Minimisation and recycling of spent acid wastes from galvanizing plants

The galvanizing process introduces environmental stresses from solid, liquid and air-borne emissions. Spent pickling acid represents the largest mass of such waste production, but its major constituent, iron chloride, could be used in the wastewater treatment industry to remove phosphate. A survey of the operational procedures adopted and the acid wastes produced by UK Galvanizers are reported. Various methods to produce spent acid of suitable composition have been investigated but elimination of zinc contamination of the acid was considered to be the only feasible method. Careful acid management is necessary to maintain low zinc levels, whilst substitution of titanium for mild steel jigs not only assists in reducing zinc in spent acid but also produces considerable savings in zinc carry-over on the jig. Application of the Kleingarn acid management system reduces waste volume, saves hydrochloric acid (HCl) and increases component throughput whilst, in conjunction with zinc elimination, could allow recycling of the majority of galvanizer's acid wastes.