Enhanced removal of mixed metal ions from aqueous solutions using flotation by colloidal gas aphrons stabilized with sodium alginate

Anionic surfactant sodium dodecyl benzenesulfonate (SDBS) was used to prepare colloidal gas aphrons (CGAs). Bio-polymeric sodium alginate was added to enhance the removal efficiencies of mixed metal ions such as lead (Pb²⁺) and copper (Cu²⁺) from aqueous solutions via flotation. Stirring speed of 3000 rpm was maintained to produce CGAs containing 500 mL surfactant solutions. The effects of concentration of metal ions, volume of liquid in the flotation column, CGAs loading rate, and pH of solution on the removal of heavy metals were examined. CGAs loading rate of 6.1 cm/min (flow rate 120 cm³/min) to the flotation column containing 2.0 mM of mixed metal ions (0.4 mM of Pb²⁺ and 1.5 mM of Cu²⁺ ions) at pH 5.35 gave the maximum removal of 96% for Pb²⁺ ions and 81% for Cu²⁺ ions. However, the net amount of copper ions removed was much higher than the lead ions. Addition of calcium chloride to the retentate solution further increased the removal to be 99% for Pb²⁺ and 92% for Cu²⁺ by producing alginate gel with metal ions that precipitated out from the solutions. Interestingly, sodium alginate stabilized CGAs improved significantly the removal of metal ions from aqueous solutions by flotation.