British Columbia Mine Reclamation Symposium

Considerations in the reclamation of cyanide heap leach dumps Struhsacker, Debra W.; Smith, Adrian


Planning for the reclamation of spent ore dumps produced by cyanide heap leach processing should begin at an early stage during project feasibility studies and metallurgical testing. The key issues influencing the reclamation of cyanide heap leach dumps are site characteristics, the design of the heap leach facility, and the cyanide neutralization behavior of the ore. Water quality permit conditions and bonding provisions for heap leach facilities in most western states in the U. S. now specify residual cyanide levels for spent heaps. One way to address regulatory concerns regarding cyanide detoxification is to provide data from column cyanide neutralization tests performed on leached columns used for metallurgical testing. Heap leach project reclamation planning and closure requirements should consider the evidence that natural degradation of cyanide and cyanide attenuation by hydrogeochemical processes are capable of minimizing or eliminating short- and long-term potential water quality impacts from heap leach systems. As an overview of this topic, this paper will integrate the theoretical chemical data on cyanide with the observed geochemical behavior of cyanide in the decommissioned heap leach environment. The cyanide species that are likely to exist within an abandoned heap leach system will be identified, and the relative toxicity and potential environmental effect of these cyanide species will be discussed. These data will then be used to evaluate reclamation requirements for spent cyanided ores with respect to cyanide detoxification regulations, and recommendations will be made for obtaining cyanide neutralization data during initial project planning.

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