Original Research Paper Sulphidic refractory gold ore pre-treatment by selective and bulk flotation methods Rezgar Badri, Piroz Zamankhan ⇑ Faculty of Industrial, Mechanical Engineering and Computer Sciences, University of Iceland, Hjardarhagi 2-6, IS 107 Reykjavik, Iceland article info Article history: Received 31 July 2012 Received in revised form 30 September 2012 Accepted 3 October 2012 Available online 7 November 2012 Keywords: Refractory gold ore Pre-treating methods Selective flotation Bulk flotation Toxic chemical elements abstract In sulphidic refractory gold ores, fine gold particles may be highly disseminated and locked up in sulphide minerals such as pyrite and arsenopyrite. Hence, pre-treating processes are necessary to extract gold for further processing methods like cyanidation. In this paper, the selective and bulk flotation methods are considered as primary sulphidic refractory gold ore pre-treating options. The results show that it is impractical to remove arsenic (As) and antimony (Sb) from downstream processes by using selective flotation. It was observed that 22% of total Sb and 31.1% of As remained in the final tailings. In this case, 24% of gold was recovered in the initial stage of flotation. On the contrary, in the bulk method of flotation, which was aimed at maximizing the gold (Au) recovery, the maximum Au recovery of 90.6% obtained after 60 min of flotation at the grind size with d 80 of 146 lm. The bulk flotation method as a pre-treating method resulted in the concentrate with less toxic chemical elements such as As and Sb. Ó 2012 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved. 1. Introduction In sulphidic refractory gold ores, fine gold particles may be highly disseminated and locked up in sulphide minerals such as pyrite and arsenopyrite [1]. All largely unoxidised ores exhibit very low gold recoveries (typically <20%) by direct cyanidation. This suggests that the primary ore, as a whole, is highly refractory in nature and will therefore have to be processed using an appropri- ate refractory method. Often, the gold bearing ores are refractory due to the gold grains and concentration by flotation is necessary, either followed by roasting, bacterial leaching, or pressure leaching in a way that the gold is liberated prior to cyanidation [2]. Two basic initial approaches are available: either treating the whole ore or processing some form of concentrate with a high proportion of the recovered gold. A moderately low grade of the bulk ore and the additional processing costs involved in whole ore treatment processes are most certainly not economically viable and therefore not being considered. A significant proportion of the sulphidic refractory gold appears to be hosted by the arsenical pyrite, arsenopyrite and stibnite components of the ore. These minerals are amenable to flotation recovery. Significant amounts of essentially barren porphyroblastic pyrite which consumes oxygen and cyanide [2] are also present and will occur with any arsenical pyrite and arsenopyrite in the flo- tation concentrates. The abundance of this barren pyrite will highly dilute the refractory gold-bearing sulphides which in turn lowers the grade of the final concentrate. The grade of the gold and the nature of this concentrate are important because they will deter- mine the rate to which the concentrate can be processed by any particular route. In fact, the value of the contained gold and the cost of its recovery are important factors. In general, the recovery of refractory gold follows the same trend as the sulphide minerals. In this case, the gold is covered by pyrite, pyrrhotite and arsenopy- rite [3]. A number of papers and several books have been published on the mineralogy of gold in ores [4]. A potential problem is also afforded by the very fine-grained nature of some of the arsenical pyrite and arsenopyrite which are intimately intergrown with sili- cate gangue minerals (see Fig. 1). Adequate recovery of these fine- grained components might be difficult to achieve, even if the fine grain size is relatively fine (e.g. d 80 = 38 lm). In contrast, the arsen- ical pyrite is present as rims and overgrowths on porphyroblastic and granular pyrite. This indicates that its recovery would require the recovery of its host phases. The overall recovery of the refractory gold-bearing sulphides might therefore be reasonable. However, this needs to be confirmed by appropriate metallurgical testwork. Orpiment (As 2 S 3 ) and realgar (AsS) are both naturally hydro- phobic and will float easily. These will thereby contaminate any sulphide concentrate with excessive amounts of arsenic. A high proportion of these minerals are, however, present in the form of relatively coarse grained vein fillings. A high degree of liberation will be attained even at a relatively coarse grind size. It is also believed that these minerals don’t host significant amounts of refractory gold. By reducing concentrate dilution and potential high arsenic content, it is possible to scalp a high proportion of these minerals in a pre-flotation stage. Disposal of any arsenic-rich product of this nature might, however, cause significant problems. 0921-8831/$ - see front matter Ó 2012 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved. http://dx.doi.org/10.1016/j.apt.2012.10.002 ⇑ Corresponding author. Tel.: +354 525 5310. E-mail address: piroz@hi.is (P. Zamankhan). 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