Recovery of Anionic Surfactant Through Acidification/Ultrafiltration in a Micellar-Enhanced Ultrafiltration Process for Cobalt Removal

In this article, removal of cobalt ions from synthetic liquid wastes aimed at surfactant and water reuse was carried out using a micellar-enhanced ultrafiltration (MEUF) process, adding an anionic surfactant (sodium dodecyl sulfate or SDS), with a lab-scale ceramic ultrafiltration membrane. In the first part of the study, ultrafiltration was studied to define the removal yields of cobalt from initial solutions. During these experiments, the effect of membrane size (1-210 kDa) and surfactant concentration (0-4-10 mM) was studied. Results showed a positive effect of surfactant on removal efficiency; maximum yields (>90%), with an initial cobalt concentration of 9.7 mg/L, were obtained by using the highest level of surfactant. After ultrafiltration, separation of metal and recovery of surfactant was carried out by acidification with sulfuric acid followed by another step of ultrafiltration. Results of the second series of experiments showed that separation yields for cobalt >96% could be obtained after acidification to a pH=1. Regarding SDS recovery, as a consequence of acidification, the pore size of the membrane was enlarged so that SDS micelles could pass through the membrane, resulting in lower yields with respect to metal rejection. In this article, hence, the technical feasibility of MEUF combined with acidification to remove heavy metals and recover surfactant was demonstrated. This last step is important to reduce the high operative costs due to the use of surfactant.