Lead (II) ion coexisting in a plating bath as an impurity, of which source is chemical agents and/or dissolution of electrode, adversely affects the plating finish. We attempted the removal of trace amounts of lead (II) ion using inorganic adsorbents. Adsorption test for 5mg dm-3 of lead (II) ion in an iron-zinc alloy plating bath [FeSO4⋅7H2O 300gdm-3, ZnSO4⋅7H2O 150gdm-3, (NH4)2SO4 30g dm-3, and citric acid 10g dm-3] with various inorganic substances was carried out by means of batchwise operation. Of these substances, hydrous antimony (V) oxide exhibited the outstanding ability, but the fact that antimony (V) ion tended to leach out to the bath was undesirable. However, it was found that silica-titania mixed-oxide gel was favorable for the adsorption of the antimony (V) ion.
After the flow of 6dm3 of the plating bath containing 5mg dm-3 lead (II) ion through two columns of 10mm inner diameter connected in series (the first packed with 3g of hydrous antimony (V) oxide and the second with 3g of silica-titania gel) at a rate of 1cm3min-1, the concentration of lead (II) ion in the effluent was still kept below 0.17mg dm-3, which corresponded to a removal rate of 97%.
