Cobalt removal from an industrial effluent by foam fractionation

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In this study, the removal of cobalt from an effluent was investigated probably for the first time by foam fractionation. Foam fractionation is considered as a green method because of its friendly nature, high removal efficiency, costs effectiveness and non-hazardous nature. Sodium dodecyl sulfate (SDS) was used as an anionic surface-active agent and the effect of gas flow rate, the initial concentrations of surfactant and cobalt and pH on the cobalt removal efficiency was investigated. The results showed that by increasing surfactant concentration and gas flow rate, the cobalt removal efficiency would be improved however, the cobalt concentration in foamate would decrease at high gas flow rates. High gas flow rates generally produce dilute foamate. Drainage of the interstitial bulk fluid that is entrapped between the foam bubbles has a key importance in the normal performance of the foam fractionation operation. Experiments showed that the well-drained foams are low in volume and high in Co2+ leading to an easier separation of their ingredients that usually follows. The efficiency reached the highest when cobalt feed concentration was about 1 mg/L, but dropped gradually in higher concentrations. By increasing pH to around 5, high removal efficiency was achieved and then decreased again. The optimum conditions for high cobalt removal efficiency were obtained when SDS concentration was about 100 mg/L and the initial cobalt concentration was below and close to 1 mg/L. The results of experiments revealed that the amount of cobalt removed per unit weight of SDS was higher for low [SDS]/[Co2+] ratios. They also showed that the air–liquid interface coverage by surface excess solute ions would not be more that 5% of the total area. Under optimum conditions for cobalt removal pH value and gas flow rate were found to be around 5 and 9 L/h, respectively. Under these conditions the removal efficiency was shown to be 99.4%.