Oxygen Pyrometallurgy at Copper Cliff—A Half Century of ProgressPaul E. Queneau and Samuel W. Marcuson

CONTENTS

INTRODUCTION OXYGEN PYROMETALLURGY

o THE DEVELOPMENT OF OXYGEN FLASH SMELTING o OXYGEN ENRICHMENT o OXYGEN TOP-BLOWN ROTARY CONVERTER o OXYGEN SMELTING o OXYGEN FLASH-CONVERTING CHALCOCITE CONCENTRATES o OXYGEN TOP BLOWING/NITROGEN BOTTOM STIRRING o OXYGEN CONVERTING CHALCOCITE CONCENTRATE

OXYGEN PRODUCTION MEASURING PROCESS PARAMETERS WINDOW ON THE FUTURE REFERENCES

INTRODUCTION

"All nonferrous metallurgy will be benefited by the use of cheap oxygen . . .the application of oxygen will revolutionize the art of smelting and it willprobably change the whole operation and equipment."

So wrote F.W. Davis of the U.S. Bureau of Mines almost 75 years ago.1 He cautioned that the existing cost of oxygen was much too high for metallurgical processes, but he forthrightly stated that "the oxygen industry is now able to make plants for supplying large quantities of oxygen to metallurgical industries at low cost." His committee's convincing Report of Investigations—primarily concerned with steelmaking—was aimed at major decreases in metal production cost. There was no consideration of environmental impact—this subject was not considered important in 1923, and the opinion would not change for decades. As pioneer environmentalist, scientist Rachel Carson warned, "A grim specter has crept upon us almost unnoticed."2 Today, engineers must heed the bell that she first tolled.3 ,4

Davis' prescient words fell on deaf ears throughout the world's nonferrous industry. Ultimately, however, they sounded in Inco's Copper Cliff Research Laboratory in 1941 and were amplified by the pertinent 1936 study of Telfer Norman5—but there was a war to win. When the veterans returned, the "innocently beloved proud plumes of heavy industry" that were billowing out of the Copper Cliff Smelter stacks were recognized for what they were. Most notably, their sulfur content was wounding Ontario and Quebec forest lands. Simultaneously, the paper-making sulfite pulp mills were importing large quantities of elemental sulfur, and the smelter was importing large quantities of coal.

Economic application of oxygen pyrometallurgy would permit replacement of this sulfur by liquid sulfur dioxide, with simultaneous replacement of the coal by low-cost tonnage oxygen, produced using low-cost hydroelectric power. Reaching this grail would achieve not only a significant decrease in metal production cost, but it would also enable an significant decrease in environmental degradation, a goal that would be increasingly stressed by government.

Inco's resulting half century of progress in developing oxygen pyrometallurgy (Figure 1) is a paradigm of the long-term teamwork that is necessary to attain such an operational shift—laboratory theoreticians, hot-metal operators, and management all working together with mutual respect.

Figure 1a. Flowsheets of nickel-copper extraction at Copper Cliff—1945.

Figure 1b. Flowsheets of nickel-copper extraction at Copper Cliff—1995.

OXYGEN PYROMETALLURGY

Intensive laboratory and tonnage pilot-plant R&D on the oxygen flash smelting of sulfide concentrates was initiated at the end of December 1945. It proceeded in classical stages: first in two-dimensional paper studies of smelting, using solely sulfur and iron as fuels; then in increasingly large three-dimensional apparatus design and operation. Excellent validating metallurgical and economic databases were established by the end of June 1947. Unfortunately, the apparent high cost of tonnage oxygen proved forbidding: the price stipulated by the dominant supplier, Linde (USA), was prohibitive.

Assistance was, therefore, sought from sound, though relatively inexperienced, sources, and the low bidder was accepted. It was the parent of Canadian Liquid Air—Air Liquide of Paris, which was then a builder of small oxygen plants; it is now the builder of the largest oxygen plants in the world. The fearful cost barrier was hurdled by the determining contributions of their brilliant chief engineer: Maurice Gobert. A worthy bid was also submitted by enterprising Leonard Pool, founder of Air Products, the supplier of reliable mobile dwarf oxygen generators for U.S. Army Engineers in World War II; Air Products is now a giant tonnage oxygen supplier.

In January 1948, Copper Cliff managers Roy Gordon (plant) and Paul Queneau (R&D) submitted their joint decision to top management:

"In view of the economic superiority and metallurgical potentialities of thenew process it is recommended that a (first step) 400 t.p.d. copper concentrateflash smelting unit and a 300 t.p.d. oxygen plant be installed at Copper Cliff.. . . There would be periods of large surplus oxygen production . . . suchoxygen could be consumed to advantage in the Smelter reverberatory furnaces forair enrichment so as to decrease coal consumption."

In those early post-war years, there were very long delays in equipment delivery, particularly of special machinery for the oxygen plant. A 500 t/d copper concentrate oxygen flash smelting furnace—supplied with low-cost oxygen by a 300 t/d plant—finally went on-stream four years later: January 2, 1952.6

This energy efficient and environmentally friendly reactor led the world of pyrometallurgy—including the oxygen steel converter—in its direct, massive-scale, use of oxygen. In the spring of 1948, convincing experiments in Gerlafingen, Switzerland, inspired by Robert Durrer, demonstrated oxygen top-blowing of blast-furnace hot metal into steel. In November 1952, VOEST's oxygen steelmaking Linz/Donawitz converter plant went on-stream in Austria.7

The Development of Oxygen Flash Smelting

The first autogenous oxygen flash-smelting laboratory experiments were conducted in a small horizontal, sheet metal-enclosed, refractory-lined furnace. Dry sulfide concentrates and flux were injected into the preheated unit using 99.5% O2 cylinder oxygen. After months of trial and error, batch runs reached rates of up to 3 t/d, with matte grades and metal recoveries at least equal to conventional copper and nickel reverberatory practice, and off-gas analyzing up to 98% SO2. Calculations based on the test data indicated that the cost of oxygen consumed per tonne of copper concentrate would be half that of reverberatory furnace coal consumption—providing the cost of oxygen was low! The total of other costs appeared at least competitive.

A pilot-plant furnace was then designed and built for the continuous smelting of dry sulfide flotation concentrates. A design principle was "keep it simple stupid," so both furnace and burner were basically adaptations of the neighboring reverberatory furnaces—with mineral concentrate and oxygen substituted for coal and air. Another difference from conventional practice was cyclic reduction drenching of furnace slag with molten FeS from flash-smelted pyrrhotite concentrate prior to tapping, which decreased slag oxygen potential and CuNi loss. This practice would have been improved by the inclusion of some coal with the pyrrhotite, but this "obvious" action was not obvious at the time. Oxygen was supplied at 95% O2 by a Canadian Liquid Air 5 t/d oxygen plant, and furnace off-gas was treated in a Canadian Industries Limited sulfur dioxide liquefaction pilot plant.

Pilot-plant operations started in January 1947 and were terminated late in 1948 with full success at 25 t/d of concentrate. Furnace dimensions had to be increased four times—mainly due to refractory erosion by flying molten particulates—before the final size was attained. Matte grades of up to 75% CuNi were produced, with pyrrhotite-cleaned slags analyzing up to 0.9% CuNi. Testing of the liquid SO2 product for sulfite pulp production by Abitibi Paper Company indicated its superiority to SO2 produced by sulfur burning.

The day after New Year's Day, 1952, a pioneering commercial oxygen reactor (Figure 2) flashed into life. In accordance with prior planning, the new plant superintendent—plant coinventor Charles Young—was the former pilot-plant superintendent; before that, he had been a laboratory engineer involved in the initial R&D. The able, invaluably supportive, up-from-the-ranks smelter manager, Duncan Finlayson, had originally been contemptuous of the "black box" furnace concept: "I can't stick my head in it—I don't like it!" His understandable skepticism was overcome by early pilot-plant exposure and by the effectiveness of the well-maintained instrumentation employed, which allowed the operator to monitor and control the key furnace variables. After the usual birth pains, the daily furnace charge averaged 500 tonnes of 28% Cu chalcopyrite concentrate, 100 tonnes of pyrrhotite concentrate, and 90 tonnes of sand flux. The matte produced analyzed 45% CuNi, the slag was 0.75% CuNi, and the off-gas was 75% SO2. The last—relatively small in volume—was condensed in a 300 t/d liquid SO2 plant, which was a decimal order of magnitude larger than any other in the world.8

Figure 2. The original Inco Oxygen flash furnace (reproduced from the July 1995 Journal of Metals).

Having well served its educational function, the innovative furnace was replaced by a rewardingly profit-making 1,000 t/d unit two years later. The critically vital, Inco-owned and operated Air Liquide tonnage oxygen plant delivered admirably—producing 95% O2 gas at a total cost of $4/t and using 0.4¢/kWh power. Low-cost production of pipeline tonnage oxygen was proven! Pyrometallurgy was reborn! The Inco staff technical paper describing this achievement,6 and the five names in alphabetical order on the covering patent9 complied with the aphorism: "Share credit, share success." Now, Inco owns and operates Air Liquide oxygen plants with a total capacity of 1,800 t/d to feed a variety of Copper Cliff furnaces. 10

Oxygen Enrichment

L.S. Austin wrote in 1919:11 "One can infer that the reverberatory furnace is primarily a combustion chamber (for the waste heat boilers), with the melting, the furnace reactions and the separation of matte secondary factors." The villain of his grievance was tonnage nitrogen. Oxygen-enrichment of the furnace's combustion air increases fuel efficiency and permits higher smelting rates. The amount of heat delivered to the waste heat boilers by each tonne of nitrogen equals that required to smelt one tonne of solid charge. This was demonstrated in Copper Cliff smelter full-scale tests on one of the seven 9.1 m X 33.5 m nickel reverberatory furnaces. These showed that one tonne of oxygen was equivalent to at least one half tonne of coal and that throughput rate could be increased 33% by a decrease in the nitrogen/oxygen ratio. Oxygen-enrichment of these furnaces' combustion air was, therefore, established as routine practice.

There were 19 air-blown 4.0 m X 10.7 m Peirce-Smith converters in the Copper Cliff main converter aisle, treating liquid reverberatory furnace matte. Oxygen utilization efficiency, in its exothermic reaction with iron and sulfur, was close to 100%. However, half of the total heat developed suffered the nitrogen curse, so it was lost. Several of these converters blew flash-furnace matte to blister copper. If blower air was enriched with oxygen (e.g., to 33% O2, thereby changing N2/O2 volume ratios from 4:1 to 2:1), the usual heat balance in the converter would be much improved. In addition to the increase in the conversion rate and decrease in gas volume, cold charge could be smelted. The limiting factor would be excessive impact on tuyere and refractory life. Converter trial operations, in which the oxygen content of blower air was varied in the 25-35% range, were launched in 1958. These indicated a 30% O2 content to be optimal. The additional useful reaction heat was employed to melt large quantities of scrap and concentrates (e.g., the 73% copper filter cake produced by the matte flotation copper-nickel separation plant). The 30% O2 level of enrichment was then systematically extended to all 19 converters.

On the basis of Inco's experience with tonnage oxygen generation and utilization, one of the authors was able to write the following in 1960:

"The pyrometallurgist will gain further benefits from the advent of low-costoxygen. The dead hands of nitrogen have been lifted from oxidation reactionswhich utilize the oxygen in air. The nonferrous metal industry is on thethreshold of understanding in this connection. As one example, oxygenenrichment of combustion air will give new life to otherwise obsolescent orobsolete conventional furnaces. Greatly improved reverberatory and rotaryfurnace design will be employed for utilization of tonnage oxygen in continuousautogenous smelting and converting. The tuyereless, top-blown oxygen steelconverter will invade and conquer the smelters and refineries of the nonferrousindustry. Decrease in nitrogen dilution of sulfurous smelter gases will permitincreased sulfur fixation and result in decreased atmosphericpollution."12

This prediction has proven accurate.13-17 Nevertheless, low-cost oxygen—the immense value of which was demonstrated on a commercial scale in 1952—continued to be greatly underemployed for decades. 18,19

Oxygen Top-Blown Rotary Converter

Inco took another major stride forward in the use of tonnage oxygen to enhance heat and mass transfer in nonferrous pyrometallurgy, by pioneering the employment of a steelmaking converter for this purpose. In the metallurgical world, it was the generally held opinion that blowing nickel sulfide to metal in a converter presents impossible-to-solve thermodynamic and operating problems. In fact, it is impossible to produce metallic nickel from nickel matte in a Peirce-Smith converter (e.g., due to disastrous nickel oxide formation). During sulfur dioxide evolution, nickel and nickel sulfide form a single solution phase extending from Ni3S2 to pure nickel, and the NiO (melting point: 1,984 °C) that forms has low solubility in matte.

However, 1941 Copper Cliff Laboratory studies had indicated that conversion was possible, given sufficiently high bath temperature and oxygen potential. Hence, the high-temperature, broad-range oxygen potential and excellent mixing capabilities of the turbulent bath, characteristic of a post-war top-blown rotary converter (TBRC) steelmaking process, appeared extremely attractive. The vessel employed provided efficient and effective gas-liquid-solid contact throughout the bath—with concomitant extraordinarily extensive control of temperature and oxygen potential. It enhanced heat transfer, increased the overall rate of the chemical reactions, minimized composition gradients within each phase, and significantly reduced diffusion barriers.

Oxygen metalmaking by tonnage nickel matte experiments in a TBRC were proposed and opposed in heated debates within Inco. Conventional wisdom said such experiments would fail and perhaps kill: the converter would produce nickel oxide instead of metal, and the nickel sulfide (melting point— 788°C), at 1,650°C, would cut through the rapidly rotating refractory lining like a knife through butter.

In 1958, Paul Queneau and John Feick, Copper Cliff Peirce-Smith converter superintendent, supported by John Thompson, Inco's chemical engineer chief executive officer, explored direct nickel sulfide conversion to oxygen crude nickel in a three tonne KALling converter at DOmnaverts Steel Works (KALDO) in Sweden. The experiment was immediately successful. This victory in novel nickel making having been achieved, opportunities in TBRC oxygen coppermaking, fire refining, and beyond were revealed and successfully pursued by Inco in a seven tonne TBRC at Port Colborne.20,21 It all seemed so obvious after the breakthrough.

In 1971, two 50 tonne TBRCs were commissioned at Copper Cliff (Figure 3) as the first stage in the transformation of complex metal sulfide intermediates to 99.98% pure nickel by the Inco Pressure Carbonyl Process. Today, the operation of these converters is routine, having produced a million tonnes of oxygen crude nickel to date.22

Figure 3. The oxygen top-blown rotary converter in action at Inco's Copper Cliff nickel refinery.

Commissioning and operation of the TBRCs completed development of an oxygen culture at Copper Cliff. Management and technical staff understood the advantages oxygen technology offered, and operators and maintenance personnel knew how to work with oxygen as a useful ally. This culture, coupled with continuing active research and development, enabled commercialization of new oxygen technologies as Inco responded to the changing economic and environmental challenges of the seventies and eighties.

Oxygen Smelting

Experimentation with roof-mounted oxy-fuel burners in reverberatory furnaces commenced in October 197723 using ideas developed at the Caletones smelter.24 The first burners generated excessive noise levels and deteriorated rapidly. Two years of development generated effective oxy-fuel smelting capabilities and yielded a rugged burner that gave a stable flame at acceptable noise levels. In October 1979, a reverberatory furnace equipped with 12 oxy-fuel burners began operation. Smelting rate increased by 45%; fossil fuel consumption and exhaust gas volume decreased by 55% and 65%, respectively.23,25 The increased productivity and lower gas volumes contributed to a major rationalization of the

furnaces and flue systems and concomitant improvements in the workplace environment. Oxy-fuel fired reverberatories operated for more than a decade, treating all of the nickel concentrates. The last such furnace was shut down in 1993 with commissioning of two oxygen flash furnaces as part of Inco's $600 million (Canadian) SO2 abatement program.10,26, 27

These second-generation Inco oxygen flash furnaces (Figure 4) are larger than the original furnaces, employ greater amounts of water cooling, and incorporate modern gas cleaning systems that are extremely compact, as allowed by the low-volume exhaust gas of tonnage oxygen smelting. Cleaned gas feeds a double-contact acid plant and the original liquid SO2 plant. 10,26 Furnace feed is a bulk copper/nickel concentrate. Petroleum coke and natural gas are added to provide supplemental heat and to allow return of converter slag and smelting of reverted material. Table I compares the original and new furnaces.

Figure 4. A schematic of a current Inco oxygen flash furnace at Copper Cliff.

Oxygen Flash-Converting Chalcocite Concentrates

From 1965 to 1985, the smelter processed its -325 mesh nickel-containing chalcocite flotation concentrate (Cu2S derived from the matte separation process) by Garr gun addition to blowing Peirce Smith converters.9,28 This procedure led to long converting cycles and was a source of large dust emissions.

Development of a novel oxygen-based flash-converting process gave a short-term, low-capital improvement.28, 29 Due to the rapid kinetics of oxygen reactions, the smelter was able to use a surplus Peirce-Smith converter shell as the vessel. The in-house development of a suitable feed system and unique oxygen flash gun that could simultaneously fire natural gas and filter cake completed the process. This process, the first commercial application of flash copper converting, started in 1985 and operated for eight years, treating 8% moisture filter cake at rates of 250 t/d to 300 t/d. More than 300,000 tonnes of molten semiblister assaying 2-3% sulfur were produced.

Oxygen Top Blowing/Nitrogen Bottom Stirring

Since 1993, Inco has commercialized several innovative techniques for oxygen converting to blister copper, all based around the top blowing of oxygen accompanied by gentle nitrogen bottom stirring. 30,31 In 1984, crucible experiments revealed that extraordinarily high oxygen efficiencies could be obtained during blister finishing by blowing oxygen onto the melt while sparging with nitrogen. Moreover, this mixing promotes desulfurization of the molten blister and enhances the approach to chemical equilibrium. Exhaustive laboratory tests demonstrated that the process was effective at low and high top-blowing rates, was insensitive to lance position, and required only small flows of sparging gas. Pilot-plant studies at the 3-5 tonne scale confirmed the results.30 Importantly, this work demonstrated the usefulness of ceramic porous plugs (Figure 5) for nitrogen injection into copper and gave the confidence needed to install them into a commercial vessel.

Figure 5. A cross-section of a porous plug.

Full scale tests began in 1989 using a Peirce Smith converter shell equipped with two porous plugs and an oxygen lance. The combined blowing approach yielded oxygen efficiencies of 85% during blister finishing, although the subsonic open pipe lance was mounted 1.8-3.7 m from the bath and blew gently to minimize splashing. By using oxygen, the converter consumed scrap at a rate of 20% of the semiblister charge (2-3% sulfur). The porous plugs performed well in copper service, and elimination of tuyeres minimized fugitive emission generation when the converter rolled into and out of stack. Finishing blister by oxygen top blowing/nitrogen bottom stirring was incorporated into the new flowsheet of the Copper Cliff Smelter in 1990.28 To conserve capital, the process was implemented in existing Peirce-Smith converter shells (Figure 6). Commercial operation began in November 1993. *

Figure 6. A schematic of a commercial oxygen top-blown/ nitrogen bottom-stirred

converter.

Oxygen Converting Chalcocite Concentrate

Continuing research into the flash converting of chalcocite showed that the 10-20% dusting rate experienced at all scales of operation was due to particle fragmentation during ignition.33, 34 Moreover, removal of this large quantity of dust in a gas cleaning system feeding an acid plant involved major handling problems.35 Hence, the search for a better way of oxygen converting chalcocite began.

Plant tests showed that tuyere injection of chalcocite accompanied by oxygen top blowing/nitrogen stirring was effective, and commercial operation commenced in 1993.36 The reactor vessel is a 18 m long, 4.5 m diameter cylinder with oxygen lances mounted on each endwall. Each of two blow-tank conveying systems is connected to a single tuyere and injects chalcocite at a rate of 25 t/h. Dusting rate is about 1%, and oxygen efficiency is in the 90% range.

Pilot-plant studies in 1994 showed the feasibility of combining top blowing/bottom stirring with a simplified feeding technique. Full-scale tests began in August 1995. The application of nitrogen stirring through porous plugs has been extended a further step. Feeding is accomplished by gravity introduction of dry, nonagglomerated concentrate (90% -44 µm) through a water-cooled pipe onto the "eye" created by the nitrogen. 37 Supplemental heat is provided in the area to promote melting. Feeding zones and converting zones are separated so that gas velocity around the feed stream is minimal (Figure 7). As a result, a dusting rate of 1.5-2% is achieved. Full-scale development continues. As demonstrated in the pilot-plant work, this simple approach can be useful for other continuous converting applications.

Figure 7. The gravity-fed oxygen reactor for chalcocite converting.

OXYGEN PRODUCTION

The continuing developments in oxygen pyrometallurgy have been assisted by major improvements in tonnage oxygen production. In contrast to 1946, the industry of today is

highly competitive with several suppliers. Cryogenic oxygen production remains the preferred technology for large tonnage applications. Developments in centrifugal compressors, improvements in the fractionation cycle, and the application of computer controls have greatly increased the energy efficiency and productivity of modern plants.38-41 Molecular sieve front-end purification eliminates the cold box, enhances gas purities, and obviates the yearly plant shutdown for deriming.41 Typically, today's oxygen plants incorporate one day's storage of liquid oxygen to ensure against plant shutdowns and are equipped with computerized load following to minimize energy consumption and costs. Capital and production costs for such plants are summarized in Figure 8. 42 Aside from capital, energy remains by far the major factor in production costs; other supply, operating, and maintenance labor costs are relatively small.

Figure 8. Oxygen production requirements: (a) plant investment for oxygen at 20 psig; (b) power requirements for oxygen at 20 psig; (c) power requirements for oxygen at pressures above 20 psig; and (d) operating costs (MIT-maintenance, insurance, and taxes).

The vacuum swing adsorption process has found application for oxygen requirements of less than 100 t/d at purities of 90%. In this technique, nitrogen is removed in two molecular sieve adsorption trains connected in parallel and operating in sequence. While incoming air is purified in one train, the other train is regenerated by pressure reversal. 40 Such an installation can be used to supply oxygen to a relatively small user or to top-up a large cryogenic plant that cannot meet ever-increasing smelter demands.

MEASURING PROCESS PARAMETERS

As the oxygen pyrometallurgy revolution continues, the reaction rates and complexity of the processes generally increase. Conventional methods of monitoring and controlling pyrometallurgical processes cannot meet these challenges. Moreover, the closed nature of modern reactors prevents the use of traditional techniques such as visually monitoring flame color or bath appearance. Necessary sensors, signal translators, and data processors must give correct and timely information to the operator. If betrayed, the operator is automatically wrong, and the process can automatically fail—possibly disastrously. All concerned must understand the vulnerability of modern "invisible" processes to uncontrolled, characteristically fast, and potentially dangerous reactions. This is especially true for single-vessel, multistaged processes. The operator needs to know not only what was going on in the closed vessel, but what is going on and what will be going on!

Incorporation of useful, well-maintained, reliable "blind flying" instruments is indispensable as is precise metering of inputs and outputs. Effective blending of feeds—minerals, scrap, and residues—is essential for steady-state operation.

Algorithms that account for both mass and heat effects in autogenous or semiautogenous reactors require comprehensive information about input and output streams. Using distributed control systems, the solid-feed rate, typically controlled with impact-type meters, can be systematically calibrated with more accurate weight loss readings from dry feed bins. These bins are subject to both filling and emptying cycles; thus, direct use of weight loss is not possible.

Recent developments in analytical techniques promise a revolution in the determination of solids composition. Prompt gamma neutron activation spectroscopy is employed in power and cement plants to provide on-line analysis.43 The solids are irradiated with neutrons and, in turn, emit gamma rays characteristic of the nuclei present and independent of matrix effects. Analysis of the spectra involves significant data processing. However, once set up, the technique can be used for continuous measurements over a moving belt. Alternatively, the technique may provide quick chemical assays with simplified sample preparation steps amenable to the shop floor.

Monitoring of pyrometallurgical processes is seriously hampered by the vulnerability of sensors to high temperatures. Moreover, liquid and solid particulates in the reactor atmosphere cause corrosion and erosion. Direct temperature measurement by insertion of thermocouples into the reactor freeboard is often impractical because they burn or short out. The development of two-wavelength pyrometers has improved temperature measurement, but even these pyrometers can be affected by the atmosphere. Thus, temperature in many pyrometallurgical reactors is currently determined by manual immersions during skimming and tapping. An interesting approach, developed by Noranda, is temperature measurement through tuyeres.44 A retractable periscope mounted on the back of a tuyere transmits light via a fiber-optic cable to a two-wavelength pyrometer located remotely from the reactor.

Accurately measuring matte and slag levels in a closed reactor is difficult. The widely used technique of bar immersion is distinctly limited with respect to both accuracy and applicability. Determination of reactor weight,45 gamma radiation, lasers, and microwaves can be used to measure levels of molten systems.

Gamma gauges for remote determination of bath levels have found application in the glass industry.46 The apparatus is mounted in the narrow forehearth area of the furnace and comprises a transmitter located on one side and a receiver on the other. Application of the technique to nonferrous applications (e.g., to indicate slag, matte, and metal levels) has so far been limited due to large reactor widths.47

Laser-based systems have found application in casting operations. In the aluminum industry, lasers measure liquid levels in furnaces and also the rate of mold fillage.48 Similar applications apply to cast iron operations.49 The application of lasers in nonferrous reactors may be limited by the presence of dust and fume.

Electromagnetic microwaves hold promise for determining bath levels in continuous oxygen pyrometallurgy. Microwaves are relatively insensitive to smoke and dust and are not affected by high temperatures or temperature gradients as are ultrasonics. In the steel industry, radar has been employed to measure metal level in basic oxygen furnaces and torpedo cars. 50,51 Microwaves can also quantify the rate of rise during bottom teeming.52 A method of measuring slag thickness during casting operations has been identified.53

Monitoring the progress of a steel converter with disposable oxygen probes based on stabilized zirconia has long been an accepted part of the process. Commercial applications in nonferrous systems are more limited. Today, highly reliable probes for measuring bath oxygen potential in copper converters and anode furnaces are available,54 and their use will increase. However, the much desired continuously operating oxygen probe remains elusive due to the sensitivity of the electrolyte. Other solid electrolyte systems are sensitive to CO2, SOx, and NOx and may find commercial application in pyrometallurgy.55 Still other potential methods of monitoring reactor conditions include optical spectroscopy56 and continuous analysis of internal and exhaust reactor gases (e.g., O2, CO, CO2, H2, SO2) by employing in-situ probes or sample withdrawals.

WINDOW ON THE FUTURE

A window on the future of pyrometallurgy is provided by metal making directly from mineral concentrate in a single, closed, continuous oxygen converter. The impossible dreams of continuous metalmaking directly from mineral feed have a long history. In 1870, a textbook on metallurgy gave a detailed description of the "Siemens Process of Producing Steel Direct from the Ore". It confidently stated: "The experiments on this important process are now so far completed, that it is expected that the process will soon be introduced into practice."57 In 1896, Oliver Garretson described a logical process for continuous copper smelting, converting, and slag cleanup, but it remained in two dimensions.58 In 1968, Howard Worner described his WORCRA concepts, "which seek to maximize energy conservation" by "direct smelting-converting in one furnace in which both smelting, dispersed-phase refining and slag conditioning and settling are combined in distinct but communicating zones or branches." The genuine merit of his thinking was demonstrated in years of pilot-plant operations, but commercial operations did not follow.59

"The overall cost advantages which accrue from continuity—not least in respect to environmental conservation—are manifest. . . .There is no reason why hydrocarbon-shielded oxygen jets cannot be advantageously employed for continuous subsurface-blowing in nonferrous converting practice."60 In 1974 the Q-S continuous oxygen converter was publicized throughout the United States and was illustrated on the cover of JOM. The inventors believed it would "prove to be a contribution to maximum economic utilization of the nation's mineral heritage, with due regard to conservation of natural resources—including the environment." 61,62 Two decades later, commercial QSL (Queneau-Schuhman-Lurgi) oxygen converters are continuously making metal directly from mineral feed. A dream is finally a reality!63-66

There are, of course, other dreams being pursued. For example, industry needs to fully harness the energy released by the oxidation of SO2 to SO3 during acid production. This energy could often produce sufficient 40 ats steam, for power generation, to supply all or most of the amount required for oxygen production. We also need to improve our ability to control the process parameters that characterize the ideal pyrometallurgical reactors of the future. These will rapidly and continuously convert mineral sulfide concentrate and appropriate recycled materials to acceptable quality metal, clean slag, and sulfur dioxide-rich gas by fully utilizing the concentrate's natural fuel content in closed, fugitive emission-free reactors. The chemical and steel industries are making great strides in process monitoring (e.g., tomography), and the nonferrous industry must also follow their lead. 67,68

Oxygen pyrometallurgy has revolutionized the industry. The changes it has wrought can be compared with developments of the turn-of-the-century decades (e.g., multihearth roasters, Dwight-Lloyd sintering machines, huge reverberatory and open hearth furnaces, by-product coke ovens, and Peirce-Smith converters). Today, oxygen usage is ubiquitous and addictive. Substituting oxygen for air vastly increases process productivity and cleanliness. Revolutionary sparks were ignited at Copper Cliff and Gerlafingen half a century ago. However, until the winds of energy conservation and environmental protection blew compellingly, the fires were confined. Now the fires burn briskly around the world—the future of pyrometallurgy is bright!69-71

References

1. F.W. Davis, The Use of Oxygen or Oxygenated Air in Metallurgical and Allied Processes, Report of Investigations no. 2502 (Washington, D.C.: Bureau of Mines, July 1923).2. Rachel Carson, Silent Spring (New York: Houghton Mifflin, 1962).3. Paul E. Queneau, "The Recovery of Nickel from Its Ores," JOM, 22 (10) (1970).4. Fred Kaplan, "Norilsk, Russia, Mining and Metallurgical Works," The Boston Globe (17 November 1994).5. T.E. Norman, Eng. and Min. J., (10-11) (1936), p. 137.6. Inco Staff, "Operations and Plants of Inco," Canadian Mining Journal (May 1946); and Inco Staff, "Oxygen Flash Smelting," JOM, 7 (7) (1955).7. F.W. Starratt, "LD—In the Beginning," JOM, 12 (7) (1960).8. R.W. Allgood, "Sulphuric Acid and Liquid Sulphur Dioxide Manufactured from Smelter Gases at Copper Cliff, Ontario," CIMM Transactions, vol. LV (1952).9. J.R. Gordon, G.W. Norman, P.E. Queneau, W.K. Sproule, C.E. Young, U.S. patent 2,668,107 (1954).10. C. Landolt, A. Dutton, A. Fritz, and S. Segsworth, "Nickel & Copper Smelting at Inco's Copper Cliff Smelter," Extractive Metallurgy of Copper, Nickel and Cobalt, Proceedings of the Paul E. Queneau International Symposium, Vol. II, Copper and Nickel Smelter Operations, ed. C.A. Landolt (Warrendale PA: TMS, 1993).11. L.S. Austin, The Mineral Industry, ed. G.A. Roush and A. Butts (New York: McGraw-Hill, 1919).12. Paul Queneau, "Foreword," Extractive Metallurgy of Copper, Nickel and Cobalt, Proceedings of the 1960 International Symposium, ed. Paul Queneau (New York:

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30. S.W. Marcuson, C. Diaz, and H. Davies, "Top-Blowing, Bottom-Stirring Process for Producing Blister Copper," JOM, 46 (8) (1994), pp. 61-64.31. C. Diaz, S. Marcuson, H. Davies, and R. Stratton-Crawley, "Conversion of Nickel and Sulfur-Containing Copper to Blister," Proceedings of Copper '87, Vol. 4: Pyrometallurgy of Copper, ed. C. Diaz, C. Landolt, and A. Luraschi (Santiago, Chile; Universidad de Chile, 1988), pp. 293-304.32. Robert Lee, "Innovations in Ferrous Pyrometallurgy—A Canadian Perspective," CIM Bulletin, 84 (June 1991), pp. 125-131.33. A. Otero, J.K. Brimacombe, and G.G. Richards, "Kinetics of the Flash Reaction of Copper Concentrate," in Ref. 28, pp. 459-472.34. G.S. Victorovich, "Oxygen Flash Converting for Production of Copper," Extractive Metallurgy of Copper, Nickel and Cobalt: Proceedings of the Paul E. Queneau International Symposium. Vol. I. Fundamental Aspects, ed. R.G. Reddy (Warrendale PA: TMS, 1993), pp. 623-637.35. H. Davies, S. Marcuson, G. Osborne, and A. Warner, "Flash Converting of Chalcocite Concentrate at Inco's Port Colborne Pilot Plant," in Ref. 34, pp. 623-639.36. C.A. Landolt, A. Dutton, T. Fritz, and S. Marcuson, "New Smelter Furnaces and Novel Copper Processing," The 96th Annual General Meeting of the CIM and the 1994 Mineral Outlook Conference, ed. N. Champigny and P. Dillon (Montreal, Canada: CIM, 1994), pp. 69-71.37. C. Diaz, S.W. Marcuson, A. Warner, and G.E. Osborne, "Reduced Dusting Bath System for Metallurgical Treatment of Sulfide Materials," U.S. patent application 08/401081: filing date 8 March 1995.38. D. Eyre, I. Gorup, and T. Pawulski, "Production of Oxygen—Keeping Pace with the Metallurgical Demands," The Impact of Oxygen on the Productivity of Non-Ferrous Metallurgical Processes, ed. G. Kachanivsky and C. Newman (Toronto, Canada: Pergamon Press, 1987), pp. 77-85.39. D.C. King, R. L. Hurchison, K.J. Murphy, and A. Odorski, "The Benefits of Optimizing Air Separation Plant Performance,"in Ref. 38, pp. 199-208.40. K.J. Murphy, A.P. Odorski, A.R. Smith, and T.J. Ward, "Oxygen Production Technologies for Non-Ferrous Smelting Applications," in Ref. 38, pp. 219-235.41. T.S. Pawulski, "Cryogenic Oxygen Plants—An Overview," in Ref. 38, pp. 121-134.42. D.A. Eyre, Air Liquide Engineering, private communication with authors (5 October 1995).43. J. Makansi, "PSI Gibson Turns Compliance into a Vision for the Future," Power (December 1993), pp. 37-40.44. A. Pelletier, J.M. Lucas, and P.J. Mackey, "The Noranda Tuyere Pyrometer: A New Approach to Furnace Temperature Measurement," in Ref. 31, pp. 489-508.45. H.W. Grenfell, D.J. Bowen, and C. McQueen, "The Role of Continuous Vessel Weighing in the Commissioning and Operation of B.S.C. Ravenscraig New No. 3 B.O.F.," Proc. Natl. Open Hearth Basic Oxygen Steel Conf., vol. 60 (1977), pp. 209-221.46. "CND Continuous Level Gauge," product brochure CN-158 (Round Rock, Texas: TN Technologies, 1995).47. Tony Hart, TN Technologies, private communication with authors (10 March 1995).48. "Selcom Laser Sensors and LaserPour Systems for Aluminium Level Control," product brochure (Southfield, MI: Selective Electronics, 1995).49. D.P. Kanicki and B.R. Krohn, "Taking the Heat Off Molten Metal Handling II-

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70. Carlos Diaz, Hermann Schwarze, and John C. Taylor, "The Changing Landscape of Copper Smelting in the Americas," in Ref. 54.71. Paul E. Queneau and Martin Hirsch, "Process for the Manufacture of Steel," U.S. patent 5,466,278 (November 14, 1995); and "Process for the Continuous Manufacture of Steel," U.S. patent application 08/503,710; filing date: 18 July 95. *Development of porous ceramic plugs began in 1947 and was led by Steven Spire and Robert Lee of Canadian Liquid Air in conjunction with the Canadian Bureau of Mines.3 In the 1970's, porous plug use became widespread in the steel industry. However, their use in nonferrous pyrometallurgy has been limited, and the usage described here represents its first commercial application in copper smelting.