重金属复合污染土壤稳定化基体材料筛选

Simultaneous immobilization of multiple heavy metals in soil: Screening of a suitable amendment type

我国土壤重金属复合污染现状十分严峻,严重威胁到饮水安全、粮食安全和人居环境安全.稳定化是土壤重金属污染治理中应用最广的风险管控技术,但由于不同类型重金属之间稳定化机制不同,同一类型重金属之间存在竞争吸附,其针对多金属复合污染土壤的适用性值得商榷.材料研发是稳定化技术的核心,本文探究了典型基体材料(炭基材料、硅基材料、磷基材料、粘土矿物、石灰类材料、铁基材料、镁基材料)针对多阴离子复合、多阳离子复合和阴阳离子复合污染土壤稳定化的适用性.结果发现,还原铁粉(零价铁)针对不同理化性质土壤砷、锑、镉和铅等重金属均能够取得较好的稳定化效果,而硫酸亚铁和聚合硫酸铁由于铁盐水解导致土壤酸化,在稳定砷、锑的同时还可能会造成镉元素活化;石灰类材料主要通过改变土壤的酸碱度与氧化还原电位的间接作用实现多金属的稳定化,其作用效果针对不同土壤具有一定的差异性,这一间接稳定化作用的长期有效性也值得进一步探究;活性炭、沸石等具有较强水相重金属吸附能力的多孔材料无法有效稳定土壤中的重金属,其投加会导致土壤砷、锑和镉等重金属的活化.研究结果可为多金属复合污染土壤稳定化功能材料的研制提供相应依据.

The current status of soil contamination by multiple heavy metals is severe in China, posing a serious threat to drinking water safety, food security and dwelling safety. Immobilization serves as the most widely used risk control method for soil heavy metals. However, its performance for the simultaneous immobilization of multiple elements deserves investigations due to the fact that different types of metals require a different soil environment(e.g., pH, Eh) for immobilization, and that competitive sorption may occur. This study investigated the effectiveness of representative soil amendments(namely, carbonaceous, silicon, phosphorous, clay-based, liming, iron-based, and magnesium-based materials) for the remediation of As, Sb, Cd, and Pb contaminated soils. Zero valent iron was the best candidate towards four elements, whereas ferrous sulfate and polyferric sulfate may mobilize Cd while immobilizing As and Sb due to soil acidification. Liming materials mainly immobilize metals in an indirect manner via increasing soil pH while decreasing Eh, whose long-term effectiveness should be further investigated. This indirect immobilization mechanism also leads to different performances towards different soils. Activated carbon and zeolite failed to immobilize these elements, which went against the common belief that these porous materials should theoretically immobilize soil metals. Results from this study support future works designing engineered soil amendments for the simultaneous immobilization of soil heavy metals.