An evaluation of the physicochemical degradation of gold ion-exchange resins in hypochlorite solutions
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INTRODUCTION
T H E use of chlorination technology for the treatment of refractory and carbonaceous gold ores has received significant attention in recent years. High contents of naturany occurring organic carbon in gold ores (0.25 to 0.80 pct C), such as those found in Carlin trend deposits in Nevada, t~ lead to difficult and expensive gold recoveries in conventional cyanidation processes. I21 The interaction of the carbon with the gold is known as "pregrobbing" behavior and is caused by the activated nature of the carbon. [3-71 The use of oxidizing media has been shown to be beneficial in treating these ores. t2,8-'~ A strong oxidizing agent, typically chlorine gas or sodium hypochlorite, is employed to destroy the deleterious pregrobbing characteristics of the carbonaceous material by oxidizing it to an inert form. It is interesting to examine the potential of ion-exchange methods for the recovery of the aqueous oxidized gold species present as complex chloro-anions from these solutions. During the past decade, interest in using ion-exchange resins for the recovery of precious metals has expanded rapidly. I1'-171 Although some work on platinum-group metals has been reported, t~81 most research efforts have been directed at developing ion exchange for gold recovery. In addition to recovering gold from nonconventional hydrometallurgical processing liquors and electroplating wastes, this technology could provide an alternative to the use of activated carbon in gold cyanidation circuits. Ion-exchange processes may have the advantages of faster kinetics and greater specificity; closedloop regeneration of the active functional groups is possible, and scaleup is readily achieved. In a resin-in-pulp (RIP) or resin-in-leach (RIL) process, the ion-exchange resin and gold-containing ore or leach solution are slurried to provide adequate contact
KATHRYN C. SOLE and PEIHAO QI, Research Associates, and J. BRENT HISKEY, Professor of Materials Science and Engineering, are with the Copper Research Center, University of Arizona, Tucson, AZ 85712. Manuscript submitted April 17, 1992. METALLURGICAL TRANSACTIONS B
between the active sites on the resin and the auro ions. The mechanical integrity of the resin beads is therefore important. Since the slurry constituents are later separated by filtration, it is also necessary to ensure that the particle size of the beads is not significantly abraded. Also of concern is the resistance of both the polymer matrix and the active functional groups to oxidation and decomposition. Fleming 1~71has recently identified three potential sources of resin loss in an RIP plant: (1) abrasion of the resin beads by physical contact with fine ore particles in the pulp; (2) fracturing of the beads as a result of impact with moving mechanical parts during mixing, pumping, or screening of the resin and pulp; and (3) shattering of the beads as a result of osmotic shock caused by the cyclical swelling of the beads in an alkaline environment (loading) and contracting in an acidic environment (elution and r
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