Enhanced desorption of Cobalt from contaminated sandy silty-clay soils

Abstract

In the present study, we investigated the potential for enhancing the desorption of cobalt contamination in a sandy silty-clay soil contaminated with Cobalt(II)-chloride-hexahydrate. In soils containing silt–clay fractions, effective remediation is primarily prevented by strong surface binding and adsorption processes. Overcoming these limitations requires the establishment of favourable conditions for desorption. In contrast to industrial practices, the potential for desorption was investigated under gradually alkalinizing and reducing conditions. Based on the results, the decrease in the ORP of the saturated system, together with the increase in pH, initiated cobalt desorption. Consequently, within the range above a redox potential from 0 mV to -80 mV and above pH 7.8, the [Co(H₂O)₆]²⁺ cobalt-complex initially formed. Further alkalinization and decreasing redox potential led to the precipitation of the remaining contaminant as Co(OH)₂ cobalt hydroxide. As a result of treatment, an average of 7.33 mg of cobalt was desorbed from the silty-clay surface within 29 days from the initiation of the desorption treatment, corresponding to about 12% of the contaminant present in the system. Furthermore, a lognormal distribution-based prediction function series (average R² = 0.941) was fitted to the obtained concentration data. The results indicate, that the applied procedure is capable of desorbing approximately 15% of cobalt contaminant, which presumably indicates the desorption capacity of the system. The applied method is widely accessible, cost-effective, and environmentally friendly which qualities that are essential for industrial application. The proposed novel approach represents an efficient and effective complementary technique for the future remediation of certain heavy metal compounds.