Adsorption and desorption of chromium on clayey soils
Department of Civil and Environmental Engineering
Master of Science
Hsieh, Hsin Neng
Chan, Paul C.
Soil absorption and adsorption
Chromium residue waste was produced during sixties in the chromium production process. It was used as construction fill. Problems associated with chromium waste sites include structure distress and surface and groundwater contamination.
The purpose of this study was to investigate the adsorption and desorption of chromium on soil. In order to achieve this purpose, experiments were conducted to study the effect of pH, type of chromium compound, and type of soil on adsorption and desorption.
Experiments were performed on kaolinite, bentonite and sand. In our study, it was found that sand had almost no adsorption for chromium. Kaolinite had less adsorption capacity compared with bentonite, which was consistent with the cation exchange capacity. Adsorption of chromium was related to the amount of the soil presented. It was found in this study that the amount of chromium adsorbed was chromium added to proportional to the concentration of chromium added to the soil. Trivalent chromium was highly attached to the soil, whereas hexavalent chromium was poorly adsorbed.
From our study, it seemed the sorption mechanisms were two: the sorption of water causing the chromium being adsorbed and the physical sorption between soil and chromium. The physical adsorption were caused by van der Waals force and ion exchange attraction force. It was found that clay would expand when there was a change of pH, or the change of the concentration of the chemical presented. Swelling property made it very difficult to separate the bentonite from supernatant. pH definitely had an impact on chromium adsorption. It was found that when the p11 reached 4.5 to 5.0, trivalent chromium precipitated. Adsorption of trivalent chromiun increased as the pH also increased. In the contrast, hexavalent chromium had a higher adsorption capacity at lower pH values.
Several desorption processes were performed in this study. Pure water could remove chromium which was adsorbed due to van der Waals force. Other processes performed included oxidization of trivalent chromium to hexavalent chromium, change of pH. The above techniques could be oxidized trivalent chromium to hexavalent chromium, and change of pH, should be able to separate the chromium which was adsorbed due ion exchange from clay. EDTA can also be used to extract chromium from soil.
njit-etd1989-015 (90 pages ~ 3,337 KB pdf)
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Created August 4, 2005