水稻秸秆生物炭中铜和镉的形态分布及释放特性

由于目前缺乏对生物质原料来源的管控办法，极有可能用产自受污染农田土壤的秸秆制备出具有高重金属含量的生物炭，因此，研究生物炭中重金属的形态分布及其释放特性对于防控生物炭应用产生的环境风险具有重要意义.基于此，分别采集江西省贵溪铜冶炼厂周边九牛岗污染区和中国科学院鹰潭红壤生态实验站清洁区种植的水稻秸秆制备生物炭（分别记为“九牛岗生物炭”和“红壤站生物炭”），分析两种生物炭中Cu、Cd的含量及其化学形态分布，考察不同固液比及pH对生物炭中Cu、Cd浸出的影响.结果表明:九牛岗生物炭中Cu、Cd的总量（以w计）分别为119.99、3.83 mg/kg，显著高于红壤站生物炭（19.50、0.96 mg/kg）.尽管九牛岗生物炭中w（酸溶态Cu）、w（酸溶态Cd）显著高于红壤站生物炭，但在形态分布上，九牛岗生物炭中Cu、Cd主要为相对稳定态（可氧化态和残渣态），二者占比分别为80.3%、76.7%，高于红壤站生物炭（二者占比分别为53.2%、48.0%）.高固液比和低pH可有效增加两种生物炭中Cu、Cd的浸出毒性，其中，九牛岗生物炭在固液比为1:20和1:60时，浸出液中ρ（Cu）、ρ（Cd）均超过GB/T 14848—2017《地下水质量标准》中Ⅱ类标准限值.动力学及累积释放试验表明，两种生物炭中的部分Cu、Cd可在短时间内迅速释放而后逐渐平稳并有上升趋势，且九牛岗生物炭中Cu、Cd释放量显著高于红壤站生物炭.研究显示，来自污染区水稻秸秆生物炭中的Cu、Cd活性显著高于清洁区生物炭，具有更高的环境风险. 

Chemical Fractions and Release Characteristics of Cu and Cd in Biochar Derived from Rice Straw

Due to the lack of regulations on the resources of biomass raw materials, some crop straw grown in contaminated farmlands may be used to produce biochar with high content of heavy metals. Therefore, it is of great significance to study the chemical forms and release characteristics of endogenous heavy metals in biochar and to reduce the environmental risks due to the unreasonable biochar applications. In the study, the rice straws collected from contaminated (Jiuniu Village near the Guixi Copper Smelter in Guixi City, Jiangxi Province)and clean soils (Yingtan Red Soil Ecological Experimental Station, Chinese Academy of Sciences) were used to produce biochars named with JN-biochar and HR-biochar, respectively. The chemical fractions of Cu and Cd in biochar were analyzed by BCR sequential extraction, and the effects of solid liquid ratio and pH on the release of Cu and Cd were investigated as well. The research results showed that the concentrations of Cu and Cd in JN-biochar were 119.99 and 3.83 mg/kg, respectively, which were significantly higher than those of HR-biochar (19.50 and 0.96 mg/kg). Although the acid soluble content of copper and cadmium in JN-biochar was higher than HR-biochar, the ratios of stable state (oxidable and residual forms) to total Cu and Cd in JN-biochar (Cu 80.3%, Cd 76.7%) were higher than those of HR-biochar (Cu 53.2%, Cd 48.0%). The high solid-liquid ratio and lower solution pH increased the leaching toxicity of Cu and Cd in the biochar. Especially for JN-biochar at solid-to-liquid ratios of 1:20 and 1:60, the concentrations of Cu and Cd in leachate are higher than the limit of the Grade Ⅱ of Quality Standard for Groundwater (GB/T 14848-2017). The dynamics and cumulative-release experiments showed that Cu and Cd in both biochars can be released rapidly in a short time and then gradually increased, and the release of Cu and Cd in JN-biochar was higher than that of HR-biochar. This study suggested that the availability and environmental risk of Cu and Cd in rice straw biochar from the contaminated soil were higher than those from clean soil.