The water balance of a heap leach pad may be detrimentally affected during the rainy season by excessive infiltration from heavy rains. Rain falling on the pad infiltrates and becomes part of the seepage from the base of the pad. Too much rain and you get too much dilution and a build up of excess water in the heap leach pad circuit.

One way to limit excess infiltration during the wet season is to put a temporary plastic cover over part or al of the pad. Such a cover sheds the water and precludes the water entering the heap leach pad circuit. A new paper by Breitenbach and Smith, both of Vector Engineering, describe the use of such covers which they colorfully call raincoat liners. They list these advantages of using raincoat liners:

  • Protect weak ore and agglomerates from degradation and fines migration due to the impact and seepage of excess rainfall
  • Reduced surplus water balance management
  • Less dilution of process solutions for improved metal recovery
  • Reduced reagent consumption in recirculated barren solutions
  • Reduced likelihood of accidental spills due to excess storm pond water accumulation.

The authors list projects where liners include HDPE, PVC, and LLDPE. Which means, I suppose that whatever you have on hand can be used. In theory, the following criteria may be formulated:

  • UV resistance for at least five years
  • Flexibility to facilitate placement, removal, and relocation
  • Puncture strength to resist damage by the rough surface of the heap leach material
  • Sufficient strength to deal with anchorage stresses and wind loadings
  • Some seam strength, although this is of lesser importance than it would be in a basal liner.

This is a fascinating idea. It appears to be practical. And it may be useful even in arid climates. The bottom line is cost. If it is cheaper to place such a cover than it is to deal with the wet season excess infiltration, this may work for you.