Study On Technology Research Of Mixed Rare Earth Tailing Roasting By Calcium And Coal-Leaching By Acid

Rare earth is a strategic resource in the world,and it is significant for development of a country.Due to the resource of rare earth is abundant in China,the storage and output level of rare earth of China is the biggest all over the world.The Bayan Obo mine,which is the biggest rare earth mine of China.It was originally defined as China's largest iron ore mine to exploitation.The magnetic tailing,which contains a large amount of rare earth resource,is subsequently stored in the tailing dam.However,the magnetic tailing not only occupies a large amount of land,but also pollutes the environment.Consequently,it is significant for researchers to investigate the properties of the rare earth minerals in magnetic tailing.The paper uses the mixed rare earth tailing of Bayan Obo mine as the fundamental raw materials,and the roasting method of different calium with industrial coal is used in the mixed rare earth tailing.There are four aims:?the REFCO3 and REPO4 is decomposed to rare earth oxide;?Fixing fluorine;?The industial coal can avoid the Ce3+oxide to Ce4+;?One of the three different calium is chosen as the best activating agent.Thereafter,in order to find the best acid to leaching the roasting ore,the leaching method of different acid is used in the roasting ore.In final,a new clean technology is developed to recycle the rare earth in the mixed rare earth tailing.A series of experiments studies and data analysis are carried out,and following conclusions can be drawn:(1)The experiment results using CaO-coal shows that:The decomposition process of rare earth minerals is divided into two stages.The first stages is the decomposition of REFCO3,and the decomposition temperature is between 380? and 431?.After two steps,the REFCO3 is decomposes to rare earth oxide.The second stages is the decomposition of REPO4,and the decomposition temperature is 605?716?.The CaO combined with CaF2 decomposes the REPO4 to rare earth oxide.Meanwhile,the fluorine racts with CaO to form CaF2 and Ca5F(PO4)3 which is left in the slag.The morphology of rare earth minerals changes greatly before and after decomposition.The surface of rare earth minerals is smooth and compact before decomposition,but after decomposition,the surface changes loose and rough.The optimum technological conditions are defined as a roasting time of 60 min,roasting temperature of 750?,and 20%CaO addition.The maximum decomposition rate of rare earth minerals reaches 99.87%.In addition,the fixing fluorine rate is 94.35%under the optimum condition of rare earth minerals.(2)The experiment results using CaCO3-coal shows that:The decomposition process contains two steps.The first step is the decomposition of REFCO3,and the decomposition temperature is 454?495?.The REFCO3 is decomposed to REOF only in the first steps.The second step is the decomposition of REOF and REPO4,and the decomposition temperature is 669?755 The REOF is decomposed to rare earth oxide,and the REPO4 is decomposed to rare earth oxide under the effect of CaCO3 and CaF2.The surface of rare earth minerals changes from smooth and compact to loosen and rough.The optimum technological condition are that roasting time 60min,roasting temperature 750? and CaCO3 addition 30%.The maximum decomposition rate is 98.01%.And the fixing fluorine rate is 94.75%under the optimum technological condition of rare earth minerals.(3)The experiment results using Ca(OH)2-coal shows that:The decomposition processes are divided into two steps.The first step is the REFCO3 decomposed to rare earth oxide,the decomposition temperature is between 380? and 441?.The second step is the REPO4 decomposed to rare earth oxide,the decomposition temperature is between 605? and 705 ?.The optimum technological condition is that roasting time 60 min,roasting temperature 700?,Ca(OH)2 addition 30%.The maximum decomposition rate is 97.85%.And the fixing fluorine rate is 96.57%under the optimum technological condition of rare earth minerals.(4)Compared with the result of the three different calium to decompose the mixed rare earth tailing shows that:Ca(OH)2 and CaO is more suitable for roasting the rare earth tailing.(5)The result of HCl leaching the roasting ore shows that:The optimum leaching condition is leaching time 60 min,leaching temperature 80?,HCl concentration 3 mol·L-1,liquid to solid 16:1,stirring speed 300 r·min-1.The maximum leaching rate of rare earth oxide is 98.68%.(6)The result of HNO3 leaching the roasting ore shows that:The optimum leaching condition are defined as a leaching time of 70 min,leaching temperature of 80 ?,HNO3 concentration of 3 mol/L,liquid to solid of 20:1,stirring speed of 300 r/min,the leaching rate is 96.98%.(7)In lower temperature,the result of H2SO4 leaching the roasting ore shows that:The optimum leaching condition are defined as a leaching time of 60 min,leaching temperature of 80?,H2SO4 concentration of 1 mol/L,liquid to solid of 20:1,stirring speed of 300 r/min,the leaching rate is 85.43%.(8)In higher temperature,the result of H2SO4 leaching and fefluorinating by distillation shows that:The optimum leaching condition of rare earth are that leaching time 90 min,H2SO4 concentration of 9 mol/L,liquid to solid of 16:1,stirring speed of 900 r/min,the leaching rate is 91.27%.Meanwhile,the defluorination rate is 98.52%under the optimum leaching rate of rare earth.(9)The result of comparative analysis between HCl,HNO3 and H2SO4 shows that:The leaching agent of HCl is the preference,and the HNO3 is the second.But H2SO4 is not suitable for leaching rare earth oxide which is roasting use Bayan Obo tailing.