Soil column studies were performed on a chromium contaminated soil from the United
Chrome Products Superfund Site currently undergoing a pump-and-treat cleanup process. The
goal of the research was to provide insight into the feasibility of chemically changing the injection
fluid of the pump-and-treat system to enhance hexavalent chromium (Cr(VI)) mobility. The
parameters tested were pH, ionic strength, and competitive anion type and concentration.
Ionic strength effects were investigated by adjusting the NaCl concentration of the
extracting solution and by observing the influence of varying anion concentrations on desorption
(bicarbonate, sulfate, and phosphate). The results indicated that high ionic strength solutions
slow the rate of Cr(VI) desorption. This possibly indicates most of the Cr(VI) was in pore water
solution and was adsorbing, slowing the removal process. Cr(VI) desorption was fastest for
distilled water solution followed by competitive anion/distilled water solutions. The high ionic
strength extracting solutions, 0.05 M and 0.10 M NaCl, had the slowest Cr(VI) desorption rates.
Effluent pHs dropped as the ionic strength was increased (increasing NaCl concentrations) which
was attributed to a Na-H exchange. Increased concentrations of bicarbonate, sulfate, and
phosphate resulted in only small pH differences in the effluent of less than 0.5 pH units.
The effect of pH was investigated by varying the pH of the 0.01 M NaCl solution with
strong acid and base and by varying the pH of phosphate competitive anion solutions. The
effects of changing 0.01 M NaCl solution pH were inconclusive. Differences between Cr(VI)
desorption rates for the soil columns with adjusted influent pHs were small. Cr(VI) desorption
curves and column effluent pH values for phosphate solutions of varying influent pH values were
nearly identical, indicating that soil buffering and effluent pH are more important factors than
influent pH in achieving Cr(VI) desorption.
Nitrate, bicarbonate, sulfate, and phosphate were investigated to determine the effect of
various competitive anions on Cr(VI) desorption. The effectiveness of each anion at extracting
Cr(VI) from soil appeared to follow the order of adsorption affinity to the soil. / Graduation date: 1992
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/36512 |
| Date | 11 February 1992 |
| Creators | Ball, Bruce L. |
| Contributors | Nelson, Peter O. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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