| With the gradual reduction of easy-to-leach gold ore,the exploitation and utilization of refractory gold ore has attracted extensive attention from researchers all over the world.China is abundant in refractory gold ore resources.How to deal with such ores is of great significance to the sustainable development of the gold industry.Cyanidation had been the main method for gold extraction for more than 100 years.However,it is difficult to extract gold from fine-grained encapsulated carbonaceous gold ore.At the same time,the high toxicity of cyanide has caused serious environmental pollution and ecological damage,which has led to the prohibition of cyanidation in some countries.Therefore,it is urgent to find a non-cyanide leaching method that can effectively treat fine-grained encapsulated carbonaceous gold ore.Thiosulfate method has the advantages of non-toxicity,rapid gold leaching,no corrosion to equipment,and suitable for leaching carbonaceous gold ore.It is considered to be the most promising non-cyanide gold extraction method.However,thiosulfate method also has problems such as high concentration of ammonia water used,large consumption of reagents,and difficulty in recovery of gold.In combination with the previous research results of the research group,ethylenediamine was used instead of ammonia in the copper-ammonia-thiosulfate system.Firstly,the thermodynamic analysis of the copper-ethylenediamine-thiosulfate system showed that the copper ethylenediamine complex in the solution is mainly Cu(en)22+,and the reduction product is mainly Cu(S2O3)35-,and a small amount of Cu(S203)23-is present.The effect of pH on the distribution of Cu(?)was studied.It was found that Cu(?)in solution mainly existed in the form of Cu(en)22+ when the pH was 6-11.The copper-ammonia-thiosulfate system is suitable for a narrow pH range,while the copper-ethylenediamine-thiosulfate system has a wider pH range.By calculating the standard redox potential of the main electric pair in the copper-ethylenediamine-thiosulfate system,it is found that the electric pair of Cu(?)complex/Cu(?)complex can meet the dissolution conditions of gold,so it is feasible to use ethylenediamine instead of ammonia.In addition,the Cu(?)complex/Cu(?)complex electrical pair in the copper-ethylenediamine-thiosulfate system does not spontaneously oxidize S2O32-to S4O62-,which can reduce the consumption of thiosulfate during the gold leaching process.Secondly,the effects of pyrite and roasted pyrite on gold leaching in copper-ethylenediamine-thiosulfate system were investigated by gold foil leaching test.It was found that both pyrite and roasted pyrite has inhibitory effect on the dissolution of gold.And the effect of pyrite on gold leaching is stronger than roasted pyrite.It was also also found that when the concentration of thiosulfate is very low,both pyrite and roasted pyrite can adsorb Au(S2O3)23-,resulting in a decrease in the concentration of Au(S2O3)23-in the solution.In this paper,a fine-grained encapsulated carbonaceous gold ore from Yunnan province was studied.The results show that the gold extraction rate is only 5.9%and 4.3%when the gold was directly leached from ore by traditional cyanidation or thiosulfate method,and the corresponding consumption of cyanide and thiosulfate reached 1.84kg/t and 20.4kg/t,respectively.In order to effectively extract gold from ore,it is necessary to destroy the sulfide minerals before leaching gold.Firstly,the gold concentrate was pretreated by roasting oxidation,and the roasting conditions were optimized by Response Surface Method.The suitable conditions of the roasting were obtained:roasting temperature was 642 0 C,and the roasting time was 240min.Gold was extracted from the roasted residue by cyanidation,copper-ammonia-thiosulfate system and copper-ethylenediamine-thiosulfate system.As a result,18 h cyanidation achieved a gold extraction rate of 80.6%,with the consumption of NaCN equaling 1.05 kg/t,whereas the corresponding values for 1.5 h copper-ammonia-thiosulfate treatment equaled 63.0%and 11.3 kg/t.Importantly,4 h copper-ethylenediamine-thiosulfate system treatment achieved a gold extraction rate of 80.3%,with the corresponding thiosulfate consumption equaling only 4.14 kg/t.Compared with copper-ammonia-thiosulfate,the pH value of the copper-ethylenediamine-thiosulfate system was more widely,and the concentration of ethylenediamine used is much lower than the concentration of ammonia used in the copper-ammonia-thiosulfate system.Therefore,compared with cyanidation and copper-ammonia-thiosulfate system,this system is more suitable for extracting gold from fine-grained encapsulated carbonaceous gold ore.The leached residue was treated with strong acid,and then extract gold by the copper-ethylenediamine-thiosulfate system.The final extraction rate of gold was 91.1%,and the consumption of thiosulfate was 5.63kg/t.It was first found that the bromate method can directly leach gold from the above-mentioned refractory gold ore.Thermodynamic analysis showed that the bromate method can destroy the sulfide minerals and then rapidly dissolve the gold from the ore.The suitable condition for gold leaching were obtained by single factor experiment:0.25M potassium bromate,0.08M ferric chloride,0.4M hydrochloric acid,stirring speed of 250 rpm,and liquid-to-solid ratio of 5.Within 5min,the gold extraction rate can reach 94.5%.It is also found that bromate method was also suitable for extract gold from gold concentrate,and the extraction rate of gold can reach 91.8%.The surface morphology and crystal structure of leaching residue were analyzed by SEM-EDS and XRD.It was found that most of the sulfide minerals in the gold ore had been oxidized and decomposed.After extracted gold by bromate method,it was not necessary to perform solid-liquid separation on the slurry.Higher gold recovery can be achieved by direct adsorption of activated carbon.In addition to being efficient and low in toxicity,the proposed leaching method can realize a high gold extraction rate in a very short time without any pretreatment when leaching gold from fine-grained encapsulated carbonaceous gold ore. |
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