On the application of the Perrin process for ferro-alloy production

Scandinavian Journal of Metallurgy 2003; 32: 157–170 Copyright C© Blackwell Publishing 2003Printed in Denmark. All rights reserved SCANDINAVIAN

JOURNAL OF METALLURGYISSN 0371-0459

On the application of the Perrin processfor ferro-alloy production

Gustaf OstbergLund University, Sweden

This paper supplements a previous review of the Perrin pro-cess for steelmaking with the same focus on its principles,technology and economics. Metallurgically, Perrin’s idea ofemulsification as a means of achieving rapid reaction alsoapplies to the production of ferro-alloys. However, the largerproportion of the amount of slag in relation to that of metalmakes it necessary to use other procedures for the intimatemixing of the two phases than was the case of steelmaking.Together with the prevailing high reaction temperatures thisrequirement means that considerable know-how is neededfor acquiring regular production. The major application of thePerrin process to ferro-alloys has been for low-carbon fer-rochromium, for which it has retained a niche market. To aminor extent it has also been used for ferromanganese and

ferronickel. The history and success of the Perrin process forsuch purposes can be understood in terms of the concept ofthe so-called development blocks. This resembles the caseof steelmaking inasmuch as its inventor has played a decisiverole. The complexity and difficulties of the procedures calledfor an important contribution by his engineering associates.

Key words: development blocks, emulsification, exploitation,ferro-alloys, kinetics, Perrin process.

C© Blackwell Publishing, 2003

Accepted for publication 13 September 2002

The principle, technology and application of the Perrinprocess for steelmaking has recently been reviewed withthe aim of contributing to the understanding of its in-dustrial use [1]. In the present paper a similar accountwill be given of the development of the process for theproduction of ferro-alloys.

Because those principal aspects of the Perrin process,which are common to both steelmaking and ferro-alloyproduction, have been comprehensively dealt with inthe previously mentioned publication, such backgroundinformation and knowledge is not covered in the follow-ing. Thus, this review should be regarded as a supple-ment of the previous one, with the same aim to broadenand deepen the apprehension of the Perrin process.

In Perrin’s own writings about his process for ferro-alloy production, the major application he deals withis for low-carbon ferrochromium [2–9]1. More or less in

1The terminology or nomenclature for designation of different kindsof ferro-alloys is not uniform. In one modern handbook the termferrochromium is used [26], whereas in a widespread directory forcommercial information the term ferrochrome is adopted [24]. In thepresent paper the former is accepted; however, as no matter of prin-ciple. Likewise, the term ferro-alloys is spelled in two parts with ahyphen in-between, according to the prevailing literature referred to

passing, he also mentions low-carbon ferromanganese[3, 7, 8], and ferronickel [8]. Accordingly, the presentreview is essentially confined to ferrochromium. A fewpieces of information about the other ferro-alloys will begiven in connection with accounts of the metallurgy andprocedures of more recent applications of the process.

Concepts and procedures

Basic chemistryThe production of ferrochromium with low carbon con-tent usually takes place in steps along two paths. In oneof them the first step is the reduction of chromium oxideore, or chromite ore, by carbon together with quartz inan electric furnace. The primary silico-chromium alloythus obtained has too high content of carbon and siliconto be used in the production of stainless steel. There-fore, this primary alloy is subjected to a reaction in a la-dle with chromium containing slag from a subsequent

in this review. Furthermore, the term production is preferred insteadof the alternative manufacture, which otherwise appears in some textson this subject. Finally, according to common usage, in the account inthis section of the process for production of ferrochromium, the termsilico-chromium is applied to alloys that are, in fact, made up of iron,silicon and chromium.

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Fig. 1. Flow sheet of the Perrin process for low-carbon ferrochromium production [20]. Indicated figures for the contents of various constituents are examplesonly, not generally valid for all plants, depending mainly on different quality of raw materials.

step, and some additional chromite ore. Although thechromium content of the intermediate silico-chromiumfrom this first refinement is higher than in the previousalloy, the silicon content is still unacceptably high.

In the second path of the process, again based onchromite ore, the intermediate silico-chromium alloy isfurther refined by treatment in another ladle by a syn-thetic slag made from chromite ore and lime. Thus, thesilicon in the alloy is oxidized by reduction of chromiumoxide in the slag. The chromium from this oxide entersthe metal phase, establishing the high level of the con-tent of chromium aimed at in the final product. The re-maining slag is used for the first refinement operationmentioned previously.

It should be noticed that the refinements describedabove are exchanges of both silicon and chromium inopposite directions between the reacting slag and metalphases. This characteristic feature is mentioned here inpassing because there is a difference in this respect be-tween the two applications of the Perrin process consid-ered in this review. In the steelmaking case the majorrefinement effect is a removal of certain elements fromthe steel, whereas the opposite transfer of elements oc-curs only to a limited degree as a consequence of theformer.

As regards the contributions of chromium to the prod-ucts in the refinement steps from the metal and slagphases, respectively, the major source in both of themis the metal. On the other hand, the initial origin ofchromium in the final alloy is the synthetic slag. It firstdelivers some of its chromium content to the metal inthe last refining step. The remaining part of it is thentransferred in the previous step.

A graphical illustration of the above account is givenin Fig. 1 [20]. In this diagram there are figures of thechemical composition of the reactants at various stagesduring the process. These data are examples only. Dif-ferent composition cases can be found in the following.

At this point an additional characteristic and impor-tant feature of the two-stage process for ferrochromiumproduction warrants mention. In a summarizing ac-count of his scientific achievements, Perrin emphasizesthe application of the counter-current principle whendealing with the development of the technology for per-forming a vigorous and intimate mixing of the reactingphases during the refining of ferrochromium [7]. Theaccount of the process given above does not imply thatthere are any phases flowing past each other as in typicalcases of counter-current. Nevertheless, this metaphormay be valid for the purpose of explaining the mecha-nism of the process chemistry in principal terms.

Using a flow sheet terminology for the transfer of re-acting elements between slag and metal, the latter phaseenters at the inlet of the first step with a compositiondetermined by the previous reduction process. It reactswith the slag phase, which at this stage has already re-acted in the second step with the metal, in which it hasentered with full refining capacity as newly formed. Ac-cordingly, the counter-current principle applies to thisexchange of reacting elements in the process in a figura-tive sense with reference to the opposite compositionsof the two phases at the inlets and outlets, respectively.

Initial developmentAs was the case of steel refining, Perrin focussed on thepossibility of reducing the time for the last step in the

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production of ferro-alloys by applying the principle ofhis process for rapid reaction. Instead of a lengthy andlaborious processing under stationary conditions, thealloy would be rapidly refined by reacting with a finelydispersed slag with lime as the major constituent besideschromium oxide. The lime renders the slag sufficientlyfluid, eventually combining with the silica produced bythe oxidation of the silicon in the initial alloy.

A further advantage would be to avoid the pickupof carbon from the electrodes in the conventional pro-cedure. In addition to this, the loss of chromium to theslag could be diminished.

The first patent of the Perrin process quoted exam-ples of refinement in one step only of silico-chromiumof high silicon content typical of the first step referredto above, i.e., 48 and 49% Si [10]. In the next patent, oneexample was a direct reduction by ferrosilicon of slagmade of chromium ore and lime into a final product[11]. Eventually, in the third patent the complete two-step refining procedure was accounted for as describedabove, applying the Perrin process for both of the steps,i.e., via an intermediate alloy with a silicon content of32 to 35% Si in the charge of the final step [12].

An obvious difference in comparison with the appli-cation of the Perrin process for steelmaking is the largequantity of the element to be removed, i.e., 45% silicon ormore. In the patents, examples are quoted of weights ofslag some five times those of the metal [11], but a lowerfigure of three times is also mentioned [12], presumablyfor the treatment of metal of a relatively low silicon con-tent. The high proportion between the amounts of therefining slag and the metal was not thought to permitthe simple technique used in steelmaking by pouringthe metal once into a ladle containing the slag. Hence,some other means of establishing the necessary violentstirring and emulsification of the slag phase had to beinvented.

The principle adopted for this purpose was to arrangefor the metal and the slag to fall together in a vesselwith heavier metal on top of the lighter slag. This wasachieved using a vessel, which could rotate vertically.First the metal was charged, followed by the slag. Byrotating the vessel half a turn, the metal was on top ofthe slag. At that stage the two phases were allowed tofall together to what then had become the bottom of thevessel where they splashed, causing the slag to break upinto droplets which were dispersed in the metal.

The first version of an apparatus to that end was aso-called ’culbuteur’ (’somersaulter’ or ’tumbler’ inEnglish). It was made up of two interconnected cylin-drical vessels with a common axis, perpendicular to theaxis of rotation [3, 15] (Fig. 2(A)). Despite the obviousdifficulty of operating such a device at sufficiently high

Fig. 2. In the early application of the Perrin concept for refining of fer-rochromium, special mechanical devices were designed for the handling oflarge amounts of slag needed for desiliconization. Two such apparatuses areillustrated in patents, first the so-called ’culbuteur’ [13], which was later re-placed by the ’shaker’ [14]. (A) In the ’culbuteur’ the metal and the slag wereboth charged into one of two interconnected vessels. By turning them aroundthe axis perpendicular to that of the vessels, the reactants were vigorouslypoured from the first to the second one, causing the slag to become finely dis-persed in the metal. This procedure was repeated if necessary for completionof the refinement. (B) The ’shaker’ consisted of a single vessel. It had an ovalcross section perpendicular to the axis of rotation by which the same dispersaleffect on the slag was achieved as in the ’culbuteur’. The design of the ’shaker’made it possible to apply special methods for desiliconizing ferrochromiumin steps using different slags.

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Fig. 3. Re-ladling during refining of ferrochromium at the Gweru, formerly Gwelo, plant in Zimbabwe.

temperature, i.e., 1800◦C, this proved in practice to bepossible, enabling a refining to be completed within afew minutes only.

The same could be achieved using a certain ladle ap-paratus, which was later developed for large-scale pro-duction, a so-called ’shaker’, (Fig. 2(B)) [15]. Eventu-ally, this procedure was later replaced by re-ladling, i.e.,pouring the reactants into each other from one ladle toanother (Fig. 3). Nowadays, this is common practice forthe application of the Perrin process, in parallel withgas stirring. Incidentally, the latter method of obtain-ing intimate contact between slag and metal is alreadymentioned in the earliest patent for the Perrin processfor ferro-alloy production [10].

Concerning temperature, it deserves to be mentionedthat the refining reaction is exothermic. Among otherthings, this means that a low initial temperature of themetal is of no importance [11]. The temperature condi-

tions also make it possible to add refining slag in solidform instead of molten form. However, if all of the addedslag is solid, it has to be pre-heated. A number of differ-ent procedures have been developed for dealing withsolid additions in combination with molten ones in or-der to keep the slag sufficiently fluid [12, 13].

On the other hand, the heat released by the exother-mic reactions is not merely sufficient for maintaining thehigh temperatures required for slag fluidity reasons. Ifthe charging procedures are not properly managed, thetemperature may rise above the range acceptable fromthe point of view of control of the process as well as theintegrity of the lining. In the patents there are preciseprescriptions of certain orders of charging the variousreactants to that end [12, 13].

Another aspect, which deserves attention in passing,is that of energy consumption. Whereas other alterna-tive methods for ferrochromium production can take

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advantage of the heat of reaction for melting the charge,the Perrin process requires a separate melting opera-tion for preparation of the slag. Furthermore, more limeis needed than in the alternatives, which means higherenergy consumption. Clearly, the larger amount of limealso contributes to the budget for raw materials.

From an economic point of view it is important toalso consider the needs imposed by the requirements ofmeasures to deal with environmental effects associatedwith the production of ferro-alloys. By that is meant theemission of dust and smoke in particular. This is truenot least for the Perrin process in comparison with al-ternative procedures for which more effective and eco-nomical means of dealing with emissions are nowadaysavailable.

With no intent to preempt the following review of laterdevelopment and use of the Perrin process for ferro-alloy production, it may be instructive at this point tomake a remark comparing different methods of achiev-ing effective mixing of the reactants in the refinementprocess. Whereas re-ladling often may be more effectivein this respect than gas stirring, the latter is neverthelesspreferred in many cases because of the possibility of ar-ranging for ventilation of emissions which, in addition,are less severe than during re-ladling. Furthermore, onedisadvantage with the latter is a certain decrease of thetemperature of the reactants. In addition, there is a riskof an increase of the nitrogen content as a consequenceof repeated re-ladling.

Finally, in this rhapsodic account of the early de-velopment of the Perrin process for, in particular, fer-rochromium production, an important economic con-dition, namely the integrity of the lining of the vesselsused should be noticed. By trial and error this plague ofall ladle processes was gradually mastered, permittingthousands of treatments before relining.

With the procedures thus applied, ferrochromiumwith 70% chromium [5] and carbon contents below0.04%, occasionally as low as 0.025% [3] or even 0.02%[7, 8], was obtained. The few published figures for theremaining silicon content vary somewhat, from 0.250%[5] to 0.5% [2]. In one patent an example is quoted, whichstates that silicon contents as low as 0.10 to 0.15% couldbe achieved [12]. For the yield of chromium two figureshave been quoted, 92% [3] and 93% [6].

Such ferrochromium in the molten state was usedfor the production of stainless steel of low carboncontent of the order of 0.03% [3–6]. At the time ofintroduction of the Perrin process, this was an achieve-ment. With modern stainless steel metallurgy, low car-bon grades can be made using ferrochromium withoutvery low content of carbon as those claimed to be typ-ical of the product resulting from using the Perrin pro-

cess. Nevertheless, the latter is still competitive for thispurpose.

Similar satisfactory results were early claimed by Per-rin for ferromanganese [7, 8, 10] as well as for alloys con-taining both maganese and chromium [3]. In the later lit-erature, industrial production using the Perrin processin modified forms is described, for instance for ferro-manganese [20, 23], and ferronickel [16, 17, 20, 21].

Scarce metallurgical informationAlthough Perrin makes points about ferro-alloy produc-tion in a number of publications about his process [2–9],he deals mainly with technical issues related to its in-dustrial practice. The only detailed metallurgical infor-mation available is some figures for the composition ofthe metal and slag phases that are quoted in the corre-sponding patents. One example is the following of analloy of 48.35% Si, 16.22% Fe, 35.20% Cr and 0.082%C, made of a slag consisting of 29.83% Cr2O3, 6.86%Al2O3, 3.21% SiO2, 45.73% CaO, 6.96% FeO and 7.25%MgO [10]2.

Otherwise, in contrast to Perrin’s often detailed elab-oration of the principles and physico-chemical theorywhen writing about steelmaking, he has only little tosay about such matters as could be important for under-standing the process of refining ferro-alloys. In fairness,however, it should be mentioned that some remarksabout the prerequisites and procedures for achievinglow silicon content in the final alloy can be found intwo patents [10, 12]. Among other things, these referto a method of performing the desiliconization pro-cess in steps for the efficient production of low-carbonferrochromium with silicon contents as low as 0.10 to0.15% [12].

Nevertheless, there is a conspicuous lack of trans-parency in the public presentations of the Perrin pro-cess for the production of ferro-alloys. However, itappears to be true for this industry in general thatthere is reluctance to publish detailed and precise in-formation, which could reveal features of the pro-cesses that are of proprietary nature. One possible rea-son could be that the chemical reactions taking placeduring the treatment of ferro-alloys are relatively lesscomplicated in comparison with steelmaking processes.Therefore, they might not need to be dealt with indetail.

Another principal aspect, which was frequently em-phasized in Perrin’s deliberations of the mechanism ofsteel refining, but was not dealt with explicitly in any

2This reference is to a patent, which explains the unusually high pre-cision of the denotation of the percentages.

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of the accounts of ferrochromium desiliconization3, isemulsification. In the former case, the occurrence of thisphenomenon was originally hypothesized by Perrin asan explanation of the very short times required for thecompletion of the reactions in question. In seems reason-able to assume that he would have referred to emulsifi-cation if he had also dealt in detail with the mechanismof desiliconization during ferrochromium production.

However, a corresponding elaboration of this issuewould have needed consideration of the much largerproportion between the amounts of slag and metal inthe case of desiliconization as compared with steel re-fining. This is true in particular for the modern practiceof handling the reactants in more simple ladles than theapparatuses used in the early stages of the developmentof the process for ferro-alloy production.

It is likely that Perrin was well aware of the compli-cations of the mechanism of desiliconization because ofthe large relative amounts of slag with respect to emul-sification. Practically, he had to deal with this aspectby prescribing that the procedure of vigorously mix-ing the reactants may have to be repeated several timesbefore equilibrium could be established in all parts ofthe two-phase system. On the other hand, the rapid de-siliconization, taking place in modern practice duringtreatment by re-ladling or gas stirring, should also war-rant some reflections about the possible occurrence ofemulsification.

Beginning with stirring, the simplest configuration toconsider is that with one phase in a layer on top of theother. The mass transfer between the reacting phasescauses depletion of the element in question in the phasenear the common interface, and a corresponding enrich-ment in the other phase. The turbulence produced bystirring within the two layers enhances supply and with-drawal, respectively, of the element to be transferredby mixing with the bulk of the phases. This basic ef-fect of stirring reduces the time of attaining equilibriumbetween the reactants to some extent. Nevertheless, itcannot, of course, account for the high reaction ratesobserved in the Perrin process, neither according to itsoriginal procedure, nor to the modified ladle treatments.

A further consequence of stirring and turbulence inthe interfacial region is the accompanying instabilityof the originally macroscopically plane interface be-tween the two layers in question, which gives rise toundulation. This effect increases the surface area acrosswhich the mass transfer takes place. Thus, the reaction

3In the following the term desiliconization is used disregarding thefact that the refining in question also includes elements other thansilicon, in particular, chromium and iron.

time is reduced, but again not to the extent observed inpractice in the cases considered here.

Following the present line of thought, in view of theexplanatory power of the assumption of emulsification,it is tempting to go one step further by suggesting thatstirring causes not only undulation as such, but alsothe formation of waves rolling up into vortices. The im-plication of this similarity for the understanding of thehigh reaction rates in ladles during desiliconization offerrochromium is the splitting up of the metal phase atthe interface against the slag phase, into droplets, i.e.,eventually resulting in emulsification.

In fact, this hypothesis seems to be supported by evi-dence obtained in studies of the hydraulics of the move-ment of fluids according to model calculations of slag–metal interactions in metallurgical ladles during gas stir-ring [25, 27, 30], corroborated by examination of samples[31] (Figs. 4 and 5, respectively). These findings appearto be directly relevant for the conditions during desil-iconizing of ferrochromium in modern gas-stirred la-dles. In principle, the mechanism in question shouldalso function for the more complicated geometries ofthe original vessels used in earlier days by Perrin andhis co-workers.

Considerations of gas stirring as a means of enhanc-ing reactions during ladle treatments of metals usuallyassume that gas from an external source is introducedat or near the bottom of the metal bath. However, inthe case of refining ferrochromium, gas may be gener-ated internally in the slag, namely by the reduction ofmagnesium oxide, producing gaseous magnesium. Themagnesium oxide in question is a companion of the cal-cium oxide in the lime that is regularly added in orderto render the slag sufficiently fluid. Obviously, this con-stituent also serves the purpose of enhancing the inter-action between the slag and the metal by stirring theformer phase.For the sake of completeness and clarity,it should be realized that emulsification is confined toa relatively narrow zone near the slag–metal interface.Because the rate of reaction enhanced by emulsificationis very high, its full effect in this respect can be obtainedonly if there is a sufficient supply of reactants from therespective bulks of the phases. Hence, it can be arguedthat the latter may be rate determining for the overallprocess, depending on the efficiency of stirring.

Finally, in this elaboration of the mechanism of emul-sification during the production of ferrochromium,based on the concept of the Perrin process, another im-portant difference in the comparison with steelmakingshould be noted. In the latter case, the minor slag phaseis emulsified into the major metal phase. In the refine-ment of ferrochromium, the proportion of slag to metalis much higher, which may mean that emulsification

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Fig. 4. Cross section of the interface between slag and metal in a continuous casting tundish showing instabilities [30].

Fig. 5. Detail of an instability in the mixing zone between slag and metal [30].

of metal into slag could also be hypothesized, i.e., asin the models of gas stirring of metal covered by slagin a ladle, to be dealt with further below [25, 27, 30,31].

The extent to which such an inverse emulsificationdoes, in fact, occur is not possible to assess with certainty,lacking direct observations or models of the physicalstructure of the two-phase system during the vigorousmixing process. It seems not unlikely that this situation

could be characterized as chaotic, one that can be dealtwith only by complicated mathematics.4

Later adaptionsIt is a matter of course that ferro-alloy metallurgy hasadvanced in different respects since the introduction of

4Inversion as a principle has a long tradition in French thinking eversince ’le bon roi’ Dagobert who, according to the well-known chil-dren’s song, turned his trousers the wrong way about.

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the Perrin process in this technology in the late 1930s.In most plants, where its basic principle have beenadopted, the original mode of operation using the spe-cial devices for a dynamic interaction between metal andslag mentioned above has been replaced by re-ladlingor gas stirring.

Although attempts have been made to perform therefining of ferrochromium in one single operation, thecommon practice is to apply the method of treatment intwo steps as described in a previous section. This wasactually recommended already in a patent of the Perrinprocess for this purpose in 1939 [12].

The corresponding modern procedures can be exem-plified as follows for the sake of providing current quan-titative information related to the principles outlined[18]. The iron-chromium-silicon alloy to be refined, typ-ically containing about 40% chromium and 45% silicon,is charged in solid form into a ladle into which moltenslag is poured. The slag in this first step is a product ofthe final desiliconization in the second step. It containsabout 12% Cr2O3, and causes the chromium content ofthe metal to increase from 40% to 60% and the siliconcontent to decrease from 45% to 25%.

In the subsequent second ladle treatment the interme-diate alloy reacts with the major original slag of a compo-sition of the order of 48% CaO and 27% Cr2O3. The finalalloy thus produced contains about 75% chromium, 1%silicon and 0.01% carbon.

The percentage figures thus quoted are but one exam-ple. Depending on specific optimization with respect tosuch factors as the quality of raw materials available, en-ergy economy, etc, slightly different data may be quoted,for instance, those indicated in Fig. 1. With respect tothe chromium content of low-carbon ferrochromium,according to an international directory of producers,there is a range between 60% and 80% in approximatefigures [28].

Generally speaking, it is the quality of the productwith respect to composition, in particular the low car-bon content, that has preserved the Perrin process forthe purpose considered. As will be elaborated below, theprocess is maintaining a position in the market for low-carbon ferrochromium for stainless steel manufacturein two instances. One is for the final adjustments of thecomposition of steels in which the major chromium ad-dition has been made using alloys of higher carbon con-tent. Another use is for mixing with ferrochromium ofhigher carbon content in order to make alloys of mediumcontent.

However, the continuous development and improve-ment of the modern Perrin process and its remainingniche role does not mean that it is free from some draw-backs and shortcomings in comparison with other pro-

cesses for ferrochromium production of other gradesthan the low-carbon variety. For instance, with today’sviews on the control of processes and product quality,the ladle procedures described have sometimes beenconsidered unsatisfactory. The same is true for the rel-atively short life of the lining in certain cases [18]. Asindicated above, environmental concerns have becomecritical in some locations of ferro-alloy plants. This prob-lem has increased since the 1970s.

The latter is true, in particular, for the production oflow-carbon ferromanganese. Even if this may be some-what outside the scope of the present deliberations,which focus on ferrochromium, the proposed devel-opment of a procedure aimed at overcoming the men-tioned difficulties, with specific reference to the charac-teristics of the Perrin process, warrants a remark [23].The procedure in question applies the counter-currentprinciple in the true sense, i.e., with slag and metal flow-ing in a furnace in contact with each other in oppositedirections. Based on simulations, it has been claimedthat such a successor of the original two-stage Perrinprocess, using the ’shaker’- type ladle, could not onlyeliminate the stated disadvantages related to the needfor repeated ladle treatments; it would also be superiorwith respect to the kinetic conditions for the mass trans-fer and, hence, for the productivity.

Comparison with steelmakingWith reference to the overall scope of the present reviewof the Perrin process for ferro-alloy production, follow-ing the preceding paper on its use for steelmaking [1],a comparison between these two applications could bewarranted in order to add further perspectives to theprevious considerations of both cases. However, beforedealing with the specific aspects of the respective pro-cesses, it should be recognized that the outcome of suchcomparisons depends to some extent on personal atti-tudes to differences and similarities. Thus it seems as if adistinction can be made between those observers of thephenomena to be compared that are inclined to focusprimarily on differences, and those that prefer to con-centrate their attention on similarities. Bearing the im-plications of such a schematic characterization in mind,the following comparison aims at providing argumentsfrom both points of view.

To begin with the scientific principle that was as-sumed by Perrin as the basis of his process, i.e., emulsi-fication, most metallurgists would nowadays agree thatthis phenomenon occurs in both steelmaking and refine-ments of ferro-alloys. This is true despite the differencesin mass transfer during the processes, the different con-ditions of handling the reactants with respect to the pro-portions of the amounts of slag and metal, the alternative

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of employing gas stirring as a means of enhancing thereactions during ferro-alloy refining instead of vigorouspouring, etc.

Considering knowledge about the chemistry of thereactions as such, Perrin’s accounts are much more elab-orate in the case of steelmaking than that of ferro-alloyrefinement. To some extent this difference is probablybecause of the general reluctance to reveal information,which could be of commercial value in the ferro-alloycommunity.

Turning to the melting shop procedures common toboth applications of the Perrin process is the need forspecial installations for the preparation of the slag. Thiswas probably more of a deterrent for steelmakers thanfor producers of ferro-alloys who, generally speaking,have always been accustomed to considering more com-plex procedures than those typical of steelmaking, atleast in the past when the Perrin process for this pur-pose was introduced before and after the Second WorldWar.

One major issue addressed in the review of the Perrinprocess for steelmaking is its limited application outsidethe French metallurgical industry. One aspect of this isthe secrecy on the part of the Ugine company mentionedabove. With respect to the technology and economy ofthe process, there are a few conditions that may accountfor the modest proliferation. The most common explana-tion, relating to the period before the advent of present-day steelmaking technology, refers to the need for spe-cial installations for slag preparation. To that complica-tion was added the radical departure from conventionalpractice that the adoption of the Perrin process wouldmean. Finally, in more recent time, the development ofmodern steelmaking technology phased it out of con-sideration in other than special cases.

In contrast, the same limiting conditions have not be-come critical for the application of the Perrin processfor ferro-alloy production. Thus, it has proved to be stillviable, although mainly for two products, namely low-carbon ferrochromium and ferronickel. For these, thePerrin process is apparently so well suited that thereare practically and economically no alternatives. Pos-sibly, the economic margins for ferro-alloy productionare wider than for steelmaking, permitting higher capi-tal costs for investments in equipment for metallurgicalprocessing and handling.

With respect to the promotion of the Perrin process,referred to previously, it is difficult to assess any dif-ferences between the two applications without havingaccess to records from the decisions made by the man-agement of the Ugine company. Again, the so-calledcomparative advantages of the process for the produc-tion of special ferro-alloys, like those indicated above,

offered a better position for negotiations about licensesthan would have been the case when marketing the pro-cess for steelmaking.

Last but not least, the managerial conditions for thedevelopment and use of the two applications of the Per-rin process deserve a perspective comment. As empha-sized in the review of the steelmaking case [1], a newtechnology is promoted by integration into a so-calleddevelopment block, aiming at a changing market, takingadvantage of its dynamics and imbalances. Hence, its in-troduction is not just simply a technical issue but a cre-ative managerial activity, depending on an entrepreneurand persevering financial support.

It appears that both applications of the Perrin processin question are similar in this respect. The reason for thisis, of course, that as projects they were developed in par-allel, technologically as well as chronologically. Possibly,the use of the process for ferro-alloy production showsmore evident features of a development block than thesteelmaking application. Another difference bearing onthe development, somewhat relating to similar condi-tions, was the access to the particular technical compe-tence, which made it possible for ferro-alloy productionto overcome the formidable difficulties associated withthe mechanical and physical handling of the reactantsat the prevailing high temperatures.

As stated in the introduction to this comparison, it isa matter of personal preference to conclude whether thetwo applications of the Perrin process should be consid-ered as similar, like twins, or differing, like members ofthe same family of ingenuity.

Industrial contexts

Early integration and connectingThere is only little information available about eco-nomic, commercial and business-related conditions forthe adaption and application of the Perrin process forferro-alloy production. Therefore, only a few reflectionsabout so-called development blocks or other conceptsof economic theory can be made about the present caseof technological development, in contrast to the previ-ous deliberations on the use of the Perrin process forsteelmaking [1].

However, one remark may be made about the pro-duction at Moutiers of stainless steel with low carboncontent accompanying the introduction of the Perrinprocess for making ferrochromium with the requiredlow carbon content. Here the alloy was transferred inthe molten state from the ferro-alloy plant to the newsteel works established nearby for the purpose of mak-ing steel ingots for further processing elsewhere.

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It should be noted that this arrangement was not assimple as what is sometimes called vertical integration,but rather a form of synergism. This was made possibleby the close association between the technical staff of theUgine company, to which the Moutiers plant belonged,and the responsible financing body with which Perrinapparently had very good relations.

Furthermore, it may be warranted in this connectionto call attention to the establishment of a ferro-alloyplant at Moutiers. At the time when this took place at theturn of the century, around 1900, the technique for long-distance transmission of electricity was not developedto its present stage. Hence, industries consuming largeamounts of electricity were located near power plants.In the regions of Ugine and Moutiers there are severalhydro-electric power plants, the erection of which prob-ably benefitted from the installation of electrochemicaland electrometallurgical industries like those of interestin this review.

Little is known about the planning of the establish-ment of the two types of related industries considered.Nevertheless, it does not seem unlikely that there wassome interconnection in this process that resembledwhat is characteristic of the formation of developmentblocks according to the description given in the previ-ous publication on the corresponding issue in the caseof steelmaking [1].

Exploitation and proliferationIn the preparation for the industrial utilization of thePerrin process for ferro-alloy production, patents wereissued at an early stage of the development on a rela-tively small scale. The first patent was granted in 1933[10], followed by two more in 1938 [11] and 1951 [12]. Itmay be interesting to note that the first patents on thePerrin process for steelmaking are from 1931, i.e., onlyone year before the corresponding one for ferro-alloys.

In the publications about the use of the Perrin processfor steelmaking referred to in the preceding paper [1], anumber of steelworks having applied it in various coun-tries during almost seven decades from the 1930s arementioned. In the corresponding case of ferro-alloys,the initial development of the process began in thelate 1920s, followed by production of low-carbon fer-rochromium in the early 1930s under the name of theUgine–Perrin process [21]. For large-scale productiona special plant was established at Moutiers near Al-bertville in Savoie, not far from Ugine. Perrin’s firstmention of these activities is from 1936 [3], but the pro-duction at Moutiers appears to have begun in 1938 afterpreliminaries from 1934 [6, 20]. For the sake of complete-ness, it could be added that the last year of operation ofthe Perrin process at this plant was 1978.

A number of new plants using the Perrin process werebuilt in France after the Second World War, but at presentthere are no longer any producers of ferrochromiumin this country. Apparently, there has been a gradualchange of the interdependence between ore suppliers,electric power utilities, and producers of alloys and theircustomers in the steel industry. In business terms, thefirst one of these significant actors has become determi-native as a consequence of the increasing demand forraw materials of strategic importance.

Outside France the Perrin process has been used inseveral countries in more or less modified forms dur-ing periods of time of varying lengths after the SecondWorld War. Licenses were issued from the beginning ofthe 1950s to some major producers of ferrochromium incountries like Germany, Italy, Rhodesia and Sweden, tomention just a few. Later, when the patents had expired,the process was used in a plant in India as well as afurther one in Sweden and one in the U.S.A.

The situation changed drastically as a result of thedevelopment of new steelmaking processes for the pro-duction of low-carbon stainless steel that could makeuse of ferrochromium with higher carbon content thanthe low ones for which the Perrin process was supe-rior and competitive. Gradually, from the beginning ofthe 1970s, the process was phased out in many plants,leaving a limited number of producers as a niche forconsumers of low carbon grades needed for the finaladjustment of the composition of stainless steels.

For obvious commercial reasons, referred to above inanother context, there is only restricted access to cor-porate sources of information about the current prac-tice of the Perrin process. One possible indication of itspotential application is information, which has been re-trieved from international directories of the ferro-alloyindustry [24, 28]. These publications list producers oflow-carbon ferrochromium, i.e., with carbon contents ofmaximum 0.10%. In 1996 [24] and 1998 [28], the capac-ities for such production existed in a number of coun-tries: Brazil, China, Germany, India, Japan, Macedonia,Mexico, Romania, Slovakia, Slovenia, South Africa,Turkey and Zimbabwe.

An inquiry was directed to 13 of those plants, whichcould be assumed to possibly be using the Perrin pro-cess for the production of ferrochromium of low-carboncontent. The response to the question was not over-whelming. Only from plants in Finland, Slovenia andZimbabwe was any answer obtained. In Finland the Per-rin process had never been used, in Slovenia its applica-tion had ceased in 1998, and in Zimbabwe the principleof the Perrin process is adopted in a modified procedure.

Admittedly, this meager result of an inquiry intothe use of the Perrin process for the production of

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ferro-alloys, in the original form or according to modi-fied procedures, is unsatisfactory as a basis for a definiteconclusion about the future of its application. Neverthe-less, for the purpose of the present review, the availableinformation could make it possible to compare the his-tory of the Perrin process for ferro-alloy production withthat for steelmaking.

In such a comparison one important aspect to consideris the establishing of relationships with the market, asit were, for the respective applications of the process.In modern language, this issue is usually discussed interms of marketing. Because this was not recognized asa particular kind of activity during the early years ofthe exploitation of the process, an account of the relatedefforts has to be based on the recollections of personswho still have impressions to report.

There are thus witnesses of the past who recurrentlyclaim that there is one major reason for the limited appli-cation of the process to steelmaking as mentioned pre-viously [1], namely the reserved character and attitudeof the management of the Ugine Company in this re-spect. Among other things, only very few selected visi-tors from other steelmaking companies were permittedto enter the Ugine plant. No doubt this lack of com-munication on the shop floor, in the literal sense of thisterm, created uncertainty among those who might havecontemplated an application of the Perrin process forsteelmaking.

Paradoxical as it may seem, the well-known extremesecrecy of the ferro-alloy industry does not appear tohave had the same restrictive effect on the proliferationof the Perrin process in this field. In the light of eco-nomic theory, that situation can be considered and un-derstood as a ’push and pull’ balance. Even without aconscious promoting effort on the part of the manage-ment and marketing representatives of the Ugine com-pany, the need for improvements in the ferro-alloy in-dustry prompted an approach to the Ugine company tothis end.

For obvious reasons, the potential interest in the Per-rin process for ferro-alloy production increased substan-tially when the related patents gradually expired. At thattime, with the advent of modern practices of producingstainless steel based on other than ferrochromium of lowcarbon grades, there was still a considerable market forthat product. The subsequent decline of this market leftonly a niche for the Perrin process for low-carbon fer-rochromium, namely for the final adjustment of the com-position of stainless steel of low carbon content, madeby modern techniques. A recent reviewer who sharesthis view of the role of the only extant application ofthe process states: ’Currently, the most important pro-cess for the production of low-carbon ferrochromium is

the Perrin process...’[26]. Similarly, in another modernaccount, it is stated: ’The commonest smelting processfor low-carbon ferro-chromium production is the two-furnace Perrin method...’ [29].

How long this situation will persist is, of course, anopen question, lacking indications of emerging alterna-tive methods or procedures serving the same purposeas the Perrin process for ferro-alloy production. Appar-ently, however, this is in contrast to the case of steel-making, for which the Perrin process gradually becameobsolete when vacuum technology and ladle refiningwere introduced after the Second World War, leavingno competitive comparative advantage for the Perrinprocess to survive in that field.

Eventual replacementAn appropriate point of departure for a reflection onthe future of the Perrin process for ferrochromium isprobably the generalizing statement of a few years ago,referred to above [26], that it had at that time a well-established position in this field. Nevertheless, judgingfrom the admittedly limited commercial and industrialinformation available, it does not seem farfetched to as-sume, for the sake of reasoning, that the long-term trendfor the process might be at least slightly negative. Inother words, it appears not unlikely that the number ofproducers having phased out the process in recent yearscould exceed those, if any, which have introduced it.

Therefore, in view of the scope of the present deliber-ations, aiming at contributing to the understanding ofthe application of Perrin’s idea and principle in the tech-nology in question, it might be elucidating to considervarious reasons for the assumed phasing out of the pro-cess. Again, in the comparative perspective adopted inthis review, it may not be redundant to call attention tothe fact, touched upon previously, that the late history ofthe use of the Perrin process for steelmaking appears tobe different from that for ferro-alloy production. In theformer case, the competitive power of the alternatives,emerging after the Second World War, was such thatnone of the comparative advantages of the Perrin pro-cess could play any critical role in the decision-makingabout potential new installations after, say, the 1960s.Hence, the gradual disappearance of the Perrin processfor steelmaking was foreseeable even relatively long be-fore that time.

In contrast, again referring to previous comments, thePerrin process for ferro-alloy production had early es-tablished a long-lasting market position by virtue of itsqualitative advantages with respect to low-carbon fer-rochromium grades. Although the share of such gradesin the total ferrochromium consumption has decreasedduring the last few decades, the growth of the overall

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market has reversed the earlier negative trend until, inthe 1980s, a positive one emerged.

Nevertheless, as far as the available limited informa-tion in this respect is representative, it cannot be ex-cluded that the role of the Perrin process for low-carbonferrochromium is diminishing both relatively and in ab-solute numbers. Technically, this would mean that it isbeing replaced by processes like the so-called Duplexprocess [20] and the Simplex process [19, 20, 26]. Theformer is similar to the Perrin process, but differs by in-volving only one alloy in solid form. On the other hand,the recovery of chromium is somewhat lower. In theSimplex process, the decarburization of ferrochromiumtakes place in solid state under vacuum by reaction withchromium oxide. The product has a higher oxygen con-tent than that of the Perrin process.

In order to understand the underlying conditions andcauses of the introductory progress as well as the even-tual phasing out of the Perrin process, it may be of in-terest to consider its relative role in the technology inquestion, from the perspective of the current views ontechnical change in general. It is then important, how-ever, to distinguish between approaches on macro andmicro levels. According to the first level, the focus ison generalized industrial trends, mostly expressed inaggregated statistical terms. Although that may be re-quested by, among others, investment analysts, the un-derstanding of the particular conditions governing thedecision-making in specific plants requires considera-tion on the relevant micro level. That is the perspectiveof the following deliberations, based on experience relat-ing to corresponding changes in the steel industry, fromthe advent of the industrial revolution to the presenttime.

Schematically, a number of so-called critical factorscan be identified in a search for an explanation of actualevents and actions taking place during a certain techni-cal change. Leaving the invention stage aside, the pre-requisite for a particular technological development isan existing or expected market. In the case of the applica-tion of the Perrin process for low-carbon ferrochromiumproduction, the market ’pull’, as it were, was the driv-ing force, rather than the ’push’ of the new technology assuch, expressed in the jargon of economic theory. Withrespect to the eventual phasing out of the process, thecontinuous transformation of the market, under pres-sure of the changing demands from the customers offerrochromium in the stainless steel industry, has beenof critical importance.

Although these reflections on the importance of mar-ket forces might seem to belong to the macro perspec-tive, they are made because of their implications fordecisions on the micro level. This view refers to the

connection between the production of ferrochromiumand its immediate use in a nearby stainless steel works.This so-called vertical integration was once a motivationfor the application of the Perrin process at Moutiers,where a stainless steel works was later established. Amore recent case of such an integration is the Out-okumpu ferrochromium plant and associated stainlesssteel works at Tornio in Finland, although the tech-nology there has not included the use of the Perrinprocess.

Despite its logical appeal, this kind of local integrationdoes not seem to have been a dominating factor in de-cisions about the preservation of a certain metallurgicalprocess at a particular location. One example support-ing this view is the last ferrochromium plant using thePerrin process in France at L’Ardoise. The productionthere ceased in the 1980s, because of the fact that thecompany in question was then no longer in sufficientcontrol of the supply of raw materials. Apparently, theexisting investment in a facility for production based onthe Perrin process did not prevent the closing down ofthe plant.

Whether this case is a special one, or illustrates a pos-sible sensitive dependence of the ferrochromium indus-try on the supply of raw materials, is not evident fromthe limited information available on such matters. It ap-pears, however, as if the macro-economical condition ofaccess to raw materials in this field has become more im-portant during the period after the Second World War,as indicated by the establishing of new plants for pro-duction in countries possessing deposits of chromium-containing ore as well as expanding the production inexisting facilities. This is true even in cases of depositsof ore of a quality which was earlier considered inferior.One reason for this has been the increasing demand ofhigh carbon grades of ferrochromium, possible to usethanks to modern methods for making stainless steel.

Still, production of ferrochromium is competitiveeven in plants located far from mines supplying the rawmaterial. This is due partly to lower costs of electricity,which compensates for the costs of transportation of ore,partly to the advantage of being nearer the consumersof the product. Furthermore, such a location in regionswith a higher population density than in most miningareas means that the cost of energy can be significantlyreduced by the utilization of waste heat from the processfor district heating.

Finally, in this reflection on the possible preservationof the Perrin process, the increasing role of environmen-tal concerns should be remarked upon. Related issuesbecame another critical factor in comparisons betweenalternative metallurgical processes after, say, the 1970s.Although it is true that no particular technical problem

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in this respect could completely and categorically ruleout a certain process, the costs of dealing with it mayhave had a decisive importance. To what extent this isthe case of the eventual replacement of the Perrin pro-cess for ferro-alloy production is probably not possibleto assess, even if the use of re-ladling procedures is ob-viously a disadvantage from an environmental point ofview. Much depends on the negotiations between in-dustry and governmental agencies. One sensitive issueis the balance between the effects on the environmentemanating from the processes as such, and on the otherhand, the effects of increased power production for thepurpose of supplying ventilation and other counteract-ing installations with electricity, in particular in case thisis provided by fossil-fuelled power stations.

Extra-metallurgical conditionsWhat follows is an elaboration of the general remarksmade previously about time-dependent relationshipsbetween ferro-alloy production on the one hand, andsupply of raw materials and electric energy, as well asmarket structure, on the other hand, with respect tothe eventual replacement of the Perrin process. The is-sue to be emphasized below is the importance of thegreat variety among the plants in the industry in ques-tion with respect to the different conditions determiningtheir competitiveness. The existing lack of uniformity isinteresting from the point of view of understanding thecorresponding diversity of the appreciation of the Perrinprocess in different quarters.

Thus, within the framework of certain restrictionscommon to most cases to be considered, local andcompany-related conditions seem to have differed to anextent, which does not permit identification of a pat-tern typical of all parts of the industry contemplatingthe application of the Perrin process. One aspect of thisvariation of current views is its time-dependence in tworespects. From the long-term perspective, the relation-ships dealt with in these deliberations change from oneperiod of time to another, which makes comparisonsbetween different cases less interesting. Secondly, andmore important for this review, is the fact that decision-making at a certain point in time about a particularchange of technology is a dynamic process.

It is true, of course, that some factors and assets arefixed physically and geographically, and are constantover time, whereas several other critical conditions aresubject to perpetual transformation taking place at dif-ferent speeds. Hence, the system as a whole can be un-derstood and handled only by applying varying andadjustable short-term perspectives to the scene wherethe new technology is supposed to play a role.

The analogy of decision making with a scene or sce-nario lacks one important dimension, namely the op-tions of actors to alter the conditions in question at will.Such a non-deterministic attitude and approach is oneof the significant characteristics of an entrepreneur. Inits most dynamic form, an entrepreneurial activity caninduce the creation of so-called development blocks, en-visaging new combinations and synergism. However, asalready stated, there is a difference between Perrin’s pio-neering achievements as an inventor and entrepreneurin the 1920s and 1930s, and the later cases of integra-tion and exploitation of certain particularly favourableconditions for ferro-alloy production. The latter do notnecessarily represent more than a relatively normal cou-pling of factors in the production system from ore to finalproduct.

Acknowledgements

In principle, this paper deals partly with the same kindof issues as the previous one on the Perrin process [1].Accordingly, thanks are also due here to Mr. Y. Franchotof the Societe Francaise de Metallurgie et de Materiauxfor providing a comprehensive bibliography of Perrin’spublications, including patents. Similarly, the authoris indebted to Professor E. Dahmen of the StockholmSchool of Economics for continued guidance in the re-flections on development blocks. Dr. P.V. Riboud of IR-SID, R&D Groupe Usinor is once again thanked for sup-port of the general arguments about the emulsificationpostulated by Perrin.

At this point, the contribution by Professor P. Jonssonof the Royal Institute of Technology in Stockholm con-cerning the kinetics of slag–metal interaction during la-dle treatment is gratefully acknowledged.

With respect to the metallurgy of the productionof ferro-alloys in general, and ferrochromium in par-ticular, as well as the industrial development in thisfield, the following professional and experienced ex-perts have generously presented important informa-tion and knowledge: Mr. N.G. Lindberg, formerly PlantManager of Ferrolegeringar Trollhatteverken AB, andMessrs. I. Widell and H. Martander, Managing Direc-tor and Manager in charge of environment and qualityof Wargon Alloys AB, respectively, both companies inSweden, Mr. J. Schalamon, Managing Director of Elek-trowerk Weisweiler, Germany, and Mr. G. Guyot, Direc-tor of Pechiney Electrometallurgie, Paris, formerly met-allurgical engineer at the Moutiers ferro-alloy plant. Forall this the author wants to express his gratitude.

A grant for covering costs of correcting the Englishand typing the text has been obtained from a researchfund administered by Wargon Alloys AB. The author

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also wants to express his thanks for this generoussupport.

Finally, thanks for the right to reproduce illustrationsare due to Arnold Publisher for Fig. 1, Zimbabwe AlloysLtd for Fig. 3, and to Professor S. Seetharaman, organizerof the Sixth Int. Conf. Molten slags, Fluxes and Salts forFigs. 4 and 5.

Note on references

No. 1 is the previous paper on the Perrin process forsteelmaking. Nos 2–9 are publications by Perrin. Nos10–12 are French patents. Nos 13 and 14 are papers onthe operation and procedures of the process. Nos 15–31are supplementary literature.

References

1. Ostberg G. Revue de Metallurgie 2001: 98: 41–53; 2001: 98:281–294.

2. Perrin R. Bull. Ste d’Encouragement 1936: Aout-Septembre: 499–509.

3. Perrin R. Revue de Metallurgie 1946: 43: 185–191.4. Perrin R. Bull. Ing. Civils, 101 annee, Fasc. IV special,

Septembre 1948: 624–636.5. Perrin R. Instituto del Hierro y del Acero 1949: 2: 5–11 (in

Spanish).6. Perrin R. Jernkontorets Annaler 1950: 134: 1–23. (In

Swedish with a summary in English. In the previous paper(1) the title of this publication was in French following alist of Perrin’s writings obtained from France.)

7. Perrin R. Les Impressions Techniques, 56, Boulevard de laVillette, Paris, 1954.

8. Perrin R. Joint Metallurgical Societies’ Meeting in Europe,1955, Technical Sessions in Paris.

9. Perrin R. (with A. Greffe). Symposium on Ferro AlloysIndustry in India, 12–15 February, 1962 (This publicationhas not been retrieved.).

10. Perrin R. Patent No. 755.939. Improvement of the processof obtaining ferro-alloys of very low carbon content. 1932,1933, 1933.

11. Perrin R. Patent No. 834.354. Process for the manufactureof alloys, in particular ferro-alloys or stainless steels. 1937,1938, 1938.

12. Perrin R. Patent No. 971.213. Process for manufacture offerro-alloys of low carbon content, and in particular ferro-chromium. 1939, 1950, 1951.

13. Perrin R. Patent No. 780.125. Process and device for real-ization of rapid reaction between a metal and a slag. 1934,1935, 1935.

14. Perrin R. Patent No. 843.661. Apparatus and process forrealization of metallurgical operations. 1938, 1939, 1939.

15. Blake JA. Proceedings of a Symposium, Institute of Mining& Metallurgy, London, 1950: 505–515.

16. Castro R. Conference faite aux cadre et ingenieurs de lasociete, Ugine, Decembre 1957.

17. Coleman EE, Vedensky DN. J Metals 1960: 12: 197–201.18. Bjorling G. Jernkont. Ann. 1968: 152: 372–386 (In Swedish).19. Durrer/Volkert, Metallurgie der Ferrolegierungen, Her-

ausgegeben von G. Volkert, KD Frank, 2. Auflage; SpringerVerlag, Berlin-Heidelberg-New York, 1972: 346–349.

20. Robiette AGE. Electric smelting processes. Griffin, Lon-don, 1973.

21. Devos H. Histoire d’Ugine: Memoires et documentspublies par l’Academie Salesienne, Tome XV bis, Annecy,1975.

22. Botte R. Revue de Metallurgie 1979: 77: 435–443.23. Nelson LR, Robertson DGC, Swany KN. In: Watten G.

ed. Thermodynamic and kinetic simulations of a novelcounter-current reaction launder process for the produc-tion of refined low carbon ferromanganese; EPD Congress1994, San Fransisco, California, USA, The Minerals, Met-als & Materials Society, Warrendale, Pennsylvania, USA.1994: 713–737.

24. Jones A. ed., Ferro-alloy directory and databook, 4th edn.Metal Bulletin Books Ltd, Worcester Park, 1996.

25. Jonsson L, Jonsson P. ISIJ Int 1996: 36: 1127–1134.26. Habashi F. (ed.). Handbook of extractive metallurgy, vol I.

The metal industry, ferrous metals: Wiley-VCH, Wein-heim, 1997: 445–447.

27. Jonsson L, Sichen D, Jonsson P. ISIJ Int 1998: 38: 260–267.28. Chromium Industry Directory; International Chromium

Development Association, Paris, 2nd edn., 1998.29. Maliotis G. In: Griffiths JB. (eds.) Industrial minerals in-

formation Ltd, 1998, p. 8030. Solhed H, Jonsson L, Jonsson P. Metall Mater Trans 2002:

33B: 173–185.31. Low-carbon ferro-chrome, Reference Document on Best

Available Techniques in the Non Ferrous Metals Indus-tries, Integrated Pollution Prevention and Control (IPPC).European Commission, Directorate General, Technolo-gies for Sustainable Development, European IPPC Bureau,May 2000: Chapter 9, 9.1.1.3.3: 511.

Address:Gustaf OstbergBox 118S-221 00 LundSweden

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On the application of the Perrin process for ferro-alloy production