Separation of Metal Ions from Aqueous Solutions Using Precipitate Dissolved Air Flotation

Dissolved air flotation technique has been applied to the separation of Zn(OH)2 and Cu(OH)2 flocs formed by addition of caustic soda to 1.0 dm3 aqueous solutions containing ions of these metals individually and together. Metal ions were precipitated as hydroxides at solution pH 8 – 10. The effect of air-to-solid ratio on flotation efficiency was quantified and tested for physical flotation and flotation preceded by addition of alum, ferric chloride and sodium dodecyl sulfate. Zinc ions are removed with high efficiency in the presence of Al or Fe (up to 92.3%). Physical flotation yielded close to 100% removal of copper ions. Residual Zn and Cu concentrations obtained were as low as 0.54-7.7 and 0.39-0.55 mg/L, respectively, depending on initial metal ion concentration, pH and air pressure. Copper removal was high at pH 8 and more while zinc removal is less efficient at pH levels below 10 due to solubility limitations.