| Oxygen pressure leaching of zinc concentrate is expected to become the mainstream production method of zinc smelting in the future,owing to its advantages of short process flow,environmental protection and high leaching efficiency.In this process,calcium lignosulfonate is generally used as a sulfur dispersant to promote zinc leaching.The mainstream view in the industry is that calcium lignosulfonate will be completely degraded during oxygen pressure leaching and will have no impact on the zinc smelting system.However,this is not the case,the concentration of organic matter in domestic oxygen pressure leaching systems has shown a cumulative upward trend.This change has had a relatively obvious negative impact on the zinc electrowinning process.In order to find out this problem,the behavior of calcium lignosulfonate in the process of zinc oxygen pressure acid leaching was investigated by means of total organic carbon,ultraviolet visible spectrum,infrared absorption spectrum,and gas chromatography-mass spectrometry.The degradation law of calcium lignosulfonate was found out,and the effect of calcium lignosulfonate on zinc electrowinning was discussed.The results showed that there was a positive correlation between temperature and the degradation of calcium lignosulfonate,while the initial acidity and oxygen partial pressure only had a certain effect at low temperature.Under the conditions of oxygen partial pressure of 0.2 MPa,acidity of 160 g/L and reaction temperature of 150 ℃,about 82.4% of calcium lignosulfonate was degraded.The degradation process of calcium lignosulfonate in zinc oxygen pressure leaching process is as follows: the benzene ring and its side chain groups in calcium lignosulfonate have been destroyed to varying degrees,and some of them have been degraded into phenols,esters and Sulfonates with slightly higher molecular weight,and then further degraded into organic compounds containing aromatic ether and sulfonic acid functional groups with smaller molecular weight and shorter carbon chain as the temperature rises to 150 ℃.These organics have good stability and are one of the main sources of organics in the oxygen pressure leaching system.Further zinc electrodeposition experiments confirmed that excessive degradation products of calcium lignosulfonate had a significant negative impact on the zinc electrodeposition process,which not only made the compactness of the cathode zinc sheet worse,but also led to the reduction of current efficiency.In view of the problem that the composition of calcium lignosulfonate is variable and the amount of organic impurities is large in the use process,which leads to the fluctuation of the effect of oxygen pressure leaching of zinc concentrate and the poor technical and economic performance,this paper carried out the research on a new additive for zinc oxygen pressure leaching,and discussed the behavior of benzotriazole in the process of oxygen pressure leaching and zinc electrowinning.The results of leaching experiment showed that 1-hydroxybenzotriazole had better promoting effect on the leaching of zinc in oxygen pressure leaching process than calcium lignosulfonate.Under the conditions of liquid-solid ratio of 8:1,benzotriazole dosage of 0.3 wt.% of zinc concentrate,acidity of 160 g/L,oxygen partial pressure of 0.8 MPa,reaction temperature of 150 ℃,reaction time of 2 h,stirring speed of 400r/min,the zinc leaching rate reached 95.41%.When the introduction amount of 1-hydroxybenzotriazole was less than 20 mg/L,it could promote the removal of cobalt from the lean cadmium solution.When the dosage of 1-hydroxybenzotriazole increased to 100 mg/L,the current efficiency decreased sharply from 91.0% to 24.65%,and the electrowinning effect was extremely deteriorated.This negative effect can be effectively improved by using adsorption or oxidation methods,especially the adsorption oxidation combined treatment process. |
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