| The gold ore is a strategic mineral resource with financial attributes.With the decreasing of disposable gold resources,the efficient development and utilization of carbon-bearing fine-grained gold deposits,which account for more than 20%of proven gold reserves,has become a research hotspot in the field of gold.In this paper,the carbon-bearing fine-grained gold deposits in Qinling area of Shaanxi Province were studied.The systematic basic research work was carried out by means of theoretical analysis,experimental study and mechanism analysis.The research results possessed academic significance and application value.By means of optical microscopy,X-ray diffraction,scanning electron microscopy and energy dispersive spectrometry,the mineral composition and relative content,occurrence state and distribution characteristics of gold in carbon-bearing fine-grained gold deposits were systematically studied.The results show that the gold in the ore exists in the form of natural gold with fine grain size,of which 83.03%is 5-10?m.Some of the gold particles are encapsulated by carbonaceous siliceous slate clasts(quartz,carbonaceous,limonite,etc.).The content of carbon is high(the graphite and organic carbon are 1.50%and 1.33%,respectively),with fine grain size(about 10 ?m),and it is closely associated with gangue minerals such as quartz.The thermodynamics of possible chemical reactions and chemical reactions between main components during oxidation roasting were calculated and analyzed using HSC Chemistry 6.0 thermodynamic software.Gibbs free energy-temperature diagrams of carbon,pyrite,dolomite and calcite were plotted.The results show that the main reactions in the process of oxidation roasting were combustion of carbon,oxidation of pyrite and decomposition of carbonate minerals,and the decomposition products(MgO,CaO etc.)reacted spontaneously with SiO2 and Al2O3 in the ore.On the basis of single factor experiment,the influence of different experimental conditions on gold leaching rate was studied by orthogonal tests.The significance of the influence of experimental conditions on gold leaching rate was determined by range analysis and variance analysis.Building on this,the prediction model of roasting operation was established by BP neural network,and the prediction model of leaching process was established by orthogonal experiment.The results show that the leaching rate of gold was only 12.50%when unroasted ore was leached directly by cyanidation,and the influence on gold leaching rate in roasting process was in the order of aeration>roasting temperature>roasting temperature × roasting duration>roasting duration.The significant influence of factors on gold leaching rate was in the order of grinding fineness>stirring rate>leaching duration>leaching agent dosage>pulp concentration.The optimum roasting conditions predicted by BP neural network were roasting duration 2.1 h,roasting temperature 655? and aeration rate 1.0 m3/h.Orthogonal test predicted that the optimum leaching conditions were as follows:grinding fineness of-0.074 mm 95%,pulp concentration of 40%,leaching duration of 21 h,NaCN dosage of 500 g/t,stirring rate of 350 r/min.Under the optimum conditions,the leaching rate of gold was 94.02%,and the leaching rate of gold was 94.43%through the model prediction.The kinetic research results show that oxidation roasting was divided into two stages:early stage and later stage.The optimum kinetic mechanism function was f(a)=1-(1-a)1/3 at the early stage of roasting(0-90 min).The process was mainly controlled by gas-curing chemical reaction.The activation energy was 212.03 kJ/mol and the pre-exponential factor was 157.85 min-1,which shows increasing the volume of ventilation and roasting temperature is beneficial to the carry out.The optimum kinetic mechanism function is f(a)=1-3(1-a)2/3+2(1-a)at the later stage(90-120 min).In solid internal diffusion control,the activation energy of reaction was 163.03 kJ/mol,and the pre exponential factor was 2459.93 min-1,which shows increasing the volume of ventilation and reducing the size of raw ore can effectively improve the roasting effect.The results of leaching kinetics show that the leaching is an internal diffusion process,and the improvement of grinding fineness is beneficial to the improvement of leaching efficiency.XRD,FTIR and XPS were used to characterize the crystal structure and phase transformation of calcine during oxidation roasting.In addition,the transformation behavior of Ca,Fe and Si during roasting was investigated.The micro-morphology and pore structure of calcine were characterized by SEM-EDS and pore structure.The variation law between chemical reaction between main minerals and pore structure parameters of calcine during oxidation roasting was found out.The internal relationship between oxidation degree of carbon,pore structure parameters of calcine,micro-morphology change,transformation behavior of main elements and gold leaching rate was revealed.Under the optimum roasting conditions,the main characteristics of calcine were complete oxidation of carbonaceous materials,oxidation of pyrite to Fe2O3,decomposition of kaolinite to metakaolinite and complete decomposition of dolomite.Cracks on the surface of calcine and pore structure in the calcine provided a channel for the diffusion of CN-in the leaching process,which was conducive to the effective contact between CN-and Au,thus improving the leaching rate of gold.The results of this study deepened the understanding of the oxidation roasting process of carbon-bearing fine-grained gold ores,enriched the theoretical system of oxidation roasting of carbon-bearing gold ores.Furthermore,they not only provided theoretical support for the key technical problems of oxidation roasting of raw ore,but also had good reference significance for the efficient utilization of other refractory gold ores. |
PDF Full Text Request