Solvent extraction of zinc from synthetic Zn-Cd-Mn chloride solution using D2EHPA: Optimization and thermodynamic studies

The extraction of zinc in the presence of manganese and cadmium from chloride solution with di 2 ethyl hexyl phosphoric acid (D2EHPA) in kerosene diluent were comprehensively investigated. The extraction experiments were carried out in order to determine the influential parameters in the conditions of A:O ratio of 1:1, pH range of 1-6, temperatures of 30 degrees C, 40 degrees C and 50 degrees C in an aqueous solution with concentrations of 5 g/L of zinc, manganese and cadmium. The variety of influential parameters in the process such as equilibrium pH, concentration of D2EHPA, temperature, contact time, initial concentration of ions and also thermodynamic parameters of zinc extraction in chloride solution were precisely evaluated. The results showed that in the optimal condition of pH = 2.5-3, temperature 40 degrees C and [D2EHPA] = 10 v/v, the extraction of Zn, Mn and Cd were 97%, 14% and 3% respectively. Delta pH(0.5)(Zn center dot mn) and Delta pH(0.5)(Zn-cd) in this condition respectively equal to 2.5 and more than 5.25. Also, the study indicated that the predominant zinc species extracted by D2EHPA was ZnCl+. Based on thermodynamic studies, the values of Delta H degrees, Delta S degrees and Delta G degrees for zinc extraction in condition of temperature 40 degrees C and [D2EHPA] = 10 v/v are 25.65 kJ.mol(-1), 79.20 J.K(-1)mol(-1) and 0.86 kJ.mol(-1) respectively. Furthermore, the results showed that under constant concentration of D2EHPA, changes in the initial concentrations of Zn, Mn and Cd in the chloride solution were most effective in their separation.