| With the reduction of high grade ores which can be treated with simple processes, refractory and low grade ores have gradually become the main raw material of gold mines in our country. Among the raw materials for sulfuric acid production, some pyrite ores and flotation concentrates contain precious metals such as gold, silver, etc. And they will be enriched during roasting process. The roasted products are traditionally called gold-containing slag from sulfuric acid production. If this kind of secondary gold resources can be effectively exploited, it will broaden the scope of-available gold resources and also reduce the burden of environment. In this paper, new processes for the extraction of gold from a gold-containing slag which contains gold of 16.1g/t, from sulfuric acid production, have been investigated. Due to the complicated and encapsulated structure of the slag, the recoveries of gold obtained from common direct leaching processes are all below 25%. Therefore, developing effective processes to recycle this gold-containing resource has important practical significance.Analyses on the property of the gold-containing slag show that particle size of the slag is fine, with -0.074mm content accounting for 84.12%, and the distributions of gold and iron are almost unanimously in each size fraction. XRD analysis illustrates that the main mineral phases in the slag are hematite, quartz, magnetite and aluminosilicate. The chemical phase analysis of iron shows that hematite accounting for 76.65%, magnetic iron accounting for 21.85%, pyrite accounting for 0.18% and other iron phases accounting for 1.32%. From the direct leaching test results, it can be known that the key reason for low gold leaching rate is due to little exposure of gold, with most gold particles not contacting well with leaching reagents. According to the leaching effect, sodium chlorate leaching system and acidic thiourea leaching system are chosen as the main methods for non-cyanide leaching research.In order to increase the contact opportunities of gold particles with reagents in leaching system, study on roasting pretreatment of the gold-containing slag was carried out. Slag being roasted at 900℃ for 100 minutes with the dosage of sodium chloride accounting for 20% of slag, the best gold recovery of 78.36% could be obtained in leaching test. And slag being roasted at 900℃ for 60 minutes with the dosage of composite additive (sodium hydrogen sulfate to sodium chlorate mass ratio 1:2) accounting for 20% of slag, the highest gold recovery of 69.49% was obtained in leaching test. In order to effectively increase the gold leaching recovery, the roasting promoter RS-1 was developed. The process conditions of sulfating roasting were as follow:roasting temperature 500℃, concentration of sulfuric acid solution 60% (dosage 960L/t), RS-1 dosage 49.5kg/t and roasting time 70 minutes. Then the roasted slag was treated in the leaching system with sodium chlorate as oxidant and sodium chloride as complexing agent. The leaching conditions were set as:NaClO3 dosage 54kg/t, NaCl dosage 44kg/t, the liquid-solid ratio 3:1, leaching temperature 80～90℃ and leaching time 1.0h. Gold slag with a grade of 3.13g/t, and gold recovery of 92.26% was obtained.In the acidic thiourea leaching system which processes the sulfating products of the gold-containing slag from sulfuric acid roasting, thiourea is used as complexing agent. The roasted slag was dissolved in water to produce ferric sulfate, and the other conditions were set as:thiourea dosage 50kg/t, pulp pH 1.5, liquid-solid ratio 5:1, leaching temperature 35℃ and leaching time 3.0h. The result shows that gold slag with a grade of 2.55g/t and gold recovery of 95.56% was obtained. But the consumption of thiourea is about 10 times higher than the normal dosage due to the high concentration of Fe3+, and the cost cannot be acceptable.Through above research, it is determined that the gold-containing slag from sulfuric acid production could be treated using the process of sulfating roasting-sodium chlorate chlorinating-leaching, and the leaching recovery of gold could be more than 92 %. It has the advantages of low cost and fast reaction. The research result provides a new approach for the recovery of gold from slag of sulfuric acid production, and has practical significance. |
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