Mining Latin America / Minería Latinoamericana pp 423-449 | Cite as
Investigation of silver extraction from a silver-sulphur flotation concentrate from the electrolytic zinc plant of Companhia Paraibuna de Metais, Juiz de Fora, Brazil
Abstract
A silver-sulphur flotation concentrate produced from the hot acid leach residue in the electrolytic zinc plant of Companhia Paraibuna de Metais was investigated for hydro-metallurgical silver extraction. This concentrate assayed 8320 g/t Ag, 20.6% Pb, and 43.7% S. It consisted mainly of lead sulphate and elemental sulphur with numerous minor components. The form of the silver was not precisely established and several forms appeared to be present.
Cyanidation of the concentrate for 48 h extracted only 42% of the silver with high cyanide and lime consumptions. A thiourea leach extracted only 24% of the silver, partly because silver re-precipitation occurred. It was evident that some form of pretreatment was needed to make the silver amenable to leaching.
Pressure oxidation with sulphuric acid at 200°C dissolved 56% of the silver in 4 h provided an initial acid strength of 90 g/L was used. Pressure oxidation with 190 g/L nitric acid at 125°C for 1 h dissolved 58% of the silver. It was found that the temperature needed to be above the melting point of sulphur (118°C) to achieve these extractions.
Acid brine leaching at 125°C, using 300 g/L NaCl, extracted over 98% of the silver in 1 h. Operation below the melting point of sulphur gave much lower extractions.
By conditioning with a solution containing 5–30 g/L NaCl and 36 g/L H2SO4, less than 1% of the silver was dissolved, as expected, but cyanidation of the resultant solid product extracted about 93% of the silver present However, cyanide and lime consumptions were high, even when the pellets of elemental sulphur formed during conditioning were first removed.
Results of the work indicate that acid brine leaching or brine conditioning followed by cyanidation are the preferred options for extraction of silver from the flotation concentrate but optimisation studies are required.
Keywords
Acid pressure leach brine conditioning brine leaching Companhia Paraibuna de Metais cyanidation electrolytic zinc plant concentrate silver extraction silver-sulphur flotation concentration thiourea leachingPreview
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