I think I understand your question now.
Leach pads designed now are closed circuits to the ground. Unless some natural disasters occur that breach the pad lining or cause an overflow, they will not pollute the ground environment around them, although I imagine that animals that could gain access to the pads could be killed. I'm thinking mainly of birds and flying things. There is zero tolerance now for polluting the environment in most countries, and most of the big boys would follow the guidelines of the most environmentally demanding countries, in all the countries they operate in regardless of the regulations.
As you know, post recovery fluids are recovered and recycled for subsequent use which would usually decrease costs in the long run. Whether they do this completely on site, or send some components of the fluids offsite would depend on the complexity of the solutions, and the relative costs of transport and treatment. I am unsure of all the processes that would be needed, given each leach pad may have a different composition of final leachate. The simplest cheapest process is probably differential precipitation of some kind, followed by some means of separation of the precipitate.
Water is generally a scarce commodity around many mines so they would seek to remove all particulates and ions through screening, filtering and/or settling steps, and partial selective precipitation of the dissolved ions by perhaps changing the ph in steps, or adding components to the water to promote differential precipation, or by evaporation of water to cause precipitation, with settling/filtering/centrifuging/skiming steps to remove the precipitates. Ion exchange columns may be used at some stage.
The steps will always be,... do something to the solution to try and precipitate some component(s), then separate the precipitate the cheapest way possible, and do this over and over until almost everything is out of the solution. Then add more cyanide etc., to the recycled solution and send it back to the leach pad for another cycle.
The resulting solids may be shipped for processing offsite, or may end up in the tailings pond to be covered in water and allowed to breakdown over time depending on their environmental toxicity. Tailings ponds and their effluants into ground and surface waters are monitored by the company for decades after the minesite is abandoned. In most countries now I believe the sites must be restored to their original state in terms of above ground, and groundwater considerations. Until this is proven, the site remains the company's responsibility, as does any environmental damage. |
