红壤中铁氧化物对羟基磷灰石固定镉的影响及其作用机制

Immobilization of heavy metal-contaminated soil by phosphorus-bearing materials have received considerable attention in recent years. Large amounts of iron oxides in red soil have strong adsorption capacities for phosphate, which will significantly influence the dissolution of phosphorus-bearing materials and its immobilization effects for heavy metals. Based on study results obtained from the immobilization of cadmium and copper contaminated soil around Guixi smelter in Jiangxi province by hydroxyapatite (HAP), this research is planned to select the goethite, hematite and ferrihydrite as the study objects. Firstly, the interaction features and mechanisms between the iron oxides and HAP will be examined by dynamic light scattering and attenuated total reflectance fourier transform infrared spectroscopy, etc, and by investigating the dissolution kinetics of HAP and speciation of Fe and P. Secondly, the effects of iron oxides on the adsorption of Cd by HAP are studied by adsorption and desorption experiments. The adsorption mechanisms of Cd on HAP, iron oxides and its complexes with HAP are explored by X-ray photoelectron spectroscopy (XPS) and synchrotron radiation technique (XANES). Finally, an indoor culture experiment will be set up to elucidate the mechanisms of iron oxides on the immobilization of Cd by HAP in red soil through the combination of Visual MINTEQ chemical speciation models and chemical extraction methods. The results of this study will provide some scientific basis for the remediation of Cd-contaminated red soil in the south of China by the application of phosphorous-bearing materials.

基于含磷材料的稳定化技术被广泛用于重金属污染土壤的修复，红壤中大量的铁氧化物对磷酸盐具有强烈的吸附作用，势必影响含磷材料的溶解及其对重金属的固定效果。本项目在申请者前期利用羟基磷灰石(HAP)修复贵溪冶炼厂周边镉铜污染土壤的研究基础上，以针铁矿、赤铁矿和水铁矿为研究对象，采用动态光散射和衰减全反射红外光谱等技术分析铁氧化物与HAP的相互作用特征，考察HAP的溶解动力学及Fe、P形态变化，探讨铁氧化物与HAP之间的交互作用机制；通过吸附/解吸实验，考察铁氧化物对HAP吸附固定Cd的影响，应用X射线光电子能谱仪和同步辐射技术解析Cd的存在形态，揭示铁氧化物和HAP的交互作用与Cd吸附/解吸之间的内在联系；通过室内培养实验，基于Visual MINTEQ化学形态模型和化学提取等方法阐明红壤中铁氧化物对HAP固定土壤Cd的影响机制。研究结果将为含磷材料治理我国南方Cd污染红壤提供科学依据。

基于含磷材料的稳定化技术被广泛用于重金属污染土壤的修复，红壤中大量的铁氧化物对磷酸盐具有强烈的吸附作用，势必影响含磷材料的溶解及其对重金属的固定效果。基于此，本项目以针铁矿、赤铁矿和水铁矿为研究对象，通过纯水溶液体系和土壤体系考察铁氧化物对HAP溶解的影响，以及不同环境因子（模拟酸雨、离子强度和有机酸）对两种体系下铁氧化物对HAP溶解及其吸附Cd的影响；进一步通过室内培养、干湿交替和持续淹水实验考察不同含量的铁氧化物对HAP固定土壤Cd等重金属化学形态、磷形态、铁氧化物形态、土壤酶活性和植物毒性的影响，结果表明：HAP的溶解是一个缓慢的过程，随着针铁矿和赤铁矿用量的增加，磷酸盐含量逐渐降低，钙离子含量增加，促进了HAP的溶解。低pH和有机酸的添加促进HAP的溶解，但是铁氧化物的添加提高体系pH，降低体系磷酸盐含量。铁氧化物和HAP的添加提高了土壤pH，降低了有效态和离子交换态重金属含量，Visual MINTEQ模拟结果以及相关性分析表明土壤淹水环境中Cd的活度可能与表面吸附和络合作用有关；HAP处理具有较高的磷释放风险，铁氧化物共存时降低了土壤树脂磷，增加了HCL提取态磷和残渣态磷，有效降低了磷素流失风险。以上研究结果表明铁氧化物的存在尽管会促进HAP的溶解，降低HAP对Cd的固定作用，但是这个负效应弱于铁氧化物本身对Cd的固定的正效应，最终导致铁氧化物会促进HAP对土壤Cd的固定作用。