农田土壤镉污染原位钝化的长效稳定性及其再释放机制

The in-situ remediation technology for farmland cadmium contamination has been widely used in the field, and its continuous passivation repair effect will be the key to future technology promotion. However, the long-term stability of in-situ passivation is constrained by many factors, and there is a lack of systematic knowledge. Based on the preliminary screening of passivated materials, this project will use biochar and sepiolite clay minerals with good passivation effect as the cadmium remediation agent, with a four-year period as the research cycle. Based on a series of experiments on indoor soil culture ,the root box,semi-enclosed rice cultivation and long-term field positioning, the interactions between cadmium contamination and multiphase interfaces such as paddy soil-passivated material and plant root system will be studied to explore the continuous stability mechanism of biochar and sepiolite passivation cadmium. Combined with morphological chemical extraction of heavy metals, coupled with Fourier infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction spectroscopy and other characterization techniques,this project will fully explained the effects of factors such as aging of passivated materials, acid rain, changes in soil moisture, and microbial characteristics of crop rhizosphere on the cadmium forms and the stability of passivation during in-situ passivated remediation,and the possible re-release mechanism of cadmium in passivation products will be revealed, followed by related agronomic regulation measures. The research results will provide an important theoretical basis for the realization of remediation and long-term safe use of cadmium-contaminated farmland and improvement of soil environmental quality.

针对农田镉污染的原位修复技术已有广泛的田间应用，其持续的钝化修复效果将是今后技术推广的关键。然而，原位钝化的长效稳定性受制于诸多因素，还缺乏系统的认知。在前期钝化材料筛选的基础上，本项目将以钝化效果好的稻秆源生物炭和海泡石黏土矿物为镉修复剂，以四年为研究周期，在室内土培、根际箱和半封闭水稻栽培以及田间长期定位等系列实验的基础上，研究镉污染与水稻土-钝化材料-植物根系等多相界面的相互作用，探讨生物炭和海泡石钝化镉的持续稳定机制。结合重金属形态化学提取，辅以傅立叶红外光谱、X射线光电能谱、X-衍射光谱等表征技术，全面阐释原位钝化修复过程中钝化材料老化、酸雨、土壤水分变化、作物根际微生物特性等因素对镉形态及钝化稳定的影响，并揭示钝化产物中镉可能的再释放机制，继而提出相关农艺调控措施。研究结果将为实现镉污染农田的治理修复和长期安全利用，改善耕作土壤环境质量提供重要理论依据。

耕地土壤特别是稻田土壤镉(Cd)污染及稻米镉安全问题已经对生态环境和人体健康带来巨大挑战。土壤原位钝化修复因成本较低，操作简单，见效快，近年来受到广泛关注。但针对钝化材料生物炭和海泡石原位钝化Cd污染的稳定性影响因素及Cd再释放机制分析目前缺乏系统认知，制约了生物炭和海泡石的实际推广应用。因此本项目采用室内土壤培养实验、根际箱水稻栽培实验和酸雨模拟实验以及田间长期定位实验相结合的方法，研究了Cd污染与水稻土-钝化材料-植物根系等多相界面的相互作用以及生物炭和海泡石钝化Cd的持续稳定机制。实验结论表明施用生物炭和海泡石钝化材料随土壤培养时间的增加，土壤中酸提取态Cd含量总体均呈先减少后增加趋势，水稻土中Cd与Fe、Mn赋存形态之间的相关性强。通过过氧化氢化学氧化方法模拟稻壳生物炭在自然环境中的氧化老化过程，发现氧化老化过程中生物炭的元素组成和比表面积变化不明显，但含氧基团增多，芳香性增强。老化前后生物炭对Cd2+的吸附均符合准二级动力学模型，但氧化老化过程抑制了稻壳生物炭对Cd2+的吸附能力。生物炭吸附Cd2+的机理主要有表面络合作用、阳离子-π作用和离子交换作用，氧化老化后碱金属元素的变化抑制了表面吸附作用。酸雨模拟实验研究结果表明，生物炭施用后土壤淋溶液中Cd 含量下降，与此同时，土壤可交换态Cd含量显著降低，铁锰氧化物结合态和有机结合态Cd相对含量则有所增加，土壤淋溶液中可溶性有机质含量有所减少，但DOM的淋失量随着酸雨酸度和淋溶次数的增加而减少。根际箱培养实验研究结果表明海泡石施加深度为5 cm时根际土壤Cd有效态含量降幅最大。生物炭配施氮肥土壤有效态Cd含量明显降低，Cd由活性较高的可交换态向活性低的残渣态转化，且总体上促进了土壤酶活性和提高了土壤细菌主要物种相对丰度，土壤细菌网络复杂性增强，从而改善了土壤环境质量。以上研究结果对重金属重新释放的风险评估预测和钝化修复技术的实际应用都具有重要的科学意义。