Separation of cobalt and nickel by nanofiltration using a FilmTec membrane

Experiments of cobalt and nickel ions separation have been carried out. The chemical process used was the nanofiltration using Filmtec-NF270 membrane as a filtration membrane, charged negatively, in a total recycling system. The optimization of separation process of Co(II) and Ni(II) chlorides, from their synthetic mixture, was conducted by optimizing one operating parameter at a time. Several parameters, such as hydraulic permeation of membrane, transmembrane pressure, initial concentration of feed solution, and pH of feed solution, were studied. The results showed that under the conditions of moderate pressure, slightly acidic medium of feed phase and at equimolar mixture of metal ions; the retentions were 100 and 91.94% for cobalt and nickel, respectively. The retention of nickel will become total if the quantity of cobalt, in mixture, was six times more concentrated. In fact, the retention of metal ions remained more quantitative when using nitrate ions as counter-ions where the rejections were of 0 and 18% for cobalt and nickel ions, respectively, at a conversion equal to 0.11. The retention of metal ions towards the used membrane was conducted by the Donnan and steric effects. This was confirmed by the form of metal ion species found by speciation software and taken by the transport mechanism by nanofiltration.