700 t/d Gold CIL Plant — Tanzania

Background

This profile represents a typical 700 t/d gold operation in Tanzania, a core market within Xinhai’s East African work. The ore was largely free-milling but carried a mild carbonaceous, preg-robbing tendency, meaning some dissolved gold could re-adsorb onto the ore during leaching if not captured promptly. The owner needed a robust circuit that would protect recovery against that risk at a moderate throughput.

Solution

Diagnostic leach testwork measured the preg-robbing tendency and fixed the grind and reagent regime. The selected flowsheet used carbon-in-leach so that activated carbon is present throughout leaching, keeping dissolved gold on carbon rather than letting it re-adsorb onto carbonaceous matter. After crushing and grinding in a closed circuit with a wet ball mill to roughly 75-80% passing 200 mesh, a gold centrifugal concentrator recovers coarse free gold. The pulp then enters a CIL train of leaching agitation tanks, and loaded carbon is stripped in a gold elution and electrowinning system.

Delivered as EPC+M+O, the project covered ore testing, in-house manufacturing, construction, commissioning and operator training. Choosing CIL over CIP was the key metallurgical decision: on a preg-robbing ore, keeping carbon in contact through the leach is the most reliable defense against soluble gold losses. The circuit ran a higher carbon concentration in the lead tanks where dissolution is fastest, and inter-stage screens moved loaded carbon counter-current toward the feed. Residence time was set with a margin over the diagnostic leach result so dissolved gold is adsorbed before the carbonaceous matter can re-capture it.

Outcome

For a mildly preg-robbing free-milling ore, a gravity-plus-CIL circuit typically achieves around 89-93% gold recovery once leach residence time and carbon concentration are tuned to the ore. Early gravity recovery and the CIL configuration together limited soluble losses during ramp-up. These figures are representative for this ore type rather than guarantees; actual recovery depends on the degree of preg-robbing, grind and residence time.

Operator training during ramp-up centered on carbon activity and cyanide dosing, the controls that keep a CIL circuit ahead of preg-robbing losses. See the broader gold processing solution for the full flowsheet logic. To diagnose preg-robbing on your ore and size a plant, contact us for an ore test.