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Completion of the material cycle in procedures for the removal of materials in process solutions: membrane application technology and testing in a hot-dip galvanising plant
- Bundesministerium für Bildung und Forschung (BMBF)
Fertigstellung des Projekts:
Fertigung / produzierende Unternehmen
The pre-treatment of steel surfaces for hot-dip galvanizing generates spent process solutions, the disposal of which is undertaken by third parties. In order to allow the completion of operational material cycles in future, this project involved the selection of various membrane processes, and their suitability has been investigated in both pilot installations and industrial plants.
The treatment of acidic degreasing solutions by cross-flow filtration has not been possible. In combination with iron ions in solution, phosphoric acids present in the acid mixture caused blockages in the ceramic membranes which it was not possible to remove.
As an alternative, the purifier was modified to a two-component system, in which the organic solution or the acid/inhibitor component can be replenished as each is consumed. In an industrial application, it was possible to reduce the organic component of the purifier by some 50%, while the acid/inhibitor component was reduced by over 20%.
The regeneration of hydrochloric acid pickling solutions of varying zinc and iron content by membrane electrolysis has not been possible on an industrial scale. This process resulted in the uncontrollable precipitation of metals.
Greater benefits are associated with the industrial application of electrodialysis for rinsing water treatment. Values of approximately 25 – 30 g/l and up to 35 g/l for the reconcentration of separated materials can be achieved for iron and hydrochloric acid respectively. This discharge of concentrate in the pickling solutions is of the order of 25 l/h. Approximately 0.5 kW/h of electric power is required for the processing of 1.4 m3/h. In order to maintain the availability of the installation over long periods, three different filters are arranged upstream of the electrodialysis stage.
Autor/Projektleiter: Volker Brücken ; Heinz Külker ; Ulrich Stieglitz
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