Treatment of metal finishing sludge for detoxification and metal value removal

L.G. Twidwell1* and D.R. Dahnke2

 1Professor of Metallurgical Engineering Metallurgical and Materials Engineering Department Montana Tech of the University of Montana Butte, Montana, USA, 59701
2Supervising Engineer Trentwood Works Kaiser Aluminum Company Spokane, WA, USA, 99200

Received 18 June 2001; accepted 13 August 2001


Metal-bearing hydroxide sludge wastes are generated by the metal finishing electroplating and electrochemical machining industries through out the world. These wastes are classified as hazardous materials in the US and have traditionally been disposed of in hazardous landfill sites. Long-term maintenance of such sites is required, and metal values are lost unnecessarily. If metals are recovered from these sludge wastes, it will alleviate or reduce the disposal problem and provide for conservation of energy and metal resources. The treatment of hydroxide sludge materials for metal value recovery will produce several beneficial results, i.e. economic benefits from the metal values recovered will help offset the cost of recovery/treatment; nonrenewable resource metals will be recycled for use by society; and there will be significantly less hazardous material to be disposed of in landfills. Detoxification will have resulted because the metal content will have been removed to such an extent that the waste products successfully pass the USEPA toxic characterization test (TCLP), or, at least, the quantity of material that has to be disposed of in hazardous waste sites will have been drastically reduced.

The experimental results from several major USEPA studies and numerous master of science thesis studies are summarized in this presentation. A methodology to treat metal-bearing sludge materials by hydrometallurgical techniques is presented. The methodology emphasis is directed toward the application of known and industrially used hydrometallurgical technology, e.g., simple precipitation, solid/liquid separation, solvent extraction, and cementation unit operations. Electroplating and electrochemical sludge materials contain a unique mixture of metal species not normally encountered in natural ores and concentrates, e.g., iron, chromium, copper, zinc, cadmium, cobalt, and nickel. The demonstration that presently used industrial unit operations can be utilized for the treatment of these new materials is an important step forward in waste management and metal value recovery processing.

Keywords: Sludge; Electroplating; Electrochemical; Phosphate

* Corresponding author
   E-mail : Ltwidwell@mtech.edu