1997 TMS Annual Meeting: Monday Abstracts

PYROMETALLURGY AND MELTING PRACTICE

Session Chairperson: David G.C. Robertson, Center for Pyrometallurgy, Univ. of Missorui-Rolla, Rolla, MO 65401

A TWO-LIQUID SLAG MIXING EXPERIMENTAL TECHNIQUE FOR STUDYING THE OXIDATIVE PRE-FUMING TREATMENT OF LEAD BLAST FURNACE SLAG: Adrian Deneys, David Robertson, and Nick Schupp Center for Pyrometallurgy, University of Missouri-Rolla Rolla, MO 65401

An experimental technique has been devised for studying the reaction kinetics of the homogeneous, liquid phase reaction: ZnO+FeO = Zn(g)+Fe203, by which zinc evolution can occur from a molten Al203-CaO-FeO-Fe203-SiO2-ZnO bath in the absence of a carbonaceous reductant. When studying the reaction kinetics by heating from room temperature, solid state reactions and poorly defined melting points may obscure the starting point of the reaction. In order to eliminate this problem, an experimental technique was devised whereby two molten slags could be melted independently, and then mixed, to provide a well defined starting point from which to begin taking measurements. Two crucibles were mounted in a vertical reaction cylinder. The upper, mild steel, crucible had a bottom pouring plug which was sealed by a steel stopper rod. A fayalite mixture was contained in this crucible. The lower crucible contained an Al203-CaO-SiO2-ZnO mixture. Once the two slags had been melted, the steel stopper rod was removed from the upper crucible. The upper, reduced slag (fayalite in equilibrium with the upper steel crucible), drained into the lower crucible where the two slags were mixed by submerged argon stirring. Dip samples were taken to measure the zinc content of the final mixture as a function of time. The experimental procedure will be described, as well as results of experiments which were conducted on synthetic slags. The system investigated was similar to the lead blast furnace slag which is produced by the primary lead smelters of Missouri, USA.

2:20 pm

QUENCH DROSSING OF LEAD BULLION:: Funsho K. Ojebuoboh, Asarco Inc., Technical Services Center, 3422 South 700 West, Salt Lake City, UT 84119

New technology has been developed for drossing lead bullion. The technique was developed to replace conventional copper drossing, so-called rough crossing, performed in kettles. With quench drossing, water granulation of bullion exiting the smelting furnace, usually above 900°C (1700°F), is used to arrest equilibrium formation of the dross species. The process is based on granulating lead bullion from the furnace, thereby quenching the bullion, and subsequently sweating lead off the granules in a rotary kiln furnace. The major benefit of the new technology is expected to be reduced air-borne lead which is normally associated with conventional drossing. The process also has the potential of making lead crossing metallurgy more susceptible to better process control. The process and its development are described.

2:40 pm

RECYCLING OF MAGNESIUM ALLOY SCRAP, A NECESSITY: Christine Brassard, Lisabeth Riopelle, Oddmund Wallevik, Hydro Magnesium Market Development Center, 21644, Melrose Avenue, Southfield, MI 48075-9705

The use of magnesium alloys is growing rapidly, particularly in die cast parts for the automotive industry. Supporting this growth in the future means that Mg has to be an economically and ecologically attractive material, and recycling of alloy scrap becomes a necessity. What kinds of magnesium scrap will be on the market? What are the opportunities and challenges for this emerging recycling industry? Different recycling processes have been developed, and operation facilities are today recycling large volumes of class 1 diecast returns based on a flux refining technology. Characterization of the recovered metal demonstrates that the performance of appropriately recycled magnesium alloy is comparable to an alloy made from primary electrolytic metal. The sludge generated from this process can also be recycled through the existing primary Mg operations in order to close the environmental loop.

3:00 pm

THE REACTION MECHANISM OF OXIDIZED CHALCOPYRITE CONCENTRATE PARTICLES AND COPPER MATTE WITH IRON SILICATE SLAG: K. Fagerlund1, P. Nurrni1, H. Jalkanen1, P. Taskinen2, 'Helsinki University of Technology, Laboratory of Metallurgy, Vuorimiehentie 2, FIN-02150 Espoo Finland; 2Outokampu Research Oy, P.O.BOX 60, SF-28101 Pori, Finland

The reaction mechanism and settling behaviour of oxidized chalcopyrite particles and coppper matte droplets introduced into synthetically prepared fayalite type slag under nitrogen and argon atmosphere have been investigated in this work. As a part of the investigation into flashsmelting reaction phenomena in a settler region, a laboratory experiments were conducted by means of a X-ray image system and a vertical tube furnace. The reaction phenomena of oxidized chalcopyrite in iron silicate slag was studied in a tube furnace, temperature being 1300°C, and inert gas flow (N2). The partly oxidized samples of chalcopyrite were blown into synthetic fayalitic slag. Reaction products were studied and analysed using light optical microscope (LOM), scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and chemical methods. Industrial copper matte and oxidized chalcopyrite were introduced into iron silicate slag. The melting and settling behaviour, the variation of the copper matte droplet shape and the movement of melting interface were continuously monitored by X-ray image system.

3:30 pm BREAK

3:40 pm

MELTING OF HIGH PURITY CHROMIUM: Raymond K.F. Lam, Giuseppe Colella, Materials Research Corporation, 542 Route 303, Orangeburg, NY 10962

Unacceptable levels of impurity were noted from high purity chromium melting operation. Analysis of past chromium melting determined that total oxygen content was the critical parameter. Thermodynamic analysis of oxides and liquid chromium was presented. Acceptable operating conditions were identified. A new process of melting high purity chromium with oxide addition for controlling the activity of Cr2O3 was recommended. Experimental results of the new melting process were presented.

4:00 pm

ADVANCED NON-FERROUS SCRAP MELTER: J.S. Becker, J.F. Heffron, R.J. Hewertson, E. Keith Riley, Air Products and Chemicals, Inc., 7201 Hamilton Boulevard, Allentown, PA 18195-1501

Technology developed and first implemented in the United Kingdom enables very low grade non ferrous scraps containing sils, organics, plastics and ferrous metals to be directly charged, without pretreatment, into a unique melting furnace. Two furnaces have been in full scale production for over four and two years, respectively. A third furnace was only recently commissioned. The oxy-fuel-based furnace design incorporates internal afterburning in the furnace's hot zone, producing excellent thermal efficiency and very low emissions. Advanced process control insures complete combustion of all volatiles in an environment that is not oxidizing to the melt. Thus metal yields have been excellent. The furnace is very low in Nox. This paper will provide both theoretical background and extensive operating results for this new melting concept. Applications describing both purpose built new furnaces and retrofits of existing reverberatory furnaces will be presented. Extensive operating emissions data will be presented.

4:20 pm

OXYGEN ENHANCEMENT OF BURNERS FOR IMPROVED PRODUCTIVITY: D.J. Krichten, W.J. Baxter, C.E. Baukal, Air Products and Chemicals, Inc., 7201 Hamilton Blvd., Allentown, PA 18195

A method of retrofitting air-fuel burners with oxy-fuel capability overcomes the potential problems associated with oxygen combustion in aluminum melting furnaces. Several years of operation in rotary furnaces reclaiming dross and UBC scrap and since 1993 in revereratory furnaces prove the usefulness of the retrofit approach. The retrofit burner uses the existing combustion air connection, burner housing, and burner tile and replaces the gas tube with an oxy-gas burner. Maintaining a portion of the air flow to the burner reduces the potential for localized overheating. This technique optimizes the mix of air and oxygen to the burner for the given furnace geometry and meltrate desired. Proper design of the burner reduces Nox emissions by moderating the flame temperature with furnace gas recirculation. Economic analysis of using merchant oxygen shows the benefits are increased productivity and reduced overall unit cost of melting. In practice, the melt rate in rotary furnaces increases by up to 50% and by up to 35% in reverberatory furnaces. Oxygen enhancement reduces melting cost by 1/2­3/4 cents per pound of aluminum melted.

4:40 pm

THE REDUCTION BEHAVIOR OF HEMATITE COMPACTS BY H2 and H2-CO GAS MIXTURES: I.J. Moon, C.H. Rhee, Materials Science & Engineering, Pohang University of Science and Technology, Pohang 790-784, Korea

The reduction behavior of hamatite by H2 and H2-CO gas mixtures was investigated to elucidate the reduction mechanism at 1073~1223K. The hetatite compacts were made by Cold Isostatic Pressing to produce compacts of uniform shape and size. The compacts were sintered at 1273K for 30 min., and showed a contraction of 29%. Mercury pressure porosimeter and BET technique were used for measuring the total porosity, pore size distribution and pore surface area of the compacts. Reduction was followed up by means of weight-loss technique using Cahn Balance (Model: TG-171, capacity 10g, accuracy ± 10 µg.) Microscopic examination (SEM, EPMA), X-ray, and carbon analysis were used to correlate the structure of reduced compacts with the mechanisms of reduction and carbon deposition. The values of apparent activation energy for H2 reduction were between 11.21 kcal/mol and 14.38 kcal/mol. Structural changes, kinetics, and mechanisms of reduction and carbon deposition with H2 and H2-CO gas mixtures is discussed.

5:00 pm

MECHANISM OF NB TRANSFER TO HOT METAL FROM SLAG: Fan Peng, Yang Tianjun, Zhou Yusheng, Dong Yicheng, Wei Shoukun, Sichuan Union University, P.O. Box 373, Chengdu, Sichuan, 610065, China

Nb-bearing iron ores are today the most significant source of niobium in China. Ferroalloy of Nb, as the main product of Nb recovered from Nb-bearing iron ores, is recently produced by the following route. Nb-bearing iron concentrate is reduced in a blast furnace to generate Nb-bearing hot metal, which is then smelted in a converter to yield Nb-enriched slag. Finally Nb- enriched slag is reduced in an electric furnace to get ferroalloy of Nb. In order to improve the recovery ratio of Nb, it is important to acquire a deep understanding on how Nb is transferred to hot metal from slag. In the present work, raw material containing niobium oxide were carbothermally reduced under the conditions of calm metal-slag interface or stirred metal-slag interface, respectively. Under the former condition, the quenched samples were found through SEM observations that NbC layer occurred at the metal-slag interface. In this case, Nb transfer to hot metal from slag slows down and the rate controlling step is Nb diffusion in NbC layer. Under the later conditions, it was found that no NbC layer occurred at the metal-slag interface, indicating that NbC formed at the interface sunk into hot metal due to the higher density of NbC than that of hot metal. In this case, the rate controlling step is Nb diffusion in slag.