SEPARATION OF COBALT AND NICKEL IONS IN LITHIUM-NITRATE SOLUTIONS BY SOLVENT-EXTRACTION AND LIQUID MEMBRANE WITH HEHEHP KEROSENE SOLUTION

The separation of cobalt(II) and nickel(II) ions in lithium nitrate solutions with 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (HEHEHP) dissolved in kerosene has been studied by solvent extraction and liquid membrane at 25.0 +/- 0.1-degrees-C. The distribution ratios of each metal increased with an increase in the HEHEHP concentration in the organic phase and pH value in the aqueous solution. However, the distribution ratio was independent of the metal ion concentration at constant pH and HEHEHP concentration. The equilibrium constants of cobalt and nickel are found to be 5.76 x 10(-6) and 5.66 x 10(-7) m3 kmol-1, respectively. The permeabilities of cobalt(II) and nickel(II) are found to be dependent on the stirring rate, the pH value of the feed solutions, the metal ion concentrations in the feed solutions and on the carrier concentration in the supported liquid membrane. The experimental data also show that the separation factor increases on increasing the stirring rate, the pH value of the feed solution and the concentration of metal ions in the feed solution. However, the separation factor decreases with the concentration of HEHEHP in the organic phase.