Merrill-Crowe is a precious-metal recovery process that uses zinc dust to precipitate gold and silver out of cyanide-bearing leach solution. It is the preferred recovery method when the solution is silver-dominant or when gold + silver concentrations are too high for economic carbon adsorption.
The Four Steps
(1) Clarification — pre-clarifiers remove suspended solids from the pregnant leach solution. (2) Vacuum deaeration — dissolved oxygen is stripped to under 1 ppm in a packed tower (oxygen passivates zinc dust and kills recovery). (3) Zinc precipitation — zinc dust is metered into the deaerated solution; gold and silver plate onto the zinc particles. (4) Filtration — the zinc-gold-silver precipitate is captured on a filter press for downstream smelting.
Why It Beats ADR for Silver
Activated-carbon adsorption (used in ADR plants) is highly selective for gold but only modestly selective for silver. When ore is silver-dominant — many Mexican and Peruvian deposits — Merrill-Crowe is far more economic because zinc precipitates both metals with equal efficiency.
Pros and Cons
Pros: excellent silver recovery, lower operating cost when solution flow is high, no carbon regeneration needed. Cons: requires high-quality clarification and rigorous deaeration, more complex than carbon adsorption, larger reagent inventory.
The KCA Track Record
KCA has delivered Merrill-Crowe plants from 30 m³/h modular units (Aurex, Peru) to the 4,772 m³/h Hycroft circuit in Nevada and the recently commissioned 1,200 m³/h Camino Rojo Merrill-Crowe in Mexico — one of the largest in North America. Full technical detail on our Merrill-Crowe Plant Design page.
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