Tailings Storage Facility

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This is the Tailings Storage Facility (TSF) for the Agbaou gold mine and it was designed to be constructed in three phases with the initial phase being built up to provide enough capacity for around 2 years of ore feed while maintaining a supernatant pond capacity of 150,000m3 after approximately 1.4 years. The succeeding Phase 2 and Phase 3 provide the capacity for the remainder of the Life of mine when the ore feed is from bedrock. Because the process plant detox phase includes cyanide destruction, the TSF does not require and does not incorporate an HDPE liner. The TSF was designed by Knight Piésold (Pty) Ltd of Perth, Australia.

In order to recover carbon that escapes from the CIL Process the CIL tails slurry is screened, with oversize screen carbon emptied into the last CIL tank, and undersize screen is processed and fed to the first of 2 detox tanks that operate in a series. If needed one tank be online at a time bypassing the other. With a live volume of 500m³ the total residence time in the detox circuit is 2 hours.

In the detox circuit Sodium metabisulphite, copper sulphate and PSA (enriched) oxygen are added to the circuit to produce sulphur dioxide, copper catalyst, and oxygen. In the next phase the cyanide complexes in the slurry are oxidized to the less toxic cyanate (OCN⁻) according to the reaction: CN⁻WAD + SO₂ + O₂ + H₂O = OCN⁻ + H₂SO₄. To neutralise the sulphuric acid that was generated, a lime slurry is added to the detox circuit to maintain the pH between a range of 8 to 10. In the final phase detoxified slurry overflows the second detox tank into the final tails sump, then pumped to the TSF. Slurry pumped to the TSF is tested to ensure it is within the weak acid dissociated cyanide (“WAD”) cyanide set point of 50ppm.