Ion flotation for removal of Ni(II) and Zn(II) ions from wastewaters

• Ion flotation is the best method for removal of heavy metals from wastewaters.
• A recovery of Zn2 + of more than 92% and a recovery of 88% Ni2 + were achieved.
• Recovery increases by increasing agitating speed, water recovery and flotation time.
• Zn2 + preferential removal is proportioned to ionic radius.
• Ni2 + and Zn2 + ion combination's presence in solution decreases ion recovery.

Ion flotation was applied to Ni(II) and Zn(II) cation removal from low concentration synthetic wastewaters. Ethylhexadecyldimethylammonium bromide (EHDABr) and sodium dodecyl sulfate (SDS) were used as collectors and Dowfroth250 and methyl isobutyl carbonyl (MIBC) as frothers. The effective parameters were investigated by the experimental design performed by DX7 software. In this regard, a two-level factorial method was used, and sixteen experiments including 6-level variables were designed. In the first step, the tests were conducted in a Hallimond tube. It was concluded from test results that the optimum conditions for the removal of Ni(II) and Zn(II) ions by initial concentrations of 10 ppm were: pH = 3, SDS = 300 ppm, Dowfroth250 = 90 ppm and air flow rate = 1.8 ml/min. In the second step, optimal results from the first step were evaluated in a mechanical flotation cell. In optimal conditions, the recovery of Ni(II) and Zn(II) ions were 88% and 92%, respectively at 60 min. This study showed that the use of ion flotation is a very effective method for Ni(II) and Zn(II) ion removal from industrial wastewaters. The flotation time in achieving an optimum recovery of Zn(II) ions is shorter than that for Ni(II) ions.