USE OF SOLUTION REJUVENATION AND PROCESS MODIFICATIONS TO MINIMIZE METAL STRIPPING WASTE

摘要

The San Antonio Air Logistics Command (SA/ALC) uses a number of acidic and alkaline solutions for metal stripping as part of the overhaul of jet aircraft engines. The spent stripping solutions, contain dissolved metals as well as acid or base. Martin Marietta is collaborating with SA/ALC to reduce chemical use and waste disposal costs for the following solutions: chromium stripping (hydrochloric acid), nickel stripping (nitric acid), aluminum stripping (sodium hydroxide), stainless steel deoxidization (MIL-C-14460C), and titanium deoxidization (Ferlon). The last two solutions contain sodium hydroxide and chelators. The project was initiated with an extensive site survey, historical data review and series of chemical analyses to provide the basis for sizing rejuvenation systems and recommending process improvements. These rejuvenation systems will use electrodialysis for precipitating metals as hydroxides and reforming nitric acid, hydrochloric acid, and sodium hydroxide for the chromium, nickel, and aluminum stripping solutions respectively. Martin Marietta is currently working with Ionsep, Corp., Rockland DE, on design and fabrication of these systems. Process improvements are currently being implemented by SA/ALC for the two deoxidization systems. These include: use of mechanical agitation to minimize carbonate formation, evaluation of alternative formulations solutions, and use of rinse water as makeup water for process solutions. Consideration of rejuvenation systems for these solutions will be deferred until the effects of the process improvements have been assessed.