Distribution Of Impurities Of Lanthanum During Zone Refining Process

In this paper,through theoretical analysis,calculation and experiments,the impurity distribution in the rare earth lanthanum zone refining process was studied in depth,the influence of process parameters on the impurity distribution was revealed,and the optimal process conditions were proposed to guide the actual production.Firstly,the thermodynamic parameters of lanthanum regional melting and purification were calculated,and the equilibrium distribution coefficients of Fe,Si,Ni,Al and Mn,the main impurities in lanthanum,were all less than 1,0.1278,0.3361,0.1465,0.1117 and 0.5040,respectively.Therefore,the feasibility of regional melting and purification of lanthanum was theoretically determined.Through the study of different zone melting rate,different induction current intensity and different zone melting times,the relevant impurity migration rules of zone melting and purification of lanthanum were obtained.The results showed that,under the same induction heating current intensity,the slower the zone melting rate was,the better the zone melting purification effect was.When the zone melting rate is 15 mm/h,the effective distribution coefficients of Fe,Si and Ni in lanthanum are 0.1672,0.3634 and 0.1582,respectively.At this point,the distribution of impurities in lanthanum is closest to the theoretical distribution of impurities after regional melting.At the zone melting speed of 60 mm/h,1 to 20 regional melting experiments were carried out respectively.When the regional melting times reached 18,16 and 14 times,the purification effect of Fe,Si and Ni impurities reached the optimal value.When the regional melting times reached 10 times,the overall purity purification effect was close to the best value,and the impurity removal rate did not increase significantly when the regional melting times continued to increase.At the same time,the influence of electromagnetic induction heating frequency was studied,and it was found that when the induction current intensity was between 30A and 60A,the regional melting rate and regional melting times were constant,and the regional melting effect would increase with the increase of the induced current.The influence of regional melting rate and heating power on the purification effect of regional melting was further clarified in the orthogonal factor experiment.With the decrease of zone refining rate and increase of heating power,the greater the degree of impurity migration during zone refining,the better the effect of regional melting and purification.The samples before and after the regional melting were analyzed microscopically.The impurities in lanthanum mainly existed in uniform dispersion and sometimes formed aggregation.Before melting,lanthanum has a clear grain boundary.After melting,the interface gradually disappears and impurities gradually accumulate to one end.Therefore,zone refining is effective in purification of the metal.