Gold: the leach–adsorb–elute–electrowin family

Gold is the path’s worked archetype, and its flowsheet composes cleanly from mechanisms taught earlier in the program. This page assembles those mechanisms into the circuit a gold plant actually runs — it names each one and what it contributes, and points back to the topic that teaches it, rather than teaching it again. Read it as the door a gold reader enters through.

The flowsheet in one line

Leach the gold into solution with cyanide, load it from the slurry onto activated carbon, strip it back off into a small, rich eluate, and electrowin it to a metal product: leach–adsorb–elute–electrowin. Four mechanism stages, each its own topic, arranged into one circuit.

What each stage is doing

The leach is alkaline cyanide tank leaching — the residence-time-and-sizing mechanism of topic 4.3 — holding a stirred slurry long enough to dissolve the gold as its cyanide complex. Adsorption is topic 6.4: carbon is moved counter-current to the pulp through a train of tanks, loading the dissolved gold onto the solid. Where the ore is preg-robbing, the carbon goes into the leach tanks themselves — that is carbon-in-leach (CIL); where adsorption follows a finished leach, it is carbon-in-pulp (CIP). Elution and regeneration is topic 6.5: the loaded carbon is stripped in a hot caustic-cyanide eluate, and the stripped carbon is reactivated in a rotary regeneration kiln before it recirculates. Electrowinning is topic 7.1: the rich eluate is plated to a gold-bearing cathode product that goes to the refining boundary (topic 7.5).

The defining numbers

Four quantities size the circuit, and three of them land on a live calculator. The adsorption train is sized by slurry residence time across its tanks — the same online-volume-over-flow calculation as a leach train — on the CIL tank residence-time calculator below. The carbon inventory and advance rate that set the loading the carbon reaches land on the carbon advance & loading calculator. The regeneration-kiln residence time is the rotary-kiln sizing shared with calcination, on the kiln residence-time calculator. And the cyanide make-up strength of the leach solution lands on the cyanide solution preparation calculator.

The Merrill-Crowe variant

Where the leach solution is clarified rather than carried as slurry — a high-grade or silver-rich ore — the adsorption route is replaced by Merrill-Crowe cementation. The clarified solution (the clarification-and-polishing front end, topic 5.6) is de-aerated and contacted with zinc dust, and the gold cements onto the zinc by metal displacement: the cementation mechanism of topic 6.3. Adsorption and cementation are two different ways to take the gold out of solution onto a solid; which one a plant uses turns on whether it runs a slurry or a clarified liquor.

Where it differs from the others

Gold sits apart from the SX-EW commodities in how it concentrates the value: it adsorbs onto a solid (carbon or resin) or cements onto zinc, where copper and the base metals shuttle through an organic by solvent extraction. Its lixiviant is alkaline cyanide, not an acid sulfate; its recovery is electrowinning from a very dilute, very pure eluate. The barren solution and tailings still carry cyanide, which the closure module (topic 8.2) treats as process chemistry — destruction and neutralisation — and which is out of scope here.