plating, anodizing, & finishing Q&As since 1989
Reduction of metal waste in the dental plating industry
The dental plating industry uses a heated mixture of HF, HN03 and water to etch denture metal structures. The resultant depletion of the etchant and increase in etching duration requires recharging of the bath or disposal. The resultant waste is generally a hazardous waste. What options are available to either plate out the etched metals (50% nickel and 50% titanium) or reduce/remove the contaminates in the bath? This inquiry would be applicable to the industry as a whole.Ken Barnes
Some recycling of acids has been achieved for very large installations like steel plants, but it hasn't proved practical for even mid-scale plants let alone small users like dental platers. It's just far more cost effective to neutralize and dispose of the old acid and buy new. Some of the hurdles are that titanium is an active metal that cannot be plated out of an aqueous solution, nickel is difficult to plate out to low levels, it is hard to conduct plating operations (reduction) out of oxidizing agents like nitric acid, and once the acids are mixed (HF-HNO3) they become more difficult to work with.
Ion exchange may be no more practical than plating, but at least you would only have practical problems to address rather than conceptual issues. Is there a particular dental plater involved, so we can talk about the specifics like volumes, concentrations, contaminant levels, hours of operation, temperatures, and costs, or is it grant money in search of a problem? :-)
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
You are searching for the same Holy Grail that every stainless steel polisher (or etcher) wants to find. Electropolishing waste is probably generated in greater volume with the same or similar characteristics. Contact the nearest electropolisher and see what he does with his spent solution. There are reportedly some folks that will collect it until there is enough to interest a buyer - like a fertilizer plant.
- Shiner, Texas, USA
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