International journal of mining, reclamation and environment
Paginering:
Jaargang 10 (1996) nr. 4 pagina's 169-180
Jaar:
1996
Inhoud:
Cyanidation heap leaching is a prevalent low-cost method to extract gold from low-grade ores in the western United States. Relatively little is known about the geochemical processes which occur when a spent heap leach dump is rinsed to reduce the levels of potentially toxic constituents, however. Given that many heap leach dumps will be rinsed and reclaimed within the next decade, information about the changes that occur during rinsing will be useful since several cyanide-complexed metals could pose a threat to the environment. Chemical data from a gold mine in the western U.S. were collected from a state agency and statistically analyzed to evaluate changes in levels of metal cyanide-complexed species in a heap leach dump. The data were collected during the period of active operation of the dump as well as during subsequent rinsing. The following items are addressed during the analysis of the operation and rinsing of a selected heap leach dump: (I) flows through the dump, (2) fluctuations of cyanide concentrations, (3) changes in pH levels, and (4) changes in metal and anion concentrations, specifically: arsenic, selenium, thallium, mercury, nitrate, and nitrite. Analysis of the data from the selected heap leach dump indicated that destruction of residual cyanide did occur because of the SO2/O2 treatment. Use of regression analysis and time-series analyses indicated a positive correlation between concentrations of selenium and thallium during operation and rinsing. However, fluctuations in metal-complexed cyanide species with rinsing indicated that more research into the heap leach geochemistry and microbial chemistry of these species, including interactions with other minerals as impurities, is required to understand the changes in chemical equilibria that occur during the rinsing cycle
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