Diffusion dialysis of sulphuric acid : crucial step for separation of cobalt (II) from an acid leaching solution

Abstract

In this work different processes are carried out to recover and separate cobalt(II) from a real mixture of sulphate and chloride leach solution. First, it is necessary to recover acid from the feed by means of diffusion dialysis. In this process different variables have been studied to determine the best operating flux rate and if the results are better with or without neutralization. In general, the results show better trend in the case of continuous neutralization of the diluate during DD because the driving force (gradient of H+ concentration) remains constant. Besides, at higher flux rates the H+ concentration in the diluate at the end of the experiment is higher which is desirable. In the case of working with different flux rates in the feed and in the diluate, it is more convenient to work with the feed faster than the diluate that backwards. But the final concentration of cobalt(II) in the diluate is lower when the flux rate of both phases (feed and diluate) is low too. For the dialysis coefficients (U) and the total acid recovery (EDD) the values are higher with lower flux rates too. About the metal ions rejection, the highest rejection for cobalt during diffusion dialysis is achieved when neutralization is carried out. After diffusion dialysis, precipitation of chromium(III) and aluminium(III) is carried out using sodium hydroxide solution. Then, it is necessary to centrifuge and filtrate the solution to obtain the clarified solution which is ready to perform the extraction (two stages) and stripping of cobalt(II). The distribution coefficient (D) for cobalt(II) after the second stage of extraction is higher with neutralization and the separation factor βCo(II)/Ni(II) is higher in the case of neutralization too. In general, the percentage of extraction (ESX) is much higher for cobalt(II) and chromium(III) than for the rest of metals. Finally, the total percentage of extraction (ΣESX) for cobalt is similar working at higher fluxes (0.057 L/min) and in the case of neutralization (approximately 80%). After the two stages of extraction, stripping is carried out and the organic phase can be regenerated which contributes to take care of the environment.