Removal of cadmium from dilute solutions by flotation

Abstract

Cadmium constitutes a priority pollutant existing in waste streams from metal plating and various other industries. The removal of this toxic metal employing the dissolved air flotation technique was investigated in laboratory batch experiments; the mechanism of precipitate flotation as the respective hydroxide was followed. Main examined parameters include: recycle ratio, pH of the solution, concentrations of added surfactant (sodium dodecyl sulphate), frother (ethanol) and cadmium. Promising results have been obtained, at the pH range between 10 and 11 approximately, showing the significance of flotation as a separation process in water and wastewater treatment for dilute solutions (around 10 mg/l of metal). Under the optimum conditions removal of cadmium was near to 100%, while the remaining concentration in the solution after flotation was less than 0.10 mg/l. A comparison was also attempted between two flotation techniques applying different bubble generation methods, i.e. dissolved air and dispersed air flotation. These experiments run in parallel and under the same conditions.