Sponsored by: Jt. LMD/EPD Recycling Committee, EPD Waste Treatment & Minimization Committee
Program Organizer: Donald L. Stewart, Jr., Alcoa Technical Center, 100 Technical Drive, Alcoa Center, PA 15069; James A. Clum, Binghamton University, Watson School of Engineering, PO Box 6000, Binghamton, NY 13902-6000
Monday, PM Room: A7
February 5, 1996 Location: Anaheim Convention Center
Session Chairperson: Donald L. Stewart, Jr., Alcoa Technical Center, 100 Technical Drive, Alcoa Center, PA 15069; James A. Clum, Binghampton University, Watson School of Engineering, PO Box 6000, Binghamton, NY 13902-6000
MINERALOGICAL AND PHYSICAL CONSIDERATIONS RELATED TO THE PHYSICAL SEPARATION AND RECOVERY OF ALUMINUM SMELTER WASTE PRODUCTS: Arthur Plumpton, Jean-Francois Wilhelmy, Denis Blackburn, Centre de recherches minérales (CRM), 2700 rue Einstein, Sainte-Foy, Québec, Canada, G1P 3W8
Several secondary and waste products of aluminum smelting were characterized mineralogically and physically in terms of their constituent mineral phases so as to evaluate the potential application of various mineral processing technologies for their partial decontamination or recovery of valuable fractions. The investigated products include red mud, bath-alumina mixtures, prebaked anode recycle residues, spent pot linings, drosses, saltcake, and dusts. Several of the materials possessed chemical and mineral compositions which varied with particle size and contained highly liberated mineral phases. The favorable mineralogy led to an evaluation of physical separation possibilities using the differing physical properties of mineral and metallic constituents. Wet processing methods such as gravity and magnetic separation and flotation are potentially attractive in several cases. Particular attention was given to the potential of recent fine particle processing techniques, as well as to dry separation technologies, such as electrostatic separation, pneumatic separation and gravity tabling, which best comply with the aluminum smelting environment. A literature review was made in regard to recovery or decontamination of aluminum smelter wastes using mineral processing technologies.
PHYSICAL RECOVERY OF CARBON AND BATH PRODUCTS FROM GROUND SPENT ANODE WASTES, Arthur J. Plumpton, Denis Cotnoir, Centre de recherches minérales (CRM), 2700 rue Einstein, Sainte-Foy, Québec, Canada, G1P 3W8
The constituent mineral phases contained within several aluminum smelter waste products are sufficiently liberated from each other to permit the application of mineral processing technologies for their separation and recovery. CRM studied both dry and wet physical processing methods for the recovery of carbon and bath products from wastes obtained during shot-peening of the spent anode assembly. The principal test material for the experiments was a composite sample of fine and coarse wastes, analyzing 30% C and 70% electrolysis bath material and having a 143um average particle size and a 16 wt% - 45 um fine fraction. Summary results are presented and discussed for two dry processing approaches, electrostatic separation and pneumatic tabling (on deslimed feed), as well as for two wet methods, gravity tabling and froth flotation. Using a limited number of scavenging and cleaning steps, each wet method yielded two clean products, one being of 95 to 98% carbon purity, the other 97 to 99% bath grade. Similar high grade products were obtained using dry separation methods, but at the expense of having to deslime and/or classify the feed, and of accepting lower product yield and a middlings fraction equal to 40% or more of the feed weight. The approximate cost of a 1000 tpy recovery facility is discussed, as are the perspectives for improved physical separation of spent anode residues.
A PROCESS FOR TREATMENT AND RECOVERY OF SPENT POTLINER (SPL): R. J. Adrien, J. Besida, T. K. Pong, T. A. O'Donnell, D. G. Wood, G. H. Covey, Department of Chemical Engineering, The University of Melbourne, Parkville, Victoria 3052, Australia; J. J. Giansiracusa, D. E. Price, DEPCO-TRH Pty Ltd., Melbourne, Victoria 3000, Australia
Spent potliner (SPL) is classified as a hazardous waste as it contains cyanides and high levels of fluorides. This paper describes a novel process for the conversion of SPL at near ambient temperatures for the recovery of useful products and a benign residue. The initial treatment of crushed SPL removes over 90% of the cyanide and a large percentage of the fluoride. By appropriate selection of the chemical species and wash conditions, aluminium fluoride and other fluorides are effectively recovered in subsequent stages. After this treatment by a series of chemical washes, the residue produced is a carbonaceous material containing only carbon and brick fragments; i.e., refractory aluminium compounds.
PRODUCTION OF VALUE-ADDED PRODUCTS THROUGH PHOSPHATE STABILIZATION OF ALUMINUM INDUSTRY WASTE: Arun S. Wagh, Energy Technology Division, Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439; W. W. Phil Robinson, Environmental Solutions Inc., 5711 Staples Mill Road, Richmond, VA 23228
Aluminum smelter plants produce potliner waste material during the electrolytic production of aluminum. For every ton of aluminum produced, ~25-35 kg of spent potliner is generated. Annual U.S. generation of this waste is ~120,000 metric tons. There is a large accumulation of this material from earlier operations in the U.S. In addition, U.S. companies produce a large amount of this material abroad, primarily in Australia. A land ban on this waste is scheduled to be enforced in the U.S. in 1996, and similar bans are already enforced in several other countries. Spent potliner contains up to 50 wt% carbon (the basic liner material), contaminated by 15% each of fluorides of several alkaline metals, and up to 0.5% free or complexed cyanide. Many companies have developed processes to destroy the cyanides, stabilize the fluorides, and convert the potliner into harmless landfilled material. However, landfilling of this material is expensive, costing ~$150 per ton in the U.S. Pacific Northwest and even more in the Northeast. For these reasons, we have conducted research to find ways to recycle this treated waste, and the results are presented in this paper. Representative samples of the waste were treated by a novel chemically bonded phosphate ceramic process developed at Argonne National Laboratory. This process is a room-temperature treatment in which an acid-base reaction route is used to develop a binder using MgO and a phosphoric acid solution. The waste, which is mixed with MgO before the reaction, also participates in the reaction; the reacted slurry sets into hard and dense ceramics within ~1 hour. Physical and mechanical properties and leaching characteristics of the stabilized product will be presented. Results of microstructure studies and mineralogy will be used to demonstrate the superior quality of the final waste form. The process can be used to produce value-added structural products. Economics of the process will be discussed. Such product development may help to delist the treated spent potliner as an EPA hazardous waste.
COMMONWEALTH ALUMINUM IMPROVES WASTEWATER TREATMENT PLANT PERFORMANCE AND REDUCES COSTS WITH NEW POLYMER TECHNOLOGY: Dr. Neil Isles, Finishing Mill-MRU Manager, Commonwealth Aluminum Company, P. O. Box 480, Lewisport, KY 42351; Scott Stedeford, Account Specialist, Betz Water Management Group, 8977 Technology Drive, Suite A2, Fishers, IN 46038
Commonwealth Aluminum, a manufacturer of aluminum coil products, located in
Lewisport, Kentucky, was experiencing problems with their wastewater treatment
process. The wastewater facility is designed to remove heavy metals from their
paint line effluent stream. At the end of 1993, Commonwealth Aluminum shut down
their old paint line and expanded the output of their modernized paint line.
The result was a reduction in effluent water flow and solids loading, creating
a problem with suspended solids carryover in the clarifier. To address this
problem, Betz proposed the use of their Novusreg. polymer technology to replace
ferrous sulfate and an anionic flocculant. The polymer trial began in December,
1994, and the process improvements were evident immediately. In January, 1995,
Commonwealth Aluminum modified their treatment process to fully incorporate the
Novusreg. technology. The results from the incorporation of this polymer
include: improvement of clarifier effluent clarity; reduction of wastewater
treatment costs; reduction in manpower; and consistent compliance of
environmental permit limitations.
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