Modeling Organophosphoric Acid-based Solvent Extraction of Light Rare Earths with Genetic Algorithms

The increasing demand for light rare earth elements (LREEs), including lanthanum (La), cerium (Ce), praseodymium (Pr), and neodymium (Nd), motivates the development of solvent extraction predictive models to design a more efficient separation system. However, LREEs solvent extraction reactions with D2EHPA or PC88A are usually assumed to follow M3++3HA2‾⇌MHA23‾+3H+, which is not correct for all cases. By implementing genetic algorithms, the present study concluded that species like MCl2+ and MCl2+ (M = La, Ce, Pr, or Nd) have more distinct roles compared to M3+ in a concentrated chloride system using D2EHPA or PC88A, proving the involvement of speciation in solvent extraction reactions. The current study evaluated and offered a genetic algorithm method to model reactions governing LREEs solvent extraction considering either a single-reaction system or a multi-reaction system involving speciation, resulting in the reactions as shown in EquationEqs. 6(6) {LaCl2++3HA2‾⇌LaClA2H2AH2‾+2H+,HA=D2EHPALaCl2++2HA2‾⇌LaCl2A2H‾+H+,HA=PC88A(6) , Equation10(10) {CeCl2++3HA2‾⇌CeClA2H2AH2‾+2H+,HA=D2EHPACeCl2++2HA2‾⇌CeCl2A2H‾+H+,HA=PC88A(10) , Equation11(11) {PrCl2++3HA2‾⇌PrClA2H2AH2‾+2H+,HA=D2EHPAPrCl2++2.5HA2‾⇌PrClA2H2AH2‾+2H+,HA=PC88A(11) , and Equation9(9) NdCl2++2.5HA2⇌NdClA2H2AH2+2H+,HA=PC88A(9) .(6) {LaCl2++3HA2‾⇌LaClA2H2AH2‾+2H+,HA=D2EHPALaCl2++2HA2‾⇌LaCl2A2H‾+H+,HA=PC88A(6) (10) {CeCl2++3HA2‾⇌CeClA2H2AH2‾+2H+,HA=D2EHPACeCl2++2HA2‾⇌CeCl2A2H‾+H+,HA=PC88A(10) (11) {PrCl2++3HA2‾⇌PrClA2H2AH2‾+2H+,HA=D2EHPAPrCl2++2.5HA2‾⇌PrClA2H2AH2‾+2H+,HA=PC88A(11) (9) NdCl2++2.5HA2⇌NdClA2H2AH2+2H+,HA=PC88A(9)