Study Of Vacuum Roasting Pretreatment And The Theoretical Basic Research On Carbonaceous Gold Ore

In recent years,with the gradual depletion of easily-recycling gold resources,the main direction of gold mining has gradually turned to refractory gold resources.Carbonaceous gold ore is one of the most important refractory gold resources,accounting for more than 20%of the proven gold reserves in China.The phenomenon of gold locked by minerals and the“preg-robbing”phenomenon by carbonaceous matters seriously hinder the recovery of gold in carbonaceous gold ore.The common oxidation roasting pretreatment process can solve the above problems,but the roasting process emits a large amount of SO₂and CO₂,which is not in line with the national goals of“Carbon neutrality”and“Carbon Peak”of China.In this paper,the carbonaceous gold ore was pretreated by vacuum roasting technology.The composition and structural characteristics of the products were characterized by X-ray diffraction,Scanning Electron Microscopy and Thermogravimetric Mass Spectrometry.The main factors affecting the roasting process,the decomposition and transformation mechanism of gold-locked minerals and carbonaceous matters were studied.The research results have important guiding significance for the development and utilization of carbonaceous gold ore resources.（1）The results of process mineralogy showed that the carbonaceous gold ore was a typical low-grade carbonaceous-siliceous gold ore with a poor dissociation.The content of exposed and semi-exposed gold was only 43.81%,in which gold locked in sulfides accounted for the highest proportion of for 47.8%of the total locked gold.The content of carbon and organic carbon in the ore was 5.58%and 72.76%,respectively.The gold direct leaching rate of the carbonaceous gold ore was only 3.55%.The high gold locking rate and high carbon content were the main factors affecting the gold leaching rate.（2）In the process of vacuum roasting pretreatment,the vacuum environment of10 Pa could significantly reduce the temperature required for the reactions of gold-locked minerals,which was beneficial to the removal of gold-locked minerals.Quartz could be reduced in the range of experimental temperature.Dolomite,pyrite and limonite could decompose or be reduced with carbon easily.In the process of vacuum roasting,temperature was the key factor to control the reaction rate,with the increase of temperature,the mass loss rate of ore increased gradually.The roasting process was divided into two stages:0-60 min and 60-120 min,which were controlled by interface chemical reaction and diffusion,respectively.The apparent activation energy of the 60-120 min process was significantly lower than that of 0-60 min process,the thermal decomposition and the weight loss of the reactions were mainly concentrated in this stage.（3）The gold leaching rate could be significantly increased by vacuum roasting pretreatment,In vacuum roasting process,roasting temperature was the most important factor affecting gold leaching,the gold leaching rate increased with the increasing of roasting temperature.The best gold leaching rate ranged from 3.55%to 88.41%under the vacuum roasting conditions of the vacuum grade was 10 Pa,the grinding fineness was-74μm accounting for 75%,the roasting temperature was 1200℃,the roasting time was 10 min,the heating rate was 7.5℃/min,and the leaching conditions of the re-grinding fineness was-74μm accounting for 80%,the leaching time was 48 h,the dosage of environmental-friendly gold leaching agent was 1 kg/t,the pulp p H value was 11 and the pulp concentration was 33%.Compared with direct leaching of carbonaceous gold ore,the gold leaching rate increased by 84.86%after vacuum roasting pretreatment,which showed that the effect of pretreatment was greatly.（4）The monomer dissociation degree of gold increased from 43.81%to 78.34%by vacuum roasting,and the dissociation degree of gold locked in pyrite reached72.37%.The decomposition reactions of organic carbon,dolomite,muscovite,pyrite and limonite（below 1000℃）and the secondary reactions between minerals（1000℃-1200℃）occurred mainly in the roasting process.In the range of400℃-700℃,the rapid desulphurization caused the developed pore structure of pyrite,which provided good channels for the separation of gold and pyrite,then pyrrhotite continued to be desulphurized slowly,and particle condensation made the separation of gold from pyrite completely.（5）After vacuum roasting pretreatment,the gold adsorption rate of carbonaceous gold ore decreased from 91.96%to 7.43%,the“preg-robbing”ability of the ore was significantly reduced.Organic carbon was the main“preg-robbing”carbonaceous matter in carbonaceous gold ores.In the vacuum roasting process,the thermal decomposition of organic carbon was the fundamental reason for the increasing of gold leaching rate.The reactions of organic carbon with minerals leaded to the consumption of it,which was secondary factor reducing its“preg-robbing”ability.The organic carbon continued to decompose during vacuum roasting process.Below 800℃,the carbon structure of the organic carbon was disordered,its“preg-robbing”ability the gold leaching rate of the ore did not change significantly.Above 800℃with the increasing of temperature,the carbon structure of organic carbon changed from disordered state to ordered state,graphitization degree increased continuously,the“preg-robbing”ability decreased rapidly,and the gold leaching rate of the ore increased rapidly.