Study On High Efficiency Recovery And Utilization Of Refractory Rare Earth Electrolytic Molten Salt Slag

Industrial use the fluoride-oxide system molten salt electrolysis method to prepare low melting point rare earth metal(alloy),in the process which produces large number of rare earth waste molten salt slag.Its composition is complex,and the recovery and utilization of rare earth have been difficult.Therefore,how to realize the efficient recycling of rare earth in rare earth waste molten salt slag has important practical significance.In this paper,the physical and energy spectra of rare earth molten salt were analyzed firstly.It is determined that rare earth mainly exists in the form of REO,REF3 and REOF,and contains impurities such as graphite.On this basis,the experiments of high pressure alkali transfer,mechanical activation alkali transfer,complex decomposition,borax roasting and sodium carbonate roasting were carried out on the rare earth molten salt residue,and the method of borax roasting and sodium carbonate roasting were selected.The products of roasting in the borax system and sodium carbonate system were analyzed via XRD respectively,and we can conclude the corresponding chemical reaction equations are:Na2B4O7·10H2O+REF3=Na2O+REBO3+BF3+H2O(borax system)and 3Na2CO3+2REF3=6NaF+RE2O3+3CO2(sodium carbonate system)Through the study of chemical reaction dynamics,come to a conclusion that the activation energy of borax and sodium carbonate to break down the slag reaction of rare earth is 159.02 kJ/mol and 159.00 kJ/mol,and the Pre exponential factor is1.15×109 min-1 and2.58×109 min-1,therate constant of reaction is 0.26 min-1 and 0.28min-1,the reaction restriction are all interfacial chemical reaction.The best technological conditions of the technology of borax baking rare earth molten salt slag are: calcinations temperature is 700 ℃,the roasting time is 1 min,Borax addition is 38 % of the quality of raw materials;The optimum leaching conditions are: the leaching temperature is 70 ℃,the leaching time is 40 min,the liquid solid ratio is 5:1,and the hydrochloric acid concentration is 3 mol/L.Under the optimum conditions,the leaching rate of rare earth is 97.35%,the leach liquor pH <0.5,leaching liquid of the F-concentration is 0.28 g/L,rare earth ion concentration is16.97 g/L,REO/F = 60.18.The optimum technological conditions for rare earth molten salt soda roasting slag: the roasting temperature is 700 ℃,the roasting time is 60 min,1.5 times the amount of sodium carbonate for rare earth content,adding 5% borax as additive,add5% thiourea in hydrochloric acid solution,and the leaching temperature is 85 ℃.The structure of the calcined product is loose,non Ce rare earth leaching rate is96.98%,the leaching rate of Ce was 80.78%,the leaching rate of Ce was 80.78%,the concentration of F is 0.12 g/L in the leaching solution,the pH value is 3.8,the rare earth ion concentration is 64.30 g/L,REO/F=559.13,Al2O3/REO=1.6 * 10-3,the leaching solution can be extracted and separated in the P507 rare earth extraction slotdirectly.