Deep Eutectic Solvent-Assisted Washing of Nickel from Polluted Mine Soil

Recently, nickel pollution in soil has become a hot topic in research. Therefore, the key solution for washing remediation is to find effective, inexpensive and ecology friendly washing agents to remove nickel from polluted soils. In this paper, diethylene glycol-choline chloride ionic liquids (DCILs) combined with composite acid was used as an eluting agent to remove nickel in contaminated mine soils. The nickel removal rates when using the composite acid or the DCILs were 48.77% and 4.5%, respectively. The removal rate increased to 57.60% when using the composite acid combined with 3% (v/v) DCILs as an optimum eluant; this experimental result indicated that the optimum eluant based on the composite acid and DCILs was successfully determined, and it had a significant effect on the extraction process. The BCR speciation analysis showed that the removal rates ranked as follows: oxidisable fraction (92.18%)>acid extractable fraction (85.41%)>reducible fraction (79.07%)>>residual fraction (23.34%) after extraction under optical conditions, which implied that the optimal eluant played a critical role in the mobility of the nickel removal rate and effectively reduced the bioavailability and environmental risk of the nickel. To sum up, DESs-assisted washing is a promising method in the field of removing heavy metals from contaminated soil.