Treatment of metal finishing sludge for
detoxification and metal value removal
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.