生物炭对矿区土壤重金属有效性及形态的影响

为探索生物炭作为改良剂修复矿区重金属污染土壤的可行性，以玉米秸秆为原料在450℃制备生物炭，采用扫描电镜、能谱分析以及傅里叶变换红外光谱等分析与测试手段对其进行表征。采用室内连续培养的方法，研究在不同培养时间条件下，添加不同施用量（0、1%、3%和5%）的生物炭后，对矿区土壤pH，阳离子交换量（CEC），土壤重金属Cu、Zn、Pb和Mn有效性以及重金属不同形态变化的影响。结果表明：生物炭能够提高土壤的pH和CEC，且都随着添加量的增加而增加。56d土壤培养后，与对照相比，1%、3%和5%添加水平下pH分别增加了1.14个、1.42个和1.67个单位，土壤CEC分别增加了2.02cmol/kg、3.60cmol/kg和5.39cmol/kg。添加不同含量生物炭后，土壤中有效态重金属均呈现不同程度的降低，而且生物炭添加量越大，降幅也越大。在5%添加水平下，生物炭分别使Cu、Zn、Pb和Mn有效态下降了49.2%、46.2%、72.5%和26.3%。重金属有效态含量与土壤pH、CEC均呈显著负相关关系。添加生物炭后，土壤中重金属的形态发生了变化，由易迁移的弱酸提取态向更加稳定的残渣态转化，且生物炭添加量越大，钝化效果越显著。综上所述，玉米秸秆生物炭的添加提高了矿区重金属复合污染土壤的pH和CEC，促进了重金属复合污染土壤中Cu、Zn、Pb和Mn的弱酸提取态向化学性质稳定的残渣态转化，降低了土壤重金属的有效性，实现了对重金属复合污染土壤的修复。

Effect of biochar on the bioavailability and transformation of heavy metals in soil of mining area

In order to explore the feasibility of biochar as amendment for remediation of heavy metal contaminated soil in mining area, biochar was prepared from corn straw at 450℃. The sample was characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR). The effects of biochar on soil pH, cation exchange capacity (CEC), bioavailability and transformation of heavy metals were studied under different incubation time and application rates (0, 1%, 3% and 5%) of biochar with batch experiments to reveal the possible mechanism of biochar as a passivating agent for the immobilization of heavy metals in mining area contaminated soil. The results showed that soil pH and CEC increased as the application rates increased. After 56 days, biochar application rates of 1%, 3% and 5%, soil pH increased by 1.14, 1.42 and 1.67 units, and the soil CEC increased by 2.02cmol/kg, 3.60cmol/kg and 5.39cmol/kg, respectively compared with control. The CaCl₂-extractable heavy metals content decreased as the application rates increased. At 5% application rate, the concentration of extractable Cu, Zn, Pb and Mn decreased by 49.2%, 46.2%, 72.5% and 26.3%, respectively. The bioavailable heavy metals content was negatively correlated with soil pH and CEC. The biochar promoted the metal ions transform from the weak acid extractable state to more stable residue state. The passivation effect could be noticeable as the application rates increased. Overall, the application of biochar elevated the soil pH and CEC, and promoted transformation of the weak acid extractable of Cu、Zn、Pb and Mn into chemically stable residual fractions, which could positively reduce the bioavailability of heavy metals in combined pollution soil near mining areas.