牛粪矿物混合蚯蚓堆肥中堆制物Pb和Cd吸附性能变化

为促进畜粪和矿物资源的生态循环利用和Pb、Cd污染土壤的原位稳定化治理,以寻求具有良好重金属吸附性能的原位稳定化修复材料为目标,该研究以高钙镁系矿物和海泡石添加下牛粪矿物混合蚯蚓堆肥为研究对象,分析堆制物性状变化及其对Pb~(2+)、Cd~(2+)的吸附性能差异。结果表明,高钙镁系矿物及海泡石添加下蚯蚓均可较好生长,蚯蚓处理可使堆制物pH值、C/N比和有机质含量降低,而使其阳离子交换量和比表面积提高;高钙镁系矿物和海泡石添加则均可提高堆制物pH值、阳离子交换量和比表面积。傅里叶红外光谱分析表明,蚯蚓处理后堆制物中醇或羧酸类物质和芳香类物质增多,而脂类和多糖类物质含量减少,且高钙镁系矿物添加使堆制物含有更多的Me-O基团。X射线衍射分析表明,蚯蚓处理后堆制物中含有更多的硅酸盐和可溶性盐;高钙镁系矿物添加则增加了堆制物中的硅酸盐含量及CaO、MgO等组分,而海泡石添加使堆制物中增加了硅酸盐含量及MgO等组分。吸附试验表明,蚯蚓处理后堆制物对Pb~(2+)、Cd~(2+)具有更大吸附量和吸持能力,且以牛粪和高钙镁系矿物混合蚯蚓堆肥中的堆制物对Pb~(2+)和Cd~(2+)吸附效果最好,其吸附率分别为77.8%、59.7%。因此,利用牛粪和高钙镁系矿物混合蚯蚓堆肥生产具有良好Pb~(2+)、Cd~(2+)吸附性能的堆制物具有一定可行性。

Adsorption property of Pb and Cd by substrate residues after vermicomposting of cow dung mixed with minerals

Abstract: High concentrations of heavy metals lead (Pb) and cadmium (Cd) in soil have triggered a serious threat to plant growth, animal health, and ecological environment for human survival. Non-biodegradable Pb and Cd contamination in soil can be easily transferred to agricultural crops through the soil-plant-food chain, easy to endanger human body health. Alternatively, in situ stabilization is an effective technology to reduce the toxicity of such heavy metals. However, it is particularly important to choose the cost-effective materials with significant stability effects in soil. This study aims to seek in situ stabilized remediation materials with a high adsorption efficiency of heavy metal. A vermicomposting experiment of cow dung mixed with high calcium and magnesium minerals or sepiolite was conducted to analyze the variation of substrate residues properties and the adsorption characteristics of Pb2+ and Cd2+. Firstly, the growth indexes of earthworms were selected for the feasibility of vermicomposting cow dung mixed with minerals. Then, the substrate residues were characterized, including pH value, cation exchange capacity, morphology under a Scanning Electron Microscopy (SEM), mineral components under X-Ray Diffraction (XRD), and surface functional groups under a Fourier Transform Infrared Spectroscopy (FTIR). Finally, batch adsorption experiments were carried out to evaluate the adsorption efficiency of Pb2+ and Cd2+ from aqueous solution. The results demonstrated that the earthworms survived well with high calcium and magnesium minerals or sepiolite addition. The earthworm treatment reduced pH value, C/N, and organic content, while, increased the cation exchange capacity, and the specific surface area of substrate residues. High calcium and magnesium minerals or sepiolite addition both increased the pH value, cation exchange capacity, and specific surface area of substrate residues. FTIR analysis showed that the earthworm treatment had more alcohol or carboxylic acids and aromatic substance, while, less lipid material and polysaccharide substance in substrate residues, compared with the untreatment. The addition of high calcium and magnesium mineral also produced more Me-O groups in substrate residues. XRD analysis showed that more silicate and soluble salts were found in the earthworm treatment, compared with the untreatment. The addition of high calcium and magnesium mineral produced silicate, CaO and MgO components, whereas, the sepiolite addition produced silicate and MgO components in substrate residues. The batch adsorption experiment showed that the earthworm treatment had better adsorption capacity of Pb2+and Cd2+ in aqueous solution. The adsorption efficiency of Pb2+and Cd2+ was the best for the substrate residues rom the vermicomposting process of cow dung mixed with high calcium and magnesium minerals. The adsorption rates of Pb2 + and Cd2 + were 77.8% and 59.7%, respectively, whereas, the desorption rate of adsorption states Pb2+ and Cd2+ were 0.02% and 6.66%, respectively. It infers that the adsorption mechanism of VG for Pb2+and Cd2+ involved in the physical adsorption, ion exchange, electrostatic adsorption, precipitation, and complexation. A high adsorption efficiency of Pb2+and Cd2+ from aqueous solution was achieved under the higher pH value, cation exchange capacity and specific surface area, abundant functional groups and mineral components in VG. Therefore, it is feasible to produce substrate residues with high Pb2+and Cd2+ adsorption capacity via adding high calcium and magnesium mineral into cow dung for vermicomposting. The findings can provide an insightful theoretical basis to effectively optimize key parameters for the vermicomposting of cow dung mixed with minerals, and thereby to promote the recycling efficiency of organic solid wastes and the safe utilization of heavy-metal contaminated soil.