负载磷酸盐生物质炭材料对重金属复合污染土壤的稳定化机制研究

为探讨负载磷酸盐生物质炭材料对重金属复合污染土壤中共存重金属的稳定化效果和迁移转化特征，以玉米秸秆和小麦秸秆为原材料，负载磷酸盐后在600 °C下无氧热解制备两种生物质炭材料，并将其用于重金属复合污染土壤中进行稳定化批处理试验. 结果表明:负载磷酸盐的玉米秸秆和小麦秸秆生物质炭材料可通过增加土壤中无定形铁、铝氧化物的含量而促进其对Cd的吸附，且负载磷酸盐后玉米秸秆生物质炭材料对土壤中无定形氧化物含量的增幅和游离态氧化物含量的降幅高于小麦秸秆生物质炭；同时，两种生物质炭材料均显著提高了土壤铁的活化度，进而有效控制了土壤重金属的生物有效性. 添加不同比例(如5%、10%和15%)的负载磷酸盐生物质炭均可降低土壤中Pb、Cd、Zn和Cu的迁移风险，并促进Pb的酸可提取态、铁锰结合态向有机结合态和残渣态转化，以及Cd、Zn和Cu的酸可提取态向残渣态转化. 两种负载磷酸盐生物质炭材料均可有效降低重金属的浸出浓度，10%及以上的添加量均可使Pb的浸出浓度降低98%以上. 15%的负载磷酸盐玉米秸秆生物质炭可使Cd和Zn的浸出浓度分别降低89%和47%，而15%的负载磷酸盐小麦秸秆生物质炭可使Cu的浸出浓度降低56%. 研究显示，施用10%~15%的负载磷酸盐生物质炭材料可显著降低重金属复合污染土壤中Pb和Cd的潜在环境风险，对矿区重金属污染土壤的安全利用具有参考和指导意义. 

Stabilization Mechanism of Phosphate-Loaded Biochar Materials in Heavy Metal Contaminated Soils

In order to investigate the stabilization effect of biochar materials and the migration and transformation characteristics of co-existing heavy metals in contaminated soil, corn straw and wheat stalk were used as the raw materials in this study. Two types of biochar were prepared by anaerobic pyrolysis at 600 ℃ after loading with phosphate, and used in stabilization batch experiments in heavy metal contaminated soils. The study indicated that phosphate-loaded corn straw and wheat stalk biochar promoted the sorption of Cd by increasing the content of amorphous iron and aluminum oxides in soil. The increase of amorphous oxides and the decrease of free oxides in soil treated with corn straw biochar were higher than that of in wheat stalk biochar treated soil. Meanwhile, these two biochar materials significantly increased the iron activation and effectively control the bioavailability of heavy metals in the multi-contaminated soil. The addition of different proportions of corn and wheat phosphate-loaded biochar, such as 5%, 10% and 15%, can reduce the migration risk of Pb, Cd, Zn and Cu in soil, and promote the transformation of acid extractable fraction and Fe-Mn oxide bound fraction of Pb to organic-bound fraction and residual fraction, as well as the transformation of acid extractable fraction of Cd, Zn, and Cu to residual fraction. The two biochar materials greatly decreased the leaching concentration of heave metals, and the application of 10% or 15% can reduce the leaching concentration of Pb by more than 98%. The addition of 15% phosphate-loaded corn straw can reduce the leaching concentration of Cd by 89%, while the leaching concentration of Zn decreased by 47%, respectively. However, phosphate-loaded wheat stalk biochar with 15% addition reduced the leaching concentration of Cu by 55%. The results have shown that the application of 10%-15% phosphate-loaded biochar materials can significantly reduce the potential environmental risks of Pb and Cd in heavy metal contaminated soils, which has practical reference and guiding significance for the risk control of heavy metal contaminated soil in mining areas.