Sorption of Lead to Slurry Trench Cutoff Wall Backfills Comprised of SHMP-Amended Ca-Bentonite
This study investigated effects of phosphate dispersant on lead (typical heavy metal) sorption capacity of the sand/Ca-bentonite backfill for slurry trench cutoff walls. Several series of batch sorption tests were conducted using backfills consisting of sand and 20% Ca-bentonite with/without dispersant, as well as amended/un-amended Ca-bentonite alone. First, amended/un-amended backfills and amended Ca-bentonite were prepared. Next, aqueous solutions with 0 to 40,000 mg/L Pb concentration were prepared. Finally, the backfills and the Ca-bentonites were mixed with the solution in liquids to solid ratio of 10 and shaken for 24 h. The mixture was then centrifuged, and the supernatant was separated and analyzed for Pb concentration. The results show that the relationship between the amount of sorption and equilibrium concentration of Pb was well quantified by Langmuir and Freundlich isotherm models. Phosphate dispersant significantly increased Pb sorption capacity of both the sand/Ca-bentonite backfill and Ca-bentonite. The sorption process of the Pb onto the backfills or Ca-bentonites was found to be favorable. Overall, phosphate dispersant is shown to be a promising additive to sand/Ca-bentontie backfill in slurry trench cutoff wall construction for effective containment of Pb-laden groundwater.
KeywordsCalcium bentonite Slurry walls Sorption Lead
Financial support for this project was provided by Primary Research & Development Plan of Jiangsu Province (Grant No. BE2017715) and National Natural Science Foundation of China (Grant Nos. 41330641, 51278100 and 41472258). The authors thank the Colloid Environmental Technologies Co. (CETCO) for providing the bentonite used in this study, and the China Scholarship Council for making it possible to undertake this research at the University of Illinois at Chicago.
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