A critical review on soil washing during soil remediation for heavy metals and organic pollutants

Soil washing is widely considered as a common method of soil remediation. This study examined the developments in soil washing during the past 20 years via a bibliometric and systematic critical review. Different washing agents (inorganic and organic chelating agents and surfactants) exhibit different effects and mechanisms under varying conditions. Most previous research has involved only laboratory-scale studies; however, pilot field studies are more relevant to actual conditions and soil characteristics. Soil factors include physical and chemical properties, coexisting ion species content, and heavy metals and their forms in the soil. Washing conditions include type of leaching agent, concentration, pH, time, and solid–liquid ratio. Combinations of remediation techniques, such as advanced oxidation, electric remediation, and phytoremediation, can avoid many disadvantages of using only soil washing. In future soil washing studies, focus must be placed on developing environmentally friendly washing agents, optimizing washing conditions while reducing economic costs and preventing destruction of the function of the soil, problems associated with complex pollution, and the entire soil–ground environment to avoid groundwater pollution. This study expects for relevant research directions and provides guidance for future research.