绿色合成纳米羟基磷灰石对水稻土Cd的钝化效应及分子机制

Studying the remediation of Cd contaminated paddy soils plays an important role in food safety. Hydroxyapatite (HAP) has been widely used in remediating Cd contaminated upland soils due to its excellent sorption performance. However, the physicochemical properties of paddy soils present periodic change in the process of dry-wet alternate cultivation, the remediation behavior and mechanisms of nHAP in this special environment is still unclear. In this project, the high dispersed nHAP (G-nHAP) which has been synthesized by using straw extraction as dispersant will be used as amendment. The specific objectives are: i) to understand the sorption mechanisms of Cd on G-nHAP by studying the molecular structures of G-nHAP and its binding Cd based on batch sorption experiments and the different synchrotron radiation analytical methods; ii) to reveal the dominant influencing factors and their response mechanisms in the process of paddy soils remediation by studying the influence of paddy soil moisture change on the Cd immobilization efficiency of G-nHAP; and iii) to evaluate the stability of remediation by studying the transformation characteristics of Cd species in aged soils and the accumulation characteristics of Cd in rice plants. The outcomes from this project will clarify the remediation mechanisms of G-nHAP and its suitable environments, providing a theoretic basis and technical support for practical remediation of Cd contaminated paddy soils.

水稻土Cd污染的修复研究对于保障我国粮食安全意义重大。纳米羟基磷灰石（nHAP）凭借优良的固Cd性能，被广泛用于旱土Cd污染的钝化修复。然而，水稻土干湿交替耕作过程中土壤理化性质呈周期性变化，该特殊环境下nHAP对Cd的钝化行为及机制尚不清楚。申请人前期已利用秸秆提取液代替传统化学分散剂绿色合成出高分散的nHAP（G-nHAP），本项目拟以此为钝化剂，首先，通过吸附试验及多种同步辐射技术，解析G-nHAP的微观结构及其吸附态Cd的分子形态，探明G-nHAP固定Cd的分子机制；其次，研究水稻土水分变化对G-nHAP钝化Cd效率的影响规律，揭示关键影响因子及其响应机制；最后，研究老化土中Cd形态的迁移转化及水稻植株对Cd的累积特征，综合评价钝化修复的稳定性。本研究将明确G-nHAP对Cd污染水稻土的修复机制及最适应用环境，为大田修复应用提供科学依据与技术支撑。

基于羟基磷灰石(nHAP)的钝化修复技术被认为是当前修复重金属污染土壤的有效方法，为获得兼具高固Cd性能和低制备成本的nHAP用于Cd污染农田土壤的钝化修复，本研究以蒸氨废液为钙源、不同秸秆提取液为绿色表面修饰剂(S-DOM)制备系列有机-nHAP复合钝化剂(G-nHAP)，结合水体吸附实验和土壤老化实验，揭示G-nHAP对Cd的吸附特性、钝化效果及相关机制。主要研究结果如下:(1)吸附实验结果显示，未添加S-DOM制得的nHAP(CK)与G-nHAP对Cd的吸附均为自发的、不可逆的化学反应过程，但G-nHAP对Cd的亲和力更强。G-nHAP对Cd的最大吸附量可达222mg/g，约为CK的1.4倍，与商品级及纯化学试剂制备的nHAP相比，应用优势明显。机理研究结果表明，G-nHAP对Cd的固定机理除涉及nHAP晶格Ca与Cd的离子交换反应外，其嵌入的S-DOM中丰富的表面官能团也参与了反应，产生协同固Cd效应。(2)酸性Cd污染水稻土钝化实验结果显示，G-nHAP输入后土壤中DTPA有效态Cd含量下降23.6%-26.7%，酸溶态Cd分数下降31.3%-34.6%，残渣态Cd分数增加24.7%-26.4%，水稻各组织对Cd的富集因子明显降低，表明G-nHAP对Cd污染水稻土具备钝化修复能力。相关性研究结果表明，钝化剂投加量与土壤pH、CEC和AP等理化性质呈显著相关，其可通过强化土壤石灰效应、阳离子交换以及形成磷酸盐沉淀等固Cd机制实现高效钝化修复。(3)弱碱性Cd污染土壤钝化实验结果显示，G-nHAP的添加不仅不会对土壤理化性质造成显著干扰，还可在一定程度上增强土壤养分，同时还可促进土壤中48.4%-56.7%的有效态Cd向更稳定的形态转变，显著降低Cd在植物体内的累积、促进植物生长。此外，分子生物学研究结果显示，G-nHAP输入后土壤微生物种群丰度和多样性也有一定提升，进一步验证G-nHAP对弱碱性Cd污染土壤钝化修复的适用性。上述研究结果对于指导G-nHAP在实际Cd污染土壤中的高效修复应用具有重要意义。