UBC Theses and Dissertations
Cupric ammoniacal thiosulfate leaching of natural acanthite ore in a continuous circuit Chao, Chih Wei
Cyanidation has been the conventional way to leach silver ore for many years. However, environmental concerns regarding the use and disposal of cyanide have increased public concern. Now, regulations have emerged that prevent or limit cyanide usage in many regions. Finding an alternative lixiviant for silver leaching is necessary to leach silver ores in these locations. Among the proposed alternative leaching agents, cupric-ammoniacal thiosulfate system is a very attractive solution. Although the research on cupric-ammoniacal thiosulfate leaching system has been conducted for many years, most of the experiments were performed in batch fashion. It is difficult to find scale-up leaching data or experiments. This thesis study aims to engineer a lab-scale continuous leaching system that uses cupric ammoniacal thiosulfate as the leaching agent. The goal is to mimic the industrial process and collect useful data for further research and application. The experiments started with a series of batch leaching tests to obtain the optimized leaching conditions for treatment of an ore sample containing acanthite received from Pan American Silver. Next, the optimized leaching conditions were applied to the continuous leaching tests. After leaching, two different types of recovery methods were studied to separate the silver from the pregnant leach solution. The two recovery methods are ion exchange and cementation. The tests results show that the leaching ability of cupric-ammoniacal thiosulfate system is good. The continuous leaching tests were run for 3 days with a 24-hour retention time in leaching and achieved an 86% silver leaching efficiency. Furthermore, the leached silver was easily recovered 100% by cementation. The ion exchange tests were not successful in demonstrating silver recovery from the leachate.
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