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Environmental Plating of Steel: I. Replacement of Cadmium by Zinc/Iron, II. Recycling of Electrolyte-Enriched Rinsing Water
- Umweltbundesamt (UBA)
Fertigstellung des Projekts:
Fertigung / produzierende Unternehmen
During the coating of materials such as car brakes, steel parts for aviation and military technology cadmium was replaced for the first time with the application of the material combination zinc/iron.
The zinc/iron coating and the acid galvanization are accomplished in closed material cycles. The half concentrates of the 3-stage rinsing cascade are prepared by means of reverse osmosis and led back into the process bath, and the salt-free retentate into the last stage of the rinsing cascade. Evaporation losses are replaced by demineralized water. Due to long service lives of the chromating baths at the subsequent treatment of the zinc layers the waste-intensive disposal has to be accomplished less frequently.
The rinsing water from the chemical nickel bath is up-concentrated by reverse osmosis, nickel is electrolytically recovered. The slightly nickeliferous waste water from the electrolysis is led to the waste water treatment, whereby the nickel remains in the iron/chrome sludge. The process stage nickel galvanization was designed as closed system. The need for rinse waters when chromium-plating is minimized by a four-fold rinsing cascade.
For the cooling of the process baths an evaporator is used. The concentrate from the evaporator is led back into the process bath. The iron-containing waste water from the pretreatment (pickling, descaling, cleaning) is cleaned together with the waste water from nickel plating and chromium plating, the resulting sludge is externally used. Altogether the electroplating process is optimized in such a way that residues are avoided or non-avoidable residues accumulate in re-usable form.
After the end of the project there were clear degradations of the product quality, so that the plant is not operated in the conceived form any more. Thus the selected procedure did not prove as practically convertible.
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