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首页> 外文期刊>Journal of Geochemical Exploration: Journal of the Association of Exploration Geochemists >Speciation of the most soluble phases in a sequential extraction procedure adapted for geochemical studies of copper sulfide mine waste
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Speciation of the most soluble phases in a sequential extraction procedure adapted for geochemical studies of copper sulfide mine waste

机译：适用于硫化铜矿山废物地球化学研究的连续萃取程序中最易溶相的形态

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摘要

Sequential extractions are widely used for exploration purposes and to study element speciation in systems such as soil and sediments, and more recently to understand the complex biogeochemical element cycling in mine waste enviornments. This method is however often the focus of criticism due to uncertainty in the selectivity of specific leaches utilized. In this study, a procedurei s presented how sequential extractions can be adapted to specific mineralogy in order to increase the selectivity and the accuracy of geochemical data interpretation. The application of dissolution kinetic tests and the control of dissolved phases in sequential extractions by X-ray diffraction (XRD) and differential X-ray diffraction (DXRD) indicate which minerals are dissolved in each leach. This information is crucial for the interpretation of geochemical data obtained from sequential extractions and enables to increase the selectivity of the sequence applied. A seven-step sequence was adapted to the specific secondary and primary mineralogy of mine tailings from Cu-sulfide ores, both from porphyry coppera nd from Fe-oxide Cu-Au deposits. As result of the study, the following seven-step sequence shows best selectivity for the aim of the study of Cu-sulfide mine waste: Step 1 liberates the water-soluble fraction (1.0-g sample into 50-mol deionized H_2O shake for 1 h at room temperatur [RT]) dissolving gypsum and metal salts (e.g., chalcanthite (CuSO_4·5H_2O), pickeringite (MgAl_2(SO_4)_4·22H_2O)). Step 2 liberates the exchangeable fraction (1 M NH_4-acetate, pH 4.5, shaken for 2 h, RT) as adsorbed ions, but also dissolves calcite and breaks down a typical secondary vermiculite-type mixed-layer mineral from the low pH oxidation zone. Step 3 addrsses the Fe (III) oxyhydroxides fraction (0.2 M NH_4-oxalate, pH 3.0, shaken for 1 h in darkness, RT) and dissolves schwertmannite, two-line ferrihydrite, Mn-hydroxides, secondary jarosite partially, as well as goethite formed acid mine drainage. Step 4 dissolves the Fe(III) oxides fraction (0.2 M NH_4-oxalate, pH 3.0, heat in water bath 80 deg C for 2 h) and removes all secondary ferric minerals occurring as higher ferrihydrite (e.g., six-line), goethite, primary and secondary jarosite, natrojarosite, and primary hematite. Step 5 consists of a change from reducing to oxidizing condition and is performed by a H_2O_2 leach (35% H_2O_2 heat in water bath for 1 h), which dissolves organic matter and supergene Cu-sulfides such as covellite and chalcocite-digenite. Step 6 (KClO_3 and HCl, followed by 4 M HNO_3 boiling) dissolves primary sulfides and Step 7 (HCl, HF, HClO_4, HNO_3) the residual fraction (silicates). The application of this extraction sequence of 5 Cu-sulfide mine tailings have shown that sequential extraction can be a powerful tool for detection of element mobilization and retention processes. This is especially the case in dry climates, where it is difficult to obtain pore-water geochemistry. A detailed mineralogical study should however go hand in hand with every geochemical study of mine waste to ensure the accuracy of the geochemical interpretations.
机译：顺序提取被广泛用于勘探目的和研究土壤和沉积物等系统中的元素形态，最近又了解了矿山废物环境中复杂的生物地球化学元素循环。然而，由于所使用的特定浸出液的选择性不确定，该方法经常成为批评的焦点。在这项研究中，一个程序提出了如何将顺序提取法适应特定的矿物学，以提高地球化学数据解释的选择性和准确性。通过X射线衍射（XRD）和微分X射线衍射（DXRD）进行的连续萃取中的溶出动力学测试和溶出相控制的应用表明了每种浸出物中都溶解了哪些矿物。该信息对于解释从顺序提取中获得的地球化学数据至关重要，并且可以提高所应用序列的选择性。根据硫化铜矿，斑岩铜矿和氧化铁铜金矿床的尾矿的特定二级和一级矿物学，采用了七个步骤。研究结果表明，以下七个步骤序列显示出最佳的选择性，可用于研究硫化铜矿山废料：步骤1将水溶性级分（1.0克样品释放到50摩尔去离子H_2O摇床中，进行1次h在室温[RT]下溶解石膏和金属盐（例如，黄铜矿（CuSO_4·5H_2O），堇青石（MgAl_2（SO_4）_4·22H_2O））。步骤2将可交换级分（1 M NH_4-乙酸盐，pH 4.5，摇动2 h，室温）释放为吸附离子，但也溶解了方解石并分解了低pH氧化区的典型次级secondary石型混合层矿物。第3步添加氢氧化铁（III）馏分（0.2 M NH_4-草酸盐，pH 3.0，在黑暗中，室温摇动1小时）并溶解schwertmannite，两线水铁矿，Mn-氢氧化物，部分黄铁矿以及针铁矿形成酸性矿山排水。步骤4溶解了Fe（III）氧化物级分（0.2 M NH_4-草酸盐，pH 3.0，在80℃的水浴中加热2小时），并除去所有以较高水铁矿（例如六线），针铁矿形式出现的次级铁矿物质，主要和次要黄铁矿，钠铁矾和主要赤铁矿。步骤5由还原状态变为氧化状态，是通过H_2O_2浸出（在水浴中加热35％H_2O_2进行1小时）来进行的，该溶解过程溶解了有机物和超生Cu-硫化物，如铜锌矿和辉绿岩-方铁矿。步骤6（KClO_3和HCl，然后4 M HNO_3沸腾）溶解伯硫化物，而步骤7（HCl，HF，HClO_4，HNO_3）则残留部分（硅酸盐）。 5个硫化铜矿尾矿的提取顺序的应用表明，顺序提取可以成为检测元素动员和保留过程的有力工具。在干燥的气候中尤其如此，那里很难获得孔隙水的地球化学。但是，详细的矿物学研究应与矿山废物的每项地球化学研究并驾齐驱，以确保地球化学解释的准确性。

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