Optimizinge The Separation Of Rare Earth From Fluorine And Aluminum In Baotou Rare Earth Concentrate Complex Leaching Solution

As the most abundant single deposit in the world,the mixed rare earth ore in Baotou occupies a pivotal position in China’s rare earth industry.However,it is also recognized as the most difficult to deal with rare earth ore.It is mainly composed of mixed ore of bastnaesite（REFCO₃）and monazite（REPO₄）.The chemical properties of the two are inconsistent and difficult to decompose at the same time.At present,there are two main methods for treating rare earth concentrate developed in China,one is sulfuric acid roasting method,and the other is caustic soda method.The sulfuric acid roasting method has become the mainstream process in the industry because of its low cost,large scale and continuous production.However,with the development of modern society,the increasingly serious environmental pollution and waste of resources have become a major problem affecting the sustainable and healthy development of China’s rare earth industry.Aiming at some problems existing in the current process,this study innovatively proposes a new green process,which adopts H₂SO₄-Al₂（SO₄）₃system to leach Baotou mixed rare earth ore,and then uses N1923 combined with triisooctylamine to extract and separate rare earth and aluminum in the leaching solution and recover acid resources.For the fluorine and aluminum resources in the raffinate,cryolite is made by adding fluorine source for comprehensive recycling,while the remaining leaching residue（mainly undecomposed monazite）is recovered by traditional alkali process.The leaching process temperature of this process is low,the aluminum salt can fully complex F^-,and will not produce waste gas pollution.The subsequent solvent extraction process not only realizes the separation of rare earth elements from fluorine and aluminum,but also the acid,fluorine and aluminum resources are recycled,reducing the waste of resources.Firstly,the optimum leaching conditions for the decomposition of rare earth concentrate by H₂SO₄-Al₂（SO₄）₃system were determined as follows:100 mesh rare earth concentrate,H₂SO₄concentration is 3 mol/L,Al₂（SO₄）₃concentration is 0.30mol/L,reaction temperature is 135℃,liquid-solid ratio is 32:1,reaction time is 2 h,stirring speed is 200 r/min.Under this condition,the concentrate leaching rate of Baotou rare earth ore is 68.00%,and the rare earth leaching rate is 66.91%.The results of phase and chemical analysis of leaching residue and rare earth concentrate showed that the leaching rate of fluorine ion in mixed concentrate was 94.42%,and the decomposition rate of fluorite reached 99.3%.Then,the leaching rule of rare earth concentrate in H₂SO₄-HNO₃-Al₂（SO₄）₃system was further explored.The optimized leaching conditions were as follows:100mesh rare earth concentrate,c（1/2H₂SO₄）:c（HNO₃）=4:1,total H⁺concentration in solution was 6.0 mol/L,liquid-solid ratio was 32:1,aluminum sulfate concentration was 0.30 mol/L,reaction temperature was 135℃,reaction time was 2 h,stirring speed was 200 r/min.Under this condition,the leaching rate of concentrate is 72.8%,and the leaching rate of rare earth is 71.02%.The leaching residue of HNO₃-H₂SO₄-Al₂（SO₄）₃system was analyzed by XRD and chemical analysis.The leaching rate of fluorine was 98.52%,which proved that the introduction of nitric acid could further strengthen the decomposition and leaching of bastnaesite,and the full leaching of bastnaesite was basically realized.Finally,the separation of rare earth and aluminum in the leaching solution of H₂SO₄-Al₂（SO₄）₃system was investigated.The leaching solution was a strong acid and high aluminum solution.The H₂SO₄and HF in the solution were extracted and recovered by triisooctylamine,which can not only realize the recycling of acid,but also make the extraction effect of N1923 the best,and realize the separation of rare earth and aluminum.Under the optimum extraction conditions,59.96%of the acid in the leaching solution can be recycled,and the extraction rates of rare earth and aluminum are 97.38%and 8.61%,respectively.After ammonium sulfate backwashing and HCl stripping,the stripping rate of rare earth is 98.05%,and the c _Al3+/c _RE3+in the stripping phase is 0.008,which basically realizes the separation of rare earth and aluminum.N1923 extracts the fluorine-aluminum complex in the raffinate water phase after rare earth extraction,and generates cryolite by adding fluorine source to realize the recovery of fluorine-aluminum resources.