Technical Report for the Maricunga Gold Mine - Kinross Gold

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Kinross Gold CorporationMaricunga Mine Technical ReportThe SART name is derived from an acronym describing the unit operations in the process,as follows:• Sulphidization• Acidification• Recycling of precipitate/s• Thickening of precipitate/sThe SART process flowsheet is shown schematically below in Figure 16-3.Figure 16-3: SART Plant FlowsheetSART Plant FlowsheetPreg Solution(Au, Cu)from HeapsLimeLimeScrubberNaSHLimeVent from Reactors,Settlers to Lime ScrubberforHCN, H 2SFlocculentFlocculentCu 2 SPrecipitationReactorNeutralizationReactorCu 2S Precipitate SettlerGypsum Precipitate SettlerSulphuricAcidCu 2S Precipitate RecycleGypsum RecycleCu 2S FilterGypsum FilterCu 2S DrierDry Cu 2SGypsumPrecipitatefor BaggingBagged Cu 2 SPrecipitateTo SmelterPrecipitatefor DisposalCa(CN) 2 Recycleto HeapsSART, as originally developed, involves adding chemical sulphide ions, such as sodiumhydro-sulphide (NaSH), to an acidified CN solution (pH 10 to pH 5 or below) to precipitatecopper, silver and zinc (if present) as metal sulphides and convert cyanide to HCN, underweakly acidic conditions. Other CN solubilized metals like Ni and Co would also beprecipitated. HCN is a very soluble gas, and remains in solution until the Cu 2 S, Ag 2 S or ZnS74
Kinross Gold CorporationMaricunga Mine Technical Reportis removed by thickening and filtration. The HCN solution is then neutralized with lime orcaustic soda, prior to recycling to leach.The overall chemical reactions applied to Cu, Zn and Ag cyanide complexes are:2Cu(CN) 32-+ S 2- + 6H + → Cu 2 S + 6HCN2Ag(CN) 2-Zn(CN) 42-+ S 2- + 4H + → Ag 2 S + 4HCN+ S 2- + 4H + → ZnS + 4HCNThe above sulphidization reactions occur rapidly in a first stage (primary) precipitationreactor from which sulphide precipitates are fed to a thickener. Recycle of thickened slurry ofsulphide precipitates back to the reactor is done until a suitable precipitate particle sizedevelops and sufficient bed depth in the thickener is achieved. A precipitate slurry of 10 –15% solids may then be drawn off the thickener underflow and washed, filtered and dried.The Cu 2 S precipitate (with Zn, Ni and other metal sulphides, if present) is then sold to asmelter as a valuable co-product.A second reactor is used to neutralize the aqueous HCN in the thickener overflow from pH 5back to pH 10. Lime or caustic soda may be used to produce CaCN 2 or NaCN for recycle tothe heap or tank leaching circuit. The neutralization reactions are:2HCN + Ca(OH) 2→ CaCN 2 + H 2 O2HCN + NaOH → NaCN + H 2 OAll three process units (2 reactors and a thickener) are sealed and have vents to a limescrubber system to capture any evolved HCN or H 2 S gases. By acidifying with sulphuric acidin the primary reactor, the SART process leads to formation of a gypsum type precipitate onneutralization of HCN in the neutralization reactor. This gypsum precipitate needs to beremoved from the neutralized CN solution prior to recovery of gold on carbon and recycle ofbarren CN solution to the leach circuit. To achieve this, a gypsum thickener is included in thecircuit with the option of recycling the gypsum thickener underflow to enhance precipitationrates and settling / consolidation in the thickener.The SART process may be applied to pregnant gold solutions prior to carbon adsorption oron barren solutions after carbon adsorption. For a heap leach operation the inherent leach75
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Technical Report for the Maricunga Gold Mine - Kinross Gold

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