| Gold is a strategic metal with important commercial value and financial properties.China is the world's largest gold producer and consumer.Thus,it is an important strategic significance to increase gold reserves for China.After years of mining,high-grade gold ores are gradually exhausted in China,and refractory gold ores have become the main resources of China's gold production.And the refractory high-sulfur and arsenic-bearing gold ores are large reserves and difficult to treat.Considering the above problems,this paper took the refractory high-sulfur and arsenic-bearing gold ores as the research object.And the studies of the biooxidation mechanism of the refractory high-sulfur and arsenic-bearing gold ores and the mechanism of strengthening biooxidation by microwave/microwave-ultrasound activation were carried out.By this study,the biooxidation mechanism of the refractory high-sulfur and arsenic-bearing gold ores was improved,the strengthening biooxidation method and theoretical system of the refractory high-sulfur and arsenic-bearing gold ores were expanded and developed,the biooxidation period decreased and the biooxidation efficiency increased.This study has important theoretical guiding significance for the industrial application of biooxidation of the refractory high-sulfur and arsenic-bearing gold ores in China.The main contents and conclusions of the present work are given as follows:(1)The biooxidation of the refractory high-sulfur and arsenic-bearing gold ores in a single stirred-tank reactor and cyanidation experiments were carried out.The results indicate that by controlling the amount of addition of the gold ores and the pH of the biooxidation system,the adaptability of bacteria to the slurry system improves,and the lag period decreases,which result in the decrease of biooxidation period and the effectively increase of the biooxidation efficiency of refractory gold ores.By batch addition of 15 g ores and controlling the pH between 1.25 and 1.29,the biooxidation period decreases to approximately 16%,and the average dissolution rates of sulfur,iron and arsenic increase to 55.4 mg·L-1·h-1,53.0 mg·L-1·h-1 and 3.4 mg·L-1·h-1,respectively.The results of cyanidation experiments show that the efficiency of the gold and silver recoveries were related to the iron oxidation as well as the sulfur oxidation.(2)The semi-continuous biooxidation of the refractory high-sulfur and arsenic-bearing gold ores and cyanidation experiments were carried out.Results show that the concentrations of free and adsorbed cells decrease with the increasing pulp density.Bacteria act as catalysts in the course of biooxidation.The decrease of catalyst concentrations(free and adsorbed bacteria)lead to the decrease of biooxidation efficiency,which resulted in the negative effect of high pulp density on biooxidation.Two biooxidation parameters including the average volume and mass dissolution rates are defined and proposed to quantitatively analyze the biooxidation efficiency.The average mass dissolution rates of Fe,S and As decrease with an increase of the actual pulp density.However,the average volume dissolution rates of minerals increase with the increasing actual pulp density in the corresponding stage.Compared to the volume dissolution rate,the mass dissolution rate is more intuitive to reflect the negative effect of high pulp density on biooxidation efficiency.(3)The biooxidation process of the refractory high-sulfur and arsenic-bearing gold ores under different conditions of adding ore was analyzed.Two dissolution mechanisms of elemental sulfur are proposed during biooxidation of the high-sulfur gold concentrate consisting of mainly pyrite(FeS2).The first dissolution mechanism of elemental sulfur was FeS2?S80?S2O32?SO42-and the second was FeS2?S80?SO42-.The kinetics analyses of semi-continuous biooxidation of the refractory high-sulfur and arsenic-bearing gold ores at different pulp densities show that the data of iron oxidation from the semi-continuous biooxidation tests are best fitted by a shrinking core model,in which the chemical reaction controls the rate.The dissolution kinetics of sulfur and arsenic are analyzed by a shrinking core model in which the internal diffusion controls the biooxidation rates.(4)The strengthening biooxidation experiments of the refractory high-sulfur and arsenic-bearing gold ores by microwave/microwave-ultrasound activation were carried out.The results indicate that microwave/microwave-ultrasound activation can effectively shorten the biooxidation period of the refractory high-sulfur and arsenic-bearing gold ores and improve the biooxidation efficiency of the minerals.By optimization,the optimal conditions for microwave/microwave-ultrasound activation are as follows:reactor diameter of 74 mm,initial solution pH of 7.00(ultra-pure water),microwave activation time of 300 s,microwave power of 349 W,target temperature of 75?,pulp density of 10%(w/v),ultrasound power of 1000 W.Compared to the untreated ores,the biooxidation period decreases by 30%?40%,and the average dissolution rate of arsenic,iron and sulfur increase by 1.5?2.1 times,respectively.(5)The heating characteristic curve and temperature field distribution of microwave activation system under different conditions were studied.The results indicate that in the microwave activation system,the solution pH had no significant influence on the heating rate of the microwave activation system.The heating rate of the microwave activation system increases with increasing microwave power,as well as the decrease of reactor diameter and pulp density.The temperature of the activation system is not uniform.Three different temperature regions including high temperature region,moderate temperature region and low temperature region are formed.(6)The dissociation behavior and structural characterization of the refractory high-sulfur and arsenic-bearing gold ores before and after activation were analyzed.The results indicate that after microwave/microwave-ultrasound activation the crystallite size of the concentrates decreased,whereas the structural micro-strain increased.Microwave/microwave-ultrasound activation contributed to the decrease of mineral particle size and the increase of specific surface area.It also can promote the oxidation of element iron and sulfur on the mineral surface,improve mineral hydrophilicity,and increase the free surface energy of mineral particles.After microwave/microwave-ultrasound activation,micro cracks appear on the mineral surface,and the mineral surface become uneven,even peeling,resulting in serious damage.(7)Based on the different phase composition of the refractory high-sulfur and arsenic-bearing gold mineral particles,the mechanism model of strengthening biooxidation by microwave/microwave-ultrasound activation for the mineral particles consisted of complex phases(two or more phases)and the mechanism model of strengthening biooxidation by microwave/microwave-ultrasound activation for the mineral particles consisted of a single phase(pyrite)were proposed,respectively. |
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