An Update to “Recent Trends in the Processing of Enargite Concentrates”

An update is presented to the paper “Recent trends in the processing of enargite concentrates” by Safarzadeh, Moats, and Miller (2014). Publications which were not included in the initial review paper, primarily to avoid redundancy, are presented and discussed here. Thus, roasting, atmospheric acidic and alkaline leaching, the dissolution of enargite in low-melting point salts, bioleaching, and pressure leaching are presented. For the first time, the modified phase stability (Kellogg) diagram and the E_h-pH diagram for the Cu-As-S system including sinnerite (Cu₆As₄S₉) have been established. According to the results from different treatment options discussed in our earlier review and also in this paper, it is evident that the most recent research activities for the treatment of enargite concentrates are centered around roasting, alkaline sulfide leaching, and high temperature pressure oxidation. Taking into account the advantages and disadvantages of the mentioned processing options, and the numerous preliminary experiments performed, the acid bake-leach process has been identified and is being studied at the University of Utah. It has been found that enargite transforms to water-soluble copper sulfate, arsenic trioxide and elemental sulfur by sulfuric acid baking of enargite at 200°C, with less than 1% of the arsenic being released to the gas phase. This process strategy provides a new possibility for the treatment of enargite concentrates.     

Thermodynamic Analysis of the Cu-As-S-(O) System Relevant to Sulfuric Acid Baking of Enargite at 473 K (200 °C)

While the growing demand for copper has compelled the industry to adapt new technologies for the treatment of copper-arsenic (enargite) concentrates, the refractory nature of such concentrates combined with the troublesome presence of arsenic has created a major metallurgical and environmental challenge. Preliminary results of the acid bake-leach process at the University of Utah have shown some potential advantages for the treatment of enargite concentrates. While the transformation of enargite to copper sulfate, arsenolite, and elemental sulfur has already been established experimentally, thermodynamic evaluation of the sulfuric acid baking process provides further understanding which should be useful. In this article, the available thermodynamic data for the species involved in the Cu-As-S-O system are compiled. These data were used to calculate the phase stability (Kellogg) diagrams as well as equilibrium compositions at 473 K (200 °C) using the STABCAL and HSC Chemistry^® 5.1 software packages. The equilibrium composition calculations indicate that enargite can transform to copper sulfate either directly or through chalcocite and/or covellite. The major gaseous species during baking were found to be SO₂ and H₂O. The results of the thermodynamic calculations were further compared with two confirmatory baking experiments involving a high-quality enargite sample. The condensed reaction products from sulfuric acid baking based on XRD results include CuSO₄, As₂O₃, CuO·CuSO₄, and S₈ under both neutral and oxidative conditions. While all these compounds were predicted through equilibrium calculations, some of the predicted compounds were not detected in the sulfuric acid-baked enargite. None of the calculations indicated any appreciable amounts of arsenic-bearing gases at the baking temperature of 473 K (200 °C). Consistent with thermodynamic predictions, no H₂S gas was detected during the sulfuric acid baking experiment. Approximately, 80 pct of the baked enargite samples were leached in water.     

RECOVERY OF METAL VALUES FROM COPPER—ARSENIC MINERALS AND OTHER RELATED RESOURCES

Copper is often associated with arsenic in mixed sulphide minerals such as enargite (Cu₃AsS₄) and tennantite (Cu₁₂As₄S₁₃). Enargite, in particular, is the principal mineral in many deep epithermal copper–gold deposits. Most mining companies avoid exploiting such resources, because the arsenic can become a serious environmental liability or may considerably reduce the resource value due to hefty treatment charges. The few enargite deposits that have been exploited so far are usually rich in gold and silver. The first challenge in the exploitation of copper–arsenic sulphides is the effective separation of arsenic phases from other valuable minerals. In the last decade, though, it was shown that this is possible by pulp-potential adjustment (oxidative conditions) combined with pH adjustments (basic conditions) prior to flotation. In this way, two types of concentrate can be produced: one rich in arsenic and another low in arsenic but rich in other valuable metals. Arsenic-rich concentrates have traditionally been processed pyrometallurgically by reduction roasting to gaseous arsenic sulphide, which is then converted to arsenic trioxide. New pyrometallurgical technologies for the treatment of copper–arsenic sulphides include sulphidization roasting, sulphidization roasting and halogenation, and carbothermic reduction to copper arsenide. The hydrometallurgical treatment of copper–arsenic-antimony resources has been done by atmospheric leaching in alkaline sodium-sulphide solutions. Ultrafine grinding and ferric oxidation at atmospheric pressure, total pressure oxidation at temperatures above 220°C, and bacterial leaching have recently been tried on copper–arsenic sulphides, some with considerable success.     

An application of acetonitrile leaching and disproportionation.: Refining segregated copper from roasted concentrates and ores

Pure copper with > 99% recovery has been obtained on a laboratory scale from a variety of copper sulfide concentrates by the following steps. An oxidative roast at 800–900°C to remove sulfur; reduction of the calcine, preferably but not necessarily under segregation roasting conditions at 650–750°C, to generate particulate copper; screening, in the case of segregation roasting, to partially separate from magnetite the over-size carbon which is coated with copper, gold and silver; selective dissolution in acetonitrile-water of the copper from both fractions; then thermal disproportionation of the copper(I) sulfate solution to remover pure copper powder. At least 80% of the silver and > 98% of the copper is recovered by this new concept. Cyanidation of leach residues recovers > 99% of the copper, > 90% of the silver and 80% of the gold, without interference from the iron in the residue. The method has been applied to the product of a segregation roast of refractory copper ores (TORCO process), to the product of a double roast of copper concentrates (Opie-Coffin process) and to the product of a non-segregation reductive roast of a dead roasted concentrate (USBM process). It is also applicable to calcines reduced in a blast furnace.Successful scale up could result in a low cost process for producing copper from copper concentrates. The energy requirements promise to be less than 6000 kJ as 25 psig steam per kg copper, if effective use of steam from the exothermic roasts can be achieved.     

Arsenic in Gold Processing

Abstract

The processing of gold bearing sulphide minerals which contain arsenopyrite and other complex arsenic sulphide minerals results in arsenic containing emissions and effluents which must be given careful consideration in relation to clean air and clean water standards. The sources of arsenic and the various process options for treating arsenical gold ores and concentrates are briefly reviewed

The problem relating to the removal of arsenic from gaseous emissions from roasting processes is considered

Residues from aqueous processing contain a variety of arsenical materials which have not been characterised, and the long-term stability of these is suspect

The use of lime to stabilise aqueous residues as cither calcium arsenate or calcium arsenite has been shown to be inadequate for long term disposal since both compounds are converted into calcium carbonate due to the influence of carbon dioxide in the atmosphere

Ferric ion solutions have been used to precipitate ferric arsenate or to form ferric hydroxide which binds the arsenic for short term disposal. The long term stability of these ferric materials is poor, but could lead to the acceptance of a slow release option rather than complete containment of residues.     

Treatment of Arsenic Bearing Raw Materials

Studies showed the possibility of arsenic removal from gold- and copper bearing ores and concentrates with high levels of arsenic (2-12%) under reducing-sulphidizing conditions, especially in the presence of pyrite. Pilot plant and industrial scale fluid bed reasting at 750-900°C showed that under reduction-sulphidizing conditions with pyrite and (or) coke the arsenic is eliminated as arsenic sulphide and greater than 99% arsenic can be eliminated from copper and gold concentrates containing 2-8% arsenic. With increasing temperature, duration of roasting, and pyrite addition, vaporization degree increases. The roasted calcine is suitable for pyrometallurgical or hydrometallurgical treatment.     

硫砷铜矿热压浸出研究现状及进展

随着全球对废气、废水和固体废弃物排放的环保规定日益严格,传统火法冶炼技术对含砷硫化铜矿的处理已很难达到环保要求,因此开发高效环保的硫化铜矿处理工艺流程已经成为一个重要的研究课题。该文简要介绍了典型含砷硫化铜矿——硫砷铜矿的性质,详细分析了硫砷铜矿热压浸出技术的主要工艺,包括热压硫酸盐体系、Platsol工艺、NSC工艺、Dynatec工艺、CESL工艺,并对其优缺点、研究现状及进展进行了阐述,同时对比了热压浸出技术与其他处理工艺技术的工程化应用可行性。     

铜矿石和精矿氮类物催化加压浸出的应用与经济估算

目前评估生产铜的新处理方法兴趣日益浓厚。铜矿石和精矿湿法加压氧化是一种环境友好、经济上可行的方法。几种侯选工艺已经出现,目前正在以中间工厂或生产规模应用。其中,第一个已经工业生产验证的方法是氧压浸出中采用氯类物催化（NSC）,通过SX—EX生产铜。该法具有很多优点,是一种很有应用前景的方法。本文介绍了该工艺的最新进展,工艺开发史及在铜精矿和铜矿石中的应用,重点讨论了从黄铜矿精矿中有效回收贵金属的无氰化物方法。最后,介绍了两个最新工业应用研究及其现场经济估算．     

Review of Recovery of Platinum Group Metals from Copper Leach Residues and Other Resources

Porphyry copper and mixed copper-gold sulfide deposits contain varying amounts of precious (gold and silver) and platinum group metals (PGMs). Currently, milling and froth flotation is the most common processing route for the treatment of high-grade base metal sulfide ores. During this process, the precious metals and PGMs are also concentrated and represent a possible opportunity for the beneficiation of these metals to increase the overall economic value of the ore. Although not yet commercialized, the high temperature pressure oxidation (POX) of copper concentrates provides an alternative processing route to traditional smelting technology. With increasingly aggressive air quality standards and rising upstream processing costs for smelting, hydrometallurgical processing options become progressively attractive. The treatment of POX residues for the recovery of precious metals has seen significant attention and multiple processing routes have been developed on various scales. Extraction and beneficiation of PGMs from copper concentrate POX residue has garnered significantly less attention and mechanistic questions remain to be answered. Based on a review of the processing options for PGM ores and concentrates, hydrometallurgical processing routes for the extraction of PGMs from copper concentrate POX residues are envisioned.     

Arsenic removal from copper ores and concentrates through alkaline leaching in NaHS media

Removal of arsenic impurity in ores and concentrates containing copper (Cu) through alkaline leaching in NaHS media was investigated in this work. Samples containing Cu from 10 to 40 wt.% and arsenic from 0.8 to 14 wt.% with enargite (Cu₃AsS₄) as main arsenic bearing mineral were used as starting materials and all leaching tests were conducted at 80 °C under normal atmospheric pressure. Solution and/or slurry potential and pH were maintained consistently below − 500 mV (SHE) and above 12.5 respectively with the addition of NaHS and NaOH, creating a reducing environment for arsenic dissolution and conversion of Cu₃AsS₄ to Cu₂S. Pulp density ranged from 100 to 1000 g/L, NaHS and NaOH reagents were added at 50–200 g/L each and leaching time varied from 10 min to 10 h.Characterization of solid samples (original and leach residue) by XRD and XRF analyses and chemical analysis of both solid and solution samples by ICP analysis showed that Cu₃AsS₄ in the starting material was completely decomposed or transformed to Cu₂S and arsenic released into solution as As (III)/As³⁺ ions (Na₃AsS₃). Over 90% of arsenic in the starting materials was removed within 1–3 h for materials with arsenic content from 1 to 4 wt.% and within 3–6 h for materials with arsenic content over 4–10 wt.%. Dissolution and analysis of leach residues obtained after leaching by ICP indicated that arsenic in the starting materials has been reduced in all cases to below 0.5 wt.%. In all test conditions dissolution of Cu and Fe into solution was not detected, indicating selective leaching of arsenic. NaHS application for removal of arsenic in Cu-ores and/or concentrates was demonstrated in this work and further research is in progress to develop a process to include treatment of arsenic leached into solution.     

高砷金精矿氧化焙烧焙砂和真空蒸馏脱砷焙砂的硫脲浸出研究

高砷金精矿经真空蒸馏脱砷后用硫脲浸出,金的浸出率可达90％以上。和金精矿直接硫脲浸出相比,金的浸出率提高了近80％,且金的浸出率随焙砂中砷含量的减少而提高;用真空蒸馏法处理高砷金精矿焙砂和常规氧化焙烧脱砷率相近的焙砂相比,在金的漫出方面具有相同的效果。     

Simulation of the removal of arsenic during the roasting of copper concentrate

To simulate the behavior of arsenic during the practical roasting of copper concentrate, a modified free-energy minimization method was developed. The calcine was assumed to be a pseudosolid solution in which the nonequilibrium arsenic species are contained as solutes, with a high activity (adjustment) coefficient. The validity of the method of calculation was checked by comparison to the results of conventional calculations. The validated procedure was then used to evaluate the effects of operating variables and to establish optimum roasting conditions. The change of the predominant gas and solid species during the course of oxidation and the effect on the volatility of arsenic are discussed. Arsenic removal from the concentrates was generally good, but it was affected by the extent of oxidation and the initial concentration in the concentrate. The extent of sulfur oxidation for optimum arsenic removal is around 70 pct. With the appropriate choice of an adjustment coefficient, the results simulated those obtained in practice.     

含砷银铜精矿中有价金属回收技术综述

本文分析了对含砷银铜精矿利用的技术方案,简述了对这一精矿进行的低温焙烧、化学除砷、浸铜以及浸银等实验研究以及取得的技术指标。     

Present and future commercial applications of biohydrometallurgy

Modern commercial application of biohydrometallurgy for processing ores became reality in the 1950s with the advent of copper bioleaching at the Kennecott Copper Bingham Mine. Early application entailed dump leaching of low-grade, low-value, run-of-mine material. Dump bioleaching has evolved into a commercially accepted option for bioheap copper leaching of higher-grade, higher value ores. This commercial practice is exemplified by at least 11 mining operations. Paradoxically, application of biohydrometallurgy in the pretreatment of refractory gold ores began with processing high value concentrates, using biooxidation-tank processes and was followed by extension to processing low-grade, lower value ores in heaps. Now, bioleaching has been extended to the commercial extraction and recovery of cobalt. Even with the current success of biohydrometallurgical applications in the mining industry, the real potential of biotechnology in mining remains to be realized. As confidence in commercial bioprocessing grows and experience extends the application's knowledge base, innovations and new commercial practices will emerge. Near-term future commercial applications will likely remain focused on recoveries of copper, gold and possibly nickel. Recent technical advances show that very refractory chalcopyrite can be successfully bioleached. Processes for copper recovery from this mineral will include both heap and stirred-tank reactors. Next generation technologies for pretreatment of refractory gold ores will be based on use of thermophilic bacteria for sulfide oxidation. For biohydrometallurgy to commercially advance, the microbiologist must work cooperatively with the practitioners of the technology for mutual understanding of operational limitations and practical constraints affecting the microbiological component.     

加压氰化法提取贵金属的研究进展

氰化法是处理金矿较为成熟的工艺。加压氰化过程通过强化反应动力学,可实现难浸金属的高效浸出,在贵金属湿法提取冶金领域是一新兴技术。分别介绍了加压氰化法处理难浸金矿、失效汽车催化剂、含铂族金属矿物等方面的研究工作及其最新进展。对我国云南大理地区低品位铂钯硫化矿的浮选精矿,采用传统火法造锍熔炼技术工序繁冗、能耗高、污染严重、贵金属易分散损失,经济上难以创效。而采用加压氰化全湿法新工艺,不但贵金属及铜镍等有价金属回收指标高,而且该工艺工序少、周期短、能源低、污染小,为开发利用我国低品位原生铂矿资源提供了一条新技术思路。     

难浸金矿预处理技术及其研究进展

随着易浸金矿的不断减少,难浸金矿应用比重越来越大,总结难浸金矿的预处理技术及其研究进展有重要意义。简要分析了难处理金矿难浸的原因,指出难浸金矿在浸出前进行预处理的必要性,对加压氧化法、焙烧法、生物预氧化法和超细磨法等难浸金矿的预处理方法以及新的预处理技术进展进行了总结,评述了各预处理方法的优缺点,在此基础上,对难处理金矿的预处理技术研究前景进行了展望。     

Oxidation of cobaltite: Part I. process mineralogy

The control of arsenic is important in oxidation roasting and leaching of cobaltite. Oxidation roasting below 823 K did not show any crystal structural change in cobaltite, but heating to 923 K yielded Co-As-oxide, whose composition is varied. Direct oxidation of cobaltite to cobalt oxides with traces of arsenic was observed by roasting at 1023 K or above. The distribution of arsenic within the particles gradually decreased from the outer region to the center of the particles. The arsenic concentration within the particles decreased with the increase of temperature, suggesting temperature dependence on arsenic removal from the lattice of cobaltite. In this article, the process mineralogy of the oxidation of cobaltite is presented at various temperatures. The results from X-ray diffraction (XRD) analysis, reflected light microscopic analysis, and scanning electron microscopic analysis of the roasted cobaltite concentrates together with a rationalized thermodynamic analysis are presented.     

从高硫多金属金精矿中提取金银铜试验研究

采用焙烧—酸浸—氰化工艺从高硫多金属金精矿中提取金、银、铜。其试验结果表明:在最佳条件下,金、银、铜的平均浸出率分别可达到96.56%、79.12%、91.33%。通过对比金精矿、焙砂、氰化渣中金、银的化学物相可知,硅酸盐包裹金、银不易被氰化浸出,而加入复合添加剂焙烧,硅酸盐包裹的金、银品位大幅度下降,由直接焙烧的2.05 g/t、163.35 g/t分别降到0.81 g/t、25.24 g/t。     

高硫富砷金矿氧化预处理工艺研究现状

高硫富砷金矿石中金通常被含砷、硫等的矿物包裹,氰化浸出困难,需要对其进行氧化预处理,常见的预处理方法有生物氧化、焙烧氧化、加压氧化、超声波氧化、化学氧化等.介绍了这些方法的发展历程和基本原理,分析了其优缺点及应用的适应性,为今后科研工作者进行相关研究提供参考.