A Study On Fundamentals Of Selective Inhibit Pyrite Bioleaching Of Chalcocite And Covellite

With the continuous exploitation of mineral resources,valuable metals grade keeps being decreased,which are frequently associated with more and more other elements.During the leaching process,the valuable metals and other harmful elements are dissolved simultaneously,which leads to a considerable deterioration of leachate.It is more difficult to separate valuable metals from pregnant leach solution.Zijin copper mine belongs to a large porphyry secondary copper sulfide deposit in Fujian of China,which is characterized by low grade copper and high levels of sulfurs.During bioleaching of the secondary copper sulfide,excess pyrite dissolution results in acid and iron ions pollution to the environment,and leads to substantial increase in costs,which is a bottleneck problem of efficient recovery of valuable metals from low grade copper ores.The present work aimed at the study on fundamentals of selective inhibit pyrite bioleaching of chalcocite and covellite,and conducted the electronic structure and electrochemical characteristics examination,kinetics measurement,microbiological behaviour by Mineral Liberation Analyzer(MLA),simulation,and high-throughput sequencing.It provides a novel technical method and important theoretical guidance for the efficient recovery of copper by revealing the dissolution kinetics of different sulfide ores and establishing a reasonable control method.Electronic structure and properties of three sulfides minerals were studied at the molecular and atomic level by using first-principles method based on density functional theory(DFT)with plane-wave pseudopotential,which revealed the differences of dissolution of three sulfide minerals in the microscopic essence.The result shows that the band gap narrows and stability gradually weakens in an order from pyrite,covelline to chalcocite.The pyrite oxidative ability is stongest among these three sulfides and obtains electrons easier.On the contrary,the chalcocite reductive ability is strongest among them and loses eleccrons easier.The crystal structures of the three kinds of sulfide minerals are different,which determines the difference of solubility.It is concluded that selective leaching of chalcocite and covellite from pyrite is feasible.Based on the shrinking core model,the Semi empirical kinetic model was computed to establish association index among the concentration of bacteria,Fe3+ concentration,pH value,temperature and the dissolution rate constant.Temperature is a key factor to promote the dissolution rate of pyrite,chalcocite and covellite,the covellite dissolution rate is more sensitive to temperature change because its activation energy(84.97kJ/mol)is the highest among them.The bacterial concentration,Fe3+concentration and pH value have weak correlation with dissolution rate constant,these factors exert little effect on the leaching process.The redox potential has less effect on the chalcocite and covellite dissolution,and the copper leaching rate is higher even at low potentials.However,the redox potential has a more significant effect on pyrite dissolution,the leaching rate of pyrite is very slow when the redox potential in the leachate less than 760mV,and the leaching rate of iron is not more than 20%after 20 days.Under low temperature and potentials,the dissolution of the pyrite and chalcocite/covellite show significant difference.The relationship between the types of minerals,the potential and microbial diversity was revealed,and the sulfur-oxidizing bacteria dominant was necessary for selective bioleaching of sulfides.Different types of metal sulfides have a certain influence on bacterial community.The iron-oxidizing bacteria Leptospirillum is dominant in the pyrite leaching process,and the number and proportion of acidithiobacillus and sulfobacillus decreased sharply with the onging leaching reaction.Acidithiobacillus and sulfobacillus are dominant in the chalcocite and covellite leaching process,but sulfobacillus is relatively higher.Leptospirillum is more sensitive to redox potentials,the Leptospirillum proportion sharply decreased with the redox potential decrease,and even no Leptospirillum was detected when the potential was less than 700mV.However,the redox potential has little influence on acidithiobacillus strains,which can become dominant under different potentials.Low temperature(?45?),low redox potential(?760mV),and dominant sulfur-oxidizing bacteria are the optimum leaching conditions for selective inhibit pyrite bioleaching of chalcocite and covellite.