Metal surface treatment processes such as degreasing, acid pickling, alloy baths or lacquering generate liquid wastes. Pickling with hydrogen chloride (HCl) is the procedure most commonly used to remove impurities from metal surfaces. Once used, the acid is diluted and cannot be reused, so it is disposed of along with the impurities it contains.
Metal finishing processes generate large amounts of this so-called ‘spent pickling liquor’ (SPL) The corrosive liquid contains dissolved metal salts of iron, chromium, copper, nickel and zinc. It is considered a toxic and hazardous waste.
Some surface treatment plants use a technique called hot-dip galvanisation, in which cleaned steel, iron or aluminium components are coated with zinc to prevent them from rusting. The process, which involves dipping metal into molten zinc at around 450°C, generates large volumes of wastewater. This spent strip liquor (SSL) is also considered toxic and hazardous.
SPL and SSL represent a serious environmental problem as they contain nitrates, fluorides, acids and a high metals content of metals. They are usually neutralised with alkali substances, but this still creates disposal problems due to the high salinity of the treated effluent and the generation of large amounts of sludge that must be made inert before it can go to landfill.
LIFE DIME will validate an innovative solution for treating wastewater from metal industry finishing activities. In particular, the project will integrate three technologies (extraction, crystallisation and membrane distillation) in a new pilot plant. This solution has never been tested before at pilot scale and it is expected to recover raw materials from this hazardous waste-stream of a value estimated at over €550 000 per plant per year. This will be achieved through the following specific actions:
The project is fully in line with the objective of the Water Framework Directive to achieve good quality status for all EU water bodies. It will also directly contribute to the implementation of the Industrial Emission Directive, as the processing of metals is included in Annex I of the Directive and LIFE DIME technology has the potential to become a Best Available Technology (BAT).