Community Research and Development Information Service - CORDIS

Treatment of waste pickling liquors from steel making by the bio-oxidation process

One of the environmental problems associated with steel production arises from pickling plants have been the steel iron ion in acid solutions. This pickling liquor is toxic and hazardous because of its corrosive properties and its high concentrations of iron, other metals and free acids. Results have been obtained from the development of new approaches, all based on converting the spent liquors into iron compounds which may have added value. This requires the F iron ion to be oxidized by Thiobacillus ferrooxidans. A marked increase in the population of Leptospirillum ferrooxidans was also observed, with the result that the two bacterial populations coexist in the strains obtained after adaptation. However, Thiobacillus ferrooxidans was found to have succeeded better in adapting to the increasing ferrous iron concentration and the lowering of the pH. The results obtained indicate that the biooxidation process kinetics can be greatly improved by a combination of bacterial supports, some of which were tested in the course of the project, and a continuous biooxidation process. Various products can be obtained from the oxidized solution. These are ammoniojarosite and zinc ferrite. The ammoniojarosite is obtained by treating a biooxidized pickling liquor under pressure and at a temperature of 160 C. Zinc ferrite is obtained by precipitation with butylamine. The physico-chemical properties of the materials allow them to be used in various fields, including the following. Catalysts are obtained by covering granulated alumina with a zinc ferrite. They can be used as a catalyst for adsorptive gas removal, as a catalyst for gas decomposition and as an adsorbent for organic compounds, particularly chlorinated hydrocarbons. Thermistors are obtained from the materiel synthesised following precipitation of the biooxidized liquor with butylamine. The thermistors are suitable for measuring low temperatures and can be used in digital thermometers, where it can be very competitive with the current materials. The final residues from the process will be sodium sulphate and concentrated sulphuric acid, which can be reused in the pickling process.

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