Gold CIL: Leach, Adsorb, Elute, Electrowin — Where the Gold Goes Missing

Carbon-in-leach (CIL) combines leaching and adsorption in the same tanks, which protects dissolved gold from being re-adsorbed by carbonaceous ore. The flowsheet is well established, and most recovery losses come from a small number of predictable places.

Route

Step	Equipment	Key parameter
1. Grinding	Ball mill, cyclone	P80 75 µm for liberation
2. Pre-aeration / leach	Agitated tanks, air sparging	pH 10.5–11, DO > 6 mg/L, CN 200–500 mg/L
3. CIL adsorption	6–8 tanks with carbon	Carbon 10–25 g/L, counter-current movement
4. Elution	Column, hot caustic	120–140 °C, 1–3% NaOH, 3–5 bed volumes
5. Electrowinning	EW cell, steel wool cathodes	3–5 V per cell, 60–80 °C
6. Smelting	Furnace	Flux recipe for doré

Where gold is lost

Preg-robbing. Carbonaceous ore adsorbs gold from solution before carbon does. Test for it; the answer is usually a pre-oxidation step or a different flowsheet entirely.

Carbon fouling. Oils, flotation reagents and scale block carbon pores. A carbon regeneration kiln is not optional in a plant handling flotation concentrate.

Fine carbon. Carbon breaks down and reports to tailings with gold on it. Screen the carbon and recover fines; it is one of the cheapest wins available.

Short-circuiting in tanks. Poor interstage screening lets pulp bypass contact. Check screen condition and tank baffling.

Pilot scale

A 50–200 L CIL train running several cycles gives you leach kinetics, carbon loading and elution behaviour on your actual ore. Bottle-roll tests give kinetics; they do not give you the adsorption profile that decides tank count.

Send the head grade, ore mineralogy and any preg-robbing test result, and we will size the leach and CIL train.