Selective arsenic-fixing roast of refractory gold concentrate
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I. INTRODUCTION
REFRACTORY gold ores, one of the major natural gold resources, are characterized by their complex mineralogy: they are finely disseminated in a massive pyrite and arsenopyrite host. This mineralogical nature makes processing of refractory gold ores less attractive, as conventional gold extraction technologies are ineffective, with a typical gold recovery ranging from 5 to 70 pct.[1] The host-mineral components such as pyrite, arsenopyrite, and stibnite in the refractory ore consume excessive cyanide and oxygen in conventional cyanide leaching, contributing further to the low gold-leaching efficiency. The depletion of pregnant solution by, for example, carbonaceous species presents another challenge, as these species adsorb aurocyanide complexes. Some sort of pretreatment of refractory ores needs to be considered to improve gold recovery to an economically acceptable level. In searching for the solutions to gold extraction from refractory ores, pretreatment of the ores by oxidative roast, autoclave oxidation, or bio-oxidation has been considered, and a certain degree of success has been achieved. Of these alternatives, oxidative roast remains the first choice in the refractory gold extraction practice.[1] A two-stage roast is commonly used in practice to pretreat arsenopyritic ores. The first stage, the so-called de-arsenic roast, is carried out at 450 8C to 550 8C in an oxygen-deficient atmosphere. The objective is to produce a low-arsenic calcine consisting mainly of pyrrhotite and magnetite as the matrix. During this stage, arsenic is released in the gaseous phase as As2O3. The second-stage roast is performed at 600 8C to 700 8C in an oxidative atmosphere to produce porous hematite.[2] Among the principal advantages of oxidative roasting are the high gold-extraction efficiency, lower capital and operating costs, and great process flexibility. Unfortunately, with this J. LIU, Ph.D. Student, R. CHI, Postdoctoral Fellow, and Z. XU, Professor, are with the Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB, Canada T6G 2G6. Z. ZENG, Engineer, and J. LIANG, Senior Engineer, are with Changsha Research Institute of Mining and Metallurgy, People’s Republic of China 410012. Manuscript submitted September 16, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS B
approach, the resultant fumes bearing As2O3 and SO2 have significant environmental consequences. It is clear that oxidative roast would be the choice for refractory gold ore processing if the accompanied generation of pollutants could be minimized. For this purpose, attempts have been made to search for a new pretreatment technique, aimed at arsenic and sulfur fixation during the roast of refractory gold ores. The key is to introduce some kinds of reactants that form stable compounds with arsenic and sulfur as they are produced during the roast. This concept was initially proposed by Barlett and Haung[3] and Haver and Wong[4] in the 1970s to treat copper sulfide concentrates. In the early 1990s, this approach was adopt
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