碳化温度对牛粪铜和锌形态及生态毒性的影响

通过设置不同的热解温度(350,550和750℃)对牛粪废弃物进行碳化处理,并使用光谱技术手段对牛粪炭的微观特点及Cu、Zn赋存形态进行了分析表征,同时结合淋溶和毒性实验探究了热解温度对牛粪炭生态毒性的影响.结果表明,高温碳化明显改善牛粪孔隙结构,使其比表面积从牛粪原料的1.15m²/g提高至牛粪炭的5.51(350℃)~195.90m²/g(750℃).随着热解温度的提高,牛粪炭pH值从8.18(350℃)提高到了10.14(750℃);牛粪炭中Cu、Zn含量则从牛粪原料中的1.22和1.23mg/g分别升高至18.29~35.11和18.58~31.24mg/g.透射电镜-选区衍射以及X射线能谱分析表明,热解处理可使牛粪中Cu、Zn离子分别转化为副黑铜矿(Cu₄O₃)和红锌矿(ZnO)等金属氧化物,从而明显降低了牛粪炭中水溶态、DTPA提取态以及HNO₃-H₂SO₄提取态的Cu、Zn离子浓度;此外,FTIR分析及混合有机酸浸提实验结果也表明,350℃牛粪炭中酚羟基、烷烃基、羧基、酰胺类等有机官能团通过吸附和络合作用固定未完全转化的Cu离子,而升高热解温度会使得这些官能团显著减少、促进Cu离子的完全转化以及无机物与Cu、Zn离子之间稳定金属氧化物化合键的形成.淋溶和生态毒性实验表明,高于550℃的热解温度能够显著降低牛粪炭中Cu、Zn的溶出率以及生态毒性,是高Cu、Zn含量牛粪废弃物无害化处理的一种推荐优选技术.

Effects of pyrolysis temperatures on occurrence speciation of copper and zinc in cattle manures and their potential ecotoxicity

Pyrolysis to biochar is an efficient technique of disposing organic solid wastes. However, pyrolysis treatment of the cattle manure (CM) containing high concentrations of Cu and Zn is scarcely investigated, and the environmental behaviors of Cu and Zn in the cattle manure biochar (CMB) accompanying with their ecological risk keep unknown. In this study, the occurrence speciation of Cu and Zn in CMB, their leaching characteristics and the ecological risk of CMB from different pyrolysis temperatures (350, 550 and 750^oC) were evaluated using spectrum technology (i.e., BET, TEM-SEAD, XPS, and FTIR), the leaching experiments, and the risk tests. Results show that carbonization of CM to CMB with an increasing temperature from 350 to 750^oC improves the pore structure of CM and enlarges the specific surface area from 1.15m²/g in raw CM to 5.51~195.90m²/g in CMB. The pH value of the CMB increases from 8.18 (350℃) to pH 10.14 (750℃). Importantly, the Cu concentration increases from 1.22mg/g in raw CM to 18.29~35.11mg/g in CMB while the Zn concentration elevates from 1.23mg/g to 18.58~31.24mg/g. Meanwhile, most of the Cu and Zn are oxidized to paramelaconite (Cu₄O₃) and zincite (ZnO), which significantly reduces the concentrations of Cu and Zn in forms of extractable ones with deionized water, DTPA-TEA-CaCl₂ and HNO₃-H₂SO₄ as extracting agents, respectively. Furthermore, many functional groups (i.e., phenolic hydroxyl, alkane, carboxyl, amide, etc.) can immobilize labile Cu through adsorption and complexation, but a high pyrolysis temperature (>550^oC) tends to arise a significant decrease in species and amounts of functional groups and promote the complete conversion of Cu ions and the formation of stable metal oxide bonds between inorganics and Cu or Zn ions. In summary, the pyrolysis temperature over 550^oC could dramatically reduce the leaching rates of Cu and Zn and mitigate the ecotoxicity of CMB, which can be a potential approach to dispose the CM wastes with high concentrations of Cu and Zn.