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, AM 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, Binghamton University, Watson School of Engineering, PO Box 6000, Binghamton, NY 13902-6000
INTERFACIAL REACTION BETWEEN AL ALLOYS AND SALT FLUX DURING MELTING: M. Mehdi Taghiei, University of Science & Technology, Materials Science Department, Narmak, Tehran, Iran
A ternary mixture of KCl NaCl and KF may be used as a molten flux cover during melting of Al scrap. This practice minimizes oxidation of the liquid metal and allows the existing oxide layer to be stripped from the scrap more readily. The coalescence of metal droplets dispersed in molten salt was found to be influenced by the formation of a high-melting layer that forms at the interface between the molten alloys and the salt. This layer was identified as KMgF3 in some cases and as the mineral Elpasolite, K2NaAlF6 in other instances. Either forms appear to depend on conditions that exist in the melt at the time of formation. There was no indication of any changes in the structure or chemical composition of the layer that occur as a function of time of contact between metal and salt. The presence of metallic potassium and sodium in the solidified Al was detected by SEM microanalysis of the sample.
EFFECT OF IMPURITIES IN INDUSTRIAL SALTS ON ALUMINUM SCRAP MELTING: Jian Ye, Yogeshwar Sahai, Department of Materials Science and Engineering, The Ohio State University, Columbus, OH 43210; Annette Revet, Kalium Canada, Ltd., Regina, Sask., Canada S4P 4B5
Aluminum scrap such as Used Beverage Containers (UBC) are melted under a protective molten salt cover. An appropriate salt protects metal from oxidation, promotes coalescence of molten droplets, and separates clean metal from the oxide contamination. Generally, the salt compositions for aluminum scrap recycling are based on equi-molar mixtures of NaCl and KCl. A small amount of fluoride is also added in the salt. In the past, laboratory research at universities and industrial laboratories has been limited to pure salts. However, the industrial salts have impurities such as sulfates and other insoluble materials. These impurities, particularly the presence of sulfates in salt, have a pronounced effect on the efficiency of the scrap remelting process. In this paper, the role of impurities in industrial salts in terms of their chemical interactions with the metal are summarized. The efficiency of different industrial grade salts containing varying amounts of sulfates and other insoluble impurities for scrap recycling is compared.
THE PERFORMANCE OF CURRENT OXY-FUEL COMBUSTION TECHNOLOGY FOR NONFERROUS MELTING: Randy Abernathy, Jim McElroy, Loo Tjay Yap, BOC Gases, 575 Mountain Ave., Murray Hill, NJ 07974
Higher thermal efficiencies, lower exhaust-gas flows, exhaust particulate loading, superstructure temperatures, and NOx emissions have contributed to more widespread cost-effective use of oxygen-based firing. Operating characteristics of oxy-fuel fired furnaces are compared with air-fired furnaces for the secondary melting of nonferrous metals. Typical performance gains resulting from oxy-fuel firing are established for reverberatory and rotary aluminum furnaces, reverberatory and rotary lead furnaces, as well as rotary brass furnaces. Representative examples are presented in detail. The large improvements in thermal performance of a novel self-cooling oxy-fuel burner providing uniform heat-transfer to large melt areas are demonstrated for aluminum furnaces.
10:10 am BREAK
THE HOT ALUMINUM DROSS RECYCLING (HDR) SYSTEM: Han Spoel, Spalco Metals Inc., 210 MacPherson Ave., Toronto, Ontario, Canada M5R 1W8; William A. Zebedee, MICA Metals Inc., 500 North Woodward Ave., Suite 350, Bloomfield Hills, MI 48304
The difficulties previously encountered by aluminum dross recyclers in directly processing hot dross from a nearby generating facility have been overcome. Dross is skimmed as usual into pots from the melting, batching, or holding furnaces. These pots are then placed in hot dross holders, and enough hot dross is accumulated for a full charge of the rotary processing furnace. The hot dross is then dumped into an accumulator and charged, together with such flux as is needed, as rapidly as possible into the rotary furnace, where it is processed in the usual way. The first HDR system became fully operational at MICA Metals, Bedford, Indiana, in March 1995. There has been a substantial improvement in metal recovery. Usage of salt flux, energy consumption, batch times, and fugitive emissions have all been reduced.
SAFETY ASPECTS OF THE DESIGN AND OPERATION OF ROTARY ALUMINUM DROSS COOLERS: Han Spoel, Spalco Metals Inc., 210 MacPherson Ave., Toronto, Ontario, Canada M5R 1W8
Rotary aluminum dross coolers are used to cool hot dross skimmed from aluminum melting, batching and holding furnaces. The dross is introduced in batch mode into one end of an unlined steel drum which rotates about the longitudinal axis. Cooled dross is discharged from the other end of the drum. The outside of the drum is water-cooled, and the cooled shell in turn extracts heat from the dross. The avoid dangerous conditions, the equipment must be designed and operated in such a way that hot aluminum dross and water do not come into contact with each other.
RECOVERY OF ALUMINUM FROM ROTARY FURNACE SALT CAKE BY LOW IMPACT ROTARY TUMBLING: David J. Roth, ALTEK International Inc., 585 Exton Commons, Exton, PA 19341
The goal of secondary dross recyclers is to maximize the aluminum units recovered from the dross they process and minimize the amount of material they have to send to a landfill. Salt Cake is a by-product of the most rotary furnace processors. Although there are systems available to totally recycle this material, the financial aspects of the process can be debated depending on the volume of salt cake generated by the facility. Normally from 5-10% aluminum is contained in this salt cake by weight. For a generator of only a million pounds a month of salt cake, even this amount of aluminum is a significant number. Before now the equipment to extract the aluminum from the salt cake has been very expensive, difficult to maintain, and taken up a lot of real estate. Most processors have not gone with this option and all of the material is sent to the landfill. The Tumbler as manufactured by Didion and ALTEK separates the aluminum from the salt cake in an efficient manner. The equipment is simple and easy to run in difficult environments. We will review the operation of this type of system on typical salt cake. White, black dross, and bath are also materials that are processed by this system and will be touched on in the paper.
THE ECONOMICS OF SALT CAKE RECYCLING: D. Graziano, J. N. Hryn, E. J. Daniels, Argonne National Laboratory, Energy Systems Division, 9700 South Cass Avenue, Building 362, Argonne, IL 60439-4815
The Process Evaluation Section at Argonne National Laboratory has a major
program aimed at developing cost-effective technologies for salt cake
recycling. This paper addresses the economic feasibility of technologies for
the recovery of aluminum, salt, and residue-oxide fractions from salt cake.
Three processes were assessed for salt recovery from salt cake: (i) base case:
leaching in water at 25deg.C, with evaporation to crystallize salts; (ii) high
T/high P case: leaching in water at 250deg.C, with flash crystallization to
precipitate salts; and (iii) solvent/anti-solvent case: leaching in water at
25deg.C, concentrating by evaporation and reaction with acetone to precipitate
salts. Base case economics were evaluated at two leaching effluent brine
concentrations, 12 and 22 wt%. All test cases for salt recovery had a negative
present value, given current pricing structure and 20% return on investment.
Although manufacturing costs (variables plus fixed) could reasonably be
recovered in the sales price of the salt product, capital costs cannot. The
economics for the recycling processes are improved, however, if the
residue-oxide can be sold instead of landfilled. For example, the base case
process would be profitable at a wet oxide value of 10 cents/lb. The economics
of alternative scenarios were also considered, including aluminum recovery with
landfilling of salts and oxides, and aluminum and residue-oxide recovery with
discharging of concentrated salt solutions. The economics associated with
additional processing of residue-oxide were also evaluated.
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