Kinetics Study on Gold Leaching with Thiourea from Acid Bio-Oxidation Slag
Biohydrometallurgy technology had been widely used in the metallurgy of copper,nickel,gold,and uranium due to its ad-vantages of economy,efficiency,and environmental protection.With the increase of gold output year by year,the number of easy to handle gold deposits is decreasing,and the low-grade hard to handle gold deposits have attracted more and more attention,and gradu-ally become an important source of raw materials for gold production.Encapsulated gold deposits are the most widely used type of re-fractory gold deposits,characterized by fine gold bearing mineral particles,high content of harmful impurities,and a large proportion of encapsulated gold.Gold is encapsulated by metal sulfides,making leaching difficult.This type of mineral requires pre-oxidation treatment to remove the minerals wrapped on the surface of gold particles before further extraction of gold can be carried out.The pre-treatment technologies for difficult to treat gold mines currently mainly include roasting oxidation,hot pressure oxidation,biological oxidation,chemical oxidation,etc.Among them,biological oxidation technology is a relatively mature technology.It has advantages such as simple operation,low equipment investment,and environmental protection,which is very suitable for the needs of China.In recent years,it has been rapidly promoted and applied in China.Since its inception,cyanide extraction has been the most widely used method in gold extraction due to its high economic benefits,mature process,and ability to adapt to various ores.However,cyanide has been restricted in development because of its toxicity and adverse effects on the environment.Therefore,it is necessary to find an efficient and environmentally friendly gold leaching agent that can replace cyanide.The non-cyanide gold leaching methods mainly in-clude thiosulfate gold leaching,halogen and its compound gold leaching,polysulfide and stone sulfur agent gold leaching,and thio-urea gold leaching.In the above-mentioned non-cyanide gold leaching methods,the thiosulfate method can only leach gold under weak acidic conditions and cannot adapt to the strong acidic environment after biological pre-oxidation.The halogen and its compound meth-od can cause serious corrosion to equipment under strong acidic conditions,accompanied by the volatilization of halogens;The poly-sulfide and sulfur agent methods are mainly used in alkaline environment and cannot adapt to the strong acidic environment after bio-logical pre-oxidation.Therefore,the thiourea method is one of the most promising gold leaching methods for treating acidic biological pre-oxidation slag.After biological pre-oxidation,the slurry becomes acidic.Thiourea leaching is used for gold,without the need for acid-base conversion,eliminating the acid-base conversion step of cyanide extraction of gold.This not only saves pharmaceutical costs but also avoids the formation of secondary encapsulation.The product Fe3+after biological pre-oxidation can serve as an oxidant in sub-sequent reactions.Therefore,the combination of biological pre-oxidation and thiourea gold leaching process avoids the acid-base is-sues in traditional cyanide gold leaching process and complements each other.However,under acidic conditions,this method also has drawbacks such as poor selectivity,strong corrosiveness,and high consumption of thiourea,which require further research and resolu-tion.According to the process mineralogy and other analysis of a refractory gold mine in Wuqia,Xinjiang,it was difficult to produce economic benefits by adopting the traditional ore dressing and smelting method.Based on this,the combined process of bio-oxidation preprocessing and gold leaching with thiourea was studied.The combined process used thiourea as gold leaching agent.Thiourea could not only directly deal with the acid biological pre-oxidation slag,but also avoid the acid-base conversion step in the traditional cyanida-tion gold leaching process,which avoided the secondary inclusion of ore,saved a lot of reagents and costs,and also avoids a series of environmental problems caused by cyanide in the gold leaching process.The experiment used ore samples treated with biological pre-oxidation for leaching experiments.The thiourea gold leaching experiments were conducted on conditions such as leaching tempera-ture,thiourea concentration,leaching pH,liquid-solid ratio,and stirring speed during the thiourea leaching process,in order to ob-tain a semi empirical kinetic model of thiourea gold leaching under the biological oxidation pretreatment system.The effects of these factors on the gold leaching rate in the process of thiourea leaching were investigated.The apparent kinetics of the leaching process of acid thiourea leaching system was discussed by using the shrinking core model.The results showed that the overall control step of the process was internal diffusion control,and the semi empirical kinetics was obtained through the experimental results.This research achievement provided guidance for the practical industrial application of the combined process and was expected to provide a new ap-proach for the mining of difficult to treat gold mines in China.In the future,the thiourea gold leaching process would be optimized con-tinually,explore more efficient and environmentally friendly technologies for difficult to treat gold mining,and contribute to the sus-tainable development of China's gold industry.
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