Optimal Removal of Cadmium from Heavily Contaminated Saline-Sodic Soil Using Integrated Electrokinetic-Adsorption Technique

Saline-sodic soil inherently exhibits extreme characteristics which challenge getting it remediated from mixed contaminants. In this study, the feasibility of removal of cadmium (Cd) in saline-sodic clay soil in presence of mixed pollutants was investigated. Fifteen (15) experimental runs, each having residence time of three (3) weeks, were designed and conducted according to Box-Behnken design to evaluate the effects of contaminants initial concentration (20-100 mg/kg), voltage gradient (0.2-1 v/cm) and polarity reversal (12-48 h) on Cd removal efficiency. The Cd removal efficiency fitted experimentally verified quadratic model (prediction error of 18.60 %) with insignificant lack of fit based on 5 % significant level (R-2 = 0.9917 and p < 0.05). Statistical analysis of the model's parameters shows that the effect of the investigated parameters follows the order: voltage gradient > initial contaminant concentration > polarity reversal rate. The optimal conditions considering optimization of all effecting parameters (both factors and responses) were found to be at voltage gradient = 0.47 V/cm; polarity reversal rate = 19.77 h; initial contaminant concentration = 65.44 mg/kg which yielded highest Cd remedial efficiency of 86 % at 22.45 kWhr/m(3)/mg energy expenditure. The study demonstrated the viability of employing integrated-adsorption technology for the removal of Cd from contaminated saline-sodic clays under extreme soil and contamination conditions. It also further underscores the intricacy of obtaining a common optimal remediation conditions for the different pollutants presence in saline-sodic soil contaminated with mixed pollutants.