Study On The Decomposition And Control Of Thiourea In Biological Pre-oxidation Residue Gold Leaching Process

With the continuous consumption of high-grade mineable gold resources,low-grade refractory gold ore has become an important source of global gold technology.Aiming at the problems of low leaching rate and poor environmental protection in the leaching of sodium cyanide,thiourea,as a non-cyanide gold leaching reagent,has been widely studied since its birth due to its low toxicity and good selectivity.However,the large consumption of thiourea reagent and the poor economic benefit have always been the key factors restricting its industrial application,and no major breakthrough has been made yet.Aiming at a low-grade arsenic-containing refractory gold ore in Xinjiang,our research group adopted the biological pre-oxidation-acid thiourea gold leaching process,and obtained better pre-oxidation and gold leaching conditions in the experiments,but there are still some problems such as the amount of thiourea is large and the decomposition law of thiourea is not clear,and engineering application has not been realized.On the basis of the research of our research group,this paper optimizes the process of acid thiourea gold leaching of microbial pre-oxidized residues,and further clarifies the influencing factors that cause a large amount of thiourea losses,and proposes corresponding control measures to reduce the consumption of thiourea gold leaching agents,which provides guidance for the next industrial application.The main factors affecting the gold leaching process of acid thiourea were identified,and the relationship between pH value,thiourea concentration,leaching temperature,pulp concentration,leaching time,Fe3+ ion concentration and gold leaching rate was revealed,and the model equations of gold leaching rate and thiourea decomposition rate between the above six influencing factors were established,and the significance of each factor was sorted.It was concluded that the thiourea concentration term had the most significant effect on the gold leaching rate,while the Fe3+ ion concentration term had the most significant effect on the decomposition of thiourea rate.Combining the two models,it was concluded that the gold leaching rate was negatively correlated with the thiourea decomposition rate,and it was concluded that the gold leaching rate was the highest at 92.12%when the Fe3+ion concentration was 0.2 g/L and the thiourea dosage was 20 kg/t,and the actual leaching rate was 92.12%.The consumption is 12.47 kg/t and is a little higher.The loss of thiourea oxidation decomposition by Fe3+ ions was firstly studied.Combining with the relationship between the concentration of Fe3+ ions and the redox potential,it was clear that the thiourea oxidation loss was caused by the redox reaction with Fe3+ ions.Adding Fe2+ ions could inhibit the forward redox reaction and improve the stability of thiourea.On this basis,thiocyanate was added as the complexation and coordination agent of Fe3+ ion to reduce the oxidative decomposition of thiourea.When the total dosage of thiourea was 25 kg/t and the mass ratio of thiourea to sodium thiocyanate was 4:1,the gold leaching rate was the highest.The actual consumption of thiourea is only 5.01 kg/t,which achieved the purpose of reducing the dosage of thiourea and saving cost.In addition to the part of thiourea oxidation loss,the adsorption loss mechanism of thiourea by the remained typical minerals of pre-oxidized slag quartz,mica and pyrite was mainly studied.The order of adsorption capacity of three minerals to thiourea in the leaching process was:pyrite>mica>quartz,and quartz hardly adsorbed thiourea.The isotherm adsorption equation and adsorption kinetic equation were established for the adsorption of thiourea by pyrite and mica.Combined with the results of infrared spectrum detection and equation fitting,the adsorption of thiourea by pre-oxidized residue was shown as a mixed process of physical adsorption and chemical adsorption.In order to reduce the adsorption loss of thiourea,the recovery effect of thiourea under different desorption conditions was studied,and the results showed that the pH was 2.0,the temperature of the washing process was controlled at 30?,and the washing process was shaken for about 1.5 to 3.0 hours,and nearly 37%of the thiourea adsorbed on the mineral surface was eluted to the washing solution,nearly 6.0%of the total thiourea consumption during leaching.The actual leaching residue desorption of thiourea accounted for 0.45%of the total amount.According to the actual leaching conditions,the loss of thiourea caused by the oxidative decomposition of Fe3+ ions to thiourea and the adsorption loss of thiourea on the mineral surface were simulated and calculated.Theoretical calculation results showed that the oxidation loss of thiourea accounted for 59.56%of the total loss,and the adsorption loss accounted for 40.44%.In this paper,the main factors affecting the decomposition of thiourea were identified,and the loss of thiourea was effectively reduced through regulation and washing,which laid a good foundation for the promotion of biological pre-oxidation-acid thiourea gold leaching technology in industrial application.