Department of Defense (DoD) electroplating shops use process solutions containing hazardous materials for plating, cleaning, anodizing, and other metal finishing operations. The effective life of these solutions is limited by the increasing levels of contaminants that are dragged in from the parts being plated or cleaned. Large volumes of concentrated hazardous wastes are generated from process solutions that become spent because of buildup of contaminants. Separation technologies including ultra/microfiltration, adsorption, electrodialysis, membrane electrolysis, and diffusion dialysis need to be evaluated and systems developed for removing contaminants from plating and cleaning solutions.
The goal of the project was to develop innovative techniques for prolonging process bath life and for recycling hazardous materials from spent process baths to reduce the generation of hazardous wastes. Objectives of the full-scale project were the following: (1) quantify accurate life-cycle costs, (2) determine surfactant replenishment techniques, and (3) identify mechanisms that determine ultimate bath life. These objectives were met through extended field testing.
Field demonstration projects were conducted utilizing crossflow ultrafiltration to separate oil and grease from alkaline cleaning solutions and applying an electrodialytic process to remove contaminants from electroless nickel plating baths. Bench-scale feasibility studies were performed in the laboratory, with two candidate technologies for decontaminating mineral acid solutions: resign adsorption and diffusion dialysis. After completion of these laboratory-scale efforts, a field demonstration was conducted with the most promising technology. Technology user guides were developed for plating and cleaning bath purification.
Test runs with the batch mode system at Tobyhanna Army Depot, PA, were conducted. Acid recovery rates ranged between 75 and 91 percent. Metal rejection rates testing ranged between 68 and 90 percent. Acid recovery rates with the continuous mode system ranged between 70 and 87 percent.
The pilot plant system at Naval Aviation Depot (NADEP), North Island, CA, was run for over 800 hours, recycling approximately 3,530 gallons of contaminated alkaline cleaning solution. This volume was reduced to 90 gallons of waste requiring disposal. NADEP, North Island conducted field testing of a crossflow ultra-filtration system for recycling alkaline cleaners. Approximately 1,800 gallons of contaminated cleaning solution were processed, and 48 gallons of oil and grease were removed by the filtration system, representing a 97 percent reduction in waste volume requiring disposal. The impact on cleaner formulation is acceptable.
Laboratory-scale testing of a diffusion dialysis process for mineral acid recovery was completed. Ten samples were tested that are representative of those used in DoD metal finishing operations. Acid recovery rates ranged from 80 to 92 percent, with 80 to 90 percent metal rejection rates. This project was completed in FY 1996.
Development of bath purification technologies provided inprocess treatment of chrome plating and anodizing, electroless nickel, acid etching, and alkaline cleaning solutions. The effective life of these solutions could be extended by up to 30 times. Navy-wide savings in disposal and material costs are over $2M/year. DoD-wide savings will at least triple. Users include Navy, Air Force, and Army metal finishing shops as well as potential users within private industry.