Continuous removal of toxic nickel from industrial wastewater by flotation-adsorption with multi-walled carbon nanotubes: kinetic and adsorption isotherms

Nickel is a toxic metal ion present in industrial wastewater. In this study, ion flotation combined with multi-walled carbon nanotubes (MWCNTs) adsorbent experiments was performed to investigate the removal of nickel ions from aqueous solution. Various parameters such as aeration time, sodium dodecyl sulfate and MWCNTs concentrations, pH, surfactant, frother concentrations and airflow rate were tested to determine the optimum flotation conditions. Sodium dodecyl sulfate was used as collectors. Ethanol was used as frother. In the airflow of 150 mL/min and after 5, 15, 30, 60, 90 and 120 min of ion flotation with MWCNTs adsorbent, the efficiency of nickel removal was 14%, 24%, 33%, 38%, 44% and 48%, respectively. The maximum reduction in the concentration of nickel occurs at 30 mg/L concentration (with removal efficiency of 71.7%). This method reduces the time to reach equilibrium point and increases the minimum concentration to adsorb. The results show that the combination of ion flotation method and adsorption with MWCNT works well for reduction in the concentrations of compounds such heavy metal ions.