The progress in phosphate remediation of heavy metal-contaminated soils
磷酸盐修复重金属污染土壤的研究进展

Phosphate has been identified as a cost-effective amendment to remediate heavy metal-contaminated soils. In this paper, research methods for phosphate remediation, reaction mechanisms between phosphate and heavy metals, and the potential risk due to excessive phosphate application were reviewed in detail. In addition, some problems and limitations were also discussed. Chemical extraction procedures, chemical equilibrium speciation models, and spectroscopic and microscopic techniques are main methods to investigate phosphate remediation. It is necessary to combine all techniques because of the limitation of every method. Phosphate-induced adsorption of heavy metals on contaminated soils, the formation of precipitates and/or minerals of heavy metal phosphate, and adsorption of heavy metals on phosphate surfaces are primary mechanisms for phosphate remediation. At present, it is difficult to effectively differentiate whether phosphate induced decrease in heavy metal availability is due to increased adsorption of metals or whether it is the result of precipitation or other fixation. Accordingly, it is more difficult to predict the long-term stability of phosphate remediation. As an amendment, phosphate is excessively applied to soils contaminated by heavy metals. There is probably some potential risk such as eutrophication of water bodies due to phosphorus leaching loss, the deficiency of medium- and micro-elements in plants caused by unbalance of nutrients, and soil acidification, etc. Thus, the species and rate of phosphoric fertilizers should be cautiously determined, with the optimum scheme where soluble phosphoric fertilizers are mixed with insoluble ones, or co-application of lime and phosphoric fertilizers. Finally, we emphasized the importance of quantitative assessment of reaction mechanisms and potential risk during phosphate remediation. Especially, one should pay more attention to the long-term solubility and mobility of stabilized heavy metals under the condition of continuous decrease in soil phosphate due to uptake by plant or other changes, and to phosphate remediation of field soils.