Transportation mechanism of chromium from tannery sludge through an electrokinetic process: role of electrolytes and operational conditions

Abstract

In the present study, a new understanding of the application of biosurfactant, saponin, has been explored, over nitric and citric acids, as an electrolyte for the remediation of chromium from tannery sludge using the electrokinetic process. The interaction effects of independent variables [such as electrolyte molarity (M) and applied voltage (V)] and the output responses were studied using the statistical tool, response surface methodology. A significant correlation has been established between responses such as chromium removal, electrolytes consumption and power consumption for the selected independent variables. In terms of total chromium removal, saponin showed maximum effectiveness of 80.01% as compared to 72.37% of citric acid and 67.06% of nitric acid removal efficiency with lowest electrolyte consumption. The proposed mechanistic strategy for maximum removal efficiency with saponin over selected electrolytes can be attributed to the synchronized effects of micelles formation and sequential complexation along with adsorption of chromium ions during electromigration process. Also, the results derived from the sequential extraction analysis revealed that the saponin-treated electrokinetic process successfully increases the transformation rate of labile speciation (i.e., exchangeable and reducible fractions) to stable speciation (i.e., oxidizable and residual fractions) of chromium. This affirmed its lower risk of recontamination during its disposal. Thus, the removal efficiency and transformation of active metal fraction into a non-reactive fraction by saponin have been highly commended.