GEOC
I will present examples of these types of titration curves and others, and also
show how curves associated with addition of small amounts of calcite can be used to
discern carbonate coprecipitates. Additionally, I will show a time series of curves
w h i c h r e fl e c t a n o n e q u i l i b r i u m w e a t h e r i n g p r o c e s s .
1 7 3 . N I C K E L S O R P T I O N K I N E T I C S O N T H E C L AY F R A C T I O N O F A S O I L . D . R . R o b e r t s
and D.L. Sparks, Department of Plant and Soil Sciences, University of Delaware, Newark,
Delaware, 19717-1303.
Soil mineral surfaces are capable of sorbing and retaining heavy metal ions and are therefore
important in assessing the fate of heavy metal contaminants in the soil environment. Past studies of
heavy metal sorption kinetics have focused on pure mineral components, with less emphasis placed
on mixed systems. However, soil clay fractions in natural environments are rarely, if ever, composed
of only one pure mineral component. This study exannines Ni(II) sorption and desorption kinetics on
the clay fraction (<0.002mm) of a Matapeake silt loam. Samples were aged (days to months) using
batch techniques at a pH of 7.5 with an initial Ni(II) concentration of 3mM. Desorption experiments
were conducted at various times to assess the effect of aging on the release of Ni(II) from the clay
fraction. Ascertaining the kinetics of nickel sorption on clay minerals is needed to propose possible
sorption reaction mechanisms and assess the metal mobility/fate in natural environments.
1 7 4 . T H E E F F E C T S O F R E S I D E N C E T I M E O N T H E R E T E N T I O N O F A R S E N AT E B Y
GOETHITE. S.E. O'Reilly and D.L. Sparks, Department of Plant and Soil Sciences, University
of Delaware, Newark, Delaware 19717-1303
Research has shown that sorption of metals on natural materials can proceed for a long time,
however the mechanisms for this slow sorption are not well understood. Accordingly, the goal of this
study was to determine the effects of "aging" or residence dme on the kinedcs of arsenate sorption and
desorption on goethite. Batch sorption and desorption studies were conducted at pH 6 for periods up to
2 months. The desorption experiments were conducted for a period up to one month on different "aged"
samples using sulfate and phosphate desorptives. Initial sorption was rapid with over 90% of the arsenate
sorbed within 24 hours. Arsenate sorption increased slowly with time. As residence time between
arsenate and goethite increased, the amount of desorbed arsenate decreased, and desorption increased
with increasing desorption equilibrium time. Phosphate was more effective in desorbing arsenate than
sulfate, but, in general. As seems to be tightly bound to goethite.
jYg KINETICS OF BIOGEOCHEMICAL PROCESSES IN SALT MARSH SEDIMENTS. E. Viol]ier. P.
Van Cappellen, A. Roychoudhuri, P. Inglett, K. Hunter, Georgia Institute of
Te c h n o l o g y , A t l a n t a , G A 3 0 3 3 2 - 0 3 4 0 .
The salt marsh developed along the Georgia coast is a dynamic ecosystem sub
jected to daily and seasonal stresses due to tidal cycles and river-borne organomineral particles. This study is an attempt to quantify early diagenetic processes and
t r a c e e l e m e n t i m m o b i l i z a t i o n / r e l e a s e i n t h e fi r s t 5 0 c e n t i m e t e r s o f a h i g h l y r e d u c i n g
sediment. On one hand, kinetic experiments are performed on undisturbed sediment cores
( p l u g - fl o w r e a c t o r ) i n o r d e r t o a s s e s s r e a c t i o n r a t e s a n d r e t r i e v e r a t e e x p r e s s i o n s o f
i n d i v i d u a l p a t h w a y s ( s u l f a t e , i r o n , u r a n i u m r e d u c t i o n , i r o n s u l fi d e p r e c i p i t a t i o n ) .
On the other hand, the latter kinetic information is utilized in Steadysed (model of
r e a c t i v e t r a n s p o r t i n a q u a t i c s e d i m e n t s ) . M o d e l fi t t i n g o f a c t u a l p o r e w a t e r d i s t r i b
utions is carried out. Predicted vertical distributions of solids are then compared
to
data
from
selective
chemical
extractions.
170 SURFACE CHARGE PROPERTIES OF AND CU(II) ADSORPTION BY SPORES OF THE MARINE
B A C I L L U S S P. S T R A I N S G - 1 . L e e M . H e a n d B r a d l e y M . Te b o , M a r i n e B i o l o g y
Research Division and Center for Marine Biotechnology and Biomedicine, Scripps
Institution of Oceanography, University of California at San Diego, La Jolla,
CA
92093-0202.
Dormant spores of the marine Mn(lI)-oxidizing Bacillus sp. strain SG-1 are
c a p a b l e o f b i n d i n g a v a r i e t y o f h e a v y m e t a l s . T h e s p e c i fi c s u r f a c e a r e a o f f r e e z e -