Study Of RE, P And F Recovery From Baotou Mixed Rare Earths Concentrate

The biggest storage and output of rare earth resource is Baotou mixed rare earth concentrate in world. This mineral is not easy to process due to its complex constituents and containing monazite which is difficult to be decomposed. Up till now the widely used methods of processing the Baotou mixed rare earth concentrate are to decompose it with sulfuric acid or NaOH, but these methods have the questions of cost and environmental protection. Therefore, exploitation and utilization of Baotou mixed rare earth concentrate with and reasonable and optimized method means a great deal to our country. In this thesis, the products from calcined Baotou mixed rare earth concentrate by CaO-NaCl-CaCl2 is investigated, a new clean technology of recovery RE, P and F from the products is designed, and the technology parameters and reactions mechanics of the new technology are studied.The results of pH value titration, spectrophotometric and FT-IR analysis testify that the mixed rare earth elements coordinate with citric acid through carboxyl and hydroxyl in water solution, and the coordination substances of REH2AOH2+, REHAOH+, REAOH and REAO-is coexistence in solution. With increasing pH value, the coordination modes change from monodentate ligands to bridiging ligands, and to monodentate ligands again. The coordination stability constants (β) of rare earth and citric acid are studied by pH potentiometric titration, and the results are lgβ1=9.1 for REH2AOH2+, lgβ2=13.4 for REHAOH+, lgβ3=14.2 for REAOH and lgβ4=16.1 for REAO- respectively. Rare earth still coordinates with citric acid when exists Ca2+, F- and PO43-. The conditional coordination stability constants are lgβ1=6.9,lgβ2=10.8,lgβ3=12.9,lgβ4=13.1 as existing Ca2+,lgβ1=6.1,lgβ2=9.3,lgβ3=11.5, lgβ4=12.2 as existing F-, and lgβ1=6.5,lgβ2=9.7,lgβ3=12.3,lgβ4=12.7 as existing PO43-.The technology parameters and the kinetic of the calcination products washed by HCl-H3AOH and basified by NaOH are studied. The results show that, when HCl concentration 0.5mol·L-1,citric acid concentration 0.05mol·L-1,liquid to solid 10:1,stirring speed 200 r·min-1.30℃and 25min, the phosphorus dissolution ratio is optimized to 99.45%. At the conditions of pH value 9, room temperature,25min, the recovery ratio of phosphorus from alkali acid washing solution is 99.51%,and the loss ratio of rare earth is only 0.98%. The hydroxyl calcium phosphate in processing of alkali precipitation is determined by theoretical calculation and XRD analyze. The process of acid washing and alkalization match to kinetic equation of 1-(1-α)1/3=Kt, and the reaction rate is controlled by chemical reaction control mode(20～40℃),mixed control mode(40-50℃) and diffusion control mode(50～60℃) respectively. The apparent activation energy of acid washing are E1=42.35kJ·mol-1for chemical reaction control mode, E2=21.31kJ·mol-1 for mixed control mode, E3=1.18 kJ·mol-1 for diffusion control mode respectively, and those of alkalization process are E1=43.3 kJ·mol-1, E2=27.4 kJ·mol-1,E3=3.03 kJ·mol-1 respectively.Furthermore, the technology parameters and the kinetic of acid washing minerals leaching by HCl-AlCl3 to dissolve RE2O3 and CaF2 are studied. The leaching ratio of RE2O3 and CaF2 is up to 70.8% and 55.8% respectively at the optimization parameters of HCl concentration 3 mol·L-1,Al3+ concentration 0.5 mol·L-1,liquid to solid 10:1,stirring speed 200 r·min-1,60℃with 60min. The leaching ratio of RE2O3 and CaF2 is to 99.62% and 98.56% respectively when quinternary contraflow leaching at the same parameters.The leaching process match to kinetic equation of 1-2/3α-(1-α)2/3=Kt, and the reaction rate is controlled by mixed control mode. The apparent activation energy of RE2O3 and CaF2 leaching process are ERE2O3=33.64 kJ·mol-1,ECaF2=23.68 kJ·mol-1.The studying results of kinetic show that the reaction rate increases with the increase of temperature, reactant concentration and stirring speed. Rare earth is recovered by P204 extraction from leaching solution, and the recovery ratio is 98.6%. The sodium fluoaluminate is recovered from faffinate adding NaOH, and the recovery ratio of fluorine is 93.8%.The treating procedures of calcined Baotou mixed rare earthconcentrate by CaO-NaCl-CaCl2 are verified by full-flow experiments. The results show that the direct recovery ratio of rare earth is 98.28%,fluorine is 84.3%,phosphorus is 96.36% and calcium is 41.17%. The loss of rare earth in full-flow is 0.7% in rare earth faffinate,0.36% in leaching slag,0.16% in filtrate of recovery sodium fluoaluminate and 0.21% when operation. The loss of fluorine is 8.16% in alkali precipitation,1.36% in leaching slag,5.69% in recovery filtrate of sodium fluoaluminate, and 0.49% when operation. The loss of phosphorus is 2.69% in leaching slag,0.13% in filtrate of recovery phosphorus, and 0.82% when operation. The loss of calcium is 1.39% in recovery rare earth oxide,0.4% in recovery sodium fluoaluminate, 7.63% in filtrate of recovery rare earth,48.9% in filtrate of recovery sodium fluoaluminate, and 0.51% when operation.The new clean technology of recovery RE, P and F from calcinations products satisfy the requirement of industry production, resource utilization, and environmental protection.