Heap leaching converts the desired minerals into a chemical compound, which, at the bottom of the leach pile
, drains into perforated pipe and is carried by gravity to the final extraction process, usually via a pregnant solution pond.
These have low ground pressures (around 6-15 lb/[in.sup.2]) allowing them to 'walk' on either the drainage layer or the leach pile
without compacting it.
Leach pile designs must take into account a lack of surface area that can create long hauls if dumps are shallow.
Morenci is also developing a leach pile model in Medsystem so that dumping coordinates taken from the trucks and material grades taken from the loading point will allow better contouring of the piles.
The negative aspect of recycling pregnant solution is an increase in gold inventory in the leach pile because the entrapped solution is of a higher grade.
The use of the pre-clarifier is particularly useful at the startup of a new operation or when leaching a new area on the leach pile when the solids content of the pregnant solution is high.
"Another negative you will hear concerning the Merrill-Crowe process is that you will need to install a carbon adsorption plant anyhow at the end of the mine life to rinse and detox the leach pile. This reasoning notes that Merrill-Crowe plants do not have the ability to handle low-grade gold solutions arising during rinsing when the grades begin to drop, whereas carbon adsorption plants can readily handle such solutions.
"When designing leach piles for wet climates, it is mandatory to dig ditches around the piles to prevent rainwater runoff into the leaching area.
The crawler tracks create low ground pressures (typically 6-15 lb/[in..sup.2]) that allow them to walk on either the drainage layer or the leach pile
, without compacting it.
Barren solution from the Pampa Larga processing plant, near the Carachugo leach pad, is pumped to the Maqui Maqui leach pile
. The pregnant solution is then pumped to the Carachugo leach pile
Run of Mine (ROM) material or dump leach piles
segregate layers of coarse and fine textured material during material placement.
In the case of the leach piles
, the geotextile membranes at their bases collect the enriched solution and stop its infiltration into the subsoil.