Effect Of Pre-oxidation On The Structure And Reduction Characteristics Of Nickel Slag

Nickel slag is a by-product of nickel smelting process,which contains about 40%iron,trace nickel,copper and other valuable metal elements.However,as the iron in nickel slag mainly exists in the form of fayalite,it is difficult to reuse it by physical means such as magnetic separation.Currently,the more effective way to utilize nickel slag is to recycle the metal elements in it.In general,it is feasible to recover the metal resources in nickel slag by coal-based reduction in both economy and technology.Based on the preliminary experiments,this paper puts forward the utilization idea of pre-oxidation to enhance reduction and recovery of valuable elements of nickel slag.The reduction effect of nickel slag could be enhanced by pre-oxidation,which is of positive significance to realize the reuse of metallurgical secondary resources.In this paper,the nickel slag was taken as the research object,and the coal was used as the reducing agent.The iron oxide in the nickel slag was reduced to metal iron by coalbased reduction after the pre-oxidation process.Thermodynamics,dynamics,combined with X-ray diffraction,scanning electron microscope,energy spectrometer and detection means of chemical analysis were applied in this paper.Phase and internal structure of nickel slag during pre-oxidation,reduction characterization of pre-oxidized nickel slag after reduction and formation characteristics of metallic iron particles during reduction of pre-nickel oxide slag were investigated.The results are as follows:(1)The oxidation process of fayalite in nickel slag follows the principle of step by step transformation:Fe2SiO4?Fe3O4?Fe2O3.After the pre-oxidation temperature reaches 900?,nickel slag has a higher degree of oxidation,up to 95%.When the preoxidation time is less than 10min,the oxidation rate increases greatly with the extension of time.When the pre-oxidation time is more than 10min,the oxidation rate increases slightly and is in a basically stable state.The pre-oxidation process destroys the structure of nickel slag,resulting in the increase of iron oxide grain defects,making the subsequent reduction process easy to carry out.(2)When the temperature was below 1100?,the metallization rate of the reduction product of pre-oxidized nickel slag increased obviously with the increase of temperature.while the temperature exceeds 1100?,the trend of increase gradually abated.When the reduction temperature was 1250?,the maximum metallization rates of nickel slag samples and pre-oxidized nickel slag samples were 68.72%and 74.51%,respectively.The pre-oxidation process had a significant effect on the reduction results of nickel slag.Prolonging the reduction time can improve the content of metallic iron in the reduced products to a certain extent.Considering factors such as reduction effect and cost,the appropriate reduction time is 30 min.(3)Reduction time and reduction temperature have a significant impact on the growth of iron particles.When the reduction time is extended from 10min to 30min,40min,50min and 60min,the corresponding maximum size of metal iron particles increases from 12?m to 22?m,45?m,70?m and 86?m,respectively.When the reduction temperature increases from 600? to 1100?,the maximum size of metal iron particles increases from 7?m to 86?m.The growth kinetic equation of iron particles in the reduction process of nickel slag is:(?)(?),and the particle growth activation energy and pre-index factor of iron particle growth during nickel slag reduction were 14.591kJ·mol-1 and 3.341,respectively.