LIFE-2-ACID

PROJECT DESCRIPTION

BACKGROUND

The pickling of steel in acid is part of the steel galvanising process. Galvanising involves coating steel in zinc to provide an impervious barrier that protects steel products from corrosion. Prior to the zinc-coating stage, pickling with acids removes rust and scale from the surface of steel, providing the required level of material purity. The pickling process forms metallic salts that generate a final residue known as spent pickling acids (SPAs). SPAs must be disposed of because the efficiency of pickling decreases with the increasing content of dissolved metals, mostly iron and zinc, in the pickling bath. The production of one tonne of galvanized metal produces about 38 kilogrammes of SPA.

SPAs are typically treated using conventional processes that involve neutralisation of the acids and precipitation of metal residues in the form of insoluble hydroxides. The precipitates are filtered and sent to landfill. Potentially useful materials, such as the remaining acid and valuable metal ions, are lost. A technology for the recovery of metals from SPAs would be an environmentally-friendly alternative in the galvanising sector and could create highly-skilled jobs.

OBJECTIVES

The LIFE-2-ACID project will demonstrate a new technology to selectively recover zinc and iron chloride from SPAs. The project will design, construct and operate a prototype pilot plant able to treat 200 litres/day of SPAs. The plant will have two units:

A separation unit based on reactive membranes that will allow the selective separation of the SPAs into two separate iron and zinc streams; and

A unit to extract zinc from the permeate stream. This unit will be based on a new technology that integrates selective membranes and electroplating techniques.

The recovered zinc will be reused as a raw material for galvanising. The process will also permit the recovery of iron chloride as a sub-product to be used as a reagent in wastewater treatment plants.

LIFE-2-ACID will contribute to the implementation, updating and development of EU environmental policy and legislation, especially the Industrial Emissions Directive. The proposed technology has the potential to be considered as a BAT (Best Available Technology) for the surface treatment and ferrous metal processing industries. By recovering raw materials and reducing waste, the project will also be in line with the EU Waste Framework Directive and the Circular Economy Action Plan. The LIFE-2-ACID approach could also reduce greenhouse gas emissions from the extraction and processing of minerals, their transportation and their management when they become waste.

Expected results:

Demonstration of a new technology able to recover 90% of metallic zinc and iron chloride from galvanising SPAs; the pilot plant will treat 20 000 litres of SPAs, preventing 28 000 litres of metallic sludge from being sent to landfill and recovering 3.24 tonnes of zinc and some 675 kg of iron chloride;

A demonstration that the recovered zinc can be reused in the galvanising process, with no loss of quality and in the same conditions as the raw material used at present;

A demonstration that the recovered iron chloride can be used as a coagulant in waste water treatment, at the same level of effectiveness as the commercial reagents used at present;

Quantification of the greenhouse gas emission reductions and other reduced environmental impacts from the application of the new technology;

A 90% reduction in waste sludge, equivalent to about 380 000 tonnes/year;

An 8% reduction in zinc extraction demand; and

Demonstration of the technical and commercial feasibility of the process. According to preliminary calculations, the total investment and operating costs of the proposed technology could enable a profit margin of 50%.