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Hybrid Vat Leaching

Hybrid Vat Leaching

The principle advantages of heap or vat leaching crushed ore are the low Capex and Opex requirements compared to conventional CIL or CIP processes. Once ore has been crushed to approximately <5mm, it is then either heaped on a pad or deposited in a vat for leaching. However, disadvantages such as low gold recovery and high reagent consumption caused by poor leach solution flow make the process inefficient and slow.

The root cause of flow constrictions is that the material being leached comprises both coarse and fine particles. Whilst solution flow through a coarse particle bed is normally unrestricted, fine particles (-600μm) cause blockages and “channelling”. If gold bearing particles are not exposed to cyanide solution, the gold recovery will be reduced and the project is likely to fail. The Hybrid Vat Leach process overcomes this problem by dividing the material into two size fractions:

Coarse = -5mm, +600μm
Fine = -600μm

Once separated, these two size fractions are processed separately. The coarse material, now unencumbered by fines, reports to a leach pad or vat for leaching. The fines report to a leach tank equipped with a Hyperjet high shear reactor followed by a standard CIP adsorption circuit. During the vat leach process, pregnant liquor is continuously drawn from an active vat to a pregnant leach solution tank and then pumped to the same adsorption circuit as the fines, meaning that the blinding issues are overcome and both coarse and fine particles have optimised leaching and adsorption processes.