq/1
zanion
meq/1
TDS
mg/g
1.0 gr Ash + 1000 gr HgO, e q u i l i b r a t i o n with atmosphere •
A2
9.05
.0.072
0.76.
0.88
9.78
0.109
1.19
1.17
90.50
Al
8.98
0.051
0.51
0.51
41.40
Ao
9.72
0.098
1 .03
1.02
79.10
A3
.
'
67.60
Table 3 ( c o n ti n u e d )
Trace Metals Water Leached from Fly Ash Samples.
Values a r e y g / g .
Sample
Cd
Cr
A2
<5.1
<5.1
AS
<5.1
<5.1
Al
<5.1
AG
Cu
Fe
Mn '
Ni_
Pb
'
Zn
B
• 183.4
<5.1
<41
<41
<5.1
264
<5.1
29.7
<5.1
<41
<41
<5.1
586
<5.1
<5.1
32.8
<5.1
<41
<41
7.2
215
<5.1
<5.1
<5.1
24.6
<5.1
<41
<41
5.1
504
Sample
As
Mo
Sr
Sei
Zr
Sb;
Co
Al
V
A2
<41
<20.5
177.2
<41
<5.1
<41
<41
—
6.15
AS
<41
<20.5
339.1
<41
<5 Jl
<41
<41
--
7.17
Al
<41
<20.5
121.9
<41
<5.1
<41
<41
788.2
AG
<41.
<20.5
304.3
<41
<5.1
<41
<41
-■
7.17
<5.1
9.22
Table 4
S u c c e s s iv e Leaches with R e s e r v o ir Water.
A2, time s e p a r a t i o n 168 h o u r s .
Sample
A2
reservoir
water .
A2concentrated
reservoir
w a te r
*
n o t in mg/1
Wash
R e s u l t s in mg/1 leache d a t 60
HCO3
CO3
Na
K
Ca
g / l , open •to atmosphere,
B
Cl
NO3
SO4
I
9.01
171
56
183 ' 10.9
33.4
41.4
IGUO
9 .3
4-5. 425
2
9.10
331
71
158
17.7
19.0
59.2
4 .8
8.8
3.2
238
3
9.12
367
55
170
20.0
20.3
53.1
2.6
9 .0
3.5
243
4
8.97
380
48
167
20.2
20.8
52.3
1.9
5. 6
2.2
222
I
9.08
280
95
323
19.1
21.1
56.7
17.0
15.3
9.4
601
2
9.22
499
125
299
34.4 - 15.4
88.1
5 .6
14.7
6.9
437
3
9.22
526
105
314
38.4
15.6
75.1
3 .3
15.2
5 .8
418
4
9.19
538
98
320
39.0
14.0
73.0
2 .6
15.2
3.3
437
Table 4 (c o n ti n u e d )
I
8.85
203
30
2
9.00
384
3
9.03
4
sT
EU
=C
O
O
CO
*
Sample
Ca
160
10.7
23.1
33.0
10.0
52
161
17.3
17.0
60.1
393
47
165
26.5
17.4
9.02
370
41
169
21.1
R e s e r v o ir w a t e r
8.30
406
140
Co nce ntra te d
R e s e r v o i r w a te r
8.8 8
542
42.5 257
A2-heated
ash in
reservoir
water
n o t in mg/1
• Na
B
K
Wash
Cl
%
SO4
12.3
2.7
338
3.0
8.2
3.0
229
55.1
1.9
8.2
3.4
245
20.6
47.3
1.4
7.0
2.3
230
9 .8
33.0
33.9
.8
6.0
3.2
189
17.9
18.0
59.6
1.6
12.6
7.1
360
ro
\
25
16 ml/ I ( 0 .3 0 mg/g) in t h e f i r s t 168 hours b u t had le a c h e d a t o t a l o f
26 mg/1 ( 0 .4 7 mg/g) by 720 ho u rs .
The use o f n a t u r a l w a t e r a s s i m i l a t e s
t h e n a t u r a l system a t t h e power p l a n t s i t e .
V a r i a t i o n o f pH w it h Time
The l e a c h i n g o f ash m a t e r i a l s d e r i v e d from w e st e rn c o a l s with
d i s t i l l e d w a t e r o r a. n a t u r a l w a t e r g e n e r a l l y pro v id e s a b a s i c s o l u ­
tion.
The pH o f t h e d i s t i l l e d w a t e r s o l u t i o n s r a p i d l y r i s e s as t h e
ox id e s d i s s o l v e , w it h s u b se q u e n t d e c r e a s e in pH due t o a b s o r p t i o n o f
carbon d i o x i d e .
This d e c r e a s e in pH as a f u n c t i o n o f time i s shown
in Figure 4 , c urv e a. and Tabl e 5.
Long-term l e a c h i n g s t u d i e s usi ng
d i s t i l l e d w a t e r w it h t h e e x c l u s i o n o f carbon d i o x i d e e x h i b i t a much
sl o w er r a t e o f pH d e c r e a s e ( 2 ) .
When t h e l e a c h a t e w a t e r has s i z e a b l e
b i c a r b o n a t e b u f f e r i n g c a p a c i t y , curve b in Figure 4 , t h e pH does n o t
e x h i b i t t h e r a p i d i n i t i a l r i s e , b u t r a t h e r gradual approach t o a
s t e a d y - s t a t e pH v a lu e as b i c a r b o n a t e i s c o n v e r te d t o c a r b o n a t e .
The '
l e a c h i n g o f ash w it h a w a t e r t h a t c o n t a i n s b i c a r b o n a t e a l k a l i n i t y
( p H = 8 . 3 , HCOg = 6 . 7 x I O- 3 M) w i l l n o t o b t a i n t h e high pH valu es
obs erved f o r t h e d i s t i l l e d w a te r le ac h ( s e e Figu re 4 , cu rve b ) .
How-
e v e r , a t h ig h c o n c e n t r a t i o n s o f ash t h e b u f f e r c a p a c i t y o f t h e w at er
co uld be e x h a u s te d and r e s u l t in h i g h e r s t e a d y s t a t e pH v a l u e s .
Summation o f sodium, p o t a s s i u m , magnesium, and c alc ium a n a l y s e s
v a l u e s , in Table 3, p r o v id e an i n d i c a t i o n o f b a s i c m a t e r i a l p r e s e n t
(
-
F ig ur e 4
pH o f Leachate S o l u t i o n s with Time.,
Curve (a) I gr A 6 / H t e r d i s t i l l e d w a t e r ;
curve (b) 60 gr A 4 / l i t e r o f Boundry Dam w a t e r .
Time, hrs
27
Table 5
. pH o f Ash S l u r r y with Time.
A6 and A4, d o u b l y - d i s t i l l e d w a te r l e a c h , I g / 1 ,
n a t u r a l w a te r leach
60 mg/1.
Time: hours
PH
A6 with doubly d i s t i l l e d w a te r
PH
A4 with n a t u r a l
w a te r
0
10.4
8.3
19
10.7
-
43
10.5 .
-
67
10.4
135
9 .9
165
9.8
250
.
-
-
9 .0
i .
28
in t h e a sh .
',
The f i n a l pH v a lu e s w i l l be dependent upon t h e number
o f b a s i c s i t e s in t h e a s h , with a l a r g e r number p r o v i d i n g a. h i g h e r
s t e a d y s t a t e pH.
:
Release o f Boron with Time
Several s t u d i e s were unde rta ken t o i n v e s t i g a t e t h e i n f l u e n c e o f
c o n t a c t time on t h e c o n c e n t r a t i o n o f boron in t h e l e a c h a t e s o l u t i o n s .
The r e s u l t s a r e summarized in Fig ur e 5 and Table 6.
The amount o f
boron r e l e a s e d e x h i b i t s a r a p i d i n i t i a l i n c r e a s e , with t h e r a t e o f
r e l e a s e d e c r e a s i n g with t im e .
72 yg B/g
ash in 216 h o u r s .
le ac he d i s o nly 36 yg B/g,
For example, sample A4 r e l e a s e s
A f t e r 720 hours t h e a d d i t i o n a l boron
ash.
Boron c o n c e n t r a t i o n e x h i b i t s a s t e a d y - s t a t e va lu e a f t e r a p p r o x i ­
m a te ly t h i r t y day s.
ash ty p e used.
Boron l e a c h i n g r a t e s a r e c h a r a c t e r i s t i c o f t h e
T h e r e f o r e , l e a c h i n g r a t e d i f f e r e n c e s shou ld be
c o n s i d e r e d when comparing a n a l y s e s o f d i f f e r e n t ash t y p e s .
To compare
s t u d i e s o f t h e same ash b u t d i f f e r e n t l e a c h i n g t i m e s , t h e I caching
v a lu e s can be c a l c u l a t e d t o s t a n d a r d i z e t h e time r e l a t i o n s h i p .
I t i s i n t e r e s t i n g t o note t h a t t h e boron c o n c e n t r a t i o n s co n ti n u e
t o change a f t e r t h e pH o f t h e l e a c h a t e s o l u t i o n s has approached i t s
steady s t a t e value.
In a d d i t i o n ,
t h e s p e c i f i c conductance remains
e s s e n t i a l l y c o n s t a n t d u r in g t h i s tim e span.
/
F ig ur e 5
Rel ease o f Boron from Ash as a Function o f Time.
w a t e r ; curve (b) 55 g
Curve (a ) 60 g
A 6 / 1 i t e r o f Pop la r River
A 4 / 1 i t e r o f Boundry Dam w a t e r ; curve (c) 55 g AS/1 i t e r o f Boundry
Dam w a t e r .
Time, Hours
30
Tabl e 6
Rel ease o f Boron with Time.A6, A4, AS, 60 g / 1 , 55 g / 1 , 55 g / 1 , open t o at mo sp here, r e s u l t s in
ug B/g
a sh .
ie: hours
216
a_
b
Cl
259
72
30
384
-
89
36
552
-
95
44
720
_
108
. 39
1680.
294
31
V a r i a t i o n o f Boron Leached with pH
Ash samples A4, AS, and AS were le a c h e d with s o l u t i o n s o f v a r i o u s
hydrogen ion c o n c e n t r a t i o n s t o de te r m in e t h e e f f e c t s upon boron Teach­
ability.
per l i t e r .
These Teachings were done a t ash c o n c e n t r a t i o n s o f 1 .0 gram
In a d d i t i o n , sample A4 was s t u d i e d over t h e same pH range
and a t an ash c o n c e n t r a t i o n o f 5 .5 grams p e r l i t e r .
The r e s u l t s o f
t h e s e s t u d i e s a r e summarized in F ig u r e s 6 and 7 and Tabl e 7.
The d a t a i n d i c a t e s t h a t boron T e a c h a b i l i t y i s i n f l u e n c e d by
hydrogen ion c o n c e n t r a t i o n and t h a t boron i s most r e a d i l y le ach ed i n t o
acid s o lu tio n s .
Sample A4 a t 5.5 g/1 le a c h e d 0 . 8 mg B/g a t pH 2.5 and
0 . 4 mg B/g a t pH 12 .0 .
Many el em en ts e x h i b i t enhanced r e l e a s e from s o l i d m a t e r i a l s
under high and low pH c o n d i t i o n s ( 3 3 ) .
S in c e boron forms a n i o n i c
s p e c i e s , i t s T e a c h a b i l i t y may be enhanced a t h i g h e r pH v a l u e s .
Other
s t u d i e s i n d i c a t e t h e boron l e a c h i n g r a t e i s g r e a t e r in a c i d , b u t t h a t
t h e t o t a l amount l e a c h e d was pH in d e p e n d e n t over t h e range o f 6-9
(13,14).
Acid t e a c h a b l e Components
The d i s s o l u t i o n o f t h e ash samples with a m ix tu r e o f a c i d s , HCl/
HNOg/HF, a t 100°C, was u t i l i z e d t o p r o v id e an i n d i c a t i o n o f t h e t o t a l
a v a i l a b l e ^ s o d i u m , p o t a s s i u m , c a l c i u m , magnesium, and boron.
a r e summarized in Table 8.
The r e s u l t s
The v a l u e s f o r p o ta s s iu m , c al c iu m , and
Figure 6
Rel ease o f Boron from Ash as a Function o f pH, I q / 1 .
Boron r e l e a s e d
A4, AS, AS, open to at mo sp here, tim e:
mg B/g
192 h o u r s .
Figure 7
Release o f Beron from Ash as a Function o f pH, 5 .5 q / 1 .
Boron r e l e a s e d
A4, open t o a tm os ph er e , tim e: 720 ho u rs .
0.73 -
0 . 5 5 -•
0 .3 7 -
PH
34
T a b le 7
Rel ease o f Boron as a Function o f pH.
AS, AS T g / 1 , A4 5 .5 g / 1 , r e s u l t s in mg/g.
pH
A4(l q /1 )
AS
AS
-
2 .6
-
-
4. 0
-
-
1.1
4.4
-
- .3 .
-
5.0
7. 0
1 .7
-
7.3
-
-
.2
.6
A 4 ( 5 .5 g/1.)
.78
—
.54
.49
-
-
-■
-
- •
7 .5
.5
8.0
-
.2.
.5
-
8 .2
.5
-
—
-
8 .7
--
--
—
.47
9 .7
-
-
-
.45
9.8
.5
-
-
-
9 .9
-
.5
-
10.0
-
.2
-
-
12.0
.6
.3
.7
.42
.
35
Table 8
Acid t e a c h a b l e Components o f Ash.
, A2, A3, A4, AS, r e s u l t s in mg/g.
Na
K
Ca
M
B
Al
39.9
8 .7
49 .4
16.9
0.68
A2- .
61.7±15.1
14 . 4± 1 .6
46.9+32.9
15.8±4.3
0.86±.51
A3
43.7
12.1
53.4
12.2
.67
A4
6 0 .3
3.9
6 4 .8
23.9
.57
AS
71 .4
17.7
37.6
13.1
2.62
ample
2 ml o f aqua r e g i a , p l u s I ml o f 48.9% HF f o r 4 hours a t IOO0C5
50 mg. o f a sh .
36
magnesium a r e comparable t o t h o s e o b t a i n e d by o t h e r i n v e s t i g a t o r s ( 3 , 7 ,
17) .
The sodium v a lu e s a r e comparable o r somewhat g r e a t e r .
The
boron v a l u e s a r e h i g h e r than th o s e obser ved by Fur r ( 7 ) , Dreesen ( I ) ,
Gladney (35) and von Lehmden ( 6 ) , b u t comparable t o t h o s e observed by
Cox ( 3 ) .
The v a l u e s o f i r o n and aluminum. Table 9 , a r e lower than
t h o s e obser ved by o t h e r i n v e s t i g a t o r s ( 3 , 6 , 7 , 1 7 , 3 3 ) .
The d a t a in
Tabl e 10 a l s o i n d i c a t e t h a t I M HCl and I M HNOg a r e not as e f f e c t i v e
in l e a c h i n g t h e i r o n and aluminum as t h e aqua regia-HF m ix tu r e a t
IOO0C.
For e xam ple , A4 r e l e a s e d 0 . 5 mg. B/g with I M HCl b u t only 0 .2
mg B/g w it h I M HNOg.
Data p r e s e n t e d in Table 11 i n d i c a t e s an
i n c r e a s e in t e m p e r a t u r e t o 150°C r e s u l t s in a l o s s o f m a t e r i a l ,
p o s s i b l y thro ugh v o l a t i l i z a t i o n , and th u s h i g h e r t e m p e r a t u r e s a re
n o t recommended.
A4 r e l e a s e d 0 .6 mg B/g a t IOO0C in t h e P a r r
Bomb d i g e s t , b u t 0 . 4 mg B/g was obser ved when t h e te m p e r a t u r e
was r a i s e d t o 150oC.
The c o n c e n t r a t i o n o f aluminum and i r o n in
s l i g h t l y b a s i c s o l u t i o n s was l e s s than 0.1 mg/g, which i s in agreement
w i t h p r e d i c t i o n based on t h e s o l u b i l i t y o f th e r e s p e c t i v e h y d ro xid e s .
Ash M a te r ia l Homogeneity
Five samples o f A2 were le a c h e d t o e s t a b l i s h t h e homogeneity o f
the m a te ria l.
The r e s u l t s a r e summarized in Table 12.
The s t a n d a r d
d e v i a t i o n s a r e s i z a b l e (59% f o r boron) and s u p r i s i n g s i n c e t h e
m a t e r i a l had pa sse d th ro ugh 100 mesh s c r e e n .
Since t h e r e a r e r e p o r t s
37
Tabl e 9
Acid Leachable Iron and Aluminum.
A l $ A2, A3, A4, AS, r e s u l t s in mg/g.
Co nditi ons
Sample
Al
A2
A3
A4
AS
I (a)
2 (b)
3 (c)
4 (d)
Fe
10.0
8.3
29.4
29.0
Al
22.5
29.3
94.5
17.1
Fe
12.2
12.2
43.1
27.2
AT
67.6
84.3
110.4
15.1
Fe
8 .0
10.1
. 32.5
24.5
Al
18.1
31.9
57.3
<1.0
Fe
13.9
14.2
20.0
21.5
Al
84.3
83 .9
92.3
4 .2
Fe
13 .4
13.7
29.1
25.3
Al
22.5
4 2 .2
86.0
<1.0
Element
(a)
I M HCl, I g. a s h / 1 , 25°C f o r 24 ho urs .
(b)
I M HNO3 , I g
(c)
2 ml aqua r e g i a p l u s I ml HF a t IOO0C f o r 4 h o u r s , 50 mg ash .
(d)
2 ml aqua r e g i a plus; I ml HF a t ISO0C f o r 2 h o u r s , 50 mg ash.
a s h / 1 , 25° C f o r 24 ho u rs .
38
Table 10
Boron Leached with I M HCl and I M HNO
A2, A3, A4, AS, I g
ash/1 , 24 h o u r s . r e s u l t s in i
I M HNO0
Sample
I M HCl
Al
0 .7
0 .5
A2
1 .0
0 .2
A3
0 .7
0 .2
A4
0.5
0 .2
AS
1.0
0 .5
39
Table 11
P a r r Bomb Acid D i g e s t i o n s .
A l, A2, A3, A4, AS, 0.050 g a s h , 2 ml aqua r e g i a , I ml HF bro u g h t t o
50 ml w i t h d o u b l y - d i s t i l l e d w a t e r . r e s u l t s in mg/g.
IOO0C1 4 hours
Sample
Na
K
Ca
. Mg,
Al
40
9
49
17
7.4
A2
42
14
92
17
9 .6
A3
44
12
S3
12
7 .4
A4
60
4
65
24
6.3
AS
71
18
38
13
8.6
%
Ca
Mg
B
I O 1 XB
150°C, 2 hours
Sample
Na
Al
60
8
45
12
1.1
A2
28
20
33
9
0.8
A3
27
9
38
.11
0 .4
A4
48
I
55
22
0 .4
AS
32
I
29
15
0.9
'
Tabl e 12
D e te r m in at io n o f Ash Homogeneity.
P a r r Bomb a c i d d i g e s t o f 5 samples o f A2,
0.50 g a s h , 2 ml aqua r e g i a
I ml HF, IOO0C, 4 hours bro ug ht t o 50 ml with d o u b l y - d i s t i l l e d w a t e r ,
r e s u l t s in mg/g.
Sample
Na
K
Ca
Mg;
B
A2r.l
63
13
72
14
0 .9
A2-2
77
14
23
17
0.4
A2-3
51
14
19
21
0.8
A2-4
75
17
29
A2-5
42
14
92
17
1 .8
mean
61.7
14.4
46.9
15.8
0.86
standard
deviation
15.1
.1.6
32.9
4 .3
0.51
.
9'
0 .4
'
41
( 1 5 , 1 6 , 1 7 , 3 6 ) t h a t com pos ition v a r i e s with p a r t i c l e s i z e , a d d i t i o n a l
s i z e f r a c t i o n a t i o n was cond uct ed .
Three subsamples o f A4 were
s e p a r a t e d , 75-100 pm, 45-75 pm, and l e s s than 45 pm.
These samples
were l e a c h e d with d i s t i l l e d w a t e r f o r 24 hours a t I g ash/1 i t e r .
r e s u l t s a r e shown i n T a ble s 13 and 141
The
S i m i l a r l y , ashe s A4, AS, and
A6 were f r a c t i o n a t e d , 125-150 pm, 75-125 pm, 45-75 pm, and l e s s than
45 pm.
These samples were le a c h e d a t t h e same c o n d i t i o n s f o r 1176
hours.
The r e s u l t s a r e p r e s e n t e d in Ta b le 15.
These d a t a i n d i c a t e
t h a t a m a j o r i t y o f t h e a v a i l a b l e boron comes from t h e s m a l l e s t
p a r t i c l e s , A6 y i e l d s 0 .5 mg/g from p a r t i c l e s l e s s than 0.45 pm b u t
o n l y 0 . 2 mg/g f o r p a r t i c l e s 125-150 pm.
Though n o t as pronounced,
t h e r e i s an i n c r e a s e in l e a c h e d sodium, c a l c i u m , p o t a s s i u m , and mag­
nesium as t h e p a r t i c l e s i z e d e c r e a s e s . . The s t a n d a r d d e v i a t i o n s a r e
c o n s i d e r a b l y s m a l l e r than th o s e shown in Ta ble 12.
Boron a n a l y s e s o f
A4 p a r t i c l e s , which were l e s s than 45 pm, had a s t a n d a r d d e v i a t i o n o f
1%.
The use o f small s am pl es , 50 mg, and p a r t i c l e s i z e v a r i a b i l i t y i s
b e l i e v e d to be t h e main c o n t r i b u t o r t o t h e l a r g e r s t a n d a r d d e v i a t i o n s
(shown in Ta ble 8 ) .
The s t a n d a r d d e v i a t i o n s f o r t h e a n a l y t i c a l
pr oc e dur es a r e much l e s s tha n t h e obs erved v a l u e s .
Except f o r t h e d a t a
in t h e p a r t i c l e s i z e s t u d i e s , a l l l e a c h i n g e xper im ent s used ash t h a t
passe d through 100 mesh s c r e e n ( s i 50 pm).
This could cause sample
inho mog en eity, b u t t h e samples a r e more r e p r e s e n t a t i v e o f ash used
in the s lu ic in g process.
Table 13
I n f l u e n c e o f P a r t i c l e Size on t h e A v a i l a b i l i t y o f Boron, Sodium, Magnesium, and Calcium.
T r i p l i c a t e samples o f A4.
I g
Mesh Size
Leach
no.
75-150 ym
1
7.5
2
7 .4
3
7 .5
pH
units
a s h / 1 , 24 h o u r s , r e s u l t s in mg/g and s t a n d a r d d e v i a t i o n . ( S . D . ).
IO1XBZS-D.
Na/S.D.
Ca/S.D.
-Ck
ro
45-75 ym
<45 ym
1
8.0
2
7.9
3
7 .7
1
8.4
5.5\
2
8 .3
5.5
3
8 .3
5.5'
.00
,17
1 .07'
Table 14.
I n f l u e n c e o f P a r t i c l e Size on t h e A v a i l a b i l i t y o f
Boron, Sodium, Magnesium, and Calcium, Composite.
A4, 24 hour c o n t a c t , I g / 1 .
Calcium
mq/q
Size
Increment
P e rc e n t
o f Tot al
Boron
uq/q
Sodi urn
mg/q
. Magnesium
mq/q
75-100 wn
10.4
73±13
0 . 9 6 ± .08
0 . 3 1 ± .03
5.90+.23
7.5+0.0
45-75 urn
9 .3
97+20
I . 00+.13
0.44±.U
7 . 98±.45
7.9+0.2
<45 Um
80 .3
548+ I
I . 32+.04
I . 02±.09
——
8.3+0.1
EU
Table 15
P a r t i c l e S iz e S tu d y , 4 S i z e S e p a r a t i o n s .
T r i p l i c a t e s o f A4, AS, A6, I g
a s h / 1 , leache d in d o u b l y - d i s t i l l e d w a t e r , 1176 h o u r s , r e s u l t s
in mg/g u n l e s s o t h e r w i s e s t a t e d , s t a n d a r d d e v i a t i o n ( S . D . ) .
Sample A4
Particle
Leach
pH
S. C ./S .D .
K/S.D.
Ca/S.D.
1
Q.68\
2
0.46
3
0.50^
7.5
1
0 . 36\
11.9
2
0.2 9 \ .08 12.0
3
0.45'
75-125
45-75
Mg/S.D.
101B/S.D.
8.6
Vl2
8 .3
10.5
1
2
3
125-150
75-125
\
1
7 .9
59\
2
8.0
53 > 3 . 1
3
7 .9
c/
56'
,30
1
.04
3
0 .9 7 '
1
.2
2
1.01
0.53.
9 . 8 > .59
0.38
8.7
0.59
10.Ox
0.90x
>. 05 10.0
>.09
10 . 2'
1
1 . 58x
1 6 . 7\
2
1.48 \
3
1 .49'
67'
0.92
8 . 8,
0 .9 5 '
8.0
3
125-150
>.35
8.5'
2
45-75
8.4
0.67
.0
1 .5
>.12
1.5 >0.0
1.5
0 .8 0 '
.06 16.0
16.9'
1
2
3
75-125
1 . 6\
9.3X
1
07
2
8.6 > .3 8
0.5 3
.62
2 .6
> .14
1 .6
>.02
3
45-75
\ \,
1
4.3x
2
0.22 > .03 12.3 >2.07
0.18 > .23
3 . 8 > .25
1 .5 > .01
3
0 .1 7 '
12.8'
0 .4 3 '
4.1'
1.7 '
0.52,
21.2,
1
8 .5 161s
2
8.4
3
8 . 5 ISSy
166
>2 .6 0.65
0.48'
> .09 20.7 > . 3 3
20.6'
0.45\
5.5
0.25 \
.12 5 .8
0.46'
5 .8
. 45
Table 16
S e p a r a t i o n o f Ash by Mesh S i z e .
A4, AS
opening
size
mesh
m
100
150
120
125
200
75
325
S i z e , urn
45
.
Upper Ash (A4)
Bottom Ash (AS)
<100
4.82%
27.1935
<120
10. 41%
50.97%
<200
9 . 33%
16.49%
<325
80. 26%
32. 25%
46
In t h e i n i t i a l s i z e s e p a r a t i o n shown in Table 16, sample
AS y i e l d e d 32.35% i n t h e s m a l l e s t f r a c t i o n and sample A4 80.26%
in t h e same s i z e f r a c t i o n .
Release o f Boron a t D i f f e r e n t Ash t o Water R a t i o s .
Tabl e 17 summarizes t h e r e s u l t s o f a l e a c h i n g s t u d y a t t h r e e
c o n c e n t r a t i o n s , o f f i v e s am pl es , l e a c h e d in' r e s e r v o i r w a t e r f o r 768
ho u rs .
Table 18 summarizes a l e a c h i n g s t u d y a t s i x c o n c e n t r a t i o n s o f
samples A4,.A5, and A6 in d o u b l y - d i s t i l l e d w a te r f o r 456 ho urs . The
c o n c e n t r a t i o n o f boron in t h e l e a c h a t e s o l u t i o n s i s dependent upon
I
t h e r a t i o o f ash t o w a t e r . Thi s dependence i s shown in Fig ur e 8 and,
in Table 19.
The n o n l i n e a r b e h a v i o r i n d i c a t e s in co mp le te r e l e a s e o f
boron when.t h e a s h - t o - w a t e r r a t i o i s i n c r e a s e d .
For exam pl e, A4
l e a c h e s 0 . 7 mg B/g ash a t I g ash/1 b u t l e a c h e s 0.1 mg
a t a c o n c e n t r a t i o n o f TOO
g a sh /1 .
B/g ash
Leached boron c o n c e n t r a t i o n i s
dependent upon ash ty p e , . . w i t h t h e l a r g e s t amount being r e l e a s e d from
t h e upper ash .
-
.
Using t h e boron r e l e a s e d in t h e I g/1 s o l u t i o n s as an e s t i m a t e
o f t h e t o t a l a v a i l a b l e boro n, i t i s p o s s i b l e t o c a l c u l a t e t h e
amount o f boron t h a t i s r e t a i n e d by t h e ash in t h e s o l u t i o n s where
the ash-to -w ater r a t i o i s higher.
The d a t a are p r e s e n t e d i n Table 20
The v a l u e s in Table 20 a r e comparable t o th o s e r e p o r t e d by Choi and
Chen ( 1 4 ) .
A p l o t o f ug boron r e t a i n e d / g o f ash as a f u n c t i o n
f
47
Ta ble 17
I n f l u e n c e o f Ash C o n c e n t r a t i o n on L e a c h a b i l i t y in R e s e r v o i r Water.
A l , A2, A3, A4, AS, 768 h o u r s , r e s u l t s in mg/1 u n l e s s o t h e r w i s e s t a t e d .
g/1
'
25 g/1
100 g/1
O
O
CU Il
I
umhos/
cm
HCO3-
NO3
Al
8 .7
751
198
—
CO
Cone.
pH
Sample u n i t s
4.4
A2
8 .7
746
221
12
8 .7
195
79
11
10
48
24
0.5
. 0 .5
A3
8 .7
777
234
• 15
3 .9
186
76
11
10
55
24
0 .7
0. 7
A4
8 .7
801
247
14
4 .6
195
79
10
10
56
26
0 .7
0 .7
AS
8 .7
744
212
8
3 .5
188
76
12
11
43
22
0.4
8.8
896
260
23
4 .0
240
82
15
11
30
49
3.1
A2
8.8
905
228
29
1.5
255
86
17
10
23
48
5.0
A3
9.0
1015
239
50
3.1
300
89
12
12
29
62
8 .5
0 .3
A4
8.8
839
158
26
2 .0
267
89
12
11
71
18
7. 9
0 .3
AS
8.7
830
263 ■
16
1.4
215
84
13
9
34
32
1 .7
0.1
Al
8.9
1141
205
50
6.1
379
101
13
14
25
73
12 .8
0.1
A2
9.1
957
-
-
1.4
339
116
15
11
62
11
11 .0
0.1
A3
9.3
991
131
7
2 .5
354
123
12
11
78
4
15.3
0.2
A4
9.5
892
14
95
2 .0
280
123
I
10
55
3
12 .8
0.1
AS .
8.8
942
246
22
1 .3
267
116
11
12
21
37
0.4
0 .0
Al
.
so;
Na+
K+
Cl"
Ca++
Mg+'+
B
B.mq/g
183
74
13
13
44
25
0 .5
0 .5
■
.
0 .4
0.1
.
0. 2
48
Table 18
Rel ease o f Boron as a Function o f Ash C o n c e n t r a t i o n .
T r i p l i c a t e o f A4, AS, AG.
I 9/1
12.5 g/'i
456 h o u r s , d o u b l y - d i s t i l l e d w a t e r l e a c h .
PU
S.C.
mmhos/
cm
A4-1
8 .4
—2
.
B ug/ml
B y g/q ash
,1.54
0.4 9
489
8.4
1.62
0.56
543
-3
8.4
1.61
0.49
A5-1
7.9
.88
0.13
1.33
-2
8.0
.86
0.17
169
-3
8.0
.86
0.13
131
AG-1
8 .3
1.31
0.42
425
-2
8.4
1.34
0.43
418
-3
8 .4
1.31
0.46
457
A4-1
8 .7
3.07
4.4
-2
8 .9
3.06 .
4.4
350
-3
8 .7
3.26.
4.4
352
A5-1
8.6
2.23
0 .83
66
-2
8.5
2.33
0 .70
56
-3
8 .5
2.34
0 .21
17 .
Avg.
509
494
.
■
144 ■’
433
348
\
350
46
49
Table 18 ( c o n t i n u e d )
25 g/1
50
g/1
EtL
S.C.
mmhos/
cm
A6-1
8.8
3.0 8
3.6
285
-2
8 .9
3.16
3 .6
.289
-3
8.8
3.12
5 ,2
419
A4-1
9.2
3.33
6 .6
264
-2
9.1
3.21
6 .2
249
-3
9 .0
3.54
7.0
281
A5-1
8.7
3.37
1.2
48
-2
8.7
3.38
1 .3
50
-3
8 .7
3.28
1 .2
46
AG-1
8 ,7
3.50
6 .4
256
-2
8.8
3.55
6 .3
252
-3
8.8
3.72
6 .3
251
A4-1
9 .5
4.26
7.1
141
-2
9.5
4.27
9 .5
190
-3
9.8
4.64
9 .6
192
A5-1
8.8
3.72
2.1
43
-2
8.7
3.89
2.1
42
-3
8 .7
3 .7 4
2 .2
43
.
B yg/ml
B u g/g ash
Avg.
-
331
265
48
253
174. .
43
50
Table 18 ( c o n ti n u e d )
75 g/1
TOO g/1
PH
S.C.
mmhos/
cm
A6-1
8 .2
4.15
8 .4
169
-2
9 .2
3.91
7 .8
156
-3
. 9.3
3.47
6.8
137
A4-1
9.6
4.05
11.1
148
-2
10.2
4.22
11.2
150
-3
10.0
4.22
12.1
162
A5-1
9.2
4.12
2.8
38
-2
8.8
4.11
2.7
36
-3
8.8
4.21
2.9
39
A6-1
9.8
4.79
9.6
128
-2
9.8
4.65
9 .5
127
-3
9.8
5.00
10.2
136
A4-1
10,3
4.35
13.0
129
-2
10 .4
4.43
12.1
121
-3
9 .6
. 5.41
15.7
157
A5-T
8.9
4.0 8
3.1
31
-2
8 .9
4.32
3 .6
36
-3
9 .0
4,24
3 ,6
36
B uq/ml -
*
B y g / g ash
Avg.
154
153
38
130
136
34
51
Table 18 (c o n t i n u e d )
M
S.C.
. mmhos/
cm
B yg/ml
1 B y q / q ash
A6-1
10.4
4.46
7 .8
78
-2
10.3
4.82
9.1
91
-3
9.8
5.21
11.4
114
Avg
94
Figure 8
Release o f Boron from Ash as a Function o f C o n c e n t r a t i o n .
tim e:
456 h o u r s .
O
40
g ash/I
120
(
53
Tabl e 19
Sunmary:
Rel ease o f Boron as a Fun ction o f Ash C o n c e n t r a t i o n .
AS, AS, ti m e : 456 h o u r s , I r e s u l t s in mg B/l and (m g/g ).
Concentration
g ash/1
1 .0
'
ML
■ 0.51
A6
AS
( 0 .5 1 )
0.14
( 0 .1 4 )
0.43I ( 0 .4 3 )
12.5
4.4
( 0 .3 5 )
0.61
(0. 05)
3.7
(0.30)
25 .0
6 .6
(0.26)
1.2
(0. 05)
6 .3
(0 .2 5)
50.0
9.5
( 0 .1 9 )
2.1
(0 .04)
7 .8
(0 .1 6)
75.0
11.3
(0 .1 5)
2.8
(0.04) .
9.6
(0. 13)
100.0
13.5
( 0 .1 4 )
3.5
(0 .04)
10.5
(0 .1 1)
54
Table 20
Boron Released and Ret ain ed a t Various Leaching R a t i o s .
A4, AS, AG,
t im e : 456 hours*
Boron Leached
(yg/ml)
Boron Retaine d
(y g/g )
R at io A s h / W a t e r ^
(g/D
M
AS
AG
M
AS
AG
1 .0
0.5
0.1 .
0.4
--
—
——
12.5
4.4
0.8
4.1
158
83
102
25 .0
6 .6
1 .2
6 .3
244
96
180
50 .0
9.5
2.1
7.7
318
102
279
75 .0
11.5
2.8
9 .8
355
107
303
100.0
. 13.6
3 .4
9.4
373
no
339
^a H o t a l volume 50 .0 ml
'
55
p f yg B/ml i s shown in Fi gu re 9.
Sample AS, which i s bottom a s h , e x ­
h i b i t s a maximum r e t e n t i o n o f 105 yg B/g a sh .
S l u i c i n g t h i s ash a t 55
g/1 shou ld p r o v id e l e a c h a t e w a te r s c o n t a i n i n g 1.9 mg B / l .
The r e ­
t e n t i o n b e h a v i o r f o r A4 and AG i s n o t as well d e f i n e d , b u t t h e shape
o f t h e cu rve i n d i c a t e s Langmuir b e h a v i o r , with a l i m i t i n g va lu e in
e x c e s s o f 400 yg B/g.
C o r r e s p o n d i n g l y , t h e s l u i c i n g o f t h e s e ash
m a t e r i a l s a t 55 g/1 would p ro v id e boron c o n c e n t r a t i o n in e x c e s s o f
t h o s e p r e d i c t e d f o r t h e bottom a sh .
The r e t e n t i o n o f boron by t h e ash
m a t e r i a l c o m p l i c a t e s t h e a ss e ss m e n t o f how much boron w i l l be r e l e a s e d
t o a n a t u r a l w a t e r system o ve r a given time span .
These r e s u l t s
i n d i c a t e t h a t t h e I mg/1 a g r i c u l t u r a l l i m i t may be ex ceeded.
However,
s i n c e n o t a l l o f t h e boron, i s removed i n i t i a l l y , t h e r e w i l l be a
dependence upon how r a p i d l y w a t e r moves thro ugh t h e system.
The boron r e t a i n e d by t h e ash m a t e r i a l i s r e a d i l y a v a i l a b l e , as
ev id en ce d b y . t h e f o l l o w i n g .
The A4 ash from, t h e 50 g / 1 , 75 g / 1 , and
100 g/1
l e a c h i n g e xpe r im en t s was i s o l a t e d and r e l e a c h e d a t a r a t i o o f
I g/1.
The t o t a l a v a i l a b l e boron was r e l e a s e d from t h e ash and found
in t h e l e a c h a t e s o l u t i o n s .
The r e s u l t s a r e shown in Tabl e 21.
There
i s good agreement between t h e boron r e l e a s e d by t h e s e r e l cachi ngs
and t h a t e x p e c te d from c a l c u l a t i o n s .
g
ash/1 r e l e a s e d 136 yg B/g
resusp en ded a t I g
ash/1.
A4 ash when l e a c h e d a t 100
ash and r e l e a s e d 498 yg B/g
ash when
A4 a t I gi ash /1 leache d 508 yg B/g
ash .
56
Figure 9
Boron R etained by Ash as a Function
o f Boron C o n c e n t r a t i o n .
A4, AS, A6,
ti m e :
456 h o u r s .
A4 c *
AS c Q
ug ES/ ml
57
T ab le 21
Re le a se o f R e t a i n e d Boron.
A4,
24 h o u r s , d o u b l y - d i s t i l l e d w a t e r .
original
concentration
g ash/1
ug B/g ash
when le ach ed
a t I q./l
I
508
50
523
75
460
100
498
58
Boron Adsorbed a t Varying S o l u t i o n C o n c e n t r a t i o n s .
Ash t h a t was c o n d i t i o n e d by w a t e r washing was mixed with s o l u t i o n s
c o n t a i n i n g v a r y i n g c o n c e n t r a t i o n s o f boron t o de te r m in e a d s o r p t i o n ,
t h e r e s u l t s a r e shown in Fig ur e 10 and Table 22.
Many d a t a p o i n t s
were c o l l e c t e d t o compensate f o r t h e s c a t t e r i n g due t o v a r i a b i l i t y o f
t h e a sh .
The ash a dsor bed boron w it h a F r e u n d li c h ty p e b e h a v i o r .
Choi
and Chen (14) have a l s o r e p o r t e d F r e u n d li c h a d s o r p t i o n is o th e rm s f o r
boron a d s o r p t i o n onto s o l i d s .
The amount o f boron a d s o r p t i o n was
dependent upon t h e c o n c e n t r a t i o n o f b o r o n . i n t h e s o l u t i o n .
example, sample A4 has t h e c a p a c i t y t o a dso r b 36 mg B/g
g ash/1 and w i t h 160 mg B/ I in s o l u t i o n .
For
ash a t 55
The amount adsor bed i s
a f u n c t i o n o f ash t y p e , amount o f ash in s o l u t i o n , and c o n c e n t r a t i o n
o f boron.
range.
The pH f o r t h e s e ex perim en ts was held a t t h e 8 . 6 - 8 . 8
Thi s i s w i t h i n t h e maximum a d s o r p t i o n pH range o f 6-9
r e p o r t e d by o t h e r s ( 1 4 , 2 5 , 3 0 , 3 1 ) .
Tris b u ffe r a t a concentration
o f 0 .5 M was used t o m a i n t a i n pH.
The e f f e c t s o f t h i s b u f f e r from 0.1
M t o 1 .0 M were s t u d i e d .
Ina de quat e b u f f e r i n g c a p a c i t y was found
below 0 . 5 M T r i s and t h e r e were no b u f f e r e f f e c t s u p . t o 1 . 0 M.
Ad sor pti on o f Boron by Acid Con dition ed Ash.
The e f f e c t s on boron a d s o r p t i o n by ash c o n d i t i o n e d with a cid
were s t u d i e d .
A sample o f A 4 was washed with I M HNOg and a n o th e r
sample o f A 4 w i t h I M H C l .
The d a t a i n Table 23 and shown in
;
59
Figure 10
Adsorption o f Boron by Water Co nditio ne d Ash.
10"
X Boron a d s o r b e n t (mg/g)
A4, 0 . 5 M T r i s b u f f e r , pH 8 . 6 , 55 g a s h / 1 .
Boron S o l u t i o n (mg/1)
Table 22
Ad sor pti on o f Boron onto Water Conditioned Ash.
A4, pH 8 . 6 , 55 9
10_1xB
b a s e l i n e mg/1
a s h / 1 , 48 hour a d s o r p t i o n , r e s u l t s in mg/1 and mg/g.
10'-1xB added
t o s o l u t i o n mg/1
J O -1 x B
change in
b a s e l i n e mg/1
10-1 xB in
s o l u t i o n mg/1
10- 1 xB
adsorbed mg/1
10- 1 xB .
adsorbed mq'/q
0 .2
0.0
0.1
0 .3
-
0 .2
0.0
0.1
0 .4
-
-
0 .2
0 .4
0.1
0 .7
-
-
0.3
0.8
0.1
1.0
0.2
0 .2
1.1
0.1
1.3
0.1
0.2
0 .2
1.2
0.1
1.3
0.2
0 .4
0.2
1.2
0.1
1 .3
0 .2
0 .4
0 .2
1.5
0.1
1.7
0.1
0.2
0 .2
1.6
. 0.1
1.6
0 .3
0.5
0.2
2.0
0,1 .
2.1
0 .2 .
0 .4
0 .3
2 .0
0.1
2 .0
0 .4
0 .7
0.2
2.4
0.1
2 .3
0 .4
0 .7
.
0 .4
-
Table 22 (c o n ti n u e d )
10_1xB.
b a s e l i n e mg/1
10- 1 xB added
to s o l u t i o n mg/1
IO- ' x B
change in
b a s e l i n e mg/1
10-1xB in
s o l u t i o n mg/1
IO- 1 XB
adsorbed mg/1
IO- 1 XB
adsorbed mg/g
0.1
2.6
0.1
0 .2
0.1 .
3 .9
0. 4
0. 7
. 0.1
5 .0
0 .4
0 .7
7 .4
0.1
7 .0
0.7
1.3
0.2
7.5
0.1
7.0
0 .8
1 .5
0 .2
9 .5
0.1
8.8
1 .0
1 .8
0.2
10.0
0.1
9 .0
1.3
2.4
0 .2
12.0
0.1
11.0
1.3
2 .4
0.3
13.0
0.1
11.0
2.4
4.4
0 .2
14.0
0.1
13.0
1.3
2 .4
0 .2
15.0
0.1
13.0
2.3
4 .2
0.2
2 .4
0 .2
4.0
0.2
5.1
0 .2
.
!
62
T ab le 23
A ds o r p ti o n o f Boron on Acid Washed Ash.
A4, pH 8 . 5 , 55 g . a s h / 1 , 48 h o u r s , r e s u l t s in mg/1 and mg/g.
O^xB added t o
s o l u t i o n mb/1
IO- 1 XB in
s o l u t i o n mg/1
10- 1 xB
adsor bed mg/1
10- 1 xB
adsorbed mg/g
1 .9
1.9
0.2
0.4
5.9
4.9
1.1
2 .0
8 .0
6.8
1 .3
2.4
9 .9
8.3
1 .7
3.1
63
F ig ure 11 i n d i c a t e s t h a t a d s o r p t i o n by t h e s e ashes was more than onto
w a t e r washed a sh . • Sample A4, when w a t e r c o n d i t i o n e d , adsorbed 0.13 to
0. 18 mg/g onto 55 g ash in a l i t e r o f 70 mg/1 boron s o l u t i o n .
When
A4 was a c i d washed i t a d s o r b e d ; 0.24 mg/g under t h e same c o n d i t i o n s .
Perhaps t h i s i s due t o i t s a b i l i t y t o "c l e a n " t h e a d s o r p t i o n s i t e s
o f in te rfe rin g species.
The e f f e c t s o f s o l u t i o n pH on t h e a d s o r p t i o n o f boron by ash A4
i s shown i n Fi g u r e 12 and i n . T a b l e 24.
The r e s u l t s show t h a t t h e ash
i s l e s s e f f e c t i v e i n a d s o r b in g boron a t pH 9 . 5 than a t 8 . 6 .
Comparison o f d a t a in T a b le s 24 and 22 shows
t h a t in a 40 mg/1 boron
s o l u t i o n , A4 w i l l adsorb 0.73 :mg B/g a t pH 8 .6 and 0.36 mg/g a t pH 9 . 5 .
Since t h e p o s s i b l e e f f e c t o f ammonia b u f f e r i n t e r f e r e n c e i s undet ermi n­
ed, fu rth er in te rp re ta tio n
ca nno t
be made.
'The d a t a c o r r e l a t e s w it h
t h e pH dependence o f boron a d s o r p t i o n onto s o i l s as r e p o r t e d by o t h e r
a u t h o r s ( 1 1 , 1 4 , 2 5 , 3 0 , 3 1 ) and s u g g e s t s t h a t ash may f o l l o w a s i m i l a r
pH dependence b e h a v i o r .
R eg e ne ra tio n o f Ash S u r f a c e .
The f i n d i n g t h a t an i s o t h e r m g e n e r a t e d u s in g a c i d - c o n d i t i o n e d ash
e x h i b i t s h i g h e r a d s o r p t i o n c a p a c i t y tha n t h e w a t e r - c o n d i t i o n e d ash
s u g g e s t s t h a t t h e s u r f a c e s o f t h e s e ashe s may be s i m i l a r and c o n ta i n
l a r g e -amounts o f i r o n and aluminum.
Those samples which had been used
t o g e n e r a t e t h e i s o t h e r m s ( F i g u r e s 10 and Tl) were r e l e a c h e d with
64
F ig ur e 11
Adsorption o f Boron by HCl Co nditioned Ash.
a s h / 1 , pH 8 . 6 .
2.91 ■
10
xBoron adsorbed (mg/g)
A4, 55 g
1 . 45-
160
Boron s o l u t i o n (mg/1)
65
Fi gure 12
Ad so rp tio n o f Boron as a Fun ction o f S o l u t i o n C o n c e n t r a t i o n .
10" xBoron adsorbed (mg/g)
A4, w a t e r c o n d i t i o n e d a s h , pH 9 . 5 , 55 g ash/ 1, 0 .5 M ammonia b u f f e r .
Boron S o l u t i o n (mg/1)
66
Table 24
Ad so rp tio n o f Boron as a Fun ction o f Boron ini S o l u t i o n .
A4, 55 g / 1 , pH 9 . 5 , w a t e r c o n d i t i o n e d a s h , r e s u l t s in mg B/ml and
mg/g.
'
1 0 ' 2 xB in
s o l u t i o n (mg/1)
B ad sorbed
(mg/1)
? '
10 xB adsorbed
(mq/q)
0 .2
0.3
• 0.5
0 .4
0 .2
0.4
0.8
5.0
9.0
1 .0
3 .3
6.0
1.2
7.5
14.0
67
I M HCl a t 55
g ash/1.
The l e a c h a t e s were analyze d f o r aluminum and
i r o n and t h e r e s u l t s a r e shown in Table 25.
Water c o n d i t i o n e d ash
samples o f A4 y i e l d e d 13 t o 15 mg Fe/g and 73 t o 91 #g A l/ g .
Acid c o n d i t i o n e d A4 le a c h e d 8 t o 9 mg Fe/g and 51 t o 62 mg Al/g
in to the acid.
Table 26 shows t h e r e s u l t s from an e xper im en t in
which samples A4, AS, and A6 were washed f o r t h r e e s u c c e s s i v e
24 hour p e r i o d s a t I g ash per l i t e r with I M HCl, I M NaOH and
d o u b ly - d i s till e d water.
The c o n c l u s i o n o f t h i s e x pe r im en t was t h a t
a c i d was e f f e c t i v e in washing i r o n and aluminum from t h e s u r f a c e
o f ash.
Sample A4 r e l e a s e d a t o t a l o f 56 mg Al/g and 13 mg Fe/g
i n t o t h e 3 a c i d washes.
A4 r e l e a s e d
u n d e t e c t a b l e amounts o f ir on
and aluminum i n t o t h e w a t e r and b a s i c washes.
The combined r e s u l t s from t h e s e two ex periments l e a d t o th e
p o s s i b l e s u g g e s t i o n t h a t t h e r e i s r e g e n e r a t i o n o f t h e ash s u r f a c e .
Thi s co uld l e a d t o an i n t e r p r e t a t i o n c o n s i s t e n t with a
sputtering-
e t c h i n g e x pe r im en t run by Campbell and co-workers (37) which showed
t h e r e l a t i v e c o n c e n t r a t i o n s o f sodium, c a r b o n , oxyge n, and s u l f u r t o
d e c r e a s e w it h l a y e r d e pth b u t s i l i c a , aluminum, and i r o n t o i n c r e a s e
upon s p u t t e r i n g t o a depth o f a ppro x im a te ly f i f t y ang stroms .
R e l e a c h a b i l i t y o f Boron
Tabl e 25 s u g g e s t s t h a t boron r e l e a s e d with a c i d from samples o f
A4 which had p r e v i o u s l y adsorbed boron ( s e e Tables 22 and 23) i s
,68
T ab le 25
Acid Releaches o f Ad sor pti on Samples.
A4, HNOg l e a c h , 12 h o u r s , w at er c o n d i t i o n e d a s h , mg/g.
Sample
Fe
Al
.
B
1
15
91
0.4
2
13
87
0.5
3
13
87
0 .5
4
14
91
0.4
A4, HCl l e a c h , one h o u r , a c i d c o n d i t i o n e d a sh .
Sample
Fe
Al
IO1XB
. 5
10
58
0 .5
6
10
62
0 .7
7
10
55
0.6
8
8
51
0.6
9
10
58
0 .9
.
69
Table 25 (c o n t i n u e d )
Boron
initial
treatm ent
mg B/q
Sample Number
1
2
3
4
-o
CU
I—
C
r—
O
4->
t/>
•rXJ
I
>>
r—
-Q
3
O
LCD
-M
fti
3:
-M
rO
L- -C
-M C/)
C rO
C
U
CJ
C
O
U
-o
5
Boron adsorbed
by sample
mg B/g________
0 .9
0 .4
1.4
0.2
1 .8
0 .3
2 .4
0 .4
0.0
-
C
O
6
-M
i—
0 .3
fti
S- -C
C J -M CO
n: c m
CU
CJ
C
O
1 .0
0.2
1.5
0.2
1 .8
0 .3
U
9
70
Table 26
S u c c e s s iv e Washes with Acid (I M HCl) , DoublyD i s t i l l e d Water and Base (I M NaOH).
A4, AS, AG , I g a s h / 1 , 24 h o u r s , r e s u l t s in mg/g u n l e s s o th e r w is e
wash
no.
pH
units
S.C.
mmhos/cm
Fe
Al.
B
I
4.2
23.9
0 .5
17
9.6
0.6
2
3 .3
4 .6
7.8
34
6 .5
0 .4
3
2.3
6 .3
4 .4
5
2 .9
0 .4
doubly - I
distilled
water
2
11.0
21.0
-
-
0 .3
0 .4
9J8
6 .9
-
-
0.8
0.1
3
10.4
5.9
-
0.8
0.1
I
11.1
2.4
-
—
0 .6
0 .5
2
10 .8
1 .0
-
~
0.9
0.2
3
10.4
0.4
-
-
0.8
0.1
9 .4
0 .3
1 .7
2.3
0.5
0.3
0.3
0.3
acid
base
AS
acid
I
3.2
23.9
2
2 .2
8.9
3
2.1
7 .7
5 .4
.
17 •:
71
Tabl e 26 ( c o n ti n u e d )
wash
no.
pH
units
S.C.
mmhos/cm
Fe
Al_
Mg.
B
doub ly- I
distilled
water
2
9.5
5 .6
-
-
0.5
0.1
10.3
4.6
-
-
0.4
0.1
3
9.8
3.5
—
-
0 .3
0.1
I
9 .9
2 .2
-
-
0.5
0.1
2
10.1
1.0
-
- '
0.4
0.1
3
9.7
0 .4
-
-
0.2
0 .0
base
A6
acid
4.2
21.7
1 .3
17
14.6
0.1
2
2 .6
5.2
5.4
17
5.8
0.2
3
2.0 '
6 .6
1 .5
-
1 .7
0.2
-
-
0.4
0.6
” '
0 .9
0 .2
-
1 .0
0.1
0 .8
0.5
doubly- I
distilled
w a te r
2
10.9
10.3
CO
r-s
I
-
3
10.3
4.3
-
I
11.1
2 .2
-
2
10.7
0.9
-
-
1 .0
0:2
3
10.1
0.4
-
-
0 .9
0.1
base
17.2
72
in de p en d e n t o f t h e amount o f boron t h e y o r i g i n a l l y a dso r b e d .
In
Tabl e 23, samples I , 2 , 3 , and 4 o f w a t e r c o n d i t i o n e d A4 ash a l l
r e l e a s e d 0 .4 t o 0 .5 mg B/g i n t o t h e a c i d le a c h i r r e g a r d l e s s o f how
much boron t h e samples had o r i g i n a l l y adsorbed ( 0 . 2 - 0 . 4 mg B /g) .
The e xp er im en t s were r e p e a t e d f o r v e r i f i c a t i o n and y i e l d e d comparable
results.
All c o n t a i n e r s were checked f o r a d s o r p t i o n l o s s t o w a l l s ;
b u t t h e amounts found d id n o t c o n s t i t u t e t h e d i f f e r e n c e between t h a t
o r i g i n a l l y adsor bed by t h e s e samples and t h a t r e l e a c h e d from them.
There a r e no s i m i l a r e x p e r im e n t a l check o f t h i s typ e in t h e l i t e r a t u r e
t o i n d i c a t e whe the r boron i s r e l e a c h a b l e from o t h e r a d s o r b e n t s .
SUMMARY AND CONCLUSIONS
T h i s i n v e s t i g a t i o n was unde rt a ken t o de te rm in e t h e i n f l u e n c e o f
c e r t a i n f a c t o r s upon t h e m o b i l i t y o f boron from coal ash t o an aqueous
system.
The T e a c h a b i l i t y o f boron was determine d t o be a f u n c t i o n ,
o f pH, t i m e , and ash t y p e .
Upper ash ta ken from t h e s t a c k , le ach ed
more boron tha n d i d bottom ash which r e s i d e s in t h e f u r n a c e and
su sta in s higher tem peratures.
Over t i m e , boron l e a c h e s c o n t i n u a l l y
u n t i l a s t e a d y s t a t e i s rea ch e d in a ppro x im a te ly 920 h o u r s .
Leaching
i s r a p i d i n i t i a l l y bu t drops o f f d r a m a t i c a l l y a f t e r 158 h o u r s .
Acid
i s most e f f e c t i v e f o r l e a c h i n g and t h e r e i s a minimum le ac he d in t h e
pH range o f 6-9.
The a sh was s p e c i f i c a l l y examined f o r aluminum, i r o n , and boron
s i n c e t h e s e have d e m onst ra te d a r e l a t i o n s h i p in t h e a d s o r p t i o n p ro c e s s
(24,25).
The ash samples c o n t a i n e d s i g n i f i c a n t amounts o f t h e s e
components.
A s i z e f r a c t i o n a t i o n o f t h e ash i n t o f o u r se gm e nts , 150 microns
t o 45 m i c r o n s , was made.
The a n a l y s e s showed t h a t c e r t a i n elements
t e n d t o a s s o c i a t e with p a r t i c u l a r s i z e f r a c t i o n s .
BorOn p re dom in a tly
a s s o c i a t e s w it h t h e s m a l l e s t p a r t i c l e s , l e s s than f o r t y f i v e microns.
The s t a n d a r d d e v i a t i o n o f t r i p l i c a t e runs o f each fragm en t i n d i c a t e d
t h a t improved homogeneity o f a n a l y s e s can be accomplished by s i z e
fractionation.
Homogeneity i s i m p o r t a n t f o r a n a l y s i s comparison.
In t h e n a t u r a l s yst e m , p a r t i c l e s o f many s i z e s add t o t h e complexity
74
o f t h e system.
.
S l u r r i e s w e r e . p r e p a r e d , va ry in g ash c o n c e n t r a t i o n s from one gram
o f ash p e r l i t e r t o one hundred grams o f ash per l i t e r .
Boron
r e l e a s e d from t h e s e s l u r r i e s was a n al yz e d and r e v e a l e d an incomplete
r e l e a s e o f boron a t high c o n c e n t r a t i o n s o f ash .
One gram o f ash per
I
l i t e r was t a k e n as an i n d i c a t i o n o f t o t a l Teachable boron .
This was
checked by r e l e a c h i n g o f ash samples used in t h e h i g h e r c o n c e n t r a t i o n
s t u d i e s a t one gram p e r l i t e r .
Based upon t h e s e c a l c u l a t i o n s o f
t o t a l a v a i l a b l e boro n, t h e c o n c e n t r a t i o n o f boron r e t a i n e d by t h e ash
was a s s e s s e d .
The r e t a i n e d boron e x h i b i t s Langmuir a d s o r p t i o n
behavior.
A ds o r p ti o n o f boron by ash was s t u d i e d by f i r s t c o n d i t i o n i n g ash
by a p r o c e s s which removed b o r o n , the n re s u sp e n d in g t h e ash in a
s t a n d a r d s o l u t i o n o f boron.
Ash was shown t o adsor b boron i n c r e a s i n g l y
w it h i n c r e a s i n g boron s o l u t i o n c o n c e n t r a t i o n in a F r e u n d li c h r e l a t i o n ­
ship.
Acid c o n d i t i o n e d ash showed enhanced boron a d s o r p t i o n .
A s tu d y
o f t h e i n f l u e n c e o f pH upon a d s o r p t i o n by ash i n d i c a t e d t h a t a t pH
9 . 5 a d s o r p t i o n was l e s s th a n a t pH 8 . 6 .
These r e s u l t s a r e c o n s i s t e n t
w i t h pH i n f l u e n c e on boron a d s o r p t i o n by s o i l s as r e p o r t e d by o t h e r
authors (14,25,26,30,31).
An a c i d r e l e a c h o f a d s o r p t i o n samples was
an al yz e d f o r i r o n , aluminum, and boron .
I f t h e a d s o r p t i o n o f boron
was a simp le s u r f a c e l a y e r c o a t i n g , one would e x p e c t t h e boron to be
e a s i l y r e l e a c h e d . Experiments did n o t a f f i r m t h i s .
Also n o t e d , from
75
t h e a c i d r e l e a c h , was t h a t t h e s u r f a c e s o f w a te r c o n d i t i o n e d ash and
a c i d c o n d i t i o n e d ash were s i m i l a r and c o n t a i n e d comparable amounts
o f i r o n and aluminum.
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MONTANA STATE UNIVERSITY LIBRARIES
762 1001
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