Lead (II) impurity in zinc or zinc-alloy plating baths has an adverse effect on the finish. To remove this lead (II) we attempted the separation of lead (II) and zinc (II) coexisting in aqueous solutions using silica-titania gel, which is known to be porous and stable at high temperatures.
It was first found that in a solution containing 10mg dm-3 of both lead (II) and zinc (II) equimolar silica-titania gel solely adsorbed lead (II) at pH 2.4 and it was therefore realized that the separation of both metals dissolved in solutions was possible at this pH range by means of gel adsorption. At the zinc concentrations up to 104mg dm-3, lead removal efficiency was high. The relationship between the equilibrium concentration in solution and the amount of metal adsorbed obeyed the Freundrich adsorption isotherm. The optimum composition of silica-titania gel here was 3:1. The silica-titania gel may be reused repeatedly with elution of the adsorbed lead (II) using 1M nitric acid, followed by surface treatment with 1M sodium nitrate solution.
