有机铁氧化物共沉淀体微观结构表征及其固定/释放重金属的分子机制

Controlling heavy metal (HM) contamination in paddy soil plays an important role in food safety. Organo-Fe oxides-Coprecipitates, i.e. OFC, were widely distributed in the paddy soil and significantly influences the transformation and bioavailability of HMs in contaminated paddy soils. Elucidating the molecular structure of OFC and their impact on the sequestration and release of HMs is essential to understand the transformation and dynamics of HMs in contaminated paddy soils. Synchrotron-based techniques provide a unique platform to characterize the molecular structure of OFC and interaction mechanisms of OFC with HMs. Taking typical heavy metal(loid)s of Cd(II)/Cr(III)/As(III) as examples, the objectives of this project are: 1) to characterize the molecular structures of Fe oxides and SOM in the OFC, obtained from various environmental conditions, organic carbon sources and Fe/C molar ratios, and the molecular speciation of HMs associated with OFC; 2) to clarify the transformation of OFC and adsorption/coprecipitation mechanisms of HMs with OFC; 3) to understand the transformation of OFC and its impact on the release of HMs under abiotic (Fe2+) and biotic factors ( Fe oxide reducing bacteria). These studies should provide theoretical bases for the safe utilization and remediation of HM-contaminated paddy soils.

稻田土壤重金属污染控制是保障我国粮食安全的前提，有机铁氧化物共沉淀体（Organo-Fe oxides-Coprecipitates ，OFC）在稻田中广泛赋存，深刻影响着重金属的形态转化及生物有效性；阐明OFC微观结构及其固定/释放重金属的分子机制是认识稻田重金属动态变化规律的关键。鉴于同步辐射技术是从分子水平揭示OFC结构及其与重金属作用机制的强力手段，本项目拟利用多种同步辐射技术，以重（类）金属Cd（II）/Cr（III）/As（III）为目标污染物，针对不同环境条件、DOC来源和铁碳组成下形成的OFC，表征OFC中铁氧化物和有机碳微观结构及其结合态重金属的分子形态，弄清OFC结构转化及其吸附/共沉淀重金属的分子机制，阐明非生物因子（亚铁离子）和生物因子（铁还原菌）对OFC在厌氧条件下的结构转化及其释放重金属的动力学机制，最终为重金属超标稻田安全利用和污染修复提供前瞻性理论依据。

本项目系统探究了不同环境条件、有机碳来源和铁碳组成对秸秆源有机铁氧化物共沉淀体（OFC）通过吸附和共沉淀作用固定重金属（Cr/As/Cd）的分子机制以及OFC结合态重金属在非生物因子（亚铁离子）和生物因子（铁还原菌）作用下的释放机制；结果表明OFC中铁氧化物和有机碳均可结合重金属，秸秆源有机碳含量与种类深刻影响OFC固定重金属（Cr/As/Cd）的效果，高有机碳含量抑制OFC形成以及竞争铁氧化物表面活性位点，降低OFC对重金属的固定；中等有机碳含量可促进铁氧化物与有机碳共沉淀而间接提高OFC对重金属的固定；同步辐射扫描透射显微术分析表明OFC中赋存颗粒态有机碳和矿物结合态有机碳两种有机组分，有机碳组分中羧基是重金属（Cr）的主要结合位点；非生物因子亚铁离子可促进OFC中水铁矿向针铁矿转化，但有机碳负载量会抑制水铁矿转化及其通过晶格置换对重金属（例如Cr）的固定作用；铁还原菌可通过OFC中铁氧化物还原而促进OFC结合态重金属（As/Cr等）释放，并诱导OFC中铁氧化物晶型转化。上述研究成果对于深刻认识秸秆还田对超标稻田中重金属形态转化及生物有效性的影响提供了前瞻性理论依据。