Evaluation of Factors Affecting Chemical Extraction of Co Ions from Contaminated Soil

Excessive concentrations of cobalt (Co) ions in the soil cause quality degradation and pose a significant hazard to biota. One of the options for the permanent separation of the pollutant from soil matrix is extraction by chemical reagents. In this study, response-surface methodology (RSM) was applied to evaluate the factors affecting Co extraction from contaminated calcareous soil. Solutions of disodium ethylenediaminetetraacetate (Na2EDTA), citric acid (CA), and HCl were considered as leaching media. Reagent concentration, soil to solution ratio, and extraction time were selected as process variable, while Co extraction efficiencies and final pH values of extracts were the measured responses. The effect of factor variation between three levels was studied using Box-Behnken experimental design. By statistical analysis, the most influential factors were determined for each reagent, and the model equations were proposed for the prediction of system responses. Overlaid contour plots were used for the analysis of the effect of process conditions on both responses simultaneously. Given that each case of contamination is unique and requires extensive research before the remediation is implemented full-scale, it was shown that experimental design methodology is a smart approach for the assessment and comparison between the treatments.