The purification of crude phosphoric acid with sodium silicate
by Joseph C Street
A thesis submitted in partial fulfillment of the requirements of the degree Masters of Science
Montana State University
© Copyright by Joseph C Street (1951)
Abstract:
Phosphoric acid that is made by the- sulfuric acid process contains most of the impurities originally
present in the starting materials. A considerable quantity of the impurities begins to come out of
solution when the acid is being concentrated and slowly continues to come out for months following
the concentration. - Treatment of the phosphoric acid with sodium silicate in solution is presented as a
method for removal of these impurities. When this treatment is used, the acid requires only a short
settling time to attain a high degree of clarity.
The treatment has the advantages of low Cost, avoidance of reconcentration, and production of a
product superior to that obtained by other methods.
100897 THE PURIFICATION OF CRUDE PHOSPHORIC ACID WITH SODIUM SILICATE
by
Joseph C. Street
A thesis submitted in partial fulfillment
of the requirements of the degree
Masters of Science
MONTANA STATE UNIVERSITY
Bozeman, Montana
1951
main ub ,
Restricted stack
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S
t H
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O p %TABLE OF CONTENTS
S e c tio n
I.
Page No.
A b s tr a c t .................................................................. . . . . . . .
3
II.
I n t r o d u c t i o n ..........................................................................................
^
III.
G e n e ra l E x p e rim e n ta l P ro c e d u re ...............................................
IV .
V.
V I.
E x p e rim e n ta l R e s u l t s .........................................
15
D i s c u s s i o n ............................
32
Summary........................................................
35
V I I 0 A cknow ledgem ents . . . . . . . . . . . . .
V III.
....................
37
L i t e r a t u r e C ite d ................................................................................
38
“ 3 "
I,
ABSTRACT
P h o s p h o ric a c id ' t h a t i s made "by the- s u l f u r i c a c i d p r o c e s s c o n ta in s
m ost o f th e i m p u r i t i e s o r i g i n a l l y p r e s e n t i n th e s t a r t i n g m a te r ia ls * A
c o n s id e r a b le q u a n t i t y o f th e i m p u r i t i e s b e g in s to come o u t o f s o l u t i o n
when th e a c i d i s b e in g c o n c e n tr a te d and. s lo w ly c o n tin u e s to come o u t
f o r m onths f o llo w in g th e c o n c e n tr a ti o n .
T re a tm e n t o f th e p h o s p h o ric a c i d w ith sodium s i l i c a t e i n s o l u t i o n
i s p r e s e n t e d a s a m ethod f o r rem oval o f tjie s e im p u r iti e s * When t h i s
tr e a tm e n t i s u se d , th e a c i d r e q u i r e s o n ly a s h o r t s e t t l i n g tim e to
a t t a i n a h ig h d e g re e o f c l a r i t y .
The tr e a tm e n t h a s tjie a d v a n ta g e s o f low C o s t6 a v o id a n c e o f re c o n ­
c e n t r a t i o n , and p r o d u c tio n o f a ,p r o d u c t s u p e r io r to t h a t o b ta in e d b y
o th e r m ethods*
100897
—
IIe
eo
INTRODUCTION
C u r r e n tl y , t h e r e a r e two g e n e r a l m ethods f o r p h o s p h o ric a c i d manu­
fa c tu re ,
th e s u l f u r i c a c id p r o c e s s and th e th e rm a l p ro c e s s ,,
The th e rm a l
p r o c e s s in v o lv e s th e v o l a t i l i z a t i o n o f p h o sp h o ru s from t r i c a l c i u m p h o s­
p h a te u n d e r re d u c in g c o n d i t i o n s .
s u b s e q u e n tly d i s s o l v e d .
The p h o sp h o ru s i s o x id iz e d to PgPj? an ^
T h is - p r o c e s s i s u se d i n th e p r o d u c tio n o f
t e c h n i c a l g ra d e a c i d s in c e i t y i e l d s a c i d o f r e l a t i v e l y h ig h p u r i t y .
In
c o n t r a s t , th e p h o s p h o ric a c i d p ro d u c e d h y th e a c t i o n o f s u l f u r i c a c id
on p h o s p h a te ro c k c o n t a in s th e g r e a t e r p o r t i o n o f th e i m p u r i t i e s o r i g i ­
n a l l y p r e s e n t i n th e s t a r t i n g m a t e r i a l s .
C o n se q u e n tly , su c h a c i d i s
u se d p r i n c i p a l l y i n th e m a n u fa c tu re o f f e r t i l i z e r s a l t s w here, i n most
c a s e s , th e p r e s e n c e o f su c h i m p u r i t i e s h a s l i t t l e
e f f e c t on th e v a lu e
o f th e p r o d u c t.
The A naconda C opper M ining Company a t A naconda, M ontana m anufac­
t u r e s p h o s p h o r ic a c id from Idaho p h o s p h a te ro c k and s u l f u r i c . a c id yriiieh
i s made from hy—p r o d u c t g a s e s from th e r e d u c t io n o f s u l f i d e o r e s .
The
p h o s p h o r ic a c i d i s u s e d i n th e co m p an y 's p h o s p h a te f e r t i l i z e r p l a n t ,
F in e l y g ro u n d ro c k , c a l c in e d a t a b o u t 900° 0 , to d r iv e o f f m o is tu r e and
o x id iz e th e o r g a n ic m a tte r , i s t r e a t e d w ith s u l f u r i c a c i d to form ca lc iu m
• s u l f a t e and o rth o p h o s p h o r ic a c i d .
The s u l f u r i c a c i d i s ad d ed a t the.
r a t e o f a p p ro x im a te ly one p a r t o f 50° Baume a c i d to .one p a r t o f ro c k
a s s a y in g a b o u t 3 0 -3 2 p e r c e n t P 2Q^,
The s u l f u r i c a c i d i s d i l u t e d to
a p p ro x im a te ly 30° Baume w ith weak p h o s p h o r ic a c id , w h ile i n th e a g i ­
ta to rs ,
i n o r d e r to s e c u re a more f a v o r a b l e r e a c t i o n r a t e .
The
p h o s p h o ric a c i d fro m t h i s r e a c t i o n h a s a c o n c e n tr a ti o n o f a p p ro x im a te ly
- 5 20 p e r c e n t PpO^ 0
The a c i d i s s e p a r a te d from th e c a lc iu m s u l f a t e by
f i l t r a t i o n w ith a b e l t - t y p e vacuum f i l t e r .
o b ta in e d from th e f i l t e r „
The Ho, I o v e rflo w i s t h a t a c i d p a s s in g
th ro u g h th e f i l t e r w ith no r i n s i n g .
cessed,
T hree a c i d s o l u t i o n s a r e
T h is f r a c t i o n i s f u r t h e r p r o ­
The Ho, 2 o v e rflo w i s o b ta in e d b y r i n s i n g th e f i l t e r cake w ith
a weak a c i d known a s th e Ho«, 3 o v e rflo w .
The Ho, 3 o v e rflo w i s th e
weak a c i d from th e f i n a l r i n s i n g o f th e cak e w ith w a te r .
The Ho, 2
o v e rflo w i s u se d to d i l u t e th e s u l f u r i c a c i d i n th e a g i t a t o r s and
a s s a y s a b o u t 12 p e r c e n t PpO^,
The Ho, 3 o v e rflo w a s s a y s o n ly I to
2 p e r c e n t PpO^,
The Ho, I o v e rflo w i s a llo w e d to s ta n d a few d a y s so t h a t any
sed im en t p a s s in g th r o u g h th e f i l t e r may s e t t l e o u t .
T h is d i l u t e a c id
m ust b e c o n c e n tr a te d t o 45 p e r c e n t PpO^ f o r u se i n th e m a n u fa c tu re of
T re b le S u p e rp h o S p h ate8 and f r e q u e n t l y a c i d i s p r e p a r e d f o r s h ip p in g
p u rp o s e s t h a t h a s a c o n c e n tr a ti o n o f 53 p e r c e n t PgO^,
T h is i s accom­
p l i s h e d b y e v a p o r a tio n i n steam ™ heated, s i n g l e - s t a g e , vacuum e v a p o r a to r s .
D u rin g th e e v a p o r a tio n when th e a c i d c o n c e n tr a ti o n has- re a c h e d ab o u t
40 p e r c e n t PgOg, a l a r g e q u a n t i t y o f s o l i d s b e g in s t o come o u t o f s o lu ­
tio n ,
The s e t t l i n g i s v e r y slow due to th e h ig h v i s c o s i t y o f th e concen­
tr a te d a c id .
M oreover, a f t e r th e i n i t i a l , d e p o s i t i o n o f sed im en t i n th e
e v a p o r a to r s , a slo w e r p r o c e s s c o n tin u e s i n w hich p a r t i c l e s o f c o l l o i d a l
d im e n s io n s g r a d u a l ly clump t o g e t h e r u n t i l a n a g g r e g a te i s fo rm ed of
s u f f i c i e n t s i z e to s e t t l e o u t,
I n t h i s way, s lu d g e may s t i l l be s e t ­
t l i n g m o n th s a f t e r th e a c i d was m a n u fa c tu re d .
I t h a s b e e n shown t h a t
t h i s s lu d g e h a s f e r t i l i z e r v a lu e so t h a t sed im en t i n th e a c i d g o in g to
/
6 ^
th e f e r t i l i z e r p l a n t i s t o l e r a t e d „
However, when a c id i s p re p a re d , f o r
s h ip p in g p u r p o s e s a h ig h e r d e g re e o f p u r i t y i s r e q u i r e d .
The p r i n c i p a l
u se f o r A naconda " s h ip p in g a c id " i s a s l i q u i d p h o s p h a te f e r t i l i z e r
a p p lie d th ro u g h s m a ll n o z z le s i n t o i r r i g a t i o n w a te r „
S o lid s o b s tr u c t
th e n o z z le o p e n in g s c a u s in g slow , e r r a t i c flo w and h ig h m a in te n a n c e
c o s ts .
The p u r i f i c a t i o n o f su ch a c i d i s q u i t e c o s t l y .
I t u s u a ll y r e q u i r e s
n e a r l y co m p lete n e u t r a l i z a t i o n o f th e a c i d w ith a b a s e w hich p r e c i p i t a t e s
th e i m p u r i t i e s a s i n s o l u b l e s a l t s w h ile th e p h o s p h a te s a l t form ed .rem ain s
s o lu b le ,
As a n exam ple, tr e a tm e n t w ith f i n e l y g ro u n d lim e s to n e p ro d u c e s
a s o l u t i o n o f m onocalcium p h o s p h a te , a c e r t a i n amount o f d i c a lc iu m p h o s­
p h a te and p r e c i p i t a t e s i r o n and. alum inum p h o s p h a te s , c a lc iu m f l u o r i d e ,
and c a lc iu m f l u o s i l i c a t e s , .
filtra tio n
These p r e c i p i t a t e s can r e a d i l y b e removed by
(Waggaman, 1 9 2 7 ),
The c a lc iu m p h o s p h a te s o l u t i o n m ust a g a in
b e m ixed w ith s u l f u r i c a c i d to r e s t o r e th e p h o s p h o ric a c i d and p r e c i ­
p i t a t e c a lc iu m s u l f a t e .
L ik e w ise , t h e . a c i d m ust a g a in be c o n c e n tr a te d
f o llo w in g su ch a p r o c e d u r e .
T ab le I g iv e s t y p i c a l a n a ly s e s o f A naconda p h o s p h o ric a c i d , p h o s­
p h a te ro c k , and a c i d s lu d g e s .
sa m p le „
The a c i d an aly zed , was a w e l l - s e t t l e d
A more co m p lete a n a l y s i s shows c a lc iu m , magnesium, a r s e n i c ,
sodium , p o ta s s iu m , chromium, m anganese, ti ta n i u m and z in c i n am ounts
. v a r y in g from l / l O to l / 2 p e r c e n t ( a s th e o x id e ) and t r a c e s o f co p p er,
le a d , n i c k e l , b ariu m , b o ro n , and s tr o n tiu m .
The a c i d i s c o lo r e d b lu e -
g r e e n by th e r e l a t i v e l y l a r g e am ounts o f vanadium p r e s e n t „
o f th e t o t a l f l u o r i n e i s p r e s e n t a s s i l i c o f l u o r i d e
A la rg e p a r t
( H i l l , M a rs h a ll and
T a b le I
. T y p ic a l A n aly ses of Anaconda P h o sp h o ric A c id s P h o sp h a te Rocks
and A cid S lu d g e s*
A cid
FegOij
• AlgO^
1 .0 0 #
0 .9 9 *
■ 0.U9
l.li 9
'
CaO
F
SiO2
V2Os
0.25*■
0 .7 7 *
o .iL #
0.L 2*
3 . LO
5 .9 0
0 .2 9
U5.o
Rock
3 0 .5
Normal A cid S lu d g e
U7.0
7 .0
3 .0
o .o 5
1 .3 0
0 .2
T r e a te d A cid S lu d g e
5 l- 7
9 .2
ke9
0 .0 1
1 .6 0
o»L3
# D ata f u r n is h e d b y t h e Anaconda C opper M ining GQmpanyt,
—3
r
- 8 Ja c o b , 1932)„
The s i l i c o f l u o r i d e i s s l i g h t l y s o lu b le i n p h o s p h o ric a c id
up to 10 p e r c e n t
becom ing l e s s so a s th e a c id i s c o n c e n tr a te d
(Hampel, 1 9 4 9 ).
The slu d .g es a r e a lc o h o l-w a s h e d s o l i d s from th e s e t t l i n g t a n k s .
The c h e m ic a l n a tu r e o f th e s e s o l i d s i s n o t e n t i r e l y c l e a r , b u t th e y a r e
e v i d e n t l y p h o s p h a te s o f i r o n and aluminum to g e th e r w ith in s o l u b l e f Iu o S llie a te s 0
The p h o s p h a te s o f i r o n and aluminum may be h y d r a te d .
The
b u lk o f th e slu d g e i s a g e l a t i n o u s m ass c o n ta in in g th e c r y s t a l l i n e
flu o s ilic a te s .
Removal o f th e c r y s t a l l i n e p a r t i c l e s e l i m i n a t e s much o f
th e d i f f i c u l t i e s w ith p lu g g e d n o z z l e s .
The p r e s e n t p ro c e d u re f o r p u r i f i c a t i o n a t th e Anaconda p l a n t
rem oves th e s i l i c o f l u o r i d e s by p r e c i p i t a t i o n w ith sodium c a r b o n a te .
T re a tm e n t o f th e d i l u t e Ho, I o v e rflo w w ith sodium c a rb o n a te i n , q u a n t i ­
t i e s i n e x c e s s o f th e t h e o r e t i c a l r e q u i r e d to p r e c i p i t a t e th e s i l i e o f l u o r i d e s p ro d u c e s an a c i d from w hich th e s o l i d s s e t t l e o u t much f a s t e r
th a n from norm al a c i d .
H e n c e fo rth i n t h i s p a p e r , .^ tr e a te d a c id " w i l l
r e f e r to a c i d t r e a t e d i n t h i s way i n c o n t r a s t w ith th e u n t r e a t e d "norm al
ac id ® .
T r e a te d a c i d e v e n a f t e r s ta n d in g f o u r to f i v e weeks i s s t i l l
q u it e t u r b i d a lth o u g h much c l e a r e r th a n norm al a c i d w hich h a s ,stood f o r
th e same le n g t h o f tim e .
Two d i f f e r e n t sam p les o f t r e a t e d . a c i d were
observed, to in c r e a s e i n t u r b i d i t y on s ta n d in g f o r lo n g p e r i o d s .
S in ce
th e s e a c id s w ere s to r e d i n w ax -lin ed , b o t t l e s , th e in c r e a s e d t u r b i d i t y
c o u ld n o t have b een due to d is s o lv e d s i l i c a t e s from th e g l a s s .
B ecause o f t h i s e f f e c t i t was s t i l l d e s ir a b le , to o b ta in a n a c id
w hich c o n ta in e d no s e d im e n t, w hich r e q u i r e d o n ly a s h o r t s e t t l i n g tim e
- 9 to a t t a i n t h i s p u r i t y , and. w h ich would re m a in c l e a r f o r a lo n g p e r io d o f
ti m e „
The p r e s e n t w ork was u n d e rta k e n i n a n e f f o r t to f i n d a p r o c e s s
w hich w ould m eet t h i s o b j e c t i v e .
As a r e s u l t o f t h i s work, tr e a tm e n t o f
th e c ru d e a c id Whth aq u eo u s s o l u t i o n s o f sodium s i l i c a t e i s b e in g
p r e s e n te d a s a f e a s i b l e p r o c e s s .
•
- 10 III.
GENERAL. EXPERIMENTAL PROCEDURE
Sam ples o f sodium s i l i c a t e h a v in g th e r a t i o s s i l i c a ”so d a o f 1 .6 9 ,
2 . 0 6 , 2 .4 0 and 3 .3 6 w ere p r e p a r e d hy f u s i n g washed s e a san d w ith sodium
c a r b o n a te .
The g l a s s e s fo rm ed w ere e x t r a c t e d w ith w a te r i n th e a u to c la v e
a t 20 p o u n d s steam p r e s s u r e f o r one h o u r .
2 5 -3 ° p e r c e n t sodium s i l i c a t e , i . e . „
e v a p o r a tio n o r d i l u t i o n ,
The e x t r a c t s w ere th e n ab o u t
25 P©1* c e n t 'NagO p l u s SiO g.
By-
s o l u t i o n s of th e d e s ir e d c o n c e n tr a ti o n s were
o b ta in e d .
A ll t e s t s w ere p e rfo rm e d i n 10—in c h t e s t tu b e s p a r a f f i n e d to p r o ­
t e c t them fro m th e c o r r o s iv e h y d ro g en f l u o r i d e p r e s e n t i n th e a c i d .
E i g h t y - f i v e m l. o f th e c ru d e p h o s p h o ric a c id (a p p ro x im a te ly 140 g .)
and 10 m l. o f s i l i c a t e s o l u t i o n w ere m ixed r a p i d l y i n a b e a k e r u s in g a
h ig 6- s p e e d s t i r r e r .
The s i l i c a t e s o l u t i o n was added t o th e a g i t a t i n g
a c i d i n a t h i n s tre a m from a p i p e t t e .
Ten m l. o f s o l u t i o n w ere added i n
th e c a s e o f n o rm al a c i d , 5 m l. i n th e c a s e o f t r e a t e d a c i d .
The sodium
s i l i c a t e im m e d ia te ly fo rm ed a g e l a t i n o u s m ass and s t i r r i n g was c o n tin u e d ^
u n t i l t h i s mass was b ro k e n up i n t o an ev e n c o n s is te n c y t h r o u g h o u t T h e
m ix tu re was th e n p o u re d i n t o a t e s t t u b e .
One sam ple was e l e c t r o l y s e d , i n a d d i t i o n to th e sodium s i l i c a t e
tr e a tm e n t, a s a n e x p l o r a to r y .e x p e rim e n t„
T h is sam ple o f 85 m l. o f norm al
a c i d r e c e iv e d 10 m l. o f 7 p e r c e n t s i l i c a t e ( r a t i o 1 .6 9 ) and. was e l e c ­
t r o l y s e d a t 0 .1 am pere and 4 .0 v o l t s f o r 17 h o u rs (a b o u t 6 ,0 0 0 coulom bs)
u s in g c a rb o n e l e c t r o d e s an d c o n s ta n t s t i r r i n g .
The sam ple was th e n
p o u re d i n t o a t e s t tu b e f o r o b s e r v a ti o n s .
A co m p le te l i s t o f t e s t s i s p r e s e n t e d i n T ab le I I w ith th e e x c e p tio n
11 -
T ab le I I
C om plete L i s t o f T e s ts P erfo rm ed
S i l i c a s Soda
R a tio
E orm al A cid
T r e a te d A cid
P e r Cent
S ilic a te
B I. o f Si:
Added
1 .6 9
1.69
1 .6 9
1 .6 9
. 1.69
1 .0
2 .0
7 .0
12.5'
25.0
10
10
10 .
10
10
2 .0 6
2 „06
2.06
2.06
9 .5
.1 3 .4
32 .0
32.0
10
10
10
5
2.40
2.40
9 .0
1 2 .6
10
10
3 .3 6
3 .3 6
3 .3 6
3 .3 6
12 .0
19 .0
12 .0
19 .0
10
10
5
5'
1 .6 9
1 .6 9
7 .0
7 .0
5
10
2 .0 6
2.06
9 .5
1 9 .0
5
5
2.40 .
2 .4 0
9 .0
1 8 .0
5
5
3 .3 6
3 .3 6
12 .0
19 .0
5
5
12 o f th e one t e s t u s in g e l e c t r o l y s i s .
S u ita b le c o n t r o l s w ere a l s o o b se rv e d
f o r e a c h c a s e , b o th a c i d w ith no s i l i c a t e ad d ed and a c i d w ith no s i l i c a t e
b u t d i l u t e d w ith w a te r to t h e ' same e x t e n t a s th e t e s t s .
R eco rd was k e p t o f th e s e t t l i n g r a t e by m e a su rin g th e c e n tim e te r s
o f c l e a r a c i d a t i n t e r v a l s o f one t o f o u r d a y s .
T h is was p o s s i b l e
b e c a u s e th e g e l a t i n o u s m ass s e t t l e d a s a u n i t and t h e r e was a w e ll d e f in e d l i n e s e p a r a t in g t h i s from th e c l e a r a c i d .
A f te r s e t t l i n g was
c o m p le te , th e r a t i o o f th e h e ig h t o f s e d im e n t•i n th e tu b e to th e t o t a l
h e ig h t o f l i q u i d i n th e tu b e was r e c o r d e d .
The d ia m e te r s o f th e tu b e s
v a r i e d m aking a r a t i o co m p ariso n n e c e s s a r y r a t h e r th a n sim p ly a h e ig h t
c o m p a riso n .
A f t e r two o r t h r e e d a y s, t h e r e was s u f f i c i e n t r e l a t i v e l y c le a r ,
a c i d t o d e c a n t an d m easu re i t s t u r b i d i t y .
T u r b i d ity was m easured a s
o p t i c a l d e n s i t y w ith a Coleman s p e c tr o p h o to m e te r , Model 11, u s in g
m atch ed , sq u a re c u v e t t e s .
Sam ples w ere com pared a t 5 6 0 ^ ,
l e n g t h o f minimum a b s o r p ti o n , a g a i n s t a n a r b i t r a r y . s ta n d a r d .
th e wave­
T h is
s ta n d a r d was p r e p a r e d b y d i s s o l v i n g ammonium v a n a d a te i n t e c h n i c a l
p h o s p h o ric a c i d (53 p e r c e n t PgO^) and r e d u c in g th e v a n a d a te to a b lu e g r e e n c o l o r a p p ro x im a tin g t h a t o f th e sam ple a c i d ,
F o llo w in g th e .
co m p a riso n , th e sam ple d e c a n te d was c a r e f u l l y r e p la c e d i n i t s tu b e .
T u r b i d ity W
i s r e l a t e d to o p t i c a l d e n s it y ( - lo g I / I o ) b y th e
e q u a tio n ,
,
- l o g I / Io =
x ,
d /2 .3 0 3
i n w hich Io i s th e i n t e n s i t y o f th e i n c i d e n t l i g h t , I i s th e i n t e n s i t y
o f th e t r a n s m i t t e d l i g h t , 6< _ is th e a b s o r p ti o n c o e f f i c i e n t , and d i s th e
- 13 —
d i s t a n c e th e l i g h t t r a v e l s th ro u g h th e medium ( c e l l t h i c k n e s s ) 0
In o rd e r
f o r t h i s m ethod t o g iv e a c c u r a te co m p a riso n s o f t u r b i d i t y , , o t . m ust n e i t h e r
v a r y i n e a c h sam ple a s s e d im e n ta tio n p ro c e e d s n o r v a r y a p p r e c ia b ly
b etw ee n sa m p le s .
T h is was n o t s t r i c t l y th e c a s e and b e c a u se o f d i f f e r ­
e n c e s i n r e f r a c t iy e i n d i c e s , d i f f e r e n c e s in . s iz e o f p a r t i c l e s , and
p o l y d i s p e r s i t y o f p a r t i c l e s , e x a c t c o m p a riso n s c o u ld n o t be m ade.
A f t e r th e sam p les had re a c h e d t h e i r maximum c l a r i t y , c e r t a i n o f'
them w ere s e l e c t e d a s r e p r e s e n t i n g s u p e r io r tr e a tm e n ts an d w ere a s s a y e d
f o r £ 205 s ^ e 2Q3 , and f l u o r i n e f o r c o m p ariso n w ith th e c o rre s p o n d in g 1
v a lu e s f o r n o n -tre a te d a c id ,
PpO5 was a s s a y e d by th e m ethod o f th e
A s s o c i a ti o n o f O f f i c i a l A g r i c u l t u r a l C h em ists (1 9 4 5 ),
The. sam ple i s
d is s o lv e d i n n i t r i c a c id an d ammonium phosp h o m o ly b d ate i s p r e c i p i t a t e d
from th e d i l u t e a c i d s o l u t i o n w ith a n e x c e s s o f ammonium m o ly b d a te ,
The
p r e c i p i t a t e i s f i l t e r e d , w ashed, an d d is s o lv e d i n an e x c e s s o f s ta n d a r d
sodium h y d r o x id e .
B a c k - t i t r a t i o n o f th e e x c e s s b a s e w ith s ta n d a r d
h y d r o c h lo r ic a c i d g iv e s a n i n d i r e c t m easure of th e P 2O3 ,
The f l u o r i n e was a s s a y e d b y t h e m ethod o f Hoffman and L u n d e ll
( 1938) an d i s g iv e n h e r e i n some d e t a i l s in c e i t i s n o t o r d i n a r i l y
e n c o u n te r e d ,
A 6 -8 gram sam ple of a c i d i s washed i n t o a 125 m l,
C la is s o n f l a s k w hich i s f i t t e d w ith r u b b e r s to p p e r s , a d e l i v e r y tu b e f o r
a d m ittin g s u l f u r i c a c id and w a te r, a th e rm o m e te r, and a c o n d e n se r w hich
d e l i v e r s th e d i s t i l l a t e i n t o a 400 m l, b e a k e r th ro u g h a c u rv e d a d a p t e r .
The end o f th e a d a p te r i s im m ersed i n 20 m l, o f a 20 p e r c e n t s o l u t i o n
o f sodium h y d ro x id e c o n ta in e d i n th e b e a k e r „
The f l a s k r e s t s i n a 4 cm,
h o le i n a n a s b e s to s g au ze an d i s h e a te d w ith a h o t flam e su ch a s t h a t o f
— 14 —
a T i r r i l T surner0
T h i r t y m l, o f d i l u t e s u l f u r i c a c i d ( l 4 l ) a r e a d m itte d
th ro u g h th e d e liv e r y - tu b e , th e f l a s k i s h e a te d t o v ig o r o u s b o i l i n g and
h e a t in g i s c o n tin u e d u n t i l th e te m p e r a tu r e o f th e l i q u i d i n th e f l a s k
r e a c h e s l6 0 ° C0
Then, w ith o u t rem oving th e so u rc e o f h e a t , w a te r i s
a d m itte d th ro u g h th e d e l i v e r y tu b e a t su ch a r a t e t h a t th e te m p e ra tu re
o f th e l i q u i d i n th e f l a s k , re m a in s b e tw e e n l 6o° an d 170° C .; 300 m l,
o f d i s t i l l a t e i s c o l l e c t e d b etw een th e s e te m p e r a tu r e s .
The a l k a l i n e
d i s t i l l a t e i s e v a p o ra te d to a volum e o f 250 m l0, 3 m l. o f 10 p e r c e n t
sodium c h l o r i d e a r e ad d ed , and th e pH i s a d j u s t e d to j u s t b a s i c to
brom phenol b l u e .
Two m l, o f d i l u t e d h y d r o c h lo r ic a c i d and 5 * 0 g„ of
s o l i d le a d n i t r a t e a r e ad d ed an d th e m ix tu re i s h e a te d on th e steam
b a t h u n t i l th e le a d n i t r a t e i s d is s o lv e d ; th e n 5 .0 g , o f sodium a c e t a t e
a r e added and th e m ix tu re s t i r r e d v ig o r o u s ly w h ile d i g e s t i n g on th e
steam b a t h .
A f t e r s ta n d in g o v e r n ig h t a t room te m p e r a tu r e , th e p r e c i ­
p i t a t e d l e a d c h l o r o f lu o r i d e i s f i l t e r e d and w ashed w ith a s a t u r a t e d
s o l u t i o n o f le a d c h l o r o f l u o r i d e ;
The p r e c i p i t a t e and f i l t e r p a p e r a r e
t r a n s f e r r e d to th e o r i g i n a l b e a k e r and 100 m l, o f d i l u t e n i t r i c a c id
a r e added t o d is s o lv e th e p r e c i p i t a t e .
The c h l o r i d e i s d e te rm in e d i n
t h i s s o l u t i o n by th e V o lh a rd m ethod an d i s e q u a l to th e f l u o r i d e con­
c e n tra tio n .
'
I r o n was a l s o d e te rm in e d by th e m ethod o f Hoffman, and L u n d e ll
( 1939) i n w hich f e r r i c i r o n i s re d u c e d w ith , s ta n n o u s c h l o r i d e and
t i t r a t e d w ith p o ta s s iu m p e rm a n g a n a te .
“ 15 —
IV 0
EXPERIMENTAL RESULTS
I n e a c h o f th e t e s t s p e rfo rm e d t h e r e was o b s e rv e d a m arked Im prove­
ment i n th e a c i d ; w i t h i n 30-40 d ay s a c l e a r a c i d was o b ta in e d „
fig u re s
I and 2 show th e r a p i d d e c r e a s e i n t u r b i d i t y a s i n d i c a t e d by th e la r g e
d ro p o f o p t i c a l d e n s i t y when no rm al a c id i s t r e a t e d w ith s i l i c a t e *
f i g u r e I shows f o u r o f th e r e s u l t s o f b e t t e r tr e a t m e n t s .
Curve I I ,
f i g u r e 2 , r e p r e s e n t s th e same sam ple a s i s r e p r e s e n t e d by th e p u r p le
c u rv e o f f i g u r e I ,
T h ere was o n ly one b e t t e r cu rv e th a n th o s e shown;
th e tr e a tm e n t was 5 m l, o f 19 p e r c e n t ( 3 »3 6 ) ,
The b a la n c e o f th e ■
t r e a t m e n t s f e l l b e tw e e n 7 p e r c e n t ( 1 ,6 9 ) , l i n e I I I , f i g u r e 2 , and 1 2 ,5
p e r c e n t ( l . 6 9 ) , l i n e I I , f i g u r e 2.
I t i s odd to f i n d t h a t th e 12.5
p e r c e n t ( 1 . 6 9 ) and th e 12 p e r c e n t ( 3 , 3 6 ) were b o th s u p e r io r to c o r r e s ­
p o n d in g p e r c e n ta g e s o f s i l i c a ; s o d a r a t i o s o f -2 ,0 6 and 2 ,4 0 ,
I t was
n o t e x p e c te d t h a t ' b o th th e extrem e r a t i o s o f s i l i c a ; s o d a would be
s u p e rio ro
C urves f o r th e c o n t r o l s a r e n o t g iv e n b u t th e y j u s t b a r e l y
le a v e th e a b c i s s a i n 30 d a y s .
These c u rv e s show t h a t t h e r e was a n e a r l y , r a p i d d e c r e a s e i n t u r ­
b i d i t y w h ich g r a d u a l ly l e v e l e d o u t and ap p ro a c h e d th e same a p p ro x im a te
v a lu e .
T h ere was no i n d i c a t i o n t h a t th e t u r b i d i t y . e v e r in c r e a s e d a g a in ,
a t l e a s t w ith i n t h r e e m o n th s.
I n s te a d t h e r e was a c o n tin u e d , b u t v e ry
slow , d e c r e a s e .
f i g u r e 2 shows th e r e s u l t s o f t r e a t i n g w ith one r a t i o
in c re a s in g c o n c e n tra tio n s .
I t i s se e n i n tr e a tm e n ts I ,
a g a in a common p o in t was a p p ro a c h e d .
e v i d e n t l y to o low a c o n c e n t r a t i o n .
( 1 .6 9 ) i n
I I , and I H
th a t
T rea tm e n t IV (Z p e r c e n t) was
T rea tm e n t I (25 p e r c e n t) had to o
P u rp le -
OPTICAL DENSITY
G reen
TIME IN DAYS
F ig u r e I
Change i n T u r b i d ity w ith Time
Normal A cid
OPTICAL DENSITY
5
IO
15
20
TIME IN DAYS
25
F ig u r e 2
Change i n T u r b i d ity w ith Time
V ario u s L e v e ls of S i l i c a t e ( 1 .6 9 ) w ith Normal A cid
30
— 18 —
much, sed im en t and w as, c o n s e q u e n tly , n o t a s d e s i r a b l e a s I I an d I I I 0
F ig u r e 3 shows th e r e s u l t s o f some tr e a tm e n ts w ith t r e a t e d a c id
and a . c o n t r o l .
The t e s t s w ith t r e a t e d a c i d w ere made i n o r d e r to
i n v e s t i g a t e th e p o s s i b i l i t y o f a c o m b in a tio n o f th e soda a s h tr e a tm e n t
w ith th e sodium s i l i c a t e tr e a t m e n t .
d i l u t e d w ith 5 m l, o f w a te r .
p o s i t i v e s lo p e , i . e . ,
The c o n t r o l was 85 m l, o f a c id
The u n d il u te d c o n t r o l h ad an ev en g r e a t e r
a g r e a te r in c re a s e in t u r b i d i t y .
The i n i t i a l
i n c r e a s e s i n t u r b i d i t y w ere due to th e g e l m ass, w hich s e t t l e d enough
i n two d a y s t o le a v e c l e a r a c i d ,
n in e te e n p e r c e n t ( 3 »3 6 ) s e t t l e d so
much f a s t e r t h a t no in c r e a s e i n t u r b i d i t y was m easured on th e second „
day.
The t e s t s w ith t r e a t e d , a c i d r e a c h e d a h ig h e r c l a r i t y a s in d i c a t e d
b y th e o p t i c a l d e n s i t y th a n c o rre s p o n d in g tr e a tm e n ts o f n o rm al a c i d
b u t e x h i b i t e d a b o u t th e same amount o f l i g h t s c a t t e r i n g .
I t i s assum ed
t h a t a d i f f e r e n t a b s o r p ti o n c o e f f i c i e n t makes r e a d in g s h i g h e r .
T hus, i n e v e ry c a s e , f o r b o th n o rm al and t r e a t e d a c i d s e x c e p t
p o s s i b l y th e 2 p e r c e n t ( l . 69) , a p a r t i c u l a r c la r it y was a p p ro a c h e d by
a l l and i n n e a r l y th e same le n g t h o f tim e .
When t h i s p o in t was re a c h e d
one c o u ld d e t e c t s c a r c e l y an y l i g h t s c a t t e r i n g when v i s u a l l y com paring
th e sam ple w ith th e s ta n d a r d .
V a r i a t i o n s i n t u r b i d i t y d u r in g th e f i r s t
few d a y s a f t e r tr e a tm e n t a r e a p p a r e n tly w ith o u t any p a r t i c u l a r s i g n i ­
f i c a n c e s in c e th e same c l a r i t y i n th e s o l u t i o n i s a c h ie v e d i n th e same
l e n g th o f tim e w ith a l l o f th e b e t t e r tr e a t m e n t s .
T h is i s d e m o n stra te d
i n F ig u r e 4 w hich shows th e r e s u l t s o f a p a i r o f d u p l i c a t e t r e a tm e n ts .
Of f a r more im p o rta n c e to th e p r o d u c e r th a n th e r e l a t i v e l y i n s i g ­
n i f i c a n t v a r i a t i o n s i n th e t u r b i d i t y c u r v e s d u rin g th e f i r s t few d ay s
- 1.0% I
- 1 2 .0 # 3
- 1 9 .0 # 3
- C o n tr o l
OPTICAL DENSITY
B la ck
Red
G reen
Brown
TIME IN DAYS
F ig u re 3
Change i n T u r b i d ity w ith Time
T r e a te d A cid
OPTICAL DENSITY
TIME IN DAYS
F ig u r e U
Change i n T u r b i d i t y w ith Time
D u p lic a te T re a tm e n ts on Normal A cid
7* ( 1 . 69)
-
21
-
i s th e am ount o f a c i d im m e d ia te ly a v a i l a b l e a f t e r tr e a tm e n t and th e
l e n g t h o f tim e he m ust w a it b e f o r e s h ip p in g th e p r o d u c t„
f i g u r e 5 shows
s e d im e n ta tio n r a t e s f o r th e same t e s t s a s th o s e a p p e a r in g i n th e p r e v io u s
g ra p h s„
The g e l m ass c o n t a in in g th e s lu d g e s e t t l e d r a p i d l y ; i n one
week th e s e t t l i n g was n e a r l y co m p lete e x c e p t f o r v e r y s m a ll p a r t i c l e s
s e t t l i n g more S lo w ly 0
T hus, th e a c i d c o u ld b e d e c a n te d and s h ip p e d
a f t e r two w eeks o f s e t t l i n g .
On r e a c h in g i t s d e s t i n a t i o n i n two to
t h r e e w eeks, i t w ould have a h ig h d e g re e o f d l a r i t y and o n ly a l i t t l e
s lu d g e w ould b e on th e b o tto m of th e ta n k c a r „
F ig u r e 6 i s a c h a r t showing th e am ounts o f a c i d a v a i l a b l e from
v a rio u s tre a tm e n ts .
Lower p e r c e n ta g e s o f s i l i c a t e i n th e tr e a tm e n t
r e s u l t i n more a c i d a v a i l a b l e ; ' b u t , a s s e e n p r e v io u s l y , a r e n o t a s good
i n rem o v in g t u r b i d i t y .
The r a t i o 3 ,3 6 i s g e n e r a l l y th e b e s t ; 12 p e r c e n t
• ( 3 , 3 6 ) b e in g n e a r ly a s good a s 7 p e r c e n t ( l , 69) w ith e q u a l tr e a tm e n ts
(10 m l.) an d , s u r p r i s i i i g l y enough, w ith o n ly o n e - h a lf a s much s i l i c a t e
i s j u s t a s go o d .
U n f o r tu n a te ly , a p e r c e n ta g e l e s s th a n 12 p e r c e n t o f
th e 3 ,3 6 was n o t t e s t e d .
I t i s p o s s i b l e t h a t a lo w er p e r c e n ta g e o f t h i s
r a t i o m ight be b e t t e r th a n any t e s t e d .
A n o th er p o s s i b i l i t y i s t h a t
r a t i o s h ig h e r th a n 3 »3 ^ m ig h t be b e t t e r ,
The e x p e rim e n t w ith e l e c t r o l y s i s was s e t up t o f o llo w i n d i c a t i o n s
t h a t a s m a ll amount o f c u r r e n t h a s te n e d d e p o s i t i o n of th e f i n e sedim ent
re m a in in g i n norm al a c i d a f t e r th e i n i t i a l d ro p o f l a r g e r p a r t i c l e s .
U sin g e l e c t r o l y s i s a lo n e , i t was fo u n d t h a t a p p ro x im a te ly 4 ,0 0 0 coulom bs,
when p a s s e d th r o u g h th e sam ple o f 400 to I , 300 gram s, w ere s u f f i c i e n t to
p ro d u c e an I n c r e a s e d r a t e o f s e t t l i n g ,
Q u a n t i t i e s l e s s th a n 4 ,0 0 0
-
2.2
~
B la ck
P u rp le
Red
B lue
G reen
TIME IN DAYS
F ig u r e 5
S e d im e n ta tio n R a te s f o r Normal A cid
T r e a te d Acid
R a tio cm. c l e a r a c i d / cm. l i q u i d colum n
Normal Acid
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F ig u r e 6
Q u a n ti tie s o f A v a ila b le A cid from V a rio u s T re a tm e n ts
Os
H
—•«24 —
coulom bs h ad no e f f e c t „
The o n ly im m ed iate change o b v io u s was a
y e llo w in g o f th e a c i d 's b l u e - g r e e n .c o l o r w hich p r o b a b ly was due to
o x id a tio n o f th e v an ad iu m .
I t was n e a r l y one m onth a f t e r e l e c t r o l y s i s
b e f o r e any in c r e a s e d s e t t l i n g r a t e c o u ld be o b serv ed £ b u t a f t e r th e r a t e
d id i n c r e a s e „ s e d im e n ta tio n p ro c e e d e d q u i t e c o n s t a n t l y an d was accom­
p a n ie d , b y a y e llo w - g r e e n d e p o s it io n on th e s id e s , o f th e tu b e e
Two m onths
a f t e r e l e c t r o l y s i s th e sam ple was s l i g h t l y more c l e a r th a n t r e a t e d a c i d
w i l l g e t ; f i v e and a h a l f m onths a f t e r e l e c t r o l y s i s i f was e x tre m e ly
c l e a r and co m p arab le to th e sam ples o f s i l i c a t e - t r e a t e d norm al a c id
a f t e r s i x o r se v e n w eeks o f s ta n d in g .
When s i l i c a t e was ad d ed to th e e l e c t r o l y t i c e x p e rim e n t, th e same
g e n e r a l e f f e c t s w ere o b ta in e d a s i n th e o th e r s i l i c a t e t e s t s .
The
d e c r e a s e i n t u r b i d i t y was more r a p i d , b u t t h e r e was more s e d im e n t.
The
e f f e c t o f e l e c t r o l y s i s was to make th e t e s t w ith 7 p e r c e n t ( l . 6 9 )
n e a r ly i d e n t i c a l w ith th e t e s t u s in g 1 2 .5 p e r c e n t s i l i c a t e .
T a b le I I I g iv e s th e r e s u l t s o f th e a n a ly s e s f o r
flu o rin e .
P e 2O^c and
The p e r c e n ta g e s g iv e n a r e f o r th e t e s t e d sam p les n o t
c o r r e c t e d f o r th e d i l u t i o n o c c u r r in g d u r in g tr e a tm e n t.
The c o n t r o l f o r
th e norm al a c i d s e r i e s was a sam ple o f th e same a c i d a s th e t e s t e d
sam p les w h ich had b e e n a llo w e d to s ta n d 12 w eeks.
At t h i s tim e i t had
d ro p p ed a l l o f th e l a r g e r p a r t i c l e 's and was ro u g h ly e q u iv a le n t to th e
t r e a t e d a c i d c o n t r o l shown i n F ig u r e 4 .
The t r e a t e d a c i d c o n t r o l was.
from th e same a c i d from w h ich th e sam p les f o r t e s t i n g w ere o b ta in e d and
had become q u it e t u r b i d a g a in .
A l a r g e r e d u c t io n o f th e two i m p u r i t i e s , i r o n and f l u o r i n e , was
“ 25 “
T a b le I I I
R e s u lt s o f A n a ly s e s
%
Norm al A cid
No s i l i c a t e
lio ( 1 .6 9 )
12# ( 3 . 36)
12# (3 .3 6 )
19# ( 3 .3 6 )
32# ( 2 . 06)
7# ( 1 .6 9 )
10
10
5
10
5
10
ml
ml
ml
ml
ml
ml4e
F#
#
5 4 .3
5 1 .6
5 1 .7
5 0 .7
5 1 .0
4 9 .9
51 .0
2 .7 0
1 .4 7
1 .1 5
1 .2 1
1 .2 8
1 .0 2
0 .9 9
0 .8 6
0 .3 9
0.30
0 .4 1
0 .1 6
0.2 0
0 .2 5
5 1 .8
5 1 .0
5 1 .1
5 0 .5
1 .3 3
1 .1 7
0 .9 8
■1.10
0 .8 6
■ 0 .5 4
0 .35
0J5
T r e a te d A cid
No s i l i c a t e
7# (1 .6 9 ) 5 ml
12# (3 .3 6 ) 5 ml
19# (3 .3 6 ) 5 ml
J
“ 26 ”
o b s e rv e d .
The low amount o f f l u o r i n e i n th e norm al a c i d c o n t r o l , e q u a l
to t h a t i n th e t r e a t e d a c i d c o n t r o l , was b e c a u se i t was v e r y w e ll
s e ttle d .
The p r o p o r t i o n a t e r e d u c t io n i n th e amount o f i r o n was g r e a t e r
w ith n orm al a c i d th a n w ith t r e a t e d a c i d a lth o u g h i n t h i s e x p e rim e n t th e
t r e a t e d a c i d c o n t r o l was more t u r b i d th a n th e norm al a c i d c o n t r o l .
im p o rta n t i n d i c a t i o n from t h i s t a b l e i s t h a t th e
g r e a t l y re d u c e d b y sodium s i l i c a t e t r e a t m e n t .
The
c o n te n t i s n o t
The a c i d i s w eakened by
o n ly a b o u t I / 2- 1 /3 th e amount one w ould weaken i t by d i l u t i o n w ith th e
volum es u s e d f o r tr e a tm e n t.
B ecause o f t h i s , i t i s assum ed t h a t concen­
t r a t i o n f o llo w in g tr e a tm e n t w ith sodium s i l i c a t e w ould n o t be n e c e s s a r y .
The v a r i a t i o n s i n v a l u e s among th e d i f f e r e n t t e s t s , e s p e c i a l l y w ith
r e g a r d to PgO^, a r e a g a in p r o b a b ly n o t s i g n i f i c a n t ; th e a v e ra g e o f th e s e
a s s a y s c o u ld b e e x p e c te d when u s in g t h i s t r e a t m e n t .
-
T hese r e s u l t s may b e b r i e f l y sum m arized a s fo llo w s ?
1.
T here was a m arked im provem ent i n th e q u a l i t y o f th e a c i d s
from n e a r l y a l l t e s t s .
2.
L i t t l e s i g n i f i c a n c e m a y b e h e l d f o r th e d i f f e r e n c e s i n v a r io u s
t r e a t m e n t s , e x c e p t i n th e am ounts o f a c i d a v a i l a b l e from th e t r e a tm e n ts .
3.
Low p e r c e n ta g e s o f s i l i c a t e a r e b e s t b e c a u se th e amount o f
V
a c id a v a ila b le i s g r e a te r .
h.
The b e s t s i l i c a ? s o d a r a t i o i n v e s t i g a t e d was 3 .3 6 .
The n ex t
b e s t was 1 .6 9 .
5.
T h ere a r e two s u g g e s te d tr e a t m e n t s f o r norm al a c i d .
P i r s t and
p r e f e r a b l y , th e a d d i t i o n o f ab o u t 8 p e r c e n t by w eig h t o f a 10 p e r c e n t
s o l u t i o n o f 3 .3 6 sodium s i l i c a t e w h ich w i l l e x h i b i t b o th a good sedim en­
-
27
-
t a t i o n r a t e and low am ounts o f sed im en t w h ile p ro d u c in g an a c i d o f f a i r
c la rity .
Second, th e a d d i t i o n o f ab o u t 8 p e r c e n t "by w eig h t o f a 10
p e r c e n t s o l u t i o n o f 1 ,6 9 sodium s i l i c a t e w hich w i l l e x h i b i t a n a c id o f
good c l a r i t y w ith a f a i r s e d im e n ta tio n r a t e and s l i g h t l y h ig h e r am ounts
o f s e d im e n t,
6,
I t i s n o t p r o b a b le t h a t any a d v a n ta g e w ould b e g a in e d by a
c o m b in a tio n o f soda a s h and sodium s i l i c a t e tr e a t m e n t s o r b y in c lu d in g
e l e c t r o l y s i s I n th e t r e a t m e n t „
-
28
-
Table 17
D a ta f o r R e s u lts Shown, i n F ig u r e I
T est
10 m l.1 2 .5 $
(1 .6 9 )
0
k
8
12
14
20
32
37
. Te s t
Sag,
5 m l.12#
0
3
4
5
8
13
17
22
35
(3 .3 6 )
O u tic a l D e n s ity
Te s t
E az
O n tic a l D en sity
' 2 .0
.720
o600
.387
.356
.288
.215
.208
10 m l.12#
(3 .3 6 )
0
3
4
5
8
13
17
22
35
2.0
1 .2 5
.940
.700
.556
.393
.328
.284
.240
T e st
E az
O n tic a l D e n s its
10 m l.1 9 #
(3 .3 6 )
0
3
4
5
8
. 13
17
22 .
35
2.0
.955
.700
.593
.469
.320
.284
.256
.233
,
,
O n tic a l D e n s ity
2.0
1.21
1 .0 1
.795
.6 0 4
.318 "
.378
.256
.250
-
29
-
T a b le V
D a ta f o r H e g n lts Shown i n F ig u r e 2
O n tic a l D e n s ity
T est
T est
Dag
O n tic a l D e n s ity
10 m l„25$
(1 .6 9 )
0
5
•8
12
14
16
20
32
37
2 .0
.4 3 7
.386
.305
.294
.2 8 2
.2 3 8
.177
.177
10 m l .1 2 .5 $
(1 .6 9 )
0
4
8
12
14
20
32 •
37
Dag.
O n tic a l D e n s ity
T e st
D§£
O n tic a l D e n s ity
0
4
10
14'
18
22
30
43
2 .0
. 1 .1 0
.583
„481
.4 3 2
.382
.253
.232
0
10
14
18
22
30
2 .0
1 .4 2
1 .3 0
1 .1 9
1 .0 9
1 .0 5
T e st
10 m l.7$
(1 .6 9 )
.
10 m l .2$
( 1 .6 9 )
2 .0
.720 .
.600
.387
.356
.288
.215
.208 ■
■
- 30 T a b le VI
D a ta f o r H e s u lt s Shown I n F ig u r e 3
T est
C o n tro l
Dag;
0
2
3
■ 4
7
12
16
21
33
T est
D§£
5 m l. 12#
( 3 .3 6 )
0
2
3
4
7
12
16 21
33
T est
O n tlc a l D e n s ity
„432
.420
.4 3 7
.475„500
.5 5 2
.545
.565
.585
5 m l. 7#
(1 .6 9 )
O n tic a l D e n s ity
.4 3 2
.940
.720
„668
.4 8 8
.347
„266
.2 2 9
.181
0
2
3
4
7•
12
16
21 •
33
Te s t
DaZ
5 m l. 19#
( 3 .3 6 )
0 .
2
3
4
7
12
16
21
33
O n tic a l D e n s ity
.4 3 2
.797
.530
.482
.3 0 0
.188
„154
.128
.111
Daz
O n tic a l D e n s ity
.
T ab le V II
D a ta f o r R e s u lts Shown i n F ig u r e 4
10 m l. 7# ( 1 .6 9 )
Daz
O n tic a l D e n s ity
0
4'
10
14
18
22
30
43
2 .0
1 .1 0
.5 8 3
„481
.4 3 2
.3 8 2
.2 5 3
.2 3 2
.
Dav
0
. 4
8
• 15
18
2.4
29
48
O n tic a l D e n s ity
2 .0
1 .1 2
„622
„375
.3 4 8
„310
„288
• .2 4 4
„432
.312
.275
.272
.219
.163
.158
.152
.143
- 31
T ab le T i l l
D a ta fo r Hes u i t s' Shown i n f i g u r e 5
T est
1-2.50 ■
(1 .6 9 )
T est
120
(3 .3 6 )
Day
Cm. c l e a r
a c id
2
4
5
8
12
32-
4 .7
9 .Q
10.0
11.0
1 1 .2
1 1 .2
Day
Cm. c l e a r
a c id
I ,
2
3
4
5
8
13 .
I?
:
T e st
Day
70
(1 .6 9 )
I
2
4
6
8
17
■ T est
120
(3 .3 6 )
5 ml.
5 .0
7 .5 .
'9 ,5
'
11.0
1 1 .4
1 2 .8
1 3 .6
14.0
T est
Pa-y
Cm. c le a r
a c id
190
(3 .3 6 )
I
2
3 .
4
' 5
8
13
17
1 .5
3 .4
5 .4
7 .9
8 .6
9 .5
10.0
10.0
,
Cm. c l e a r
a c id
'
2 .5
5.8.
11 .0
1 3 .4
14.0
' 14.8.
'
■
bay
Cm. c l e a r
a c id
I
2
3
4
5
8
13
17
2 .2
3 ,4
. - 4jr6
7 .0
8 ,5
1 1 .8
1 2 .8
1 3 .2
•
'
- 32 7.
S I SOUSS IOH .
!
Those sodium s i l i c a t e s h a v in g s i l i c a ? s o d a (HagO) m o le c u la r r a t i o s
ly i n g b e tw e e n 1 (1 ( m e t a s i l i c a t e ) and 4 ? I ( o r t h o s i l i c a t e ) a r e known
c o l l e c t i v e l y a s w a te r g l a s s e s o r s o lu b le s i l i c a t e s .
S in ce th e a b i l i t y
of th e S i l i c a t e to p ro d u c e a p a r t i c u l a r e f f e c t o f t e n i s a f u n c t i o n o f
th e above m o le c u la r r a t i o , i t was d e s i r a b l e . t o i n v e s t i g a t e th e e f f e c t s
i n t h i s c a s e o v e r a ra n g e o f r a t i o s .
The p a r t i c u l a r r a t i o s w ere Qhosen
b e c a u se s p e c i f i c g r a v i t y - c o n c e n t r a t i o n t a b l e s a r e a v a i l a b l e f o r th e s e
ra tio s .
When a s o l u t i o n o f sodium s i l i c a t e i s added to a c o n c e n tr a te d a c id ,
s i l i c a i s p r e c i p i t a t e d a s a g e l a t i n o u s h y d r a te , s i l i c i c a c i d .
A cco rd in g
to Hurd (1 9 3 8 ), sim p le m o le c u le s o f s i l i c i c a c i d a r e u s u a l l y form ed by
th e r e a c t i o n o f th e sodium s i l i c a t e w ith a n a c i d and th e s e sim p le m ole­
c u l e s s lo w ly co n d en se to fo rm a more com plex s t r u c t u r e .
W ater i s s p l i t
o u t b e tw e e n s im p le r s i l i c i c a c id m o le c u le s t o form a h e a v i ly h y d ra te d
p o l y s i l i c i c a c id s tr u c t u r e .
When enough o f th e s e l a r g e s t r u c t u r e s have
a c c u m u la te d , th e system fiS e t s '6 i n t o a s e m is o lid , e l a s t i c m ass.
I f 10 m l, o f sodium s i l i c a t e a r e ad d ed to 85 m l, of. t e c h n i c a l
p h o s p h o ric a c i d (53 p e r c e n t PgO^), 30 m in u te s w i l l e l a p s e b e f o r e th e
system s e t s i n t o a n e l a s t i c m ass w h ic h .w i ll n o t p o u r fro m th e tu b e ,
H o th in g re s e m b lin g t h i s p r o c e s s o c c u r s when sodium s i l i c a t e i s added
to c ru d e p h o s p h o r i c .a c i d .
I n s te a d , t h e r e i s an im m ediate f o r m a tio n of
a g e l a t i n o u s mass w hich w i l l n o t s e t and i s n o t e l a s t i c .
to th e p r e s e n c e o f s i l i c o f l u o r i d e „
T h is i s due
When h y d ro fI u o s i l i c i c a c i d i s m ixed
w ith th e t e c h n i c a l p h o s p h o ric a c i d and sodium s i l i c a t e ad d ed , t h e r e i s
-
33
-
an Immediate form ation o f a g e la tin o u s mass ju st a s w ith crude a c id .
The sodium io n from, d is s o c ia t io n o f th e sodium s i l i c a t e im m ediately
p r e c ip it a t e s th e s i I i c o flu o r id e and th u s in t e r f e r e s , somehow, in the
form ation of the polym eric str u c tu r e .
Host m e ta llic s a l t s r ea c t w ith
sodium s i l i c a t e s o lu tio n s to produce a c o llo id a l m etal s i l i c a t e accom­
panied "by a th ick en in g o f the whole mass, e 0g„, aluminum phosphate g iv e s
a te n a c io u s mass (M ellor, 1925)e
T his suggested th a t aluminum and
.
.
•
oth er m etal io n s might he removed w ith sodium s i l i c a t e ; however, no
s ig n if ic a n t amount o f aluminum seemed to he removed from s o lu tio n s of
AlPOjj, in te c h n ic a l phosphoric acid ,-
iro n was shown to he removed
from the crude a cid (Table I I I ) , hut t h i s was prohahly ju st the
removal o f suspended ir o n ph osp hates.
A side from t h is p o s s i b i l i t y th a t m e ta llic io n s might he remoyed
by th e treatm ent, another e f f e c t tihich d e f in it e ly has a r o le in the
treatm ent i s th e m echanical dragging down o f p a r t ic le s by the g e la ­
tin o u s mass a s i t s e t t l e s .
Although t h i s i s undoubtedly a very
important e f f e c t , i t i s not the e n tir e mechanism, of p u r if ic a t io n fo r
when a sample o f a c id was tr e a te d w ith sodium s i l i c a t e and immediately
c e n tr ifu g e d , an acid was obtained.w hich had r e la t iv e l y l i t t l e tu rb i­
d it y .
However, i t s tu r b id ity then in crea sed fo r two or th ree days
a fter , which i t again began to d e c re a se ,
She same th in g occurred when
a sample was c en tr ifu g e d on the second day a ft e r treatm ent, but by
the f i f t h day th ere was no in crea se in tu r b id ity d etected fo llo w in g
c e n tr ifu g a tio n .
T his su g g e sts th a t a slow r e a c tio n , p o s s ib ly a
p o ly m erisa tio n o f s i l i c i c a c id , was o ccu rrin g .
I f i t were a
—
'
34
™
p oly m eriza tio n r e a c tio n , i t could co n ceiv a b ly entrap c o llo id a l par­
t i c l e s of the im p u r itie s in s id e the polym eric stru ctu re and thus carry
them down as th e polymer or aggregate s e t t l e d .
I f t h i s p rocess i s to he econ om ically f e a s ib le , ah important .consid­
e r a tio n i s the c o s t .
The method of p u r if ic a t io n w ith sodium carbonate,
which i s now in use a t the Anaconda p la n t, r eq u ir es a la rg e e x c e s s o f
a lk a li m etal io n to e f f e c t i v e l y remove the f l u o s i l i c a t e s ,
At the
p r e se n t, 35 pounds of soda ash (presumably 58 per cen t Ua2CO^) are
added to each ton of I o c I overflow th a t i s p ro cessed .
T his i s equiva­
le n t to ?4 pounds per ton of concentrated a c id , .Based on the A p ril
16, 1951 q u otation fo r dense soda ash in the llO il, P a in t, and Drug
R eporter , 11 t h is treatm ent c o s ts 9 6 ,5 c e n ts per ton of shipping a c id ,
■t
In c o n tr a st, assuming th a t con cen tratin g from 51 per cent P 2O5 i s not
required and th at 8 per cent by w eight o f a 10 per cent sodium s i l i c a t e
s o lu tio n i s added to concen trated a c id , the proposed treatm ent req u ires
4 ? 02 pounds o f sodium s i l i c a t e per to n o f a cid and c o s t s 4 4 ,8 cen ts
per ton based on the qu otation fo r 40° Baume sodium s i l i c a t e .
- 35 -
' VIe
SUMMARY
Producers of"phosphoric a c id th a t use the s u lfu r ic a cid p ro cess
have a problem w ith slu d ges coming out o f s o lu tio n when the a c id i s
con cen trated .
These s lu d g e s ,-c o n s is t in g p r in c ip a lly of ir o n and alu ­
minum phosphates w ith some s i l l c o f l u o r i d e s , s e t t l e very slo w ly .
Furthermore, they con tin u e to form and s e t t l e fo r months fo llo w in g
manufacture o f the a c id .
The continuous form ation and s e t t l i n g of
s o lid s i s e s p e c ia lly troublesome when the a c id i s used a s liq u id f e r t i ­
l i z e r and i s d is tr ib u te d through sm all n o z z le s in to ir r ig a t io n w aters.
P r e c ip ita tio n o f the s i I i c o flu o r id e s a s sodium s i I i c o flu o r id e by
adding sodium carbonate improves the a cid by shortening th e s e t t lin g
tim e to about fou r w eeks.
However, t h e . a cid so trea ted w i l l not
remain c le a r but g ra d u a lly becomes in c r e a s in g ly tu rb id again , at
le a s t i f i t i s perm itted to stand in contact w ith i t s sedim ent,
A more d e sir a b le method of p u r if ic a t io n was sought which would
produce a b e tte r acid w ith in the same length , of time as required by the
soda ash method.
I t was found th at tr e a tin g the tu rb id a cid coming from the evap­
orator w ith about 8 per cent by w eight o f a 10 per cent sodium s i l i c a t e
s o lu tio n i s a s a t is f a c t o r y method of p u r if ic a t io n .
A nalyses showed th at the acid was only s lig h t l y weakened, by t h is
treatm ent w hile la r g e amounts of the im p u r itie s were removed.
The mechanism o f th e p rocess i s p a r tly the mechanical dragging
down of s o lid s by the g e la tin o u s mass o f s i l i c i c a cid formed in the
r e a c tio n of the sodium s i l i c a t e w ith th e crude a c id , p a r tly the
— 36 —
p r e c i p i t a t i o n o f sodium s i l l c o f l u o r i d e s and p o s s i b l y th e rem o v al o f
v e r y f i n e p a r t i c l e s th ro u g h s e t t l i n g o f s lo w -fo rm in g , p o ly m e ric s t r u c ­
t u r e s o f s i l i c i c a c id w hich have e n tra p p e d th e p a r t i c l e s *
Some advantages o f tr e a tin g w ith sodium s i l i c a t e may he l i s t e d as
fo llo w s ;
I*
A superior product i s produced*
2.
The s e t t lin g tim e req uired i s shorter^ thereby in c r ea sin g the
p rodu ction c a p a c ity .
3*
The c o st o f p u r if ic a tio n i s lower*
L ikew ise, some disadvantages are:
1.
L e s s a c id i s a v a i l a b l e fro m e a c h to n e v a p o ra te d due t o th e la r g e
am ounts. tr a p p e d i n th e g e l m ass a n d slu d g e*
However, th e s e s o l i d s a re
su ch t h a t th e y may b e e a s i l y f lu s h e d from ta n k s an d p a s s e d o v e r a f i l t e r .
The d i l u t e a c i d r e c o v e re d co u ld be. u se d i n much th e same way a s th e Ho. 2
and No. 3 o v e rflo w s a r e now u s e d .
2.
An en gin eerin g problem i s in v o lv ed in th at th ere must be a way
of r a p id ly and thoroughly mixing th e sodium s i l i c a t e in to the acid;
otherw ise the s i l i c a t e c o a g u la tes in la rg e lumps a n d .is l e s s e f f e c t i v e .
3.
The a cid i s d ilu te d to some e x te n t, but t h is may p a r t ia l ly be -
overcome by u sin g higher s i l i c a r a t io s in le s s e r q u a n titie s a s in d ic a te d
in the experiment w ith 5 m l. of 12 per cent (3=36) in ste a d o f the usual
10 ml.
-
V II.
37
-
AGKIOWIEDGEMEKTS
The a u th o r t a k e s t h i s o p p o r tu n ity t o e x p r e s s h i s th a n k s to
P r o f e s s o r P 0 G0 G a in e s , D r0 E 0 W0 A n a c k e r0 an d D r0 L0 H0 Jo h n so n f o r
t h e i r h e lp and s u g g e s tio n s .
A p p r e c ia tio n i s e x te n d e d to th e A naconda
Copper M ining Company who f u r n is h e d sam p les, d a t a , and th e g r a n t making
th is re s e a rc h p o s s ib le .
- '• ’ •
- 38 V III.
(1949)
LITERATURE CITED
(1)
Hampel, C. A .,
Ghem. E n g r. Hews 2%, 2420.
(2 )
H i l l , W0 L . , M a r s h a ll, H. L ., and J a c o b , K. D ., (1932)
I n d . E ng.
Chem0 24, 106 4 .
(3)
Hoffman, J . I . ,
and L tm d e ll, G. E 0 E 0, (1938)
J . R e s e a rc h R a t l 0
B u r 6 S ta n d a rd s 20, 607.
(4 )
H urd, C ., (1938)
Chem0 R ev. 22, 4 0 3 .
(5 )
O f f i c i a l M ethods o f A n a ly s is , s i x t h e d i t i o n , p . 23, A s s o c ia tio n of
O f f i c i a l A g r i c u l t u r a l C h em ists, W ash in g to n , D. C0, 1945..
(6 )
M e llo r , J . W0, (1925)
A C om prehensive T r e a t i s e on I n o r g a n ic and
T h e o r e t i c a l C h e m is try . V o l. VI S i l i c o n , S i l i c a t e s p . 322, Longmans,
G reen and C o ., London.
(7 )
Waggaman, W. H0, (192?)
P h o s p h o ric A cid . P hospha t e s a n d P h o sp h ate
F e r t i l i z e r s , p . 200, The C hem ical C a ta lo g C o ., Rew Y ork.
I
7V
100897
U&
M^ 8
S -b 8 3 p
cop .
innes?