REFRAKTER KARAKTERLİ ALTIN CEVHERLERİNİN DEĞERLENDİRİLMESİ

Abstract

Cyanidation of the gold ores is the most commonly used gold extraction process since19th century. Although cyanidation can economically be applied for low grade and fine sized ores, it does not give good results for refractory ores. Encapsulated fine gold particles in refractory gold ores consume high cyanide and/or oxygen during dissolution and also cause passivation on the gold surfaces. Gold ores which include high grade sulphide (>%2) and carbonaceous constituents and fine gold encapsulating in the mineral structure can be called as “refractory”. These ores require alternative processing techniques and/or pre-oxidation treatments. One of these pre-treatment methods is roasting aimed at decomposing refractory sulphide and carbonaceous constituents at high temperatures in oxygen medium to produce a porous iron oxide calcine and thus prepare the material for suitable application of cyanidation. In this study, a composite sample with high sulphide and carbon contents and containing dolomite was subjected to direct cyanidation. 2n experimental design was used in the direct cyanidation tests of 8 samples and the effects of cyanide concentration (500-1000 ppm), particle size (38-150 µm) and reaction time (48-96 hour) were examined. The results showed that gold recoveries differed between % 42.96-63.01 and reaction time which increased gold recovery from % 45.33 to %58.79 was found to be the most effective parameter. Considering the literature findings which impose that ultra-fine grinding effects gold recovery significantly, a series of 4 cyanidation tests were conducted. Although fine sizing (20-38 µm) and longer reaction times (48-196 hour), the results obtained were not in acceptable levels. Gold recoveries changed between % 44.10-81.88, lime consumption and cyanide consumptions increased to 5.01 kg/ton and 2.39 kg/ton, respectively. Because of low gold recoveries and high chemical consumptions, composite sample was roasted to decompose the dolomite structure verified by XRD analysis. Roasting was performed at 800°C for 1 hour considering the TG/DTA analysis result. After roasting, cyanidation tests were repeated and it was observed that gold recoveries were reached to % 92.51-94.09. Since CaO and MgO formed during roasting were enough to create the required alkalinity for cyanidation, no additional lime was required and cyanide consumption was decreased to 0.98 kg/ton. Although reasonable gold recoveries and chemical consumptions were figured out, it was suggested that the test program could further be improved for coarser particle sizes and shorter reaction times.