SULFIDIZATION-CYANIDATION OF JAROSITE SPECIES - APPLICABILITY TO THE GOSSAN ORES OF RIO-TINTO

During the cyanidation of Rio Tinto gossan ores, the extraction values obtained are 75-80% Au and only 40-45% Ag. A pretreatment with sulphi de solutions makes it possible to increase the silver extraction up to 75%. The silver is in the ore as simple halides, Hg/Ag sulpho-halides , sulphide and as argentojarosite in solid solution in jarosite-beudan tite phases. This paper reports the results of a sulphidization study of different jarosites and jarosite-beudantite species, showing that i t is possible to decompose the jarosite-beudantite phases with this tr eatment in various alkaline media. These results applied to the gossan ores show that, by the conventional cyanidation of Rio Tinto gossan o res, silver from halides, sulpho-halides acid sulphide is dissolved. T he pretreatment with sulphide solutions decomposes the jarosite-beudan tite phases, increasing the silver extraction up to 75%. The rest of t he silver remains in the residue enclosed in the goethite matrix.