Servicio de Información Comunitario sobre Investigación y Desarrollo - CORDIS

Metallurgical pre-treatment of coated steel scraps in solid state

After thermodynamic consideration, a reactive gas mixture with sulphur potential was selected. Investigation on the behaviour of metal-coated steel sheets under such a reactive gas mixture were made at different temperatures and gas compositions by using a device for continuous measurement of weight change.

The results from the sulphidation of tinplate show that treatment temperature is an important parameter for designing an industrial process for detinning with reactive gas. For given temperature, a minimal concentration of the reaction gas in the gas phase must be determined, so that the negative influence on the environment is reduced to a minimum. The reaction product which formed as a layer containing Sn-compounds must be removed in time in order to keep the whole process controlled by the boundary reaction. According to the results of the present work, the treatment temperature should be set at around 500 C and the treatment time must be longer than 6 minutes. The S-potential in the gas phase can be controlled just above the level of the equilibrium value of the sulphidation reactions.

Results of sulphidation of Cr-coated steel sheets reveal that the sulphidation rate of Cr-coated steel sheets is lower than that of tinplate under the same conditions. This means that it is more difficult to remove Cr than Sn from the iron base using sulphidation. On the other hand, the results reveal the ability of Cr to resist corrosion of reactive gas containing sulphur.

For a realisation of an industrial process based on the sulphidation principle, a conceptual process was suggested and a process cost estimation model was introduced to evaluate the economic viability of such a process. If the process is really designed, the cost can be estimated with the model when all necessary data is collected. This should be the subject of a further research project.

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