Comparative study on properties, mechanisms of anionic dispersant modified nano zero-valent iron for removal of Cr(VI)

Abstract

For the first time, nano zero-valent iron (NZVI) was successfully modified by an environmental friendly surfactant, fatty acid methyl ester sulfonate (MES), and at the same time the roles of a series of anionic dispersants (anionic polyacrylamide (APAM), sodium dodecylbenzene sulfonate (SDBS), and MES) in controlling the dispersity and physicochemical properties of NZVI were investigated. Results indicate that the dispersion and activity of modified NZVI were beneficially affected by the electronegativity strength of anionic dispersants according to the order of APAM > SDBS > MES. Compared with unmodified bare NZVI, the stabilization and antioxidability of anionic dispersant modified NZVI were significantly enhanced. Possible removal mechanisms associated with different anionic dispersants were proposed. A new revised kinetics model was provided for an insightful evaluation of reactive kinetics of Cr(VI) removal by anionic dispersant modified NZVI. In addition, dispersant content, initial Cr(VI) concentration, pH value and solution temperature were important parameters influencing Cr(VI) removal. Decreasing initial concentration of Cr(VI) and lower pH values were generally more favorable to accelerate the removal of Cr(VI). Moreover, the temperature will affect the surface complexation and electrostatic interaction which have a complex effect on the removal of Cr(VI).