Investigation of organic losses in solvent extraction circuit due to solubility/degradation

Solvent losses in a solvent extraction circuit are some of the most important issues. The losses of solvents may occur in a several ways in any solvent extraction process, which include solubility in the aqueous phase, entrainment, evaporation/volatilization, crud formation and degradation. To prevent the loss of the extractant during metal extraction process the solubility/degradation loss of different organophosphorus acidic extractant were investigated. Two types of extractant candidates such as Cyanex 272 (bis-2, 4, 4-trimethylpentylphosphinic acid) and D2EHPA (Di-(2-ethylhexyl) phosphoric acid) were examined. Sulphuric acid (H₂SO₄) was used in this experiment as an aqueous medium. Phosphorus (P) content in the aqueous phase was measured by inductively coupled plasma spectroscopy (ICP). Initial concentrations of phosphorus in all the reagents were measured before contacting with aqueous phase which acts as a baseline concentration of phosphorus. After contacting with organic phase the solution were transferred to the seperatory funnel for at least 24 hr to attain equilibrium and complete phase separation. The aqueous phase was separated and centrifuged to avoid any kind of entrained organic. To be more accurate SP1 filter paper was used before ICP analysis of the aqueous solution. Based on phosphorus content in the aqueous phase, the effect of different parameters such as acid concentration, extractant concentration, temperature, diluent concentration, metal concentration and impurity concentration were investigated. The kinetics study on the solubility/degradation was also investigated in this research at 25 °C and 50 °C. -- Phosphorus in the aqueous phase might come due to the solubility or degradation or phosphorus dissolution of Cyanex 272 and D2EHPA. In order to ascertain the source of phosphorus a gas chromatographic (GC) analysis of the organic sample was performed followed by mass spectrometry (MS). Initially, gas chromatography of each reagent and solution were performed separately before and after contacting with acid. No degraded compound or material was found from the GC-MS analysis. By combining and analyzing the results from ICP-MS or GC-MS, the conclusion is that though there are some solvent losses in the aqueous phase due to the phosphorus dissolution, there is no degradation of Cyanex 272 and D2EHPA in the experimental condition that had been used