Copper extraction from the 60's. into the 21'' century

W. G. Davenport Dept. of Materials Science and Engineering University of Arizona Tucson, AZ, USA 85721

ABSTRACT

Changes in copper extraction from 1960 till today are documented. The top ten changes have been:

replacement of reverberatory smelting by high intensity oxygen rich smelting growth of the Outokumpu flash smelting to over 50% of the world's smelting capacity successful development of single furnace coppermaking but only for low slag fall concentrates replacement of the batch Peirce-Smith converter by continuous converting, but only in a few cases increased SO2 capture throughout the industry, mainly as sulfuric acid development of low initiation temperature 'big bight' Cs catalysts for treating the continuous high-SO2 strength gases from continuous smelting/converting complete replacement of reverberatory anode scrap and cathode melting h a c e s by the Asarco shaft furnace adoption of stainless steel permanent cathodes and automated stripping technology for electrorefining and electrowinning complete elimination of wire bar casting by continuous bar castinghod rolling development and adoption of extractants for turning weak impure leach solutions into strong pure electrolytes.

It is postulated that the biggest possible change over the next 20 years would be complete replacement of smelting/converting by hydrometallurgical processing. However, this seems unlikely due to copper purity, precious metal recovery, and economic concerns. The increasing value of sulfuric acid to many copper companies gives chalcopyrite smelting/oxide-supergene leaching a nice synergy especially with the energy credits now coming from continuous smelters and their acid plants.

Proceedings of Copper W-Cobre 99 Lnlernational Conference

Volume I-PlenaryLectures/Movement of Copper and Industry Outlook/ Copper Applicalions and Fabrication

Edited by G. A. Eltringham, N.L. Piret and M. Sahoo The Minerals, Metals & Materials Society. 199

VOLUME I

INTRODUCTION

Around. 1960, when I first became,interested in copper smelting, the reverberatory furnace was king around the world (1). It was very effective .at recovering copper fr.om concentrate and it was very reliable, having (been used for over a century in various forms.

As many have found out by thinking that old reverberatory slags might serve as ore for a money-making enterprise, its slags contained only 0.3 or 0.4% Cu showing just how efficient it was. Not only that, converter slags could be recycled back through it, getting their Cu-in-slags down to that same low level. . -

However, the reverb didn't make much use of the energy available in its sulfide concentrate feed to provide the heat for melting slag and matte. More importantly, its SO2-in-offgas concentration was so low as to make SO2 removal almost impossible. So, it usually vented all its SO2 to the atmosphere.

There were also a few blast (shaft) h a c e s around in the 1960's. Collection of their SO2 was also difficult. The Momoda modification allowed quite good SO2 collection but its production rate was so slow as to make it uneconomical. The last Momoda adoption was in 1967 at the Huelva smelter (2). The Legnica and Glogow I smelters in Poland still operate six blast (shaft) furnaces for copper concentrate.

It was clear even in 1960 that this reverbblast furnace situation could not go on forever. Processes that would efficiently capture S& would have to be found and adopted.

Likewise, the Peirce-Smith converter, though chemically very efficient, was not a good device for capturing SOz. Its SO2 concentrations of 5 - 8% SO2 were certainly better than those of the reverberatory smelting furnace. But its discontinuous batch nature made efficient SO2 capture difficult.

So, the writing was on the wall. Processes would have to be developed and adopted that would pennit (i) efficient capture of smelting and converting offgases and (ii) efficient fixation of the SO2 from those gases in a useful form, almost always sulfuric acid.

PROCESSES AVAILABLE IN THE 1960's

Of course, flash smelting already existed in the 1960's. Outokurnpu Oy had installed its first flash furnace shortly after World War I1 (Table 1) to minimize fossil fuel consumption. lnco had developed its flash smelting process a little later to make use of the nearly pure oxygen that could be made cheaply from hydroelectricity. Both produced continuous streams of strong-SO2 offgas from which SO2 could be recovered as

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VOLUME I 58

As for Outokumpu flash smelting, the role of the Furukawa engineers in making it a viable economic process cannot be overly praised. Anyone who has scrutinized their paper 'The Development of Flash Smelting Process at Ashio Copper Smelter, Furukawa Mining Co., Ltd' (3) cannot fail to realize the huge contribution these engineers made in advancing flash fUrnace technology for the world.

As far as I can remember, these were the only smelting processes that could be said to offer the promise of.high efficiency SO2 capture. Electric furnaces held out some promise but only by shifting SO2 evolution to roasters ahead of the smelting furnace.

So that was it in the 1960's. But there were whispers ofnewcopper smelting technology coming on the scene, particularly from Noranda and 8Mitsubisbi. And in 1967 patents were issued for Noranda and Worcrasmelting.

THE 1970's

The winds of change began to blow in the late 60's and early 70's. Converter gases began to be caught and' their SO2 processed. Outokumpu smelting began to be adopted more fkequently and new processes came on the scene (Table 1)(4). The 70's may be thought of as the golden age of new copper smelting processes with the adoption of

Electric furnace smelting Kivcet smelting Mitsubishi smelting Noranda smelting Outokurnpu flash smelting TBRC smelting Teniente smelting

and the .trial ofi

Worcrasmelting.

Worcra smelting never reached the commercial scale and Kivcet smelting for copper has never developed past one or two small units in the former Soviet Union. Likewise, TBRC copper smelting was adoptedi in several; places but. has not expanded for smelting copper concentrates.

FATE OF PROCESSES ADOPTED IN THE 1970's

Table 2 follows through the 1980's and 1990's the processes developed and adopted in the 1970's. It shows that Outokumpu smelting was the most widely adopted followed by Teniente smelting, Mitsubishi smelting and Noranda smelting. Not shown

PLENARY LECTURESIMOVEMENT OF COPPER AND INDUSTRY OUTLOOK1 59 COPPER APPLICATIONS AND FABRICATION

in the table is the fact that many electric furnaces went out of service during this period due to high energy costs.

So the three manifestations of copper smelting:

particulate smelting (Outokumpu flash) submerged tuyere smelting (Teniente and Noranda) lance smelting (Mitsubishi)

proceeded together: flash smelting in the lead, submerged tuyere smelting second and lance smelting third.

Teniente smelting has a somewhat unusual position in this list because it seems to always need 'seed' matte from another process, e.g. reverberatory smelting (5) or flash smelting (6): Seed matte production may account, however, for as little as 10% of the smelter's total smelting capacity. Nevertheless, as now operated, it is mainly a process for expanding existing smelting. capacity rather than for greenfield smelters.

NEW AND NEWLY ADOPTED PROCESSES IN THE 1980's AND 1990's

The 1980's and 1990's saw continued adoption of Outokumpu flash, Teniente, Noran& and Mitsubishi smelting. They also brought some new actors on to the scene:

Contop cyclone smelting Inco flash smelting Isasmelt lance smelting Vanyukov submerged tuyere smelting

Contop cyclone smelting was first used to increase the smelting rate of reverberatory furnaces. The Asarco El Paso smelter then successfully operated a stand- alone Contop furnace from 1993 to 1999. After early problems with cyclone burner corrosion, this furnace operated well, albeit with a somewhat high energy consumption (7). Unfortunately, the El Paso smelter has been temporarily mothballed because of copper's low price so that the future of Contop smelting is somewhat cloudy.

Inco flash smelting had a brief flurry of activity in the 80's with two retrofit adoptions as reverberatory replacements, both in the southwestern United States. These two units have operated reliably since the early 80's. They are now producing at up to twice their design smelting rates. But no further units have been adopted outside Inco since this brief flurry. Perhaps Inco's lack of enthusiasm for selling technology has limited the process' adoption. It should be noted however that Inco recently built two

VOLUME I 60

Table 2 Smelting Processes Adopted 1980-1999

198.1 ) Norilsk, Russia I

-~ .- -. . .. a-7 -

1987 I Srednogorie, Bulgaria 1988. 1 Chuquicamata, Chile

1982 1983

1 1985* 1986*

Camacari, Brazil Isabel, Leyte, Philippines Guixi,China El Taio. Mexico

1998 1998 1999*

znco Flash

Gujarat, India Minas Cerais, Brazil Olympic Dam, Australia

in.progress in :progress in.pr0gres.s

Ronnskar, Sweden i 110,. Peru (smelting) : 110, Peru (converting)

Noranda Process 1990* I Port Kembla, Ausbalia 199? 1: Daye, China.

1983 * 1984* 1995

I 2000 I Shenyang, China

Hayden, Arizona Hurley, New Mexico Sudbury, Ontario (2)

Teniente Procers - - - . - - - - - - - - 1984* 1 Chuquicamata, Chile 1984* 1 Las Ventanas, Chile 1 1985. Polrerillos, chile 1989 I Paiuote. Chile. I

Nkana, Zambia

La Caridad, ,Mexico 1998

Mitsubishi'Smeltinn/Cowerling 1991 * .I. Naoshima, Japan. 1998 I Onsan. Korea

t - - . . , ---- - -

1998 '1 Gresik, Indonesia

Contop 1993* '1. .El,Paso, Texas#

Isasamelt 1992* 1997

in progress

Miami, Arizona Tuticorin, India :Belgium

PLENARY LECTURESIMOVEMENT OF COPPER AND INDUSTRY OUTLOOK/ 6 1

COPPER APPLICATIONS AND FABRICATION

furnaces for its Sudbury smelter and plans to use the technology for its Voisey's Bay operation.

Vanyukov smelting is tuyere smelting. Unlike Teniente and Noranda smelting its furnace is not rotatable, leading to potential problems with unexpected tuyere-blowing outages. This process was examined closely by Western Mining for its Western Australia operations but it was not adopted. The Ballcash Copper Smelter Vanyukovs were being operated in conjunction with a reverberatory furnace - it was not clear that they were being operated "stand-alone". Only one (of two) could be operated at a time.

Isasmelt lance smelting was adopted in 1992 by Cyprus's Miami Arizona operation and it continues to be adopted slowly around the world. It has been adopted for copper smelting by Sterlite (India) and is being constructed at Union Miniere. Lance lives were originally rather short but adoption of matte-resistant alloys and better control procedures have considerably smoothed production. The Isasmelt furnace has small conductive, convective and radiative heat losses and it is particularly good for low sulfur concentrates and mixed charges of moist concentrates, residues and scrap.

Of these 198Oys/90's processes, then, only the Isasmelt seems to be moving ahead.

The 1990's saw improvements to all the previously-adopted processes. However, they did not see radically new developments. Converting, on the other hand, saw the radical development of flash converting and continuous submerged tuyere converting, discussed next.

CONVERTING IN THE 1966's

Just as the reverb was king for copper smelting in the 19607s, the Peirce-Smith converter was king for converting. As I remember, it was the only available converting process. It was great except for its :batch nature and its inefficient capture of its SO2 offgas.

This deficiency has been attacked on,nurnerous fronts since then by:

(a) Hoboken converting - axial flue gas collection and continuous blowing of Peirce- Smith type converters

(b) Mitsubishi and TBRC lance converting (8,9) (c) Kennecott-Outokumpu flash converting (1 0) (d) Noranda continuous submerged tuyere converting (1 1).

Hoboken converting began to be adopted around 1970. About 20 Hoboken converters are currently in place and three more were planned for the Thai Copper smelter (Rayong, Thailand). The Hoboken's advantages of efficient, continuous gas

VOLUME I

collection seem to have been partially offset by problems with splash and dust buildup in the gas offtake system. This appears to have slowed wider adoption of the process.

One aspect of tuyere smelting/converting that should be mentioned here is Noranda's late 1960's development of the Gasp6 tuyere-punching system. Operating almost everywhere now, and,.automatically in some smelters, it significantly improved the rate and uniformity of.air and oxygen flow into the converter.

Mitsubishi converting has followed along with adoption of the Mitsubishi smelting-converting system, so there are now four MI converters in place (Table 3). Significantly, the first stand-alone Mitsubishi converter is under construction at the Port Kembla Copper smelter in New South Wales (12). Its outcome is eagerly awaited.

The 1990's saw two new players come on the scene - Kennecott Outokumpu flash converting (10) and Noranda continuous converting (1 1). Neither can yet be said to be 'arms 'length' tested but both are working well for their developers. An 'arms-length' flash converter is being built at Southern Peru Copper's 110 copper smelter.

Flash converting takes high-grade matte from the smelting flash furnace and:

(a) granulates it with water (b) grinds and dries it in a vertical roller mill (10) (c) oxidizes it to high sulfur blister copper in a small, highly-oxygen enriched, single

burner flash converting bee.

There 'have been a few teething problems with the Kennecott flash converting installation, but the operation. has stabilized enough to convince Southern .Peru Copper to. include a flash converter in its new 110 smelter.

Noranda continuous converting is submerged tuyere converting (1 1). It is similar in many ways to the Noranda smelting process in that it continuously feeds Fe- and S- bearing materials into a rotary fiunace while continuously blowing 02-enriched air into the bath through tuyeres running about half the length of the rotary furnace. The feeds to continuous converting will usually be molten Noranda smelting process matte added through a small mouth, and solid materials added via slinger at one end of the furnace.

Gas is continuously drawn from the converter through a second mouth and hood, an evaporative atomized water spray cooler, a dust removal system and on into an acid plant. From Noranda's ,point of view, it extends to converting the expertise gained with the Noranda smelting system.

PLENARY LECTURESFIOVEMENT OF COPPER AND INDUSTRY OUTLOOK/ 63 COPPER APPLICATIONS AND FABRICATION

Table 3 Continuous Converting Installations

Mitsubishi Converting 1974* 1 Naoshirna, J a v d

1998 I Onsan, Korea 1998 I Gresik, Indonesia

1979* 1 99 1 *

1999 1 Port Kembla, Australia

.

Timmins, Ontario Naoshima 3a~an

Flash Converting " 1995* 1 Garfield, Utah

in Droeress I 110. Peru

Noranda Continuous Converting 1998 1 Noranda. Ouebec

*Visited by author. #Closed

Converting Slag

Submerged tuyere converting processes use traditional silica-base slag. It is a convenient match for the silica base slags used in smelting and it, or a slag concentrate made from it, can be conveniently recycled back to the smelting furnace for copper recovery.

Mitsubishi found that this slag was not compatible with lance converting because solid magnetite formed where the lance oxygen impacted the slag, greatly inhibiting the converting reactions. They developed a CaO based Ca - Cu - Fe - 0 slag which has a large liquidus region at converting temperatures. A similar slag is used by the Kennecott flash converter. This slag appears to be more corrosive than the traditional silica based slag so it is only used where absolutely necessary. Noranda submerged tuyere continuous converting does not use it because the turbulence created by submerged tuyere blowing prevents formation of a solid magnetite layer.

It seems that the traditional silica slag will continue to be used wherever possible.

Through this all we can see the trend that converting is continuing to develop exactly as smelting, i.e.:

submerged tuyere converting (Hoboken, Nomda Continuous) lance converting (Mitsubishi) flash converting (Kennecott/Outokumpu).

VOLUME I

SINGLE FURNACE PRODUCTION OF COPPER

The avowed goal of chemical and metallurgical engineers in the 1960's was single furnace production of copper. This was a natural hope because smelting and converting both oxidize Fe and S from the smelter's sulfide concentrate feed. Combining smelting and converting to produce metallic copper by the reaction:

CuFeS2 + oxygen + CuO + iron oxide + SO2

seemed to be the natural way to go.

The ,potential advantages of single furnace metallic copper production were seen to be:

(a) maximum use of sulfur and iron combustion energy with consequent minimization of industrial oxygen and fossil fuel consumptions;

(b) restriction of S& emissions to a single continuous source; (c) no moving of matte between furnaces with consequently less emission of fugitive

SO2-bearing gas; (d) elimination of a process step.

As it turned out, single furnace' copper metalmaking ,had two significant disadvantages:

(e) the slags from the process contained up to 20% Cu hence a significant fraction of the Cu-in-feed;

( f ) impurity levels in the copper were high due to their continuous absorption into molten metallic copper in during smelting.

Through the years a number of single furnace coppermaking configurations were developed namely:

Noranda continuous submerged tuyere smelting Worcra continuous lance smelting flash direct-to-blister smelting.

Worcra lance smelting never left the pilot plant stage due to its, short lance -lives. The Noranda process, on the other hand, successfulljr produced metallic copper for several: years before being switched to high-grade matte production. Short tuyere .lives, slag foaming and high impurity 1evels.h copper seem to have sled to this new direction

However, direct-to-blister flash smelting has operated continuously since 1977, fust at the Polish Glogow I1 smelter (13) and then also at the Australian Olympic Dam smelter. The rather small direct-to-blister-flash furnace at Olympic Dam has just been replaced by a significantly larger unit, showing complete confidence in the process.

PLENARY LECTURESIMOVEMENT OF COPPER AND INDUSTRY OUTLOOK/ 65 COPPER APPLICATIONS AND FABRICATION

In Poland, the flash furnace process produces a Cu-Fe-Pb alloy that requires converting to metallic copper. It is not clear, then, that the process should really be called single-furnace copper making. It is operated in competition with the blast furnaces in the Glowgow I and Legnica smelters, which have turned out to be somewhat better at removing impurities (specifically As and Pb) than the direct-to-blister furnace (1 3).

The Olympic Dam direct-to-blister flash furnace has, on the other hand, been a great success, resulting in installation of a new, larger furnace to match an expanded rate of concentrate production. Initially the Olympic Dam smelter did not have a remelting unit for melting copper skulls and other revert materials, so it was hampered somewhat in the handling of its recycle products. Installation of an electric furnace solved this problem.

Interestingly this smelter operates alongside a uranium leaching operation which uses all the smelter's sulfuric acid product. In fact, sulfuric acid production from the flash furnace gases is sometimes -augmented by burning sulfur. This is a far cry from the excess acid production situation of many smelters.

FUTURE FOR SMELTING AND CONVERTING

Well, where are smelting and converting going? We have seen the ,three competitive trends:

flash smeltinglconverting submerged tuyere smeltinglconverting lance srneltinglconverting.

Are there others, I wonder. Or are there combinations of the above that might make sense? And what about hydrometallurgy? It is already nibbling at the edges as a good way to treat supergene sulfide minerals (CuS, Cu2S). Might it not also nibble into chalcopyrite extraction? This will be mentioned again later.

FLASH SMELTING

It has always seemed to me that, in principle, flash smelting is the perfect way to treat the fine flotation concentrates - because the concentrates are exactly the right size for flash oxidation. Just blow the concentrate particles uniformly into a space, surround them with 0 2 and let #them react. Supply (i) just the right 02/concentrate ratio so that the reaction can proceed exactly to the desired extent and (ii) just the right amount of N2 to get the heat balance right while producing the desired matte grade and temperature.

VOLUME I

Of course the concentrates need to be dried, but thermodynamically, it is better to dry concentrates in a low temperature dryer (say with steam) than in a #high temperature smelting furnace.

The ,technical downsides of the flash furnace have been said to be its. excessive amount of auxiliary equipment, namely its:

(a) blast heating system (b) multiple burner feed system (c) waste heat boiler.

Recent years have seen (i) oxygen replace blast heating and (ii) single concentrate burners replace multiple concentrate burners. So disadvantages (a) and (b) have disappeared.

However it is certainly true that waste heat boilers have caused significant downtime in many Outokumpu flash furnace.smelters. Safe and Jones (14) identify tube leaks as the most serious problem and indicate the following causes:

(a) excessive rapping of the tubes to remove dust (now of diminished importance because of single-burner flash smelting dust reduction, 14a)

(b) poor welds (c) uneven expansion in the boiler during temperature fluctuations.

The temperature fluctuations often arise because of erratic operation of the flash furnace during startup teething problems.

Overall, however, generation of steam by the waste heat boiler for electricity and heating has a thermodynamic attractiveness that is absent in processes that cool their gases by vaporizing water. Its electricity can be extremely valuable where electricity prices are high. As with metallurgical processing, 1999 boilers are much improved over 1960's era boilers.

INCO FLASH SMELTING

ih ,the 1976. edition of Extractive Metallurgy of Copper, Anil Biswas and I made the statement:

"The Outokurnpu design is not well adapted to the use of oxygen because the combustion tower [reaction shaft] tends to overheat while at the same time remote comers of the hearth require fuel-fired heating. Thus, for the use of oxygen, flash furnace designs will likely evolve towards 'the INCO system of horizontal concentrate burners, which are particularly well suited to heating the entire hearth area."

PLENARY LECTURES/MOVEMENT OF COPPER AND INDUSTRY OUTLOOK1 67 COPPER APPLICATIONS AND FABRICATION

Well, we could not have been more wrong. It has tuned out that an aerodynamic central single concentrate burner in an efficiently water-cooled cylindrical reaction shaft has been a super concentrate combustion combination (1 5). Oxidation conditions can be made uniform and they can be adjusted to increase or decrease the thickness of a magnetite layer on the inside of the shaft. Changes in cooling water temperatures around the shaft quickly tell the operator when his reactions are not uniform.

Reaction shaft control has, therefore, turned out to be readily manageable especially with a single central concentrate burner. Furthermore, steady operation of the Outokumpu furnace at high smelting rates has greatly reduced the need for fossil fuel combustion in the settler part of the furnace.

With the Inco furnace, smelting rate may ultimately be limited by keeping the roof above the horizontal burners from overheating. There does not seem to be a way to run the Inco furnace with a single burner, single feed system.

SUBMERGED TUYERE SMELTING

TenienteMoranda tuyere smelting accounts for about 15% of world smelting capacity, a very significant amount. The advantages of tuyere smelting area very high specific smelting rate and violent turbulence in the matte-slag-gas bath. The latter is especially important for the Noranda process which is designed to smelt large quantities of copper and precious metals scrap. Teniente smelting seems to be well-adapted to smelter production rate augmentation as its development throughout Latin America has shown (Tables 1 and 2).

LANCE SMELTING

Mitsubishi (8) and Isasmelt (16) smelting account for about 10% of the world's smelting. Both processes continue to be adopted around the world.

The compact Isasmelt furnace with its small heat losses will continue to be adopted for smelters which treat low sulfur concentrate, revert, scrap charges. The process' strongestpoint is its ability to treat a wide range of feed materials.

The Mitsubishi process continuously produces copper metal from concentrate. Its current commercial competitors are (i) direct-to-blister flash smelting, (ii) flash smeltinglflash converting, and (iii) Noranda submerged tuyere smelting/converting.

Its advantage over direct-to-blister flash smelting is that it can continuously produce copper from concentrates that have a high slaglmetal product ratio (i,e. chalcopyrite concentrates) without pushing too much. Cu into slag. A discardable slag is created between smelting and converting and the small amount of slag produced in the converting furnace is easily handled by recycle to the smelting furnace.

VOLUME IN 68

Its advantage over flash smeltingMash converting is that it does not (i) solidify its matte between ,the two processes or (ii) recover its Cu-hm-smelting-slag as solid slag concentrate that requires complete resmelting.

Itsadvantage over Noranda smelting/converting is its well-tested methodology.

So one has to ask why it has not been adopted more. My guess is that in most locations flash smeltingPeirce-Smith converting have been efficient enough to meet current environmental requirements. This combination is so well known ,that there has been little risk in adopting it.

However, the coming of fiash srneltinglflash converting may force new smelters to avoid the Peirce-Smith converter and go for:

flash smeltinglflash converting (Kennecott/Outokumpu) lance smeltinflance converting (Mitsubishi) tuyere smeltinglcontinuous tuyere converting (Noranda)

or some combination thereof.

In this race, the Mitsubishi process might well do well. Whatever, the race will be interesting.

FUTURE OF CONVERTING

While one can extol the natural virtues of the flash furnace for smelting particulate concentrates, it is not so easy to do this for converting. After all, the natural product of smelting is l&uiJ matte, not solid articulate matte. Thermodynamics would seem to ask that the matte be kept liquid.

So might we see flash smelting followed by 'lance or submerged tuyere converting? My own view is that, against my thermodynamic wishes, we are likely to see the above mentioned pairings kept intact just to make the smelting and converting expertise interchangeable. So far this has been true, except perhaps at Port Kembla where we are seeing lance converting adopted to follow Noranda submerged tuyere smelting.

ACIDMAKING

A smelter typically produces 2.5 to 4 tonnes of sulfiuic acid per tonne of product copper. This underscores acid's importance in the overall smelter flowsheet. Also, a smelter cannot do business if its gas collectionfacid plant system does not achieve its government-mandated SO2 removal efficiency.

PLENARY LECTURES/MOVEMENT~OF COPPER AND INDUSTRY OUTLOOK/ 69 COPPER APPLICATIONS AND FABRICATION

The main success in recent years has been the low initiation temperature, big bight cesium activated vanadium pentoxide catalyst (17,18). This catalyst permits greater S02+S03 conversion in the catalytic converter and lowers the emission of SO2 fiom the plant. It has been particularly useful for the continuous high SO2 strength gases from Mitsubishi and flash smeltinghlash converting.

Catalysts with even bigger temperature bights will be very useful as smelter offgas SO2 strengths continue to increase.

Production of steam from gas sensible heat and SO,-absorption heat during acid manufacture is an advantageous aspect of the continuous high SO2 strength gases produced by continuous smelting/converting. This practice may now considered to be conventional. It is the methodology of choice for future acid plants.

My first experiences with fire refining were at Canadian Copper Refiners in 1967 and the Gasp6 smelter in 1968. What spectacular changes there have been since then.

CCR was completely dominated by a row of large hearth furnaces for melting spent anodes and scrap. They resembled open hearth steelmaking furnaces with. their huge long-armed charging machines. A batch of scrap took forever (about a day) to ,melt and refine with a spectacular expenditure of labor.

The deoxidation was done with green poles.

Even in the early 1980's the Phelps Dodge El Paso refinery had its row of scrap- melting hearth furnaces, out of service but ready to go. I'm glad to say that they're now gone.

These changes were all brought about by the Asarco shaft furnace.

The Asarco shaft furnace has had a huge impact on (i) scrap anode melting and (ii) cathode melting, equally as ,big an impact as the new smelting and converting processes have had on extraction from concentrate. Its energy expenditure is well under half that required by the hearth furnaces it replaced and its labor expenditure is very small indeed.

In the 1960's wood poles were a common way to deoxidize copper during anode casting. However gas 'poling' had already begun. Wood poling may have been appropriate in hearth furnaces but submerged.tuyere gas deoxidation in rotary furnaces is certainly the better process.

VOLUME I 70

ANODE CASTING

Continuous casting of anodes by the Hazelett or Contilanode system has been available for 40 years. Yet only a half dozen smelterslrefmeries have adopted it. Obviously traditional wheel-and-mould casting, equipped with an expert weighing system and anode preparation machine is the process to beat.

Perhaps production of a solid strip of solid copper followed: (by cutting odd- shaped anodes from it is fundamentally the wrong way to make anodes. It is, after all, making a two-step process from a one step process. Or it may be simply that the maintenance :costs of the continuous-castinglcutting system .are rather high.

The CCR rehery in which 1. worked in 6'967 had been built about 1930. Its defining feature formewas how labor intensive it was. Mind you, I should have known about extractive:,metallurgy .labor intensity because in the 1950's I worked pulling and stripping zinc cathodes by hand as a university student.

An interesting sidebar to my CCR employment was a visit to the Phelps- Dodge refinery in Laurel Hill, New York City. Laurel Hill was still using the series refining system which had a high productivity (very useful in New York City) but produced a somewhat low grade product.

The major changes in electrorefining since the 1960's have been (19):

(a) adoption of stainless steel permanent cathode technology throughout the industry, along with automated stripping

(b) installation of anode preparation machines to ensure flat, uniform anodes (c) development of new electrolyte purification techniques, particularly solvent

extractionlion exchange (d) installation of polymer concrete cells in place of all earlier cell technologies (e) use of periodic reversal of current to increase plating rate (now rather rare) (f) on-line determination of addition agent chemistry (g) electrolyte filtration.

From the point of view of what one sees in the 1999 refinery, it is the degree of mechanization that is most evident. Cells are filled automatically, emptied automatically, drained automatically and so on. So electrorefining has gone from a labor-intensive industry to an automated industry.

And these trends are continuing.

PLENARY LECTURESFlOVEMENT OF COPPER AND INDUSTRY OUTLOOK1 7 1 COPPER APPLICATIONS AND FABRICATION

LEACHINGISOLVENT EXTRACTIONIELECTROWINNING

Copper leachinglcementation has been practiced for centuries, in Spain and Wales for example. It is still being practiced in a few spots. However, its product is an impure copper metal that requires complete smeltinglrefining to produce copper for market. It has been completely overtaken by leachinglsolvent extractiodelectrowinning, which directly produces market-grade copper metal.

Likewise copper ,leachinglelectrowinning was practiced extensively in Chile and Zaire. Unfortunately its .product grade was lower than needed for electrical use.

So until the late 6OYs, copper leaching could not produce the quality of copper needed for the electrical industry. This greatly inhibited any growth of leaching as a major influence on copper production. Hydrogen reduction of Cu from solution was being tried but it did not stick as an industrial-scale process even though reasonable copper purity could be obtained. In fact, just as Anil Biswas and I were writing the first edition of Extractive Metallurgy of Copper, hydrogen reduction of copper at the Bagdad mine in Arizona had just given way to solvent extractiodelectrowinning (20,21).

Unfortunately Anil and I were not exactly brave with our 1976 prediction as to the outcome of solvent extraction. Our exact words were:

"Industrial copper solvent extraction plants are few in number as of yet, but this process MAY assume considerable importance in the near future."

We wish now that we had been more adamant.

The coming of solvent extraction, particularly with LIX hydroxy oximes ended the impurity problems of electrowinning and made leachinglsolvent extraction/ electrowinning the successful process it is today. In 1999, 15% to 20% of the world's primary copper is produced by this method. Quality-wise, LISXEW copper is fully competitive with smeltedlrefined copper. Lead is the only significant impurity (from the Pb-Sn-Ca anodes). This is often complemented by the low-lead cathodes of electrorefining (if a company produces both refined and electrowon cathodes).

The process has improved markedly since its early days. The extractants and diluents have improved as have techniques for avoiding their degradation and loss. Reagent consumptions are down 30 to 40% over the last few years (to about 2 kg extractant per tonne of copper) and their price has come down a shilar.amount. This has had one unfortunate side .effect, restriction of extractant production to only .a couple of manufacturers, a disturbing competitive situation.

Other improvements have been an enhanced ability to prevent C1, Fe and other impurities from advancing forward to electrowinning. This has improved cathode quality and made the SXEW process easier to control.

VOLUME I 72

Also, leach/SX/EW costs are almost independent of plant size, which means that a small operation can compete with a large one. As one looks around the Chilean SXEW plants, it is not unusual to see large plants (100 000 tomes copperfyear) operating within a few kilometers of quite tiny operations (2000 tonnes copperfyear).

Because most of the electrowinning half of SXEW operations are so new, most use or are adopting stainless steel permanent cathode technology and polymer concrete cells. They are also highly mechanized with mechanical stripping machines and cell loading unloading systems. There are two competitive permanent cathode technologies, Isa and Kidd. The main difference between them is cathode edge stripping and the stripping machine technology. They seem to be competitive.

WHERE IS HM)ROMETALLURGY GOING?

In 1999 leaching for copper is treating 'oxide' minerals and supergene sulfide (Cu2S, CuS). Some mines now have to make a decision as to whether to send the supergene-rich ore to 1eacWSXIEW or to flotation/smelting!reflning. The tendency today seems towards leach, the lower cost option. Of course, this depends on ore grade, the amount of unleachable CuFeS2, acid availability and equipment needs.

Chalcopyrite ores, on the other hand,.:must always be sent tothe concentrator, because their leach rate is too slow to be economic.

In 1981, when I moved to Arizona, Duval's chloride leach CLEAR Process was producing about 80 tonnes per day of electrowon copper from chalcopyrite. And several other processes were operating at about 1/10 that scale.

However, all shut down during-the low copper price days of the mid-1980's. The problem was cost and the purity of the copper that was being elkctrowon. frdm the chloride leach solutions.

It seems to me that a hydrometallurgical process must be able to produce marketable cathode copper rather than any other form. Based on electrowinning history, this will require a solvent extraction step between leaching and electrowinning.

A factor not yet clear is as to. whether the byproducts of leaching will be more acceptab1e:environmentally than those of smeltinglrefining. It may be that SO2 gas. is as easy to handle as sulfur-bearing leach residues.

PLENARY LECTURES/MOVEMENT OF COPPER AND INDUSTRY OUTLOOK1 73 COPPER APPLICATIONS AND FABRICATION

CATHODE MELTINGICASTINGIROD ROLLING

Wirebar casting was king in the 1960's. These 75 to 150 kg bars were easily transported and fed into rodwire mills for further manufacture. However, development of the Asarco shaft furnace and Southwire and Hazelett continuous bar casting quickly put an end to casting individual bars.

The continuous bar is fed hot into a hot rolling machine which produces the rod feed for wire drawing. The only limitation on the length of rod that is produced is convenient rod coil shipping length. The coils, once in the wire drawing machine, can be welded to give as much wire as needed.

Replacement of individual wire bar casting with continuous bar casting is clearly advantageous. It is, in fact, the opposite of the anode casting situation where individual anodes are the desired product rather than long (weldable) lengths of rod.

The Southwire system entails casting between a wheel-rim mould and a steel band. The Hazelett system entails casting between two steel bands. They seem to be competitive.

Other. operative castingholling systems are Properzi wheel-and-band casting, dipforming.and Outokumpu upwards vacuum casting. They account for considerably less tonnage that the Southwire and Hazelett systems..

Concluding about casting, then, the cathode melting and casting area of a refinery is virtually unrecognizable from the 1960's version. In many refineries it consists of only two things - an Asarco shaft melting furnace and a continuous bar castinghod rolling machine.

CONCLUSIONS AND PREDICTIONS

1. Oxygen-rich smelting will continue to be the process of choice for copper smelting, whatever the furnace configuration. It increases productivity and simplifies gas collection.S0~ fixation.

2. The Outokumpu flash furnace reaction shaft is ideally suited to oxidation of flotation concentrates. All that is needed is to distribute the particles evenly in the shaft, surround them with just enough oxygen to produce the desired matte and add just the right amount of nitrogen to balance the furnace thermally. Feeds such as reverts and scrap are better handled by other smelting processes namely submerged tuyere smelting and lance smelting.

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Outokumpu flash furnaces will continue to adopt single concentrate burners for new furnaces and as retrofits of existing furnaces. The single burner configuration offers:

(a) a simple feed system (b) more uniform feed and blast distribution in the reaction shaft (c) better reaction shaft conGol, particularly of the magnetite coating

on the inside of the reaction shaft (d) significantly reduced dust evolution.

Copper matte converting will move away from discontinuous Peirce-Smith converting to continuous processing.

,.. ..

The feed to converting is liquid matte. Thermodynamically this favors.converting processes that treat liquid matte, i.e. lance converting and submerged. tuyere converting.

These two processes and flash converting will continue, to compete for 'the continuous converting market.

Flash converting has the advantage of an easily-controllable oxidation system with an excellent ability to capture S02. It has the disadvantages of requiring (i) that its matte feed be solidified and ground and (ii) that Cu be recovered from its slags by resmelting. It also lacks the ability to melt scrap and revert materials. In its present manifestation, it seems to require a somewhat corrosive lime-based slag to prevent solid magnetite formation in the converting furnace.

Lance @litsubishi$ converting has the advantages of being truly continuous with a molten matte feed. When combined with Mitsubishi smelting it also produces a discardable smelting slag rather than slag concentrate for resmelting. It does, however, require the somewhat corrosive lime base slag mentioned for flash converting.

Submerged tuyere (Noranda) converting has the advantages of using a molten matte feed and the ability to melt large quantities of scrap. It also has the advantage of being able to use conventional silica-base slag, because the intense stirring caused by tuyere-injected aidoxygen keeps a layer of solid magnetite fiom forming. However, as currently practiced, it requires ladle transfer of matte rather than continuous flow between smelting and converting. It also requires resmelting of the copper from its smelting and converting slags.

Single-furnace coppermaking will. be restricted to those concentrates which produce little slag. Concentrates with large slag falls send too much Cu to slag, recovery of which, is expensive.

PLENARY LECTURESIMOVEMENT OF COPPER AND INDUSTRY OUTLOOK/ COPPER APPLICATIONS AND FA,BRICATION

If existing smelters are forced to drop Peirce-Smith converting in favor of continuous converting processes, they will likely stick with their existing technology, i.e. flash smelters will adopt flash converting, submerged tuyere smelters will adopt submerged tuyere converting and lance smelters will adopt lance converting.

Greenfield smelters will now look at smelting and converting as a package, i.e. flash smelting will be followed by flash converting; lance smelting by lance converting and submerged tuyere smelting by tuyere converting. These pairings will greatly simplify a project's .technology.

When choosing a process for recovering the heat fiom a smelter's offgas, a boiler should always be given first consideration. It has a thermodynamic energy advantage over water vaporization.

A critical part of any smelter is its sulfuric acid plant. Continuous srneltinglconverting technologies produce stronger SO2 .gas, which is putting increased demands on SO2 conversion and SO3 absorption. Low initiation temperature, large temperature range ('big bight') cesium base catalysts are helping with these strong gases but further research into low initiation temperature, big bight catalysts would be beneficial.

Production of steam from sensible heat and SO3-absorption 'heat during acid manufacture is an advantageous aspect of the continuous, high SO2 strength gases produced by continuous smeltinglconverting. This practice may now considered to be conventional. It is the methodology of choice for future acid plants.

. ..

Anode casting will continue to be predominantly done by mould-and-wheel casting/followed by an anode preparation machine rather than by continuous casting of copper sheet followed by cutting of anodes fiom it. Mould-and-wheel casting is a single unit process while cutting anodes from a continuously cast copper sheet is a two-step process.

Continuous bar castinglrod rolling, on the other hand, has many advantages over individual wire bar casting and will always be the process of choice.

Leachinglsolvent extraction/electrowinning will continue to grow for 'oxide' and supergene sulfide minerals. This is the cheapest way to produce electricaVelectronic grade copper fiom these resources. This process will continue to grow especially in Chile, Argentina and Peru. The huge leachable resources in Africa will not be exploited until a solid infrastructure is built up in that region.

Solvent extraction plants have reduced their extractant losses some 30 to 40 percent in the last few years down to about 2 kg per tonne of copper cathode. Separation of the pumping and mixing functions in the mixer-settlers has

VOLUME I 76

accomplished much of this along with newly efficient organic-fiorn-aqueous recovery systems. The price of extractant has likewise dropped 30 or 40% over the last few years. An unfortunate side effect of this has been reduction of extractant suppliers down to two, a disturbing trend for the leach/solvent extraction1 electrowinning industry.

20. Copper electrorefining and electrowinning tankhouses will continue to adopt stainless steel permanent cathodes. Their main advantage is that they allow almost complete automation of tankhouse materials handling. They also:

(a) avoid starting sheet manufacture (b) give excellent cathode verticality (by avoiding the curling

of copper starting sheets).

Important benefits of the verticality are: (c) purer cathodes (d) fewer short circuits (e) higher current efficiencies (f) tighter anode/cathode separations (g) higher productivity.

21. Polymer concrete will continue to be the material of choice for electrolytic cells. Polymer concrete cells greatly simplify cell installation, operation and maintenance.

22. Leaching of chalcopyrite concentrate was quite successful in the 1980's and work is continuing today. Impurity problems with the copper from these 1980's processes lead to the conclusion that electrowinning will always be preceded by a solvent extraction step.

ACKNOWLEDGEMENTS

The author wishes to acknowledge the following persons who so kindly provided him with information during the preparation of this paper.

Cameron Hanis (Kvaerner) Jackson Jenkins (Cyprus) David Jones (BHP Copper) Brian Kennedy (Simons) Matt King (Phelps Dodge) Gary Kordosky (Henkel) Phil Mackey (Noranda) Eric Partelpoeg (Winters Co.) Tim Robinson (CTI-Ancor) Akira Yazawa (Tohoku University)

PLENARY LECTURES/MOVEMENT OF COPPER AND INDUSTRY OUTLOOK/ 77 COPPER APPLICATIONS AND FABRICATION

This paper was written while the authorZwas visiting Professor at the Institute for Advanced Materials Processing, Tohoku University, Sendai, Japan (Professor Yoshio Waseda, Director). The author wishes to thank the faculty and staff of 'the Institute for their wholehearted assistance.

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PLENARY LECTURES/MOVEMENT OF COPPER AND INDUSTRY OUTLOOK1 79 COPPER APPLICATIONS AND FABRICATION

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