Experimental Study On The Volatilization And Condensation Of Zinc In Non-condensable Gas Under Vacuum

Vacuum carbon thermal treatment of zinc minerals and its secondary regenerative zinc-containing electric-arc furnace dust is becoming a more promising method in the field of zinc smelting because of its high efficiency,low cost,low energy consumption,and environmental protection.However,after many years of research,it is found that whether zinc vapor can be efficiently condensed in a non-condensable gas CO/CO₂system is the key to the research of vacuum carbothermal zinc smelting process.Therefore,in this paper,theoretical and experimental studies on the effect of zinc on the volatilization-condensation of metallic zinc and the effect of non-condensable gases on the condensation behavior of metal zinc under vacuum are carried out in order to provide theoretical basis and guidance for the condensation purification of volatile metals,the preparation of metal zinc by vacuum carbothermal reduction and zinc metal-containing materials volatile enrichment.In this paper,first of all,the study of zinc volatilization and condensation is carried out,and the effects of system pressure and temperature on the volatilization and condensation of zinc are theoretically determined.When the system pressure was 10 Pa and the inert gas Ar was introduced,the experimental study found that increasing the heating temperature and holding time will increase the volatilization rate of metallic zinc.At 10 Pa and 973 K,the average volatilization rate of metallic zinc first increases and then decreases.The maximum average volatilization rate of the experiment is8.9460 10^-4 g/（cm²·s）.At 10 Pa,the condensation temperature range of zinc vapor,in the range of 503～623 K,is not affected by the heating temperature.When the vacuum pressure is 10 Pa,the heating volatilization temperature is 973 K,and the holding time is 30 minutes,the raw material zinc of 99.50%can be purified up to 99.9993%after one distillation,and the aluminum and iron content is reduced by 3 orders of magnitude.Experimental studies on the interaction of zinc with CO and CO₂ have shown that CO will react with zinc vapor,when heating volatilization temperature is 973 K,controlling CO flow rate at 2.232×10^-3 mol/min,the thin film needle-like zinc oxide is generated under the conditions of the experimental.The oxidation of CO₂ to liquid zinc and solid zinc is stronger than that of CO.And zinc oxide and carbon generated by the reaction of zinc with CO and CO₂ will not co-deposit.By comparing the SEM test results of zinc volatile condensate under vacuum pressure 10 Pa,it can be known that the passage of Ar,CO and CO₂ gas will lead to an increase in the grain gap,which indicates that non-condensable gas participate in the condensation process of zinc vapor and destroy the crystallization of zinc.The grain size and grain shape of zinc are changed,which affects the morphology of zinc crystals.At the same time,the vacuum and non-condensable gas（Ar/CO/CO₂）systems are analyzed,and find the effect of temperature on the preferential growth of zinc condensation products.The preferred growth orientation changes from（002）with higher condensation temperature range to（101）with lower condensation temperature range.