Pretreatment Of Zinc-containing Dust-vacuum Carbothermal Reduction With Efficient Recovery Of Zinc

Iron and steel enterprises will produce a large number of zinc-containing dust in the production process.Zinc-containing dust contains a large number of valuable elements such as Zn element and Fe element,directly stacked or landfill treatment zinc-containing dust,not only will cause the loss and waste of valuable resources such as Zn element and Fe element,but also the greatest environmental burden.Based on the shortage of zinc and ore resources in China,so,how to realize the efficient utilization of secondary resources of zinc-containing dust has become a key problem.High purity metallic zinc can be obtained by one step separation of zinc from other valuable metal elements by vacuum carbothermal reduction.In this paper,electric arc furnace dust（EAF）was studied by the way of water leaching and vacuum carbothermal reduction.The following main conclusions were obtained:（1）The experimental results showed:With the increase of solid-liquid ratio,stirring speed and water leaching time,leaching rate of K element and Na element in EAF increased;the influence of solid-liquid ratio,stirring speed and water leaching time on the leaching rate of K element and Na element was as follows:solid-liquid ratio>water leaching time>stirring speed;at the solid-liquid ratio of 1:10（g/ml）,water leaching time of 300 r/min,stirring speed of 70 min,immersion time under these conditions,leaching rate of the K element reached the optimal value of 91.09%,leaching rate of Na element reached the optimal value of 85.68%.So,the best water-soaked slag of EAF could be obtained.（2）The results of thermodynamic calculations showed:As the pressure decreased,the reaction Gibbs free energy decreased gradually,the saturated vapor pressure of metal elements in water-soaked slag of EAF is becoming smaller and smaller,especially the change of metallic zinc was the most significant.When the pressure dropped from1 atm to 10Pa,saturated vapor pressure of zinc was reduced by 509℃.With the increase of reduction temperature and carbon content,volatility of metallic zinc increased.When the reduction temperature was 950℃,the carbon content exceeded 6%,volatility of metallic zinc was up to 99.8%,for cost considerations,the optimum reduction temperature was determined as 950℃and optimal carbon was determined as 12%.The change process of the main phase of zinc was as follows:Zn Fe₂O₄→Zn O→Zn,the change process of the main phase of iron was as follows:Zn Fe₂O₄→Fe₃O₄→Fe O→Fe.（3）The experimental results of vacuum carbothermal reduction showed:With the increase of reduction temperature,reduction time and carbon content,the volatilization rate of zinc in water leaching slag of EAF increased,the content of Zn element in reduced slag decreased,the content of Fe element increased,and the quality of condensate collected increased.When the pressure was 10 Pa,carbon content was 12%,reduction temperature was 950℃,and reduction time was 60 min,the reduction rate of zinc was as high as 99.52%,and the high grade iron slag with the zinc content of 0.18%could be obtained,and 6.2g condensate could be collected.（4）Through thermodynamic calculation and experimental research,the optimum technological parameters of water leaching slag containing EAF by vacuum carbothermal reduction was as follows:the system pressure was 10Pa,reduction temperature was 950℃,carbon content was 12%,and reduction time was 60 min.