Apparent Viscosity of Phosphate Dispersant-Amended Soil-Bentonite Backfills

When exposed to contaminants, soil-bentonite mixture tends to form a flocculate structure, leading to an increase in permeability while decreasing in performance of mitigating contaminants. To solve this problem, dispersants can be added to the soil-bentonite mixture to maintain a dispersed structure, relatively low permeability, and homogeneous. This study focuses on the viscosity property of soil-bentonite suspensions amended with dispersants. Three commercially available phosphate dispersants were used, which include sodium hexametaphosphate (SHMP), sodium tripolyphosphate (STPP) and sodium pyrophosphate decahydrate (TSPP). The designed bentonite content was 0, 5, and 10 %, whereas that of dispersant was 0, 0.01, 0.05, 0.1, 0.5, 1, 1.5, and 2 %, respectively. Both are based on the dry-weight of kaolin-bentonite powder. The result shows that with an increase in the content of dispersant, the viscosity of the mixture decreased and then tended to remain stable, irrespective of the type of dispersant. Three types of dispersants resulted in marginal differences in the measured viscosity regardless of the bentonite contents. Bentonite content of backfills can be improved by the addition of dispersants. In addition, optimum dosages of dispersants are 0.05, 0.1-0.5, and 0.5 %, corresponding to the mixtures with bentonite content of 0, 5, and 10 %.