Silver Processing Solution

Silver is rarely a simple ore. It occurs as sulphides such as argentite, as native silver, locked in galena, and very often alongside gold. That variety means there is no single silver flowsheet; the right route, flotation, cyanidation, or a combination, depends on how the silver is mineralized and how much of it there is. Two design decisions dominate: whether to concentrate by flotation before leaching, and how to recover silver from the leach solution, Merrill-Crowe or carbon-in-leach.

Flotation, cyanidation, or both

Where silver sits in sulphides or with galena, froth flotation produces a silver-rich concentrate that can be sold or leached intensively, and in lead-zinc ores the silver naturally follows the lead concentrate. Where silver is free-milling and amenable, direct cyanide leaching dissolves it, much as for gold. Many ores justify both: flotation to make a high-grade concentrate, then cyanidation of that concentrate at high reagent strength. The key difference from gold is kinetics, silver minerals generally dissolve more slowly than native gold, so silver cyanidation runs at longer residence times and higher cyanide concentrations, which the leach circuit must be sized for.

The recommended flowsheet

Crushing, grinding and classification

Ore is crushed with a jaw crusher and cone crusher, then ground in a wet ball mill closed with a hydrocyclone cluster, typically to 70-85% passing 75 micron. Fine-grained silver minerals usually need a finer grind than gold to liberate and to expose surfaces for leaching.

Concentration and leaching

For sulphide and silver-gold ores, a rougher-cleaner circuit of mechanical flotation cells, part of the broader flotation equipment range, produces a silver concentrate. Free-milling silver is leached in cyanide agitation tanks sized for the slower silver dissolution kinetics. The complete gold and silver extraction range covers leach and recovery duties.

Recovery: Merrill-Crowe vs CIL

This is the defining choice for silver. Merrill-Crowe precipitates silver (and gold) from a clarified, deaerated pregnant solution with zinc dust, and it is the preferred route for high-silver ores because activated carbon has limited loading capacity and is slow to strip the large mass of silver involved. For lower-silver or silver-gold ores, a carbon-in-pulp or CIL plant with a elution and electrowinning system is simpler and avoids solid-liquid separation. As a rule of thumb, the higher the silver tenor, the more Merrill-Crowe wins. For the leaching trade-offs behind these routes, see our guide to CIL vs CIP vs heap leach.

Dewatering and refining

Precipitate or loaded-carbon product is smelted to doré; tailings are detoxified, thickened on a thickener and stored with process water recycled.

Design choices that drive results

• Mineralogy: sulphide vs free vs refractory silver decides flotation-versus-leach and whether pre-treatment is needed.
• Silver tenor: the main driver of Merrill-Crowe vs CIL; high silver favors zinc precipitation.
• Gold association: silver-gold ores often suit a combined circuit; both metals report to doré.
• Cyanide and residence: sized higher and longer than for gold because silver dissolves more slowly.

Because silver mineralogy varies so widely, the flotation-versus-leach split and the recovery route must be set from testwork, not assumed. Xinhai runs the ore test, designs the flowsheet and delivers the complete processing plant under an EPC+M+O contract. To choose between flotation, cyanidation, Merrill-Crowe and CIL for your ore, contact us for an ore test.