Water Balance
Make-up water is required to replace losses by evaporation, and to compensate for water removed with the solution bleed stream and the oxidized concentrate thickener underflow. Inflows to a GEOLEACH™ system include water added with the ore, heap rinse water (if employed), and precipitation on pad and pond surfaces. Deficiencies in the water balance are made up by the addition of fresh water, either to the ILS pond or as rinse water.
The typical GEOLEACH™ solution application rate of 10L/m2/hr corresponds to 240mm of solution applied to each square meter of heap daily. Short-duration precipitation events are, therefore, comparable in intensity to routine solution application operations and no adverse effects on the system are anticipated from such events. During periods of prolonged heavy rainfall, however, it may be necessary to stop the irrigation to maintain the heat balance.
Depending on climatic conditions at the site, an emergency storm water pond may be required to handle runoff resulting from storm events. A water balance based on site-specific meteorological data will determine the surge capacity required.
In any case, the water balance issues involved are the same as those that are routinely addressed in the design of heap operations for cyanide leaching of gold ores or acid leaching of copper ores. The principles are well understood, and provided that adequate meteorological data is available for the site, a solution management plan can be developed to ensure a safe and environmentally acceptable operation.