Effect of hydrogen peroxide and lead nitrate in the cyanidation leaching of gold ore sample

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Date
2016-03-01
Authors
Ong Pek Ling
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The Au ore sample used was obtained from a local gold mine in Malaysia. In the cyanidation, the ease of Au extraction would depend on the nature of the ore. Hence, ore characterization via mineralogical studies plays a vital stage prior to Au extraction. The presence of Fe, As, and S were detected and the finely disseminated Au particle with the grain size of about 10.0 μm, was found to be interlocked in aluminosilicate. Au (bulk leachable extractable Au) present from the free milling and refractory ore was determined by cyanidation followed by fire assay respectively. About 1.9368 g/t Au was extracted. The Au ore samples were not amenable by conventional cyanidation due to the detrimental effects caused by the sulphide minerals. Therefore, H2O2 was used as a source of O2 and Pb(NO3)2 was added to stabilize the Cu and Fe from passivating the Au surface. Preliminary experiments of cyanidation were conducted at pH 11 with 33.3% solid before the optimization studies using response surface methodology–central composite design. The vicinity of the optimum condition was at 467.3 ppm NaCN, 94.96 ppm Pb(NO3)2 and 0.01M H2O2, with 1.7231 g/t (88.97%) Au extracted after using path of steepest ascent. Conventional cyanidation only able to extract 62.02% of Au, which indicates that Pb(NO3)2 and H2O2 assisted in the Au cyanide dissolution. From Van’t Hoff differential method, the reaction order was found to be of second order with the rate constant of 0.0501/hour. The auro complex formed from the cyanidation reaction is dependent on the concentration of cyanide and dissolved oxygen produced by H2O2.
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