Gold Heap and Pad.

Each heap leach is unique and the design of the heap and pad require the assimilation of a number of influencing factors. These include ore type, origin, metallurgy, leachibility, site topography, site geotechnical and geohydrological characteristics, and site climate. Three basic methods of heap and pad construction and operation are currently used, these being the reusable pa d, the permanent expanding heap, and the valley leach. These approaches very discussed later.

The heap and pad need to be designed to be stable structures which will contain both the solid and leachate. Each of the three types of heap/pad construction previously identified requires the consideration of different criteria in design and operation.

Ore placement on the heap can be performed by various methods, and is primarily dependant on the nature of the ore. Methods vary from end dumping to placement by front-end loaders, to conveyor stacking. The main criteria in selecting a heap construction method are to limit layering, compaction, and segregation of particles and to prevent damage to the liner during construction.

Frequently, few feasible choices for the heap location are available due to constraints such as haul distance, land status, or topography. The foundation for the heap must be capable of withstanding the loads applied by settling across the heap. Differential settlement may adversely affect the heap drainage and damage the liner and pad. In the case of valley heaps or sites with steeply sloping topography, the ability of the foundation materials and the foundation liners interface to resist sliding must be considered in the heap leach design.

Liners are needed principally for the purpose of containing the leach solutions within the facility, and although environmental regulations often require redundancy in design, liner should be chosen to meet this containment objective. Pad liners generally fail into four categories these being: synthetic membrane liners, natural or modified-natural liners, composite synthetic and natural liners, and double liners.