Demonstration of an Innovative technology for the Minimization of the Environmental impact of metal finishing processes.

PROJECT DESCRIPTION

BACKGROUND

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.

OBJECTIVES

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:

Demonstration of a zero liquid discharge process capable of reducing the potential environmental damage of SPL and SSL from pickling and galvanising operations, with no further sludge generation;

Mitigation of hazards from pickling wastewater, by regenerating ≥99% of the hydrogen chloride used to perform pickling operations;

Recovery of up to ≥99% of metal salts contained in SPL and SSL, with ferrous sulphate heptahydrate (Fe2SO4·7H2O) crystals commercialised as by-product (fertiliser), and zinc chloride (ZnCl2) fully reused in the galvanising process;

Evaluation of the feasibility for full-scale application of the solution in a real-world galvanising plant that generates 480 m3/year of SSL hazardous wastewater;

Creation of business models to establish a strategy for approaching the European market with a commercial solution for ferrous industries (steel) that is also replicable for non-ferrous ones (e.g. aluminium, copper) and other metal surface treatments (e.g. electroplating, coating with oxides).

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).

Expected results:

An innovative, economically-feasible and environmentally-friendly solution for the treatment of wastewater from the metal finishing industry;

A fully operational 2 000 litres/day demonstration plant, recovering more than 594 tonnes/year of hydrogen chloride, and reusing more than 284 tonnes/year of ferrous sulphate heptahydrate and 41.5 tonnes/year of zinc chloride in the Ingalsa galvanising plant;

Cost savings of €60/m3 of HCl at 35% by recycling acids from spent liquors;

Cost savings of €289/tonne associated with zinc recovery as zinc chloride is used in the fluxing phase of the galvanising process;

Marketable by-products (ferrous sulphate heptahydrate) that can be sold to horticulture and viticulture sectors as fertiliser. Incomes from selling this by-product can reach net €40/tonne; and

No liquid discharge, avoiding extra costs derived from sludge management, with expected cost savings of €40/m3 by eliminating the need to neutralise and to dispose of SPL and SSL in landfills.