ZERO PLUS - Best Technologies applied to trivalent chromium-based passivations

The BREF document “Surface Treatment of Metals and Plastics” considers in its chapter on consolidated BATs the substitution of hexavalent chromium-based passivations by those based on trivalent chromium. However, the document is not fully decisive in this regard due to the anticorrosion characteristics of the layers obtained. The ZERO PLUS Project presents a proposal that consists in applying a technique that allows the continuous regeneration of chromium (III) baths beforehand, such as the separation of these metals through cation exchange. This paper presents the tests carried out with the selective cation exchange technique using extractant-coated resins to achieve cation selectivity. This technique, applied to colorless chromating baths, is still far from being a BAT candidate due to the poor results obtained. However, this experience is valuable considering the other alternatives available or the progress in the development of new resins with improved selectivity and, consequently, separation capacity.