Solution equilibrium calculations were performed in this study to understand the impact of contaminant metal ions on the precipitation efficiency of selected rare earth elements(Ce^(3+),Nd^(3+),and Y^(3+))using oxalic...Solution equilibrium calculations were performed in this study to understand the impact of contaminant metal ions on the precipitation efficiency of selected rare earth elements(Ce^(3+),Nd^(3+),and Y^(3+))using oxalic acid as a precipitant.Trivalent metal ions,Al^(3+) and Fe^(3+),are found to considerably affect the precipitation efficiency of REEs.When Al^(3+) and Fe^(3+)concentrations are increased by 1×10^(−4) mol/L,in order to achieve an acceptable cerium recovery of 93%from solutions containing 1×10^(−4) mol/L Ce^(3+),oxalate dosage needs to increase by 1.2×10^(−4) and 1.68×10^(−4) mol/L,respectively.Such great impacts on the required oxalate dosage are also observed for Nd^(3+) and Y^(3+),which indicates that oxalic acid consumption and cost will be largely increased when the trivalent metal ions exist in REE-concentrated solutions.Effects of the divalent metal ions on the oxalate dosage are minimal.Furthermore,solution equilibrium calculation results show that the precipitation of Fe^(3+) and Ca^(2+)(e.g.,hematite and Ca(C_(2)O_(4))∙H_(2)O(s))likely occurs during the oxalate precipitation of REEs at relatively high pH(e.g.,pH 2.5),which will reduce rare earth oxalate product purity.In addition to the metal ions,anionic species,especially SO_(4)^(2-),are also found to negatively affect the precipitation recovery of REEs.For example,when 0.1 mol/L SO_(4)^(2-) occurs in a solution containing 1×10^(−4) mol/L Ce^(3+) and 4×10^(−4) mol/L oxalate,the pH needs to be elevated from 2.0 to 3.3 to achieve the acceptable recovery.Overall,findings from this study provide guidance for the obtainment of high-purity rare earth products from solutions containing a considerable amount of contaminant metal ions by means of oxalic acid precipitation.展开更多
文摘Solution equilibrium calculations were performed in this study to understand the impact of contaminant metal ions on the precipitation efficiency of selected rare earth elements(Ce^(3+),Nd^(3+),and Y^(3+))using oxalic acid as a precipitant.Trivalent metal ions,Al^(3+) and Fe^(3+),are found to considerably affect the precipitation efficiency of REEs.When Al^(3+) and Fe^(3+)concentrations are increased by 1×10^(−4) mol/L,in order to achieve an acceptable cerium recovery of 93%from solutions containing 1×10^(−4) mol/L Ce^(3+),oxalate dosage needs to increase by 1.2×10^(−4) and 1.68×10^(−4) mol/L,respectively.Such great impacts on the required oxalate dosage are also observed for Nd^(3+) and Y^(3+),which indicates that oxalic acid consumption and cost will be largely increased when the trivalent metal ions exist in REE-concentrated solutions.Effects of the divalent metal ions on the oxalate dosage are minimal.Furthermore,solution equilibrium calculation results show that the precipitation of Fe^(3+) and Ca^(2+)(e.g.,hematite and Ca(C_(2)O_(4))∙H_(2)O(s))likely occurs during the oxalate precipitation of REEs at relatively high pH(e.g.,pH 2.5),which will reduce rare earth oxalate product purity.In addition to the metal ions,anionic species,especially SO_(4)^(2-),are also found to negatively affect the precipitation recovery of REEs.For example,when 0.1 mol/L SO_(4)^(2-) occurs in a solution containing 1×10^(−4) mol/L Ce^(3+) and 4×10^(−4) mol/L oxalate,the pH needs to be elevated from 2.0 to 3.3 to achieve the acceptable recovery.Overall,findings from this study provide guidance for the obtainment of high-purity rare earth products from solutions containing a considerable amount of contaminant metal ions by means of oxalic acid precipitation.
