Sorption of Cadmium in Surfactant-Amended Soils

Abstract

Surfactants can play an important role in controlling metal mobility when added to the soils. Proper selection of type and concentration of surfactant is crucial. The influence of cationic (cetyltrimethylammonium bromide, CTAB) and anionic (sodium dodecyl sulfate, SDS) surfactants on Cd sorption by three soils was studied in laboratory using batch systems. The initial Cd concentrations in solutions ranged from 5 to 160 mg L -1 . Surfactants were added to each soil at rates ranging from zero to >5.3 times the critical micelle concentration (CMC). In general, Cd sorption was found to conform to Freundlich isotherm. The cationic surfactant (CTAB) reduced the amount of Cd sorbed by the soils with the effect increasing from sub-CMC to supra-CMC levels. At the highest surfactant concentration tested (5.3 CMC), the Freundlich coefficient (K f ) values for Cd sorption decreased to 28.7, 61 and 62.9% of the values in the surfactant free soil for clay, calcareous, and sandy soils respectively. The influence of anionic surfactant (SDS) on Cd sorption by soils depended on the concentration of surfactant. Addition of SDS at sub-CMC increased the amount of Cd sorbed by soils studied, but at SDS concentration equivalent to 6.1 CMC, Cd sorption was decreased. Freundlich K f values decreased from 2.58, 2.05, and 1.86 to 2.19, 1.84, and 1.66 for clay, calcareous, and sandy soils respectively as a result of adding SDS at supra-CMC.