The study was carried out on the mechanism of stripping and crystallization of Co extracted in Versatic Acid 10-kerosene solution by applying high pressure CO2 and water. At the experimental condition of 25°C, 0.5 mol/l of VA10 concentration and 15 atm CO2 pressure, the degree of Co stripping was found to decrease slightly from 99.9 to 98.4% with initial concentration of Co in organic phase in its range of 2.56×10-3 to 0.109 mol/l. In these runs, any solids were not observed in aqueous phase inside the autoclave after opening it. At more than 0.124 mol/l, there were observed two different appearances of crystallization. In one case (0.124, 0.134 mol/l), organic and aqueous phases were separated each other clearly and the latter contained fine powders, which was probably caused by reducing pressure. In the other one (0.216mol/l), the content in a vessel showed a mixed state of suspension of organic, aqueous and solid phases, which was supposed to have already occurred under high pressure. The distribution ratio in the stripping runs was found much smaller at the same pH values than in the extraction ones. The thermodynamic equilibrium on Co stripping reaction by CO2 was calculated using the extraction data and found to represent the actual behaviors of stripping qualitatively. Furthermore, the calculation of ionic product for CoCO3 revealed that the aqueous phase after stripping was supposed to be under supersaturation throughout the corresponding region of non-crystallization.
