Study On Efficient Extraction Of The Rare Earth From Mixed Rare Earth Concentrate By Calcification Transition Process

Rare earth is a unique resource in China with its advantage of abundant reserves,considerable variety and high grade.With the application of rare earth and its alloys in the military,information,energy,biotechnology and other areas,efficient rare earth extraction methods are being paid more and more attention by academia and industry.The mixed rare earth concentrate is a rare earth mineral with its important industrial value.Currently,the traditional process of "strong sulfuric acid method of roasting" is mainly used in the production of mixed rare earth.However,one of the major factors,which limits the development of sulfuric acid decomposition,is that the off-gas of SO2 with HF because of the difficulty of recycling the off-gas causing the environmental pollution.Considering the characteristics of such minerals and disadvantages in the traditional process,a new hydrometallurgical technology of "calcification transformation-acid leaching" is proposed in this paper.The process of calcification is strengthened mechanically by homogeneous reactors,which aims to make the decomposition of bastnaesite and monazite,so that valuable rare earth elements in the mixed rare earth could be extracted effectively and cleanly.In this paper,the thermodynamics and basic issues of calcification transition process of mixed rare earth had been studied,the conclusions were reached as follows:(1)According to the particle size of mxied rare earth concentrate used in the experiment and ball movement theory analysis of homogeneous reactors,the best ratio of different size balls is calculated:4mm:5mm:6mm:10mm:12mm=2:3:4:3:2.(2)The thermodynamic date is difficult to calculate in detail as the mixed rare earth concentrate ore is composited by some kinds of rare earth elements.Therefore,the thermodynamic in the process of calcification transformation is calculated simply by utilizing the solubility equilibrium constant of each component in the system of calcification at 25?.And the advantage area of thermodynamic is drawed for the systems of Ce-F-CO32-H2O and Ca-F-H2O.(3)Effect of calcination temperature,time etc.On the transition performance of mixed rare earth were investigated,the results showed that under the optimal condition of ball to material weight 80:1,the content of NaOH 35%,the content of CaO 20%,the calcification temperature of 250?,time of 4h,the ratio of L/S 5:1,the highest leaching rate of rare earth was obtained:Ce 86.93%,La 97.85%,Nd 99.96%and the total leaching rate of rare earth was 92.16%.(4)The loss rate of fluorine in the transition process of calcification was 8.17%under the optimal conditions of calcification transition,and the phosphorus almost had no loss.(5)The calcified residue and acid leaching slag were analyzed by XRD and SEM to study the transformation mechanism of each component in the mixed rare earth concentrate in the process of calcification transition.The resluts showed that bastnaesite and monazite were decomposed and the elements of rare earth were found as the form of hydroxide after the transition of calcification;And fluorine was translated into the fom of fluorite,which was still stable in the process of acid leaching;phosphorus combined with calcium was translated into the form of calcium metaphosphate with the decomposition of monazite.