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 (R2 = 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/m3/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.