Remediation of Heavy Metal-Contaminated Soils with Soil Washing: A Review

Soil with heavy metals' contamination has caused worldwide concern, and there is an increasing interest in the application of washing agents for the remediation of soils with heavy metals' contamination. The review summarizes the recent findings about soil washing with different washing agents. For soil washing technologies, the solubilizing capability, toxicity, and biocompatibility of agents are essential concerns. Washing agents can enhance heavy metals' desorption and removal from soil. Inorganic acids/bases/salts, synthetic surfactants, and synthetic chelators are often limited due to their adverse effects on soil. Biosurfactants, HAs (humic acids), and LMWOA (low-molecular-weight organic acids) are suggested washing agents, but the limitation of their low production needs to be conquered. Moreover, both washing with a mixture agent and sequential washing have often been adopted to improve the overall capacity of the washing agent for decontamination. Mixture washing can obtain the synergetic effect for soil washing and increase washing efficiency. Sequential washing can apply an agent with a high heavy metals removal rate. However, this may cause environmental risks in the early stage, and then remove the washing agent injected in the early stage by the secondary washing stage. Overall, the already known cases reveal the good prospect of soil washing for soil remediation.