Water management and affects on process design and materials of construction for copper heap leach projects

ABSTRACT

The management of the overall water balance on sites using the heap leach process for copper recovery is extremely complex as a result of the differing requirements for the various parts of the operations. It is usual to incorporate the control of ARD into the overall water management strategy, as this provides an ideal method of actively treating the acid produced. The ‘nil discharge’ site has even more complex requirements as the build up of salts can have detrimental effects on the materials of construction used for the plant items.

Major fluid loss throughout the operation is via evaporation from the heap leach irrigation. However ion ‘ loss’ is only in the residual moisture in the leached solids. Due to their coarse size this loss can be as low as 5% w/w. The resultant concentration of ionic species can be as much as six times the input concentration. This high ionic strength means that potentially detrimental species can be in sufficiently high concentration to cause accelerated corrosion of pumps and pipes. The factors affecting the concentration are discussed and methods of controlling the final ionic strength are explored. A number of recent plant designs have incorporated non-metallic materials to reduce the corrosion problem and these are discussed. 

The main features of a typical copper heap leach water balance are described with special reference to the interactions between the plant process systems. The overall water balance and ionic species build up can have an effect on the actual process design, particularly of the solvent extraction section. A number of alternative process selections are discussed and their use illustrated by reference to actual operations.

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