International Journal of Minerals, Metallurgy and Materials Volume 17, Number 1, February 2010, Page 1 DOI: 10.1007/s12613-010-0101-6 Processing technologies for gold-telluride ores Jian Zhang1), Yao Zhang1), William Richmond2), and Hai-peng Wang1) 1) Department of Metallurgical Engineering and Extractive Metallurgy, Curtin University of Technology, WASM, Kalgoorlie, WA 6430, Australia 2) Department of Applied Chemistry, Curtin University of Technology, Bentley, WA 6102, Australia (Received: 28 November 2008; revised: 6 January 2009; accepted: 1 March 2009) Abstract: Gold telluride ores are important gold refractory ores due to the presence of sulfides and other gangue materials. The classification and main physical properties of gold telluride ores were described, and possible treatment methods including flotation, leaching, and oxida- tion were reviewed. The results show that flotation procedures are much easier for gold tellurides compared to other refractory gold-bearing ores. For the conventional cyanide leaching process, pretreatment such as oxidation is required to achieve high gold recovery. Roasting is a relatively simple but not environment-friendly method; bio-oxidation technology seems to be more suitable for the oxidation of flotation concentrate. Other treatment methods involve cyanide leaching, thiourea leaching, ammoniacal thiosulfate leaching, carbon-in-pulp, and resin-in-pulp, all of which are less commonly utilized. Keywords: gold-tellurides; flotation; leaching; oxidation 1. Introduction 2. Classification of gold-telluride ores Gold occurs primarily in its native form and secondarily It was well known that gold was commonly associated as gold solid-solution of which tellurides are an example [1]. with tellurium minerals. The cooccurrence of tellurium with Gold extraction from tellurides has attracted increasing at- noble metals such as gold and silver was attributed to the tention over the past decades. Gold tellurides have been semi-metallic nature of tellurium. The composition varied commercially treated in Kalgoorlie (Western Australia), significantly from different tellurium minerals. For instance, Vatukoula (Fiji), Cripple Creek (Colorado), and Kirkland gold-telluride ores could be classified into six mineral Lake (Ontario). The first modern treatment of gold-telluride groups: calaverite (AuTe2), sylvanite [(Ag,Au)2Te4], mont- ores was performed in 1891 in the Cripple Creek goldfield brayite [(AuSb)2Te3], krennerite [(Au1x,Agx)Te2], petzite near the Rocky Mountains in Colorado. Kalgoorlie, in (Ag3AuTe2), and muthmannite [(Ag,Au)Te2]. Western Australia, had the honor of being the second major The physical properties and deposit location of these six goldfield, and tellurides were successfully processed to ex- minerals are tabulated in Table 1. Among them, Calaverite tract gold. In a modern gold processing plant, the recovery was the simplest and most common association of tellurium can be up to 98% with the aid of the latest concentration and with gold. It was also the most common gold bearing min- smelting techniques. A successful gold recovery strategy re- eral apart from native gold. lies on a fundamental understanding of the ore mineralogy and its chemical/physical behaviors under various leach, 3. Processing options flotation, and oxidation conditions. An overview of the processing techniques/options for gold telluride ores was Unlike free gold, gold tellurides do not undergo rapid given and their advantages and limitations were discussed in dissolution in the conventional alkaline cyanide leach solu- this paper. tion. Therefore, alternative treatments must be applied to Corresponding author: Hai-peng Wang E-mail: [email protected] © University of Science and Technology Beijing and Springer-Verlag Berlin Heidelberg 2010 2 Int. J. Miner. Metall. Mater., Vol.17, No.1, Feb 2010 break down the gold-telluride structure and release free gold. gold and obtain a concentrate for further cyanidation. Re- The general processing methods are: oxidation, flotation, fractory ores, however, require fine grinding and a further and leaching. pre-treatment step, such as roasting and pressure oxidation, to render the gold ores amenable to extraction. Usually, gold 3.1. Oxidation telluride ores appear to be refractory as they are always as- Generally, gold ores can be classified into two categories: sociate with pyrite and other sulfides. This would ‘lock’ the the ‘free milling’ and ‘refractory’ ores. Free milling ores are gold and give rise to elevated cyanide consumption. For this those that require only conventional physical pre-treatment, reason, oxidative pre-treatments are generally conducted to such as grinding and sulfide flotation, to liberate the free improve gold recoveries. Table 1. Physical properties and deposit location of main gold-telluride minerals [2] Specific Mohs hardness Mineral Formula Colour Location gravity scale Cripple Creek (USA); Nagyag (Romania); Kirk- Silver white to Calaverite AuTe 9.10-9.30 2.5-3.0 land Lake Gold District and Rouyn District (Can- 2 brassy yellow ada); Kalgoorlie (Australia). Cripple Creek (USA); Nagyag (Romania); Big- Steely gray to Sylvanite (AgAu)Te 8.20 1.5-2.0 stone Bay and Kirkland Lake Gold District (Can- 2 silver gray ada); Kalgoorlie (Australia), Vahatala (Fiji). Creamy white to Robb-Montbray (Canada); Enasen (Sweden); Montbrayite (AuSb) Te 9.94 2.5 2 3 yellowish white Changjin (China); Voronezhsky Massif (Russia). Silver white to Krennerite (Au ,Ag )Te 8.53 2.5 Sacarîmb, Nagyag, and Szekerembe (Romania.). x x 2 blackish yellow Bright steel gray Petzite Ag AuTe 8.70-9.14 2.5 Kalgoorlie (Australia); Viti Levu (Fiji). 3 2 to iron black Muthmannite (Ag,Au)Te2 Pale bronze 11.04 2.5 Sacarîmb (Romania). The presence of gold telluride minerals may render an been used to overcome the refractory nature of tellurides. ore refractory, the extent of this depends on the telluride These methods can possibly enhance the recovery of gold, mineral present and the mineralogical association [3]. Gold, however, the consumption of reagents and energy should be silver, and gold/silver-telluride minerals in ores dissolve taken into account. The current practice at Kalgoorlie Con- more slowly than native gold in cyanide solutions, which solidated Gold Mines Pty Ltd. (KCGM) is to produce a sul- results in less efficient gold extraction [4]. Similarly, cya- fide-telluride concentrate that is fluid-bed roasted. The re- nide leaching tests on synthetic calaverite (AuTe2) and syl- sulting calcine is leached with cyanide and the gold is re- vanite (AuAg)Te2 result in lower gold recoveries [5]. covered by the carbon-in-pulp (CIP) process [7]. A few Jayasekera et al. [6] studied the dissolution of calaverite chemical oxidative pre-treatments have been investigated to electrochemically in both acidic and alkaline media. It improve gold recoveries, including bromocyanidation, showed that the slow dissolution rate in alkaline cyanide leaching with thiourea, and pressure cyanidation. However, solutions was due to the formation of a passivating film of these pre-treatments have not been developed to commercial H2TeO3 that protected the mineral surface from further oxi- application. dation (see Eqs. (1) and (2)), and this film dissolved at 3.1.1. Roasting higher pH. Roasting is the simplest and most frequently used oxida- 2 AuTe2(s)+CN +8OH →Au(CN) +2H2TeO3(s)+2H2O+7e tive process. Roasting consists of heating the (1) ores/concentrates below the fusion point in contact with air, oxygen, water vapor, carbon, sulfur, or chlorine. This aims HTeO(s)2OH TeO2 2HO (2) 233 2 to produce the desired chemical and/or physical change that Major gold deposits containing tellurides occur in Colo- will be beneficial to downstream processing for the recovery rado (USA), Vatukoula (Fiji), and Kalgoorlie (Western of the metal [8]. Roasting may be realized through one of Australia). As mentioned above, fine grinding, the extension the following processes: oxidizing roast, volatilizing roast, of leach residence time or the excessive addition of lime has chloriding roast, sulfatizing roast, magnetizing roast, reduc- J. Zhang et al., Processing technologies for gold-telluride ores 3 ing roast, carburizing roast, and sintering or blast roasting. tion process. The high temperature can sufficiently decompose the tellu- Bio-oxidation of refractory gold ores in heaps [11] and of rides and leave behind the valuable gold residue. flotation concentrates in stirred reactors [12] are proven One concern with the procedure is that during oxidation technologies applied all over the world on a commercial roasting, pyrite and other sulfide minerals will emit poison- scale, while in Australia, three bio-oxidation plants have ous gas such as SO2. For example, been operated successfully: Harbour Lights (1992-1994), Youanmi (1994-1997), and Wiluna (1993-current). All the 2FeS2+5.5O2→Fe2O3+4SO2 (3) three are in Western Australia. Three further plants are A further issue is that a considerable amount of gold may planned or under construction, at Beaconsfield Gold Mine deposit on the internal wall and other parts of a roaster, and (Tasmania), Perseverance Gold Mine (Victoria), and Maud this gold can only be collected when the roaster is shut down Creek (Northern Territory) [9]. [9]. These two factors are the primary concerns when roast- ing gold telluride ores. 3.2. Flotation Gold tellurides float well [13-15], however, their recov- 3.1.2. Bio-oxidation eries are likely to be compromised by the presence of solu- A more promising