Fe0-As(III)/As(V)-H2O体系中砷的可控还原机制及产物稳定性研究

The reduction of arsenic is one of important behaviors in the system of Fe0-As(III)/As(V)-H2O. Due to the low production of arsenic element, the study on reductive behavior of arsenic in the system of Fe0-As(III)/As(V)-H2O has always been ignored. Our preliminary study found that reduction of arsenic by Fe0 was obviously strengthened after controlling the behavior of arsenic adsorption or changing reaction way, and even single arsenic element with high purity was obtained. Base on the first-principles calculation of the interface structure for Fe-As, the thermodynamic stability phase diagram of the interface structure for Fe-As was given, the mechanism of arsenic reduction was revealed by means of electrochemistry method in this project. Furthermore, the effects of environment, medium and solution composition on reductive behavior of arsenic in the system is systematically investigated via characterization on shape and structure of reductive product. The controllable reductive mechanism of arsenic element was also revealed. Based on the results, the bioavailability, solubility stability, environmental stabilization and potential ecological risk of reductive arsenic products in the system are quantitatively evaluated, and the mechanism of the chemical composition, structure and stabilization for the reductive products was also clarified. This study is expected to solve the key issue on controllable reduction of arsenic in the Fe0-As(III)/As(V)-H2O system and to enrich and perfect the theoretical system of arsenic removal with Fe0, which provides a new idea for the treatment of arsenic pollution with Fe0 system.

还原是Fe0-As(III)/As(V)-H2O体系中砷的化学行为之一，但由于以往单质砷的生成量较低，使得该体系砷的还原行为长期被忽视。申请者前期研究发现，在改变反应方式或调控零价铁对砷的吸附行为后，可明显强化砷的还原，甚至获得纯的单质砷。针对Fe0-As(III)/As(V)-H2O体系砷还原机制未知、细颗粒单质砷环境稳定性不明的问题，基于Fe-As界面结构热力学的第一性原理，本项目通过绘制界面结构稳定性热力学相图，结合电化学研究方法，揭示砷的可控还原机理；进一步查明环境条件、介质类型以及溶液组分等因素对砷还原行为的影响规律，获得单质砷高选择性还原制取的调控机制。基于此，定量评价所得单质砷的生物可利用性、环境稳定性和潜在生态风险，解明产物成分-结构-稳定性的内在机制。通过本研究可完善和丰富零价铁除砷的基础理论，实现单质砷的可控制备，达到脱砷与固砷的双重功效，为“砷害”治理提供新的思路。

通过理论计算，查明了Fe0-As(III)/As(V)-H2O体系砷和和铁的行为，掌握了砷还原的反应历程。理论研究证实了铁粉表面氧化膜以及Fe3+水解产物对砷的还原十分不利。尽管As(V)的还原较As(III)容易，但As(V)易与铁粉表面的FeO和Fe2O3均发生沉淀，分别形成Fe3(AsO4)2和FeAsO4，使得铁粉表面被钝化，从而导致砷的还原被抑制。.开展了铁粉活化工艺在As(III)-Fe0-H2O体系的行为和反应规律研究，铁粉所含杂质以及铁粉本身的物理性质对砷的行为也有较大影响。尽管通过活化酸种类、以及活化次数可以促进砷的还原，但仍有较大改善空间。当然，仅从已有的铁粉入手，通过活化或其他预处理，来解决砷难以被还原的问题是不够的，需要从多方面多层次多梯度考虑。.在水热条件下利用ZVI可从高酸高砷溶液中高效去除砷。所得最佳反应条件为：溶液初始酸度为1 mol/L H2SO4，Fe/As摩尔比为2.25，反应温度为150℃，反应时间为4 h。在该条件下，砷的去除率可达98.89%。所得反应产物中砷的XPS图谱显示，两个不同的特征峰出现在41.7 eV和42.3 eV的结合能处，但均属于As(0)，且未发现其他价态As。