Adsorption of Cr(VI) onto SHMP-Amended Ca-Bentonite Backfills for Slurry-Trench Cutoff Walls
Several series of batch adsorption tests are conducted using slurry-trench cutoff wall backfills composed of sand and 20% Ca-bentonite with and without sodium hexametaphosphate (SHMP) amendment and also using Ca-bentonite alone with and without SHMP amendment. First, amended/un-amended backfills and Ca-bentonites are prepared. Next, aqueous solutions with 0 to 1000 mg/L hexavalent chromium [Cr(VI)] concentration are prepared. Batch adsorption tests are conducted at a liquid to solid ratio of 10:1 to investigate the adsorption of Cr(VI) onto the backfills and Ca-bentonites. The results show that phosphate dispersant causes significant increase in Cr(VI) adsorption of both the soil/Ca-bentonite backfill and the Ca-bentonite. The relationship between the amount of adsorption and the equilibrium liquid concentration is assessed using Langmuir, Freundlich, and Dubinin-Radushkevich isotherm models. The adsorption of Cr(VI) on the backfills or Ca-bentonites is attributed to chemical adsorption mechanism.
KeywordsCalcium bentonite Slurry walls Adsorption Chromium
Financial support for this project is provided by National Natural Science Foundation of China (Grant No. 41330641, 51278100 and 41472258) and Primary Research & Development Plan of Jiangsu Province (Grant No. BE2017715). The authors thank the Colloid Environmental Technologies Co. (CETCO) for providing the bentonites used in this study.
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