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Hydrometallurgy 62 (2001) 165 – 173 www.elsevier.com/locate/hydromet

Mechanochemical processing of enargite (Cu3AsS4)
N.J. Welham*
Department of Applied Mathematics, Research School of Physical Sciences and Engineering, Australian National University, Canberra, ACT 0200, Australia Received 29 June 2001; received in revised form 14 August 2001; accepted 7 September 2001

Abstract Acommercial enargite (Cu3AsS4) concentrate was mechanically milled in inert and oxidising atmospheres for up to 50 h. No substantial effect was observed in either an inert atmosphere or in air other than a broadening and weakening of the diffraction peaks. Milling in oxygen was dramatic with significant reaction evident even after 1 h. The products were As2O3 and CuSO4Á5H2O, both of which are readilysoluble; a small amount of SO2 was also formed. Dissolution in acid left CuS as the major phase; this phase was thermodynamically predicted to be a minor phase during the oxidation process and appeared to be stable for long periods under milling. Milling for 1 h at 100 °C resulted in the same products but showed a greater extent of oxidation. The small fraction of tennantite in the sample wascomparatively resistant to oxidation. D 2001 Elsevier Science B.V. All rights reserved.
Keywords: Mechanochemical processing; Copper ores; Enargite

1. Introduction Enargite is a copper arsenosulphide (Cu3AsS4) which is often found in small quantities within chalcopyrite ores but does not present substantial difficulties to the conventional processing route. However, in ores where the arsenic content isrelatively high there are problems with direct smelting of the ore due to the expense of sequestering arsenic into a stable end phase. Most smelters consider arsenic a major penalty element and the price of the concentrate is diminished accordingly, sometimes to the point where the penalties are greater than the values making the ore uneco-

*

Tel.: +61-2-6249-0520; fax: +61-2-6249-0511.E-mail address: nicholas.welham@anu.edu.au (N.J. Welham).

nomic to process. In high arsenic systems, there is frequently an elevated antimony content also, this partially substitutes for arsenic and the minerals present are usually Cu3(As,Sb)S4 and Cu12(As,Sb)4S13 (tennantite/tetrahedrite). There has been comparatively little published on solution treatment processes for these minerals due totheir relatively low commercial importance with other, more amenable, copper ores being dominant. The general conclusion is that these minerals are not amenable to many conventional processing routes. Ferric oxidation recovered 75% enargite, 15% tennantite and < 5% tetrahedrite after 40 h at 95 °C, the low recovery into solution was considered to be due to elemental sulphur blocking the surface(Dutrizac and Macdonald, 1972). Ammoniacal pressure oxidation gave 56% Cu dissolution after 9 h at 82 °C with optimum conditions of 4 atm of oxygen at pH 10 and

0304-386X/01/$ - see front matter D 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 3 8 6 X ( 0 1 ) 0 0 1 9 5 - 5

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total ammonia of >5 g L À 1 (Gajam and Raghavan,1983). Only 70% of copper was extracted from a tennantite/tetrahedrite concentrate after 5 h at 130 °C with 3 atm oxygen and 300 g L À 1 ammonium chloride and it was noted that using ferric chloride decreased copper extraction due to precipitation (Correia et al., 1993). Using highly alkaline sulphide solutions 300 g L À 1 Na2S + 53 g L À 1 NaOH and a particle size of > 84% < 5 mm, Balaz (Balaz,2000; Balaz et al., 1999, 2000) reported > 99% Sb and > 92% As extraction into solution from a calcined enargite/tennantite/tetrahedrite feedstock. However, this process would be very difficult to use in practice as there is little information on routes to safely recover and neutralise such solutions. Bacterial oxidation has been examined on several occasions (Acevedo et al., 1998; Curreli et...