Adsorption of gold on activated carbon in bromide solutions
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I.
INTRODUCTION
B R O M I N E has an excellent potential to become an important reagent in gold metallurgy. Although it would not replace cyanide generally, bromine has its place in several niche applications. It could outperform cyanide in several important process areas: kinetics, toxicity, simplicity, and operating costs, tl-71 The product of gold dissolution with bromine is gold bromide, AuBr4-: Au + Br2 + 2Br- = AuBr~-
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If the leach solutions are separated from the leach residues by filtration, then the recovery of gold from the gold bromide leach solutions is straightforward and can be achieved readily by many different conventional methods: (1) direct electrowinning or electrowinning after concentration by solvent extraction and ion exchange, (2) cementation, and (3) chemical precipitation (ferrous ion, oxalic acid, sulfur dioxide, etc.). However, filtration can be a difficult and expensive step to include in a flowsheet. Instead, direct recovery of gold from the pulp is preferable. Activated carbon has demonstrated its applicability for direct recovery of gold from cyanide solutions. Activated carbon properties warrant its application to gold recovery from the gold bromide solutions too. With respect to the application of bromine in the hydrometallurgy of gold, most of the research has been done on the characterization of ores according to the gold leaching characteristics. Much less work has been done on gold recovery from gold bromide solutions. There are only a few studies published in this area. Read and BATRIC PESIC, Professor, and VICTOR C. STORHOK, Research Assistant, are with the College of Mines, University of Idaho, Moscow, ID 83843. Manuscript submitted March 25, 1992. METALLURGICAL TRANSACTIONS B
Mensah-Biney t8J evaluated several adsorbents for gold bromide. Several ion exchange resins (PAZ-1, PAZ-4, DOWEX* 11, and Arnborane 345) and an activated car* D O W E X is a trademark of Dow Chemical USA, Midland, MI.
bon were examined by Reid et al. t91 Recently, Dadgar and Sanders I~~ also evaluated several weak-base and strong-base ion exchange resins for gold recovery from bromide solutions. The lack of information about the gold bromide adsorption on activated carbon and the importance of activated carbon for direct recovery of gold from the leaching pulp prompted this research. II.
EXPERIMENTAL METHODS
Gold bromide stock solution, 1000 mg/1, was prepared by dissolving 0.1 gram of pure gold powder in a 0. l-liter solution containing 1 ml Br2 and 5 ml HBr. The stock solution was used to prepare gold bromide solutions for carbon adsorption studies. PICA-type activated carbon was used9 All other chemicals were of reagent grade. An experiment was initiated by the addition of a known amount of carbon in an experimental gold bromide solution at fixed temperature, pH, and volume. Experimental standard conditions were: T -- 25 ~ pH = 1 or pH = 8, carbon = 0.1 g, volume = 100 ml, and Au concentration = 5 mg/l. A water bath was used to maintain constant temperature. The kinetic experiments were per
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