毒砂在酸性溶液中的水-矿表界面反应机制研究

Study of water-mineral surface and interface reaction of arsenopyrite in acid solutions

为了解毒砂（Apy）在风化过程中其矿物表面的化学成分的变化和风化进程，并评估这一过程及其产物带来的潜在环境风险，我们采用边长切割为2.5mm左右具有“立方体”外形的毒砂样品，将其分别与pH为0、1、3的硫酸溶液在反应釜中进行100-300℃的水矿反应实验。对反应淋出液进行了电感耦合等离子原子发射光谱（ICP-AES）分析，并对反应残余固体进行了包括表面产物的X射线光电子能谱（XPS）、电子探针微分析（EPMA）、X射线粉晶衍射测试（XRD）及扫描电子显微镜（SEM）形貌观察等分析和测试。本研究的ICP-AES测试结果表明，有大量的砷（As）进入溶液（其价态未测定），且随着温度的升高或酸浓度的增加，溶液中的As离子浓度显著升高。对反应产物的形貌观察（SEM）显示，毒砂的溶解反应从矿物颗粒的裂隙边缘和立方体边缘部位开始进行，反应界面逐步向立方体内部迁移。XPS对反应残余固体表面的元素窄扫描显示，表面有Fe3＋、S8、SO32-、SO42-、As3＋、As5＋和少量的As1＋生成，其中含量较多的是As3＋离子。样品的As2p3/2 深度剖析显示，随着剥蚀深度的增加，还原态As含量增加，而氧化态As含量减少，表明反应促使毒砂氧化，生成氧化态As。由于氧化态的As大量转移至溶液中，暗示了毒砂的氧化造成了As元素从含As的矿物、岩石中溶解活化，并通过地下水等方式参与地表及地下水循环，从而对生态环境构成巨大的潜在威胁。

In an effort to understand what happened at the mineral surface or interface during the arsenopyrite（Apy）weathering/oxidation process, and to assess the potential environmental risks of this processand its products as well, fifteen arsenopyrite specimens were cut into cubes （length side about 2.5mm） and reacted with sulphuric acid under 100-300℃ in the reaction pots. The pH levels of the acid solutions are 0, 1, and 3, respectively. Inductively Coupled Plasma Atomic Emission Spectroscopy （ICP-AES） was taken to analyze the remaining solutions after reaction. The productspresentat the residual solid surface were tested by the X-ray Photoelectron Spectroscopy （XPS）,Electron Probe Microanalysis （EPMA） and X-ray Powder Diffractometry （XRD）. Scanning Electron Microscopy （SEM） was used to accomplish the morphological analysis. Results from ICP-AES present that a large number of As move into solution （the valence untested）, and the level of total As ion in the solution significantly increased with the rise of temperature and acid concentration. Themorphological observation from SEM shows that the dissolution of arsenopyrite starts from the edges of cube and the fracture. Then, thereaction interface gradually migrates into the innerpart of the arsenopyrite cube. XPS narrow scan of the residual solid surface indicates that Fe3＋, S8, SO32-, SO42-, As3＋, As5＋ and a small amount of As1＋ are generated at the surface, among whichAs3＋ dominates. XPS profile analysis of As 2p3/2 manifests that with the increase of the erosion depth, the concentration of oxidized As grows -- the reaction prompts arsenopyrite to oxidize and generates the oxidation state of As. Due to a mass of oxidized As being transferred to the solution from the As-containing minerals and rocks, the oxidation of arsenopyrite means As would be released into the superficial water and participate in the groundwater circulation, and thus, pose a huge potential threat to the ecological environment.