• GEOCOAT^®
• Process Overview
• Design Concept
• Pad and Ponds
• Support Rock
• Coating and Stacking
• Irrigation and Solution Management
• Aeration and Temperature Control
• Solution Treatment
• Heap Reclaim and Concentrate Separation
• Water Balance
• Inoculum
• GEOLEACH™

Solution Treatment

To maintain acidity and metals concentrations at target levels, a portion of the recirculating solution stream is continuously bled from the circuit and either neutralized or advanced to downstream recovery processes.

Concentrates in which pyrite constitutes the major sulfide mineral generate acid during biooxidation. Unless this acid is neutralized in situ by carbonates or other acid-consuming constituents in the concentrate or support rock, the acid concentration in the recirculating solution will increase as biooxidation proceeds. Replacing the solution bled to neutralization with fresh water allows the pH to be controlled to the desired value.

Concentrates containing arsenic, usually as arsenopyrite, generate soluble As(V) during biooxidation. Neutralization of the solution results in precipitation of arsenic as ferric arsenate. Solid residues from the neutralization of biooxidation solutions containing arsenic meet the requirements of the U.S. EPA's TCLP and SPLP tests for stability.

Neutralization is carried out in a series of four or more agitated tanks, using ground limestone and lime. Overall neutralization costs can be minimized by using limestone to raise the pH to approximately 5, and then adding a small quantity of lime to further raise the pH to 7-8. Retention time in the neutralization tanks is typically 4-6 hours.

In the GEOCOAT^® processing of base metal concentrates, the solution bleed stream is the feed to downstream metals recovery processes, such as solvent extraction and electrowinning. The high permeability of the GEOCOAT^® heap allows recirculation of solution to build up metals concentrations without fear of losses by retention in the heap.