Speciation and characterization of arsenic in gold ores and cyanidation tailings using X-ray absorption spectroscopy
Speciation and characterization of arsenic in gold ores and cyanidation tailings using X-ray absorption spectroscopy
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DOI：
10.1016/j.gca.2003.07.013
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发表时间：
2004-03
影响因子：
5
通讯作者：
D. Paktunc;A. Foster;S. Heald;Gilles Laflamme
中科院分区：
文献类型：
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作者：
D. Paktunc;A. Foster;S. Heald;Gilles Laflamme
需要了解As的矿物学和分子结构，以便更好地了解金矿石加工产生的废物中As的稳定性。在这项研究中，光学显微镜，扫描电子显微镜，电子探针，X射线衍射和X射线吸收精细结构（XAFS）光谱（包括XANES和EXAFS制度），以确定矿物组成和局部协调环境的金矿石和工艺尾矿的实验室规模的试验，旨在模仿一个共同的工厂的做法。在矿石和尾矿中鉴定的含砷矿物包括羟基氧化铁、臭葱石（FeAsO 4·2 H2O）、砷酸铁、砷菱铁矿（Ca 2Fe 3（AsO 4）3 O2·3 H2O）、砷酸钙铁、毒菱铁矿（KFe 4（AsO 4）3（OH）4·6- 7 H2O）、黄钾铁矾（K2 Fe 6（SO 4）4（OH）12）和毒砂（FeAsS）。羟基氧化铁（III）含有从痕量到约22重量%的可变水平的As和高达约9重量%的Ca。细磨矿石和尾矿样品进行了检查散装XAFS和选定的矿物颗粒进行了分析，微聚焦XAFS（微EXAFS）光谱，以调和多个作为源在复杂的散装EXAFS光谱的模糊性。XANES谱表明，所有样品中As均以As ~（5+）形式存在。微EXAFS光谱的个别铁（III）羟基氧化物颗粒与不同的浓度点内球双齿双核砷酸盐配合物作为主要形式的As。有迹象表明存在第二个铁壳对应于双齿单核安排。铁（III）羟基氧化物与高浓度的最大吸附密度相对应的可能发生的纳米粒子。在铁（III）羟基氧化物中，原子间距离为4.14-4.17 μ m处的Ca原子和配位数的发现表明，通过共沉淀而不是简单地将Ca吸附到铁（III）羟基氧化物上来形成砷华样纳米簇。相关的钙与作为铁（III）羟基氧化物，通过电子探针分析确定支持共沉淀起源的存在下，钙在铁（III）羟基氧化物。含较高丰度的砷酸铁的样品在氰化试验期间释放较高的As浓度。高溶解性砷酸铁和钙铁砷酸盐的存在下，相对不稳定的铁（III）的羟基氧化物与铁/砷的摩尔比小于4的矿石和工艺尾矿表明，不仅在蓄水池的尾矿将继续释放作为，但也有动员的天然来源，如未开采的矿石的潜力。
The knowledge of mineralogy and molecular structure of As is needed to better understand the stability of As in wastes resulting from processing of gold ores. In this study, optical microscopy, scanning electron microscopy, electron microprobe, X-ray diffraction and X-ray absorption fine structure (XAFS) spectroscopy (including both XANES and EXAFS regimes) were employed to determine the mineralogical composition and local coordination environment of As in gold ores and process tailings from bench-scale tests designed to mimic a common plant practice. Arsenic-bearing minerals identified in the ores and tailings include iron (III) oxyhydroxides, scorodite (FeAsO4·2H2O), ferric arsenates, arseniosiderite (Ca2Fe3(AsO4)3O2·3H2O), Ca-Fe arsenates, pharmacosiderite (KFe4(AsO4)3(OH)4·6–7H2O), jarosite (K2Fe6(SO4)4(OH)12) and arsenopyrite (FeAsS). Iron (III) oxyhydroxides contain variable levels of As from trace to about 22 wt% and Ca up to approximately 9 wt%. Finely ground ore and tailings samples were examined by bulk XAFS and selected mineral grains were analyzed by microfocused XAFS (micro-EXAFS) spectroscopy to reconcile the ambiguities of multiple As sources in the complex bulk EXAFS spectra. XANES spectra indicated that As occurs as As5+in all the samples. Micro-EXAFS spectra of individual iron (III) oxyhydroxide grains with varying As concentrations point to inner-sphere bidentate-binuclear arsenate complexes as the predominant form of As. There are indications for the presence of a second Fe shell corresponding to bidentate-mononuclear arrangement. Iron (III) oxyhydroxides with high As concentrations corresponding to maximum adsorption densities probably occur as nanoparticles. The discovery of Ca atoms around As in iron (III) oxyhydroxides at interatomic distances of 4.14–4.17 Å and the coordination numbers suggest the formation of arseniosiderite-like nanoclusters by coprecipitation rather than simple adsorption of Ca onto iron (III) oxyhydroxides. Correlation of Ca with As in iron (III) oxyhydroxides as determined by electron microprobe analysis supports the coprecipitate origin for the presence of Ca in iron (III) oxyhydroxides. The samples containing higher abundances of ferric arsenates released higher As concentrations during the cyanidation tests. The presence of highly soluble ferric arsenates and Ca-Fe arsenates, and relatively unstable iron (III) oxyhydroxides with Fe/As molar ratios of less than 4 in the ore and process tailings suggests that not only the tailings in the impoundment will continue to release As, but also there is the potential for mobilization of As from the natural sources such as the unmined ore.