Fe(II)催化铁(氢)氧化物矿物相重组耦合重金属环境行为机制研究

Iron cycle is the driving force for cycling of many elements in soils, of which the direct interactions between the structured Fe(III) (Fe(III)oxide) of iron (hydr)oxides and free state Fe(II) (Fe(II)aq) coexisted in soils are the recently found important component of soil iron cycle. The present proposal focuses on studying the key reactions of Fe(II)aq-Fe(III)oxide and plans to systematically investigate the mechanism of Fe(II)aq-catalyzed recrystallization of iron (hydr)oxides coupling environmental behavior of heavy metals. Firstly, based on the research of the electron transfer and recrystallization of iron (hydr)oxides during reaction processes of Fe(II)aq-Fe(III)oxide, the active sites on the surface of iron (hydr)oxides for crystal growth of recrystallized secondary iron (hydr)oxides and reductive release of Fe(III)oxide, together with changes of electric potentials on different crystal planes in iron (hydr)oxides, will be mainly investigated. With the obtained results, the mechanisms and driving force for surface electron transfer and bulk electrical conduction of iron (hydr)oxides are expected to be elucidated. And then, based on the above results, the effects of different soil anions, the free state metal ions, and the structurally substituted chromium in iron (hydr)oxides, on the reaction processes of Fe(II)aq-Fe(III)oxide will be investigated. The environmental behavior, including adsorption, release, and stabilization, of the heavy metals on iron (hydr)oxides during the processes will be analyzed. Through further analyses of the existing forms and structural properties of the stabilized metals in the structure of the iron (hydr)oxides before and after reactions, the comprehensive mechanism of Fe(II)aq-catalyzed recrystallization of iron (hydr)oxides coupling environmental behavior of heavy metals will be discussed and disclosed. The outputs of this research project are expected to improve and expand the theoretical system of soil iron cycle, and also provide scientific supports for developing in situ control technologies for soils contaminated by heavy metals.

铁循环是诸多土壤元素转化的驱动力，共存游离态亚铁与铁(氢)氧化物(简称氧化铁)中结构态三价铁之间直接作用是近年来发现的土壤铁循环的重要组成。本项目以游离态亚铁-结构态三价铁(简称亚铁-三价铁)作用过程为核心，系统研究亚铁催化氧化铁晶相重组耦合重金属环境行为机制。首先，以亚铁-三价铁作用的电子传递及氧化铁晶相重组为基础，结合过程中二次矿物晶体生长和铁还原释放的活性位以及不同晶面电势变化研究，阐明亚铁-三价铁作用的表面和体相电子传递过程及其驱动力；在此基础上，研究典型土壤阴离子等条件影响下，体系共存重金属及氧化铁的铬结构取代对亚铁-三价铁作用过程电子传递及氧化铁晶相重组的影响，阐明过程中重金属的释放/吸附/固定等环境行为，解析二次矿物中重金属成键方式等结构性质，揭示环境条件下亚铁催化氧化铁晶相重组耦合重金属环境行为机制。预期成果可完善和拓展土壤铁循环理论，为土壤重金属污染原位控制提供科学支撑。

Fe(II)aq-Fe(III)oxide之间的电子转移及其催化铁(氢)氧化物晶相重组过程是土壤铁循环的重要组成，这一过程也对土壤中污染重金属的迁移转化及有效性产生重要的影响。虽然从“宏观”角度已经有足够的实验证据证明这一过程中Fe原子交换以及铁(氢)氧化物晶相转变的发生，电子在固体表面(或固体中)的传递过程及铁(氢)氧化物晶相重组的驱动力问题，仍然缺乏足够的实验证据，这也是全面阐释这一过程的前提和理论核心。同时，从土壤环境地球化学角度出发，复杂的厌氧土壤条件下Fe(II)aq催化铁(氢)氧化物晶相重组过程及其如何影响重金属的释放、迁移、固定及有效性等环境行为，是土壤体系中需要明确的更为普遍和重要的过程。..本项目以 Fe(II)aq/铁(氢)氧化物体系为研究对象，系统阐明Fe(II)aq-Fe(III)oxide过程的电子传递机制，揭示Fe(II)aq催化铁(氢)氧化物晶相重组过程中重金属的环境行为。以Fe(II)aq/赤铁矿体系为对象，采用57Fe标记及穆斯堡尔谱手段，阐明了Fe(II)aq催化赤铁矿晶相重组过程中游离态Fe(II)与氧化铁中结构态Fe(III)之间的Fe原子交换及电子转移机制，揭示了赤铁矿晶体中不同晶面与Fe(II)aq的Fe原子交换速率，明确了Fe(II)aq催化铁(氢)氧化物晶相重组的电势差异驱动机制；以Fe(II)aq与水铁矿、针铁矿等铁氧化物体系为对象，明确了Pb2+、Cd2+、及稀土金属离子等重金属阳离子作用下Fe(II)aq催化铁氧化物晶相重组过程的影响机制，揭示铁氧化物重组过程中阳离子重金属的吸附及结构化固定机制；系统解析了该过程中阴离子重（类）金属As和Cr的影响极其转化过程机制，明确了Fe(II)aq催化铁氧化物晶相重组过程中As(III)的氧化转化过程机制，解析了该过程中Cr(III)的吸附固定及释放过程；揭示了土壤中含铁矿物在Fe(II)aq作用下的晶相重组过程机制，并明确了土壤体系中Fe(II)aq催化作用下铁氧化物的老化重组及其钝化重金属过程，形成了具有一定应用前景的基于铁氧化物形态结构调控的土壤重金属污染治理技术。..本项目的研究成果从原子水平阐明了Fe(II)aq-Fe(III)oxide作用机制，完善了铁循环理论体系，同时为建立基于铁(氢)氧化物环境地球化学过程的土壤重金属污染原位控制策略提供科学依据。