Simultaneous Removal of S and As from a Refractory Gold Ore in a Single Stage O 2 -Enriched Roasting Process
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I.
INTRODUCTION
WITH the exhaustion of amenable gold ores, refractory gold ores have become an important source of gold production. Extraction of gold from its refractory ores is difficult. The challenges lie in three broad areas. First, the gold is dispersed as micro-fine particles in the associated minerals or occurs in solid solution in various sulfide minerals. Ultra-fine grinding which consumes much energy is required to expose them for extraction.[1,2] Second, the associated minerals such as sulfides of pyrite, arsenopyrite and stibnite contain impurity elements of S, As and Sb that consume extra lixiviant such as cyanide and oxygen, and react to form insoluble by-products on the surface of gold particles during leaching, limiting the recovery of gold.[3–6] Third, the presence of carbonaceous or clay minerals also hinders gold leaching because of the preg-robbing effect on leached gold.[7] Pre-treatment of ores to remove the impurities mentioned above before leaching is a necessary step in the extraction of gold from refractory gold ores. Oxidative roasting, pressure oxidation, chemical oxidation and biological oxidation are currently the four commonly
XIAOLIANG LIU, QIAN LI, YAN ZHANG, TAO JIANG, YONGBIN YANG, and BIN XU are with the School of Minerals Processing and Bioengineering, Central South University, Changsha, Hunan 410083, P.R. China. Contact e-mail: csuliqian208018@ csu.edu.cn YINGHE HE is with the College of Science and Engineering, James Cook University, Townsville, Queensland 4811, Australia. Contact e-mail: [email protected] Manuscript submitted December 10, 2018. Article published online April 29, 2019. 1588—VOLUME 50B, AUGUST 2019
adopted pre-treatment methods with oxidative roasting being the most widely utilized method owing to its maturity and high recovery rate.[8–10] Due to the conflicting requirements for the removal of As and S, however, the roasting is commonly carried out in two stages. Still, there are issues with two-stage roasting including difficulties in the co-ordination of temperatures between the stages that could cause secondary encapsulation of gold particles and, more importantly, long roasting time, which significantly increases the production costs.[11–13] Compared to the conventional air roasting, oxygen-enriched roasting is found to notably improve the gold extraction from its refractory ores.[14,15] Wang et al.[15] roasted a carbonaceous sulfide gold ore in an oxygen-enriched (75 pct, v/v) atmosphere and found that the removal rates of S and C were significantly enhanced. Even when the roasting temperature was lowered by 100 C and roasting time shortened by 1 hour, gold recovery increased by 2.16 pct. However, there is also literature that suggested that a high oxygen concentration was disadvantageous to the removal of As from As-bearing gold ores.[12] Gold concentrates produced from floatation often contain S, As, C and Sb. Extraction of gold from these concentrates proved to be extremely difficult. Previous research work from our group[16,17] showed that, without the removal
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