Selective recovery of heavy metals from hot-dip galvanising effluent streams by membrane-based solvent extraction

The hot-dip galvanising process produces a large quantity of acidic effluent high in iron, zinc and chloride ions. The current method for disposal of the waste acid is to neutralise the remaining hydrochloric acid (HCl) to precipitate a worthless, environmentally harmful mixture of iron and zinc hydroxides that be disposed of to specialised landfill sites. The recovery of any of these species is of economic interest due to the minimisation of waste-transport costs and the recovery of saleable by-products. In this work, a membrane-based solvent extraction process is being developed for the selective recovery of zinc over iron. Using a laboratory scale hollow fibre contactor, the key operating parameters including feed and organic flow rates, as well as their position within the contactor (shell or tube-side), are being systematically analysed. The results of the project should provide sufficient process information to permit the construction of a pilot scale effluent treatment process.