Solution Application/Collection Systems

Leach solution is sent from the barren pond to the heap through a piping system. A pump system is usually required to give sufficient pressure for sprinkler application of the leachate. Few operations use ponding on the heaps as a means of solution application. Application can be done with sprinklers, wigglers, or similar equipment. The major requirement is even distribution of the leachate. Typical application rates are from 0.003 to 0.005 gpm/ft² (0.002 to 0.003 l/s/m²).

Application rates normally result in the partially saturated flow of leachate through the heap material. The corollary of the above application rates is that a minimum permeability of 10-4 cm/sec is required for the ore within the pad.

The chemical reaction in which the metals are dissolved by the cyanide requires oxygen. The unsaturated condition of the ore allows oxygen to be available for the dissolution process, while sprinkling also enhances oxygen entrainment in the leach solution.

Some applications techniques have been adopted in which introduction of leach solution is performed by buried pipe networks or beneath a heap cover. Such techniques can alleviate problems of freezing or high evaporation losses in the sprinkling process.

The flow of solution through the heap is essentially vertical from the surface to the base of the heap. Some methods of heap operation are designed to store solution within the heap itself. When this is the case, the solution simply progresses vertically to the level of the store solution.