Research On Influencing Factors And Mechanism Of Gold Leaching With Alkaline Thiourea Solution

In recent years,with the gradual improvement of environmental requirements,the thiourea which is a kind of hypotoxic and environment-friendly non-cyanide agent for leaching gold has been paid more attention by researchers.At present,the research of leaching gold with thiourea falls into two categories:the acid system and the alkaline system.Compared with the acid system,leaching gold with thiourea in alkaline system has better selectivity and no corrosion to the equipment.However,the theory of leaching gold with alkaline thiourea is not perfect,and the leaching rate of gold is lower than that of cyanide leaching,and improper choice of oxidant may cause a large consumption of thiourea.This paper took the gold ore provided by NMIC company in Ethiopia as the experimental sample.The leaching property of the ore was studied by conventional cyanide leaching and acid thiourea leaching tests,and their leaching rates were 92.41%and 74.50%respectively under the optimum conditions.Therefore,it can be seen that the ore is easy to leach.The oxygen in the air was selected as the oxidant according to the theory of redox potential,and the influences of factors such as oxidant,calcination pretreatment,carbon-in-leach process and bubble generation mode on leaching rate were investigated by alkali thiourea Au-leaching tests.In order to generate bubbles in different modes in the experiment,three kinds of bubble generation devices,such as conventional device,spiral air duct device,and microporous material device,were designed.It is proved by determining the total oxygen transfer coefficient that the oxygenation capacities of these devices are enhanced in tum.The test results show that the leaching rate of gold can be increased by about 30%by using microporous material device,while it can be increased by about 10%by using the process of calcination pretreatment or carbon-in-leach.The single factor tests of alkali thiourea Au-leaching using microporous material device were carried out to research the influences of thiourea dosage,stabilizer dosage,liquid-solid ratio,the initial pH of pulp,leaching time,air flow rate,stirring speed on leaching rate.And the optimum conditions are as follows:the dosage of thiourea is 1.5 kg/t,the dosage of sodium hexametaphosphate is 1.5 kg/t,the liquid-solid ratio is 3:1,the initial pH of pulp is 11.5,the leaching time is 8 h,the air flow rate is 0.8 L/min,the stirring speed is 300 r/min.The leaching rate of gold was 54.27%under these conditions.The dissolution tests of gold foil in acid and alkaline thiourea solution were carried out.At the same time,AFM and SEM-EDS were used to analyze the dissolution process of gold,and the two stage leaching tests were used to verify the analysis results.In addition,the gold leaching tests inflated with different gases in alkaline thiourea solution were carried out.The dissolution test results show that the dissolution rate of gold in alkaline thiourea system is far lower than that in acid thiourea system,and it is easier to form a passivation film during the gold leaching process with alkaline thiourea solution.The leaching test results show that the amounts of dissolved oxygen in the pulp were 1.6 mg/L,8.1 mg/L and 32.9 mg/L respectively and the leaching rates were 48.64%,52.94%and 53.64%respectively when inflated with nitrogen,air and pure oxygen.The difference between the amounts of dissolved oxygen is obvious,but the leaching rate changes little.The analysis shows that in addition to the amount of dissolved oxygen in the pulp,the large amount of turbulence formed by bubble generation is also an important reason for the increase of leaching rate.