| Baotou rare earth resources of China are mainly mixture mineral of bastnaesite and monazite, and relative content of two mine was9:1-1:1, has nothing to do with the grade of rare earths. The chemical formula of bastnaesite and monazite are the REFCO3and REPO4, respectively. It is deemed the most difficult to deal with rare earth mine because the chemical properties of monazite and bastnaesite are different, and the monazite is stable than the bastnaesete. At present, the decomposition methods of industrial production are mainly concentrated sulfuric acid roasting and caustic soda, baotou rare earth ore smelting enterprises of more than90%adopt the method of concentrated sulfuric acid roasting at high temperature, but it is easy to produce large amounts of waste gases, high energy consumption and serious environmental pollution. Method of alkali decomposition was limited because of high quality requirements, the production process of rare earth concentrate discontinuous long wait for a reason and longer decomposition time. In this paper, we studied a method of leaching bastnaesite of baotou rare earth concentrate by different complexing leaching agent based on the principle of complexation extraction, and determined a optimization conditions, then rare earth elements in the solution was separated by the method of double salt precipitation, and aluminum and fluoride elements in the waste liquid were changed into available resources. The main content of paper summarized as follows:1. Through thermodynamic calculation, complex stability constant comparison and experiment, preliminary exploration of the experiment system of complexing leaching effect is better than that of ferric salt system complexing effects, through the preliminary conditions experiment contrast HCl-AlCl3system for rare earth concentrate leaching rate and the concentrate of rare earth leaching rate are higher than HCl-FeCl3system by about30%.2. First, leaching rare earth concentration of HCl-AlCl3system condition of experiment were analyzed, and discussed the concentration of HC1, AlCl3concentration, temperature, solid-liquid ratio, stirring speed, time and so on. Conditions on the leaching effect, optimize the leaching conditions and technology as follows:the concentration of HC1is4mol·L-1, AlCl3concentration is1.5mol·L-1, leaching temperature is85℃, liquid-solid ratio is20:1and mixing speed is300rpm, the leaching time is90min. In the optimization of process conditions, the leaching rate of rare earth concentrate is76.83%, rare earth leaching rate is73.89%, the leaching rate of fluoride is98.74%, and the rare earth leaching rate of bastnaesite reaches98.76%.Second, the rare earth concentrate and HCl-AlCl3system leaching residue detection of the XRD, SEM, EDS and chemical analysis, the results show that the rare earth concentrates in bastnaesite and monazite in primary phase, concentration and surface between particles there are a lot of white particles, particles exterior smooth is, for the most part, smoothly, leaching slag only appeared in the solitary quarries, concentrate the white debris disappear, particle surface becomes uneven, obvious effect of the erosion and leaching residue in addition to the elements in the monazite also contains a small amount of Si and Fe elements. Through the above analysis can prove the bastnaesite concentrate with solitary stone has completely separated.Finally, study the bastnaesite leaching dynamics of the process, the analysis results show that the interfacial mass transfer and diffusion through the product layer hybrid control dynamics equations of1/3ln(1-α)+[(1-α)-1/3-1]=Kot well describe the process of leaching kinetics. Through graphic analysis and calculation can determine the concentration of rare earth leaching dynamics equation and the concentration of fluoride leaching dynamics equation.3. Same with the above method2, first of all, the HNO3-Al(NO3)3leaching system mixed rare earth concentrate of Bao Tou the conditions of the experiment were analyzed, and it is concluded that the optimization of the extraction technology conditions are as follows:concentration of HNO3is3mol·L-1, Al(NO3)3concentration is1.5mol·L-1, leaching temperature is100℃, liquid-solid ratio is30:1, mixing speed is300rpm, the leaching time is90min. Under the condition of optimization of rare earth concentrate leaching rate has reaches71.15%, the leaching rate of rare earth also reaches73.18%, the leaching rate of fluoride reaches97.59%, through the analysis of bastnaesite rare earth leaching rate reaches97.81%. The comprehensive comparison, HCl-AlCl3system has more advantages than HNO3-Al(NO3)3system.Second, the HNO3-Al(NO3)3system analysis of the XRD, SEM and EDS testing, the results are the same with experiment2, which shows that the HNO3-Al (NO3)3system is able to mix in Bao Tou rare earth concentrate in bastnaesite leaching.Finally, the leaching process of dynamic analysis, through the product layer interface dynamics equations of mass transfer and diffusion mixed controlled1/3ln(l-α)+[(l-α)-l/3-l]=Kot can well describe HNO3-Al(NO3)3system dynamics in the process of leaching. Temperature, concentration of HCl concentration, AlCl3and L/S are the main factors influencing the leaching speed, identified by graphical analysis and calculation in HNO3-Al(NO3)3system leaching rare earth concentrate when rare earth leaching kinetics are equation and fluorine elements leaching dynamics are equation. 4. Adopting double salt precipitation separation complexing extract of rare earth and rare earth elements, the system of AlCl3-HCl leaching Bao Tou rare earth mine rare earths effective precipitation in the leach liquor obtained, the results showed that the acidity of leach liquor has almostly no effect on rare earth yield; When the concentration of rare earth leaching liquid is20g·L-1, the reaction temperature is90℃, the reaction time is90min, sodium sulfate and the ratio of the rare earth oxide are4:1, under the condition of this optimization, rare earth leaching liquid of rare earth yield reaches97.53%.For double salt deposits are analyzed by XRD and SEM, the analysis result by XRD, sodium sulfate double salt precipitation from rare earth complex salt precipitation for mixed rare earth complex salt precipitation, with light rare earth is given priority to, loss of main heavy rare earth rare earth elements. SEM morphology analysis for the spindle, and evenly distributed. EDS spectrum analysis shows that in the process of double salt precipitation, Al and Fe, F the rare earth impurities without formation of precipitation. The above results show that the double salt precipitation leach liquor can be implemented effective separation of the rare earth and rare earth elements.5. By the conductivity method and fluorine ion tracer method and spectrophotometry for aluminum ion and fluorine ion complexing reaction behavior, the complex process of the two effective analyses. Aluminum ion and fluorine ions are in acidic condition, producing complexation reaction, and can form the coordination number is2～6complexes. Aluminum ion and fluorine ions in acidic condition, the formation of the complex complexes, the average coordination number is4, the highest coordination number is6.6. Using the double salt in the filtrate after precipitation of aluminum fluoride complexes, the applied fluoride saltand Na2CO3is adjusting pH conditions, can be synthesized cryolite, the optimal process conditions of synthetic cryolite process:pH=4.5, the synthesis temperature is75℃, aluminum fluoride ratio F/Al is6:1; in this condition, the crystallization of cryolite is better, fluorine and aluminum of the solution recoveries more then96%and97%.The synthetic cryolite for XRD, SEM-EDS and particle analysis, determined that the product synthesized is cryolite phase which flake stack together irregularly, the main elements in the crystal F, Na, Al, crystal concentrated in particles are between5μm-20μm powder cryolite, are of good filterability. |
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