| The efficient extraction of gold from arsenic-containing refractory gold resources is attracting significant attention,with the depletion of easy-to-treat gold resources.However,in the face of increasingly stringent environmental protection requirements,traditional pretreatment methods have obvious shortcomings in the separation and enrichment of arsenic.The pyrolysis pretreatment method in an inert atmosphere can not only break down the dense mineral structure of coated-gold,but also separate and enrich arsenic and sulfur with low-toxic substances,which is one of the main directions for the development of arsenic-containing refractory gold resources in the future.Therefore,this research proposes a new technical system of"selective separation of antimony by slurry electrolysis-arsenic and sulfur separation from residue via pyrolysis in inert atmosphere-gold cyanide extraction under promoting of lead nitrate" for high-arsenic-antimony gold concentrates of complex refractory gold resources.This thesis,a systematic study on the key technology and theoretical mechanism has been carried out for "arsenic and sulfur separation from slurry electrolytic residue(SER)via microwave pyrolysis in inert atmosphere",which is one of the key processes of the new technology system.The mineralogical characteristics of SER which were prepared from higharsenic-antimony gold concentrates through selective extraction of antimony by slurry electrolysis,has been systematically studied employing XRD,ICP,SEMBSE&EDS,optical microscope,chemical phase analysis methods,the composition of main minerals and the occurrence of target elements have been determined.The results show that the contents of the main elements Au,Fe,As and S in SER were 61.50 g/t,19.25%,7.45%and 32.59%,respectively.The main minerals were pyrite,arsenopyrite,elemental sulfur,and quartz.Pyrite and arsenopyrite existed separately with dense structure.Arsenic mainly existed in the densely structured arsenopyrite.Sulfur mainly existed in pyrite,arsenopyrite(minerals that coating gold)and elemental sulfur(which was consuming gold leaching reagent components);56.68%of the gold was locked in gold carrier minerals with an invisible or submicroscopic form.The gold was difficult to achieve complete leaching by increasing the addition of sodium cyanide and fine grinding,and the maximum leaching rate was only 37.61%.Therefore,it is necessary to break down the dense structure of the coated gold minerals and remove the components that are not conducive to gold leaching,before the gold is impregnated.The thermodynamic and reaction trend for the main sulfide minerals in SER under an inert atmosphere were studied using HSC 9.0 software.And then the thermodynamic analysis results were verified by pyrolysis and thermogravimetric analysis experiments.The decomposition temperature(952 K)of arsenopyrite is relatively high.The presence of elemental sulfur and pyrite is helpful to reduce the reaction temperature of arsenic removal from arsenopyrite,and arsenic forms arsenic sulfide gas.The reaction trend analysis shows that sulfur can replace arsenic to form FeS2 or Fe7S8 in the arsenic removal reactions of arsenopyrite;Oxygen has a stronger ability to bind arsenic than sulfur,therefore,in order to remove arsenic as arsenic sulfide,it needs to be in an inert atmosphere.It has been verified by experiments that,the addition of elemental sulfur and pyrite can lower the arsenic removal temperature of arsenopyrite by 142 K and 128 K,respectively,and arsenic can be removed as arsenic sulfide.Thermogravimetric analysis was used to determine the reaction behavior of SER under conventional heating in nitrogen atmosphere,the Asym2Sig deconvolution function was used to separate and fit the overlapping peaks of the reactions,then the mechanism-free model and function model fitting methods of thermal analysis kinetic method were used to calculate,the data was compared,and the selected models were verified via comparing the changes in the microstructure of the mineral phase during the roasting process,finally,the most probable kinetic mechanism and parameters of each reaction under conventional heating were determined.The results show that the heating reaction of SER sequentially undergoes four stages of elemental sulfur volatilization,thermal decomposition of arsenopyrite,pyrite and pyrrhotite;The reactions of elemental sulfur volatilization,thermal decomposition of pyrite and pyrrhotite are consistent with the "random nucleation and growth of the Avrami-Erofeev model";The arsenic removal reaction of arsenopyrite is consistent with the "Jander’s three-dimensional diffusion model";The relationship between activation Gibbs free energy,enthalpy and entropy of each reaction and temperature was established.The kinetic mechanism of microwave pyrolysis was determined and verified via the model fitting and comparison of the microstructure changes of mineral phases.The results show that the reaction mechanism model of arsenic removal via microwave from arsenopyrite is consistent with conventional heating as the "Jander’s three-dimensional diffusion model".As the reaction extends from the outside to the inside,arsenic is continuously replaced by sulfur,forming a pyrite-like ore.Through the experimental study of the conventional heating pyrolysis process for SER,found that the main influencing factors are temperature and holding time.At 873 K,SER pyrolysis for 45 minutes,the gold leaching rate in the calcine was more than 1.3 times higher than that of the raw material.But the pores formed in the calcine were not uniformly distributed.Microwave heating dielectric and heating characteristics of SER were studied,and it was found that the SER has good microwave heating characteristics;and the relationships between the dielectric parameters and the temperature,as well as the microwave power,sample mass and heating time and temperature have been established.The process optimization of removal arsenic and sulfur from SER via microwave in nitrogen atmosphere has been studied.The results show that,the main influencing factors are roasting temperature and time,followed by protective gas temperature;Under the optimal conditions,the average removal rates of arsenic and sulfur were 97.96%and 50.43%,respectively.The process optimization of lead nitrate promoting cyanide leaching was studied.Under the optimal conditions,the leaching rate of gold in microwave pyrolysis calcine was 95.20%,and the sodium cyanide consumption was 8.25 kg/t calcine,lead nitrate can effectively promote the leaching of gold and reduce the consumption of sodium cyanide.The condensation law of pyrolysis volatiles with decreasing cooling temperature was studied,the condensation product is in different colors of gray→brown→red→yellow successively as the cooling temperature decreases;An 83.35%of arsenic was condensed as liquid arsenic sulfide at 638 K;The condensate was a mixture of arsenic sulfide and elemental sulfur.The cumulative condensation rates of arsenic and sulfur were 99.97%and 98.02%,respectively.The reaction mechanism of microwave pyrolysis process has been clarified by studying the changes of the mineral phase structure during the process.The results show that,the arsenopyrite and pyrite decompose successively to form a porous structure,as the microwave roasting temperature increases;Firstly,the arsenic in arsenopyrite undergoes a substitution reaction with elemental sulfur,and presents a"shrinking nucleus" reaction process,forming in a pyrite-like with many microcracks and holes;Pyrite decomposes and desulfurizes in the order of FeS2→Fe7S8→FeS,and presents a "random" reaction process,forming numerous and uniform pore structures in the matrix minerals of calcine. |
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