Characterization of secondary arsenic-bearing precipitates formed in the bioleaching of enargite by Acidithiobacillus ferrooxidans K. Sasaki a, ⁎, K. Takatsugi a , K. Kaneko b , N. Kozai c , T. Ohnuki c , O.H. Tuovinen d,e , T. Hirajima a a Department of Earth Resources Engineering, Kyushu University, Fukuoka 819-0395, Japan b Department of Materials Science and Engineering, Kyushu University, Fukuoka 819-0395, Japan c Research Group of Heavy Elements Biogeochemistry, Japan Atomic Energy Agency, Tokai 319-1195, Japan d Department of Microbiology, Ohio State University, Columbus, OH 43210, USA e Department of Chemistry and Bioengineering, Tampere University of Technology, FI-33101 Tampere, Finland abstract article info Available online 25 June 2010 Keywords: Acidithiobacillus ferrooxidans Copper leaching Enargite bioleaching Ferric arsenate Jarosites The purpose of this study was to characterize secondary minerals that were formed in the bioleaching of enargite (Cu 3 AsS 4 ) by Acidithiobacillus ferrooxidans. Two parallel cultures were used: one was adapted to arsenic in the growth medium and the other was wild-type. The progress of the solubilization of As in A. ferrooxidans cultures was stepwise and different from that observed in the non-adapted culture. In contrast, the bioleaching of Cu and Fe from enargite was not affected by prior adaptation of the culture. Minor presence of jarosite was observed by X-ray diffraction (XRD) in solid residues after the bioleaching, and no other peaks of secondary crystalline minerals were detected. The relative intensities of As 3d and Fe 2p to Cu 2p in X-ray photoelectron spectroscopy (XPS) for the solid residues were at maximum at 46 days after the bioleaching with As-adapted A. ferrooxidans. The results from the examination of solid residues with XPS, transmission electron microscopy with energy-dispersive microprobe (TEM-EDS) and XRD after 46 days of contact with As-adapted A. ferrooxidans showed the presence of metastable, amorphous ferric arsenate as an intermediate on the surface of enargite and minor amounts of jarosite. The amorphous ferric arsenate phase did not appear to have an adverse effect of the dissolution of Cu from enargite. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved. 1. Introduction Enargite (Cu 3 AsS 4 ) is often associated especially with epithermal high sulphidation deposits (Arribas, 1995) and porphyry copper ores (Lattanzi et al., 2008). Enargite is mined as a representative arsenic- bearing copper mineral with primary Cu-sulfide ores. Arsenic-bearing Cu-sulfides are also valuable copper resources, although the arsenic in the mineral makes it environmentally problematic because of toxicity and environmental emissions associated with smelting (Dutré & Vandecasteele, 1995). Although the separation of enargite from non-arsenic Cu-sulfides is required for further processing, conventional flotation techniques have not been successful because of the similarity in physicochemical characteristics of Cu-sulfides and Cu,As-sulfides. Some chemical pretreatments have been tested in efforts to modify physicochemical properties of Cu,As-sulfides and Cu-sulfides (Fornasiero et al., 2001). The oxidation rate of enargite is slower as compared to Cu-sulfides such as tennantite (Cu 12 AsS 13 ) and chalcopyrite (Sasaki et al., 2010). It suggests that bioleaching may be one of the potential approaches to recover copper from enargite. However, the mechanisms of bioleach- ing and passivation in the bioleaching of enargite have yet to be well understood, perhaps because of only small quantities of research- grade enargite available (Lattanzi et al., 2008; Corkhill et al., 2008). The purpose of this study is to characterize the bioleaching of enargite. For this study, A. ferrooxidans was adapted to arsenic in the growth medium. The effect of arsenic adaptation of A. ferrooxidans on the formation of secondary minerals and the dissolution of Cu and As from enargite was characterized. 2. Materials and methods A sample of enargite-containing Cu-ore was originally obtained from the Jinguashi mines, Taipei, Taiwan. The sample was fractured to particles several mm in diameter and based on visual observation enargite grains were picked manually. Only enargite was detected by X-ray diffraction (XRD) in the final sample. The final sample contained (per g) 422 mg Cu, 171 mg As, 288 mg S, 35.4 mg Si, 3.91 mg Sb, 4.59 mg Fe, 13.7 mg Al, 34.2 mg Na, 4.62 mg K, 1.34 mg P, and 1.25 mg Zn, corresponding to a molar ratio of 2.91 Cu: 1.00 As: 3.94 S. The purity was estimated as 88.1% on the basis of the Cu-content. The Hydrometallurgy 104 (2010) 424–431 ⁎ Corresponding author. E-mail address: keikos@mine.kyushu-u.ac.jp (K. Sasaki). 0304-386X/$ – see front matter. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.hydromet.2009.12.012 Contents lists available at ScienceDirect Hydrometallurgy journal homepage: www.elsevier.com/locate/hydromet