生物炭负载铁前后对复合污染土壤中Cd、Cu、As淋失和形态转化的影响研究

复合污染土壤中Cd、Cu等阳离子重金属与As具有不同的化学性质和迁移转化行为.本研究以负载铁前后的小麦秸秆生物炭作为修复材料,研究酸雨淋溶条件下两者对复合污染土壤中Cd、Cu、As淋失量及赋存形态的影响;通过分析淋滤液pH值、电导率和溶解性有机碳含量等,探讨其可能的作用机制.结果表明,生物炭和负载铁生物炭均显著提高了淋滤液pH值和电导率.溶解性有机碳淋失量在生物炭处理中较对照(CK)处理提高3.4%~15.9%,而在负载铁生物炭处理中则降低27.3%~60.8%.与生物炭不同,负载铁生物炭能够不同程度地降低Cd、Cu和As的淋失,5%施用量下累积淋失量较CK处理分别降低85.7%、19.0%和62.1%.对淋溶后土壤中重金属和As赋存形态进行分析发现,施用生物炭促进了土壤中Cd和Cu由酸提取态向残渣态转化,却使As由无定形及弱结晶铁铝氧化物结合态向专性吸附态转化.负载铁生物炭能够降低土壤中有效态Cd、Cu和As含量,相较于CK处理酸提取态Cd、Cu和非专性吸附态As含量分别减少3.6%~13.4%、7.5%~24.4%和19.0%~58.8%,而可还原态Cd和残渣态Cu、As含量分别增加4.3%~43.3%、2.2%~18.1%和44.9%~53.5%,其中,5%施用量下差异达到显著水平.综合而言,在5%施用量下,生物炭能够降低土壤中有效态Cd、Cu含量,却提高了As的迁移性和有效性;而负载铁生物炭既降低了酸雨淋溶条件下Cd、Cu、As的淋失,还促进了土壤中Cd、Cu、As由有效态向潜在有效态或稳定态转化,是修复重金属和砷复合污染土壤的有效材料.

Effects of biochar and Fe-loaded biochar on the leaching and fraction transformation of Cd, Cu and As in multi-contaminated soil

Cationic heavy metals such as Cd and Cu have different chemical properties and transformation behavior from As. As remediation materials, the effects of biochar and Fe-loaded biochar on Cd, Cu and As leaching and fraction distribution under the acid rain conditions were investigated. The pH, electric conductivity and dissolved organic carbon contents of the leachates were also analyzed to explore the possible mechanism. The results showed that both biochar and Fe-loaded biochar application can significantly enhance the pH and electric conductivity of the leachates. Compared with the CK treatment, the leaching amounts of dissolved organic carbon increased by 3.4%~15.9% in biochar treatments, while reduced by 27.3%~60.8% in Fe-loaded biochar treatments. Unlike biochar, Fe-loaded biochar can decrease the leaching of Cd, Cu and As. The cumulative leaching amounts of Cd, Cu and As reduced by 85.7%,19.0% and 62.1%,respectively,at Fe-loaded biochar application rate of 5%. The analysis of heavy metals and As fraction in soils after the leaching showed that the application of biochar promoted the transformation of Cd and Cu from the acid-extractable fraction to the residual fraction, while transferred As from amorphous and weak-crystallized hydroxides of Fe, Al combined fraction to specifically adsorbed fraction. Fe-loaded biochar can simultaneously immobilize available Cd, Cu and As in soils. Compared with the CK treatment, the contents of acid-extractable Cd and Cu and non-specifically adsorbed As reduced by 3.6%~13.4%,7.5%~24.4% and 19.0%~58.8%,respectively,and the contents of reducible Cd and residual Cu and As increased by 4.3%~43.3%,2.2%~18.1% and 44.9%~53.5%,respectively,and a significant difference was found at the application rate of 5%. In summary, biochar application at the rate of 5% can decrease available Cd and Cu contents in soils, but As mobility and availability was increased. While the application of 5% Fe-loaded biochar can effectively reduce the leaching of Cd, Cu and As under the acid rain conditions, and promote the transformation of Cd, Cu and As in soils from the available fraction to potentially available or stable fractions. Therefore, it can be used as a remediation material in heavy metal and arsenic multi-contaminated soil.