Coagulation of soil suspensions containing nonionic or anionic surfactants using chitosan, polyacrylamide, and polyaluminium chloride

Abstract

Effective coagulation and separation of particles in a soil-washed solution is required for a successful soil washing process. The effectiveness of chitosan (CS), a polycationic biodegradable polymer, as a coagulant was compared to polyacrylamide (PAA) and polyaluminium chloride (PAC) for the coagulation of a soil suspension (5 g L −1). The effect of surfactants in the coagulation process was investigated using Triton X-100 (TX-100), a nonionic surfactant, and sodium dodecyl sulfate (SDS), an anionic surfactant. CS (5 mg L −1) removed 86% and 63% of the suspended soil in the presence of TX-100 (5 g L −1) and SDS (5 g L −1), respectively, after 30 min at a pH of 6. The results prove that coagulation in the presence of TX-100 is more effective than with SDS. CS was found to be more efficient compared to PAA and PAC under all coagulation conditions. The optimum concentration of CS required for maximum coagulation of soil suspension was 5 mg L −1. PAA and PAC could not achieve the same degree soil removal as CS even after increasing their concentrations up to 50 mg L −1. Maximum levels of 50% and 60% soil removal were achieved using PAA (50 mg L −1) and PAC (50 mg L −1), respectively, after 30 min from a 5 g L −1 suspension containing TX-100 (5 g L −1). The soil coagulation process was found to decrease with an increase in the pH of the suspension, and maximum coagulation was achieved with an acidic pH.