磷酸盐修复重金属污染土壤的研究进展

从研究方法、反应机理以及风险评价等方面综述了磷酸盐修复重金属污染土壤的研究进展,分析和讨论了其中存在的问题和不足,提出了今后加强研究的重点。目前磷酸盐修复重金属污染土壤时,使用的主要研究方法有化学形态提取法、化学平衡形态模型法和光谱及显微镜技术,各个方法都有其优缺点,应该结合使用并探索新方法。磷酸盐稳定重金属的作用机理主要有3个:磷酸盐诱导重金属吸附、磷酸盐和重金属生成沉淀或矿物和磷酸盐表面吸附重金属,但磷酸盐与重金属反应的机理十分复杂,人们尚不完全清楚,因此难以有效区分和评价诱导吸附机理和沉淀机理或其它固定机理,相应地对磷酸盐修复重金属的长期稳定性难以预测。磷酸盐修复重金属污染土壤时由于其较高的施用量可能会造成磷的积聚从而引发一些环境风险,如磷淋失造成水体富营养化,营养失衡造成作物必需的中量和微量元素缺乏以及土壤酸化等。所以应该谨慎选择磷肥种类和用量,最好是水溶性磷肥和难溶性磷肥配合、磷肥与石灰物质等配合施用。今后应着重研究磷酸盐与重金属相互作用的机理区分和评价;关注磷酸盐修复重金属污染土壤时存在的潜在风险,特别是加强植物长期不断吸收磷或其它环境条件变化致使土壤磷素持续减少过程中稳定的重金属溶解性和移动性的研究,磷酸盐修复重金属污染土壤的长期田间实践等。

The progress in phosphate remediation of heavy metal-contaminated soils

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.