A study of the removal of metal ions from aqueous solution by adsorptive bubble separation methods

Abstract

A study has been made of the removal of copper (II) and zinc (II) metal ions from aquous solutions and effluents by dissolved-air flotation. The process involves the precipitation of the metal hydroxide species as floc particles and their subsequent flotation by small gas bUbbles' which are produced by the release, under shear, of pressurized air-saturated water into the solution at atmospheric pressure.
Optimum conditions for the removal of copper (II) and zinc (II) in the concentration range 10.0 ppm to 50.0 ppm have been established using a laboratory-scale apparatus. In addition the effects on flotation of using coagulation aids including iron (III) chloride aluminium (III) sulphate and a polyelectrolyte have been evaluated.
Selective removal of copper (II) andzinc (II) from admixture in solution has been achieved by careful ph adjustment and flotation of the particles formed.
The effects of variables including recycle, gas pressure, ionic strength and ph on the removal of metal ions have been studied and the results discussed in terms of the flotation process. The amount of gas released from solution at various pressures and the diameters of the gas bubbles produced have been experimentally determined. From these results optimum air to solids ratios have been calculated for a given system and an estimate made of the number of gas bubbles released.
The application of the laboratory dissolved-air flotation process to the treatnent of aqueous zinc (11)-bearing effluents from a rayon plant has been studied. The results obtained led to the design, construction and operation of a semi-continous pilot-plant apparatus on-site at the factory. Using this equipment optimum conditions were established for theremoval of zinc (II) from effluent solutions of varying composition and pt-I.