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Productionof magnesium by vacuum carbothermicreductionof calcined dolomite

R. Winand, M.van Gysel, A. Fontana, L. Segers and J.-C. Carlier

SynopsisIt is well known that MgO can be reduced by carbon atattnospheric pressure at temperatures in the range19So-2000°C. A study was made of the selective reduc-tion of MgO.CaO by carbon under moderate vacuum(1 mm Hg) and at temperatures of about 1400°C.

After a short introduction to the thermodynamics ofthe process a description is given of the experimentalapparatus, which permitted continuous production of20 kg/day magnesium; the process included a stage ofcondensation on a cool surface. Since the best conden-sate obtained consisted of 80 wt% magnesium metal,purification by sublimation was required to recover apure molten ingot.

Today, magnesium is essentially produced either by molten-salt electrolysis or by silicothermic reduction of oxides.!However, carbon can also be used as a reductant formagnesium oxide, and it was used on an industrial scale2,3,4in the Hansgirg process (with some eventual modifications) atRadentheim (Austria), Swansea (Wales, United Kingdom),Konan (Korea) and Permanente (California, U.S.A) until themid-1940s. The main difficulties were considered to be dueto the high temperature (about 2000°C) that must be main-tained to reduce magnesia with carbon at atmosphericpressure and to the necessity to quench the gases leaving thereacting chamber to avoid the back-reaction betweenmagnesium vapour and carbon monoxide. Various quenchingmedia were considered:3 hydrogen gas, liquid hydrocarbon,molten metal (tin, lead, mercury, zinc, aluminium ormagnesium) and, at Permanente, natural gas. Others tried toavoid back-reactions by removing the carbon monoxide in astream of inert gas or under vacuums or to condensemagnesium on a cold surface at reduced pressure.6 None ofthese process modifications allowed the recovery ofmagnesium of sufficient purity after quenching to permitdirect melting and casting as an ingot. At Permanente thequenched product contained only 50' wt% metallicmagnesium, the balance consisting of 20 wt% MgO and30 Wt% carbon.

Recently, a process has been described for the carbo-thermic production of magnesium that makes use of a moltenslag bath as a heat-transfer medium and as a sink for impuri-ties contained in the feedstock.7 Condensation, however, wasnot studied.

Since carbon is a cheap reductant and calcined dolomite(MgO.CaO) is easily available in large quantities and at lowcost, the senior author thought that the process could bemade economically viable provided that the back-reactioncould be controlled and excessive contamination ofmagnesium by calcium could be avoided. Indications in theliterature were that working under reduced pressure could beadvantageous: Khazanov8,9 studied the influence of pressure

Manuscript first received by the Institution of Mining and Metallurgyon 19 March, 1990; revised manuscript received on 12 July, !990.Paper published in Trans. Imtn Min. Metall. (Sect. C: Mineral Process.Excr. Metall.), 99, May-August 1990. iD The Institution of Miningand Metallurgy 1990.

and temperature on the back-reaction and demonstrated thatit slows down at pressures less than 10 mm Hg. On the otherhand, Gulyanitzkii and Chizhikov!O showed that thereduction of magnesia by carbon under reduced pressure ispossible, although it slows down at less than 0.1 mm Hg.Accordingly, it was decided to investigate the reduction ofMgO.CaO by carbon at reduced total pressures of between10 and 1.0 mm Hg. The process studied would include astage of condensation of magnesium on a solid surface main-tained at a temperature sufficiently low to retard theback-reaction but high enough to allow the metal to condenseas columnar crystals to reduce its specific area.

The present contribution describes experiments that wereperformed at small and large laboratory scales during .theperiod 1972-76, at first as part of a thesis submitted towardsa metallurgical engineering degree!! and later under contractto Vieille Montagne S.A. It is only recently that permissionhas been given to publish the results.

Thermodynamics

Fig. 1 shows the equilibrium carbon monoxide pressures forthe most important reactions in the reduction of MgO.CaOwith carbon, induding that of silica as a contaminant. For thetwo first reactions (those producing elemental Mg and Ca)the partial pressure of the metal vapour is taken to be equal tothat of the carbon monoxide.

1~~o I=::==::=:=::=::=::=::=::=::=::=::=::=::=::~:~.:5::':~~~~:;=::=::=:~_._n

101

100

-~ - - - - - - - - - - - - - - - - - - - - - - - - - - --

10,1bD

::r: 10-2EE 10,3

;;, 10-4

10,5 A

B

D

1000 1500 2000Temperature, K

Fig. I Equilibrium Peo for reactions: A, MgO + C -4 Mg + CO;B, CaO + C -4 Ca + CO; C, 2MgO + 5C -4 Mg2Cj + 2CO; D, CaO+ 3C -4 CaC2 + CO; E, Si02 + 3C -4 SiC + 2CO. Bl'OkclZlIllcs.rangeof pressures envisaged. For reactions A and B, P.\I,' = Peo.(Thermodynamic values fromBJ!rin and co-workers12)

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'N . - ~- ,."-="-'"~ " -~_.

~- --- ", ~- "",.'~ "

-'., ~rFor the first reaction it can be seen that, instead of a

temperature of more than 2000K at atmospheric pressure,temperature$ in the range 1400-1700K would be sufficientfor equilibrihm to be attained under the range of reducedpressures considered. Besides silicon carbide formation, thereduction of magnesia will be favoured over that of lime,

Pea/PMg ratios falling between 1.2 x 10-3 at 1400K and 3.1 x10-3 at 1700K. This ratio increases, however, with temp-erature (4 x 10-3 at 1800K), except that above 1680K theformation of calcium carbide can be expected to detract fromthe production of calcium vapour. On the other hand, theproduction of magnesium carbide may be ignored. Thepartial pre~sure of silicon monoxide was shown to remainquite low (7 x 10-3 mm Hg at 1600K and only 1 x 10-1 mmHg at 2000K), while, owing to the higher free energies offormation of calcium silicates than of magnesium silicates,contamination of magnesium metal by calcium would bereduced.

Concerning condensation, Fig. 2 gives the equilibriumstates for calcium and magnesium. It can be seen that anycalcium vapour will condense before magnesium, so an evalu-ation of PeiPMg under reducing conditions gives a good ideaof the likely contamination of the condensate.

760102

101

r 100

6 10-16~' 10-2;:3~ 10-3:t 10-4

10-5

Mgs

600 600 1000 1200 1600

Temperature, K

Fig. 2 Equilibrium states for calcium and magnesium

Condensation of magnesium as a liquid would certainlynot be efficient and is only possible if Pea (Fig. 1) exceeds2 mm Hg. However, the condensation of magnesium as asolid on a surface maintained at a temperature of 350°Cwould give a theoretical condensation efficiency (withoutback-reaction) of 99% under the worst conditions (Pea =5 x10-2 mm Hg).

Experiments perfonned at small laboratoryscale

The experimental apparatus used for small laboratory-scaleexperiments is shown schematically in Fig. 3. The reactionchamber was evacuated by a Balzers DU 025 mechanicalpump backing a Balzers DIFF 500 diffusion pump. Agraphite crucible containing a 100-g charge as compressedtablets was heated by induction (ACECN2616 10 kHz-45 kW generator) by a graphite susceptor. To avoid excessiveheat losses a spiral molybdenum coil was positioned aroundthe susceptor. The condenser was filled with oil and cooledby water circulated through a copper tube. Three thermo-couples were attached to the condenser: one Pt-(Pt +18% Rh) unit was placed in an alumina sheath and measuredthe temperature of the charge, the others (chromel-alumel)

CI06

=---=-

- 11

10

5

0000

~000

6

10 emI I

~7Fig. 3 Small laboratory-scale experimental apparatus: 1, graphitecrucible; 2, graphite susceptor; 3, molybdenum-coil heat shield;4, quartz tube; 5, induction coil; 6, alumina block; 7, argon inlet(closed during experiments); 8, Pt-(Pt + 18% Rh) thermocouple inalumina sheet; 9, oil-cooled condenser; 10, water-cooled jacket;11, to pumping system

measuring the temperature at the bottom of the condenserand in the oil.

In each experimental run, as soon as a vacuum of 0.05 mmHg was attained induction heating was started (at a powersetting of 8 kW) and, since the crucible took only 5 min toreach a temperature of 1700K, it was not necessary to apply acorrection for the time required to heat the charge. Thetemperature in the crucible was automatically controlled to:t5K. A MacLeod mercury gauge was used to measure thepressure at the entrance to the pumping system, where thetemperature was taken to be 298K. The only pressuremeasured was that of CO, and its partial pressure in thefurnace must be evaluated from

J

TPea (furnace) =P298 -

298

where temperature, T, in the crucible is in kelvins.

9

8

4000

g---1b----..

2

3

. or. - 0 ~ ~-~~~-JiilF---'-~~ '~'.,-':F .""--'Or'" - ~.: ~

The first experiments were performed with pure MgO(prepared from calcined Merck 5828 MgC03) mixed withcrushed (-200-mesh) metallurgical coke (85.3 wt% carbonwith 4.94% weight loss on heating in an inert atmosphere and9.8 wt% ash). Cylindrical tablets 3.5 cm in diameter and1 cm thick that were prepared from the mixture by com-pression (at 1 tlcmZ) contained C and Mg in the atomic ratio1.2:1 (70.5 wt% MgO, 29.5 wt% coke). Other experimentswere performed with crushed, calcined (5 h at 1050°C)dolomite from Carmeuse (50% -100 mesh), which contained59 wt% CaO, 39.6 wt% MgO and 1.9 wt% FeZ03' Thetablets prepared from this material also had an atomic C:Mgratio of 1.2: 1 (86 wt% calcined dolomite, 14 wt% coke). Thetotal pressure in the reaction vessel was in the range 0.04-5 mm Hg, the higher values being obtained at 1700K.

The experimental results are summarized in Figs. 4, 5 and6. As can be seen, reaction efficiency increased markedly attemperatures greater than 1600K for both MgO and

100

Mg

"*""~Ca

1500 1700

Temperature, K

Fig. 4 Loss of magnesium and calcium from charge as function oftemperature after 3 h reaction time: circles, pure MgO; crosses,MgO.CaO

100<f2

~Q)'CO....

1 50u

x1\11(

Ca

,-(:;0

J:::U)U)0-J 0

0 2 3 4

Time,h

Fig. 5 Loss of magnesium and calcium from charge as function oftime at 1700K: circles,pure MgO; crosses,MgO.CaO

100

Mgx::;>:: 50 x?

0 Ca

0 3 42

Timl',h

Fig. 6 Ratio of metal condensed to metal lost from charge asfunction of time at 1700K: circles,pure MgO; crosses,MgO.CaO

MgO.CaO. At 1700K a reaction efficiency of 70% wasachievable in about 4 h without excessive loss of calcium.

Moreover, calcium did not condense efficiently (about 60%).However, condensation was markedly better in the experi-ment~ performed with tablets prepared from pure MgO(:0;97%) than in those in which MgO.CaO was used(maximum, 65%).

The metallographic structure of the condensates showedthe expected columnar structure perpendicular to the sub-strate. The magnesium metal content of the condensate wasbetween 75 and 85 wt%, with calcium contents less than0.5 wt%.1t should be noted, however, that when the total pres-sure in the reactor was allowed to reach 5 mm Hg at 1700K themagnesium metal content of the condensate dropped to42 wt%, whereas the calcium content rose to about 2.5 wt%.

At this stage a first economic evaluation of the processindicated that it could be competitive with electrolysis andwith the Magnetherm process. It was accordingly decided totest it at the semi-pilot scale.

Experiments at semi-pilot scale

The objectives of the experiments performed at a semi-pilotscale were to discover the technical difficulties that mightarise in converting the process from discontinuous mode in alaboratory apparatus to a continuous, industrial process. Thesemi-pilot scale equipment was dimensioned for a theoreticalproduction rate of 3 kg/h Mg, with an entrance load of20 kg/h and residue production of 10 kg/h. The main criteriaadopted in designing the equipment were efficientcondensation of magnesium and continuous recovery of thecondensate.

It was decided to employ a solid cooling surface orientatedperpendicularly to the gas flux leaving the furnace. In a firstdesign the use of a thin, continuous steel belt, moved bymotorized rollers and cooled by an oil box with a convexsurface against which the belt maintained fric~ional contact,was considered. The condensate was to be removed by ablade adjacent to one of the rollers (Fig. 7). As this designturned out to be too difficult to realize on a small scale, it wasreplaced by another that made use of an oil-cooled steel diskequipped with a mechanical means of scraping off thecondensate. Fig. 8 shows the two main systems that wereused during the experiments. In the design illustrated inFig. 8(a) the steel disk rotated and the deposit was scraped

A5

t

E~

5

Fig. 7 Continuous condenser for magnesium-unused first design:A, continuous steel belt; B, motor-driven rollers; C, oil box forcooling; D, blade to scrape condensate from belt; E, condensate

C107

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-, ." -. -'",--.~~

E

c "-----S-F

G

(a)

. ~'-,,"' ~-,.-. - '.. - -- ~--

D-----------------

~ H

(b)

Fig. 8 Oil-cooled steel condenser designs: (a) with rotating cooling box-A, rotating disk; B, oil in; C,oil out; D, gases from furnace; E, gases out to pumping system; F, scraping pins fixed to wall; G, scrap-ing pins fixed to rotating disk; H, to condensate recovery; (b) with fixed cooling box-A, fixed coolingbox; A " steel honeycomb structure to increase resistance to heat transfer; B, oil in; C, oil out; D, gasesfrom furnace; E, gases out to pumping system; F, rotating scraper blade (can be moved to scrape wall orcondenser surface); H, to condensate recovery

off by pins attached radially to the wall of the condenser box.Other pins were added to the rotating disk itself to clear thepath of the condensate to the storage bin. This system wasfound to be unsuitable. The surface of the steel disk did notremain sufficiently flat during the runs owing to thermalexpansion and the pressure difference between the oil-coolingsystem and the vacuum in the furnace. The pins were eithernot strong enough and bent during runs or prevented the diskfrom rotating. It was impossible to obtain condensationtemperatures in excess of 250°C without oil leakage andconsequent risk of fire. In the alternative design (Fig. 8(b»the oil-cooled box did not rotate and its surface was fittedwith a steel honeycomb structure to increase its resistance toheat transfer. The scraping system consisted of a rotatingsteel blade that could be moved in a direction parallel to itsaxis to scrape either the surface of the condenser or the wallof the condenser box.

It should be added that the outlet, H, of the condenser boxwas equipped with two exhaust valves in series. The first wasto prevent the hot condensate from contacting the second,which had to be vacuum-tight. At first, condensate was re-covered in covered storage bins, but the system was toodangerous and the bins were replaced by movable furnacesdesigned for induction melting in graphite crucibles underinert atmosphere.

Charging and discharging systemsThe charge for the experiments performed on a semi-pilotscale consisted of pellets 15 mm in diameter. -These wereprepared at Vieille Montagne, at first from highly impuremagnesia (87 wt% MgO, 2.0 wt% CaO, 3.4 wt% Si°z,4.7 wt% AlZ03, 3.0 wt% FeZ03) and crushed metallurgicalcoke, and had an atomic C/Mg ratio of unity. Water wasadded for initial binding. After drying at 500°C in a separatefurnace the pellets were sufficiently strong to handle, butwere brittle. Owing to partial sintering in the furnace atreaction temperatures, which caused clogging, a purer formof magnesia was tried (95 wt% MgO, 0.5 wt% CaO, 2.4 wt%SiOz, 0.7 wt% AlZ03' 0.8 wt% FeZ03)' Sintering then ceasedto be a problem. It was also decided to continue withmagnesia rather than calcined dolomite so that magnesiumcondensation could be studied under the best conditions.

CI08

\..

The pellets were introduced at the top of the furnacethrough a side vacuum lock. The ashes and any unreactedmaterial were recovered at the bottom of the furnace bymeans of a rotating partitioned box leading to a storage binvia two exhaust valves in series, as for the condensate.

The heating part of the furnace was rectangular in shape,with internal dimensions of 0.23 m x 0.46 m in section and1.5 m in height. The internal refractory lining was made fromRadex pure magnesia bricks. Thermal insulation -wasprovided by Belref Isomul C bricks and Belref insulating slab1000. Heating was by graphite resistors machi,ned fromUnion Carbide AGLX-58 plates, each capable of an outputof 12 kW at 1800K. Four resistors were positioned in thecharge and a fifth was later added above the charge to avoidany condensation or back-reaction at the level of thecondenser inlet. Each resistor (Fig. 9) was fed separately byan Arcos TO 600 transformer-rectifier, the current feed tothe resistors being water-cooled.

",:"--'...~;:-;,

ii~.~." ',yF "', .. .._~-,- ........

Fig. 9 Graphite resistor and its water-cooled current feeders

Peripheral equipment included water-cooling for the oil(Monsanto, Santotherm 66) leaving the condenser and thepumping system. This comprised two cyclones in parallel,each followed by two filters filled with ceramic rings, aLeybold WA 2000 Roots pump and a Leybold E 250 rotary-piston primary pump. The Roots pump started automaticallyas soon as the pressure dropped below 40 mm Hg. Pressurewas measured by a thermistor at the entrance of the Roots

A' AI

E--c

!L'.:::'::",,,,,,"-

- ..~ "T E~. - -

~~ -- ~. --"-- . ~-~..........

pump and, occasionally, by a Kamerer gauge in thecondenser box.

A schematic layout of the semi-pilot scale plant ispresented as Fig. 10 and different views of the plant areshown in Figs. 11-14.

CF

DCF

R

Fig. 10 General layout of semi-pilot scale plant: F, furnace;E, loading vacuum lock; R, heating resistors; D, unloading rotatingbox; UVS, unloading vacuum lock and storage bin; CF, coke filter(only used for last experiments); C, condenser; DC, condenserunloading system with vacuum lock; Cy, cyclones; Fi, filters;PR, Roots pump; PP, piston pump; B, CO burner

Fourteen runs were performed, each lasting from one tothree weeks. After the first three runs it was decided toprovide the equipment with a fifth heating resistor in front ofthe condenser, with a second cyclone and filter and withviewing windows. Runs 4, 5 and 6 were difficult because of alack of vacuum-tightness, and a helium leak detector wasbought. Run 7 showed that the cooling oil was always toocool, with the consequence that the condensing temperaturewas always too low, resulting in the production of a black,pyrophoric condensate that contained elongated, metalliccrystals. Accordingly, the oil circuit was modified to include aheating system.

Run 8 was the first in which more or less steady conditionswere achieved at 0.4 mm Hg (corresponding to an estimatedPea of 2 mm Hg in the furnace) and at an oil temperature inthe condenser of 230°C. The condensate obtained underthese conditions was of poor quality, containing only 36 wt%

metallic magnesium with 15 wt% C and 49 wt'\'o MgO. Theproduction rate of condensate was in the order of 0.15 kglh.

Run 9 demonstrated that thermal expansion and oil

Fig. 11 View of semi-pilot scale plant showing charging system andupper part of furnace

II

leakage rendered it impossible to raise the temperature of thecondenser cooling oil to 250°C. It also established that therotating condenser and its pin-based scraping system wereinefficient. Very hot plates or droplets of condensate (at aminimum 600-700°C) were observed to fall in the remeltingfurnace during scraping. This meant that condensingconditions could not be considered as precisely known. Toimprove this state of affairs the rotating condenser wasreplaced by a fixed condenser provided with a steel honey-comb to increase its resistance to heat transfer and with ascraping system in the form of a rotating blade.

In Run 10 more or less steady conditions were obtained at0.7-1.1 mm Hg (estimated Pea of 3.5-5.5 mm Hg in thefurnace) with a condensing temperature (at the condensersurface) of 230-300°C. The quality of the condensate wassomewhat better, at 55-62 wt% metallic magnesium with8 wt% carbon. The production rate of condensate was in therange 0.6-1 kglh.

For Run 11 a different steel honeycomb structure wasattached to the surface of the condenser to enable highercondensation temperatures to be reached. The attempt wasnot successful because of air leakage.

In Run 12 steady conditions were obtained at 0.5-1 mmHg (estimated Pea in the furnace, 2.5-5 mm Hg) with acondensing temperature of around 350°C. The condensatewas again better: 70-75 wt% metallic magnesium with5-8 wt% carbon. The rate of condensate production was inthe range 0.3-0.5 kglh.

Runs 13 and 14 were performed after a heated coke filter(CF in Fig. 10) had been inserted between the furnace andthe condenser. The purpose was to convert to CO any CO2that might have been produced in the upper part of the fur-nace owing to air leaks. The heating resistor was similar to

Fig. 12 View of semi-pilot scale plant showing condenser withstorage bins and two cyclones

CI09

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Fig. 13 View of semi-pilot scale plant showing loading andunloading systems

the others and raised the temperature in the coke filter to1100°C. Because of clogging problems in the filter it was onlypossible to realize steady conditions at a vacuum of 0.7-1 mmHg (3.5-5 mm Hg estimated Pea in the furnace) with acondensing temperature of about 200-220°C. Thecondensate, which was produced at a rate of 0.3-0.4 kglh,contained 70-80 Wt°jo metallic magnesium. There was,accordingly, some improvement in its quality, but this did notcompensate for the new clogging problems introduced by thecoke filter.

The main results obtained during the 14 runs are summa-rized in Table I, and Fig. IS shows a typical platy fragment ofcondensate as recovered before melting.

It can be concluded that increasing the temperature of thecondenser improved the quality of the condensate and alsothat the heated coke filter gave further improvement. It

Table 1 Main results obtained during semi-pilot scale runs

,'~-" ,-~.- ---~-- "- - m.~

,"."..,- >T--- ~~.- "--.~,~

= ", - -

~1'1

Fig. 14 View of semi-pilot scale plant showing pumping system

Fig. 15 Typical platy fragment of condensate as recovered fromcondenser before 'melting' (approximately actual size)

Equipmentcharacteristics

Estimated Peo infurnace, mm Hg

Condensertemperature, °C

Production rate of

condensate, kglhMetallic Mg incondensate, wt"/.

Rotating-diskcondenser

>230 0.152

Fixed condenserwith insulation*

3.5-5.52.5-5

230-300350

Asfixed condenser plusheated coke filter

3.5-5 200-220

*Two rows refer to two different steady-state conditions achieved during runs.

ClIO

36

55-6270-75

0.6-1.00.3-0.5

70-80 0.3-0.4

.. .;i. .. ~ - ~-.;....,,=--""-,~~ '~"''''' -----

appears, however, that it would be difficult to obtain betterresults than those described so far. To increase the tem-

perature of the condenser further it would be necessary toincrease the production rate of the furnace, but when this wastried it resulted in dramatic clogging everywhere-not only inthe heated coke filter but also in the cyclone-filter systemleading to the pumps or, after a time, in the pumps them-selves. Moreover, after 'melting' most of the condensateremained as a powder that contained some droplets ofmetallic magnesium (Fig. 16).

Fig. 16 Droplets of metallic magnesium recovered after 'melting' ofcondel)sate (approximately actUal size)

Accordingly, it was decided to investigate the possibility of

sublimating magnesium from the condensate prior to re-melting. This was done, at laboratory scale, in a resistance-heated furnace that contained an oil-cooled condenser and

was more or less similar to that illustrated in Fig. 3.

Sublimation was performed on 600 g condensate with acontent of 75 wt% metallic magnesium, a pressure of about0.2 mm Hg being maintained in the furnace. The tem-perature of the crucible varied between 300 and 560°C andthat of the condenser between 190 and 300°C. Condensation

efficiency was about 94 wt%, the condensate produced beingmainly metallic magnesium (with 2.4 wt% carbon and 1 wt%oxygen) .

Fig. 17 shows a typical sample of the condensate obtainedby sublimation. This metal is suitable for melting, includingsome production of dross.

Fig. 17 Magnesium condensate after sublimation under vacuum

At this stage a fresh economic evaluation of the processwas made, the possible technical answers to the operatingdifficulties encountered-including the additional sub-limation stage before melting-being taken into account. The

re-evaluation was based on the use of calcined dolomite,exhausted at 75%, with 20 wt% coke in excess of stoichio-metry; and energy consumption was taken to be 17.4 kWh/kgMg produced (12.4 to heat the furnace; 2.2 for pumping; 0.1for p~lletizing; and 2.7 for sublimation and remelting).

The conclusions were that, despite the sublimation stage,the process could still be competitive with the Magnethermprocess, but that the potential advantage was insufficient tojustify further investment in research and development owingto the technical difficulties encountered. The final decisionwas to halt the research.

Conclusions

A study was made of the technical and economic feasibility ofa process incorporating the vacuum carbothermic reductionof calcined dolomite to produce magnesium.

Thermodynamic calculations had indicated that theprocess, with recovery of magnesium as a solid, was possiblewith Pea in the kinetically interesting range 0.1-5 mm Hg.These estimates were confirmed in a laboratory-scaleapparatus, from which condensates containing 75-85 wt%magnesium metal were obtained with less than 0.5 wt%calcium contaminant.

At semi-pilot scale, however, technical difficulties wereencountered in keeping the equipment vacuum-tight,avoiding clogging problems and maintaining constant condi-tions. Under optimum conditions condensates containing70-80 wt% metallic magnesium were obtained, but at a rateof production that was lower by a factor of eight than thatexpected. It was necessary to add a sublimation stage beforemelting the recovered magnesium.

Finally, an economic evaluation of the process demon-strated that although it was still competitive with theMagnetherm process, it was insufficiently so to pay forfurther investment in research and development, and a finaldecision was taken to halt the research.

Acknowledge~ent

The authors wish to thank Vieille Montagne S.A. for financialsupport and also for permission to publish the results of theresearch.

References1. Ullmans Encyklopadie der technischen Chemie, 4th edn (Weinheim:Verlag Chemie, 1978), vol. 16,319-29.2. Ullmans Encyklopadie der technischen Chemie, 3rd edn (Miinchen:Urban und Schwarzenberg, 1960), vol. 12,95-6.3. Elkins D. A. Placek P. L. and Dean K. C. An economic andtechnical evaluation of magnesium production methods (in threeparts). 2: Carbothermic. Rep. Invest. U.S. Bur. Mines 6946,1967.4. Elkins D. A. Dean K. C. and Rosenbaum J. B. Economicaspects of magnesium production. Paper presented to AlMEExtractive Metallurgy Division operating conference, Cleveland,Ohio, Dec. 1968.5. Kn6fier O. and Ledderboge H. German Patent 49329,1889.6. Kirk R. C. U.S. Patent 2257910, 1941.7. Cameron A. M. et al. Carbothermic production of magnesium.In Pyrometallurgy '87 (London: IMM, 1987), 195-2228. Khazanov E. 1. Tr. Vost.-Sibirsk. Filiala, Akad. Nauk SSSR, 43,1962,95-111. (Russian text)9. Khazanov E.!. Tr. Vost.-Sibirsk. Filiala, Akad. Nauk SSSR, 24,1959, 143-59. (Russian text)10. Gulyanitzkii B. S. and Chizhikov D. M. Izvest. Akad. NaukSSSR, Otdel. Tekh. Nauk, 11, 1955, 13-24. (Russian text)11. van Gysel M. Etude des possibilites d'elaboration du magne-sium a partir de la dolomie par reduction sous vide par Ie carbone.Metallurgical engineering degree thesis, Universite Libre deBruxelles, Department Metallurgy-Electrochemistry, June 1973.12. Barin 1. Knacke O. and Kubaschewski O. Thermochemicalproperties of inorganic substances (Berlin, etc.: Springer), vol. I, 1973;vol. II, 1977.

Clll

-, .- " >.' ,~- -- .. ,-,. '" "~~-,~ .' - -"" -~ '" ~ - .~-- ~. .~ iiiiiiI

Authors

R. Winand Fel/ow obtained the degrees of M.Eng. and Ph.D. inmetallurgy in 1954 and 1960, respectively, from the Universite Librede Bruxelles, Belgium, where, since 1968, he has held the position ofhead of the Department of Metallurgy-Electrochemistry.

M. van Gysel graduated in metallurgy from theUniversite Libre deBruxelles, Belgium, in 1973. He is currently working for IDE S.A.,Rochefort, Belgium.

A. Fontana was awarded a Ph.D. in metallurgy from the UniversiteLibre de Bruxelles, Belgium, in 1969. Formerly associate lecturer inthe University's Department of Metallurgy-Electrochemistry, he isnow a professor and head of the Department of General Chemistry atthe same University.

L. Segersobtained the degrees of M.Eng. and Ph.D. in metallurgyfrom the Universite Libre de Bruxelles in 1978, where he is now alecturer.

J.-C. Carlier gained the degree ofIngenieur civil metallurgiste fromthe Universite Libre de Bruxelles in 1975. He is currently head ofresearch and development at Formetal, Herstal, Belgium.

MMIJ/IMMJoint Symposium

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Papers presented at the MMIJ/IMMjoint symposium held in Kyoto, Japan,from 2 to 4 October, 1989

Sixty-seven papers grouped into sections devoted tohydrometallurgy; mineral economics; new technologyin exploration; rock engineering, including undergroundtechnology; separation and mineral beneficiation;automation and monitoring in mining, including minesafety; recent development of new materials process-ing technology in Japan; and pyrometallurgy

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RecyclingofMetalliferousMaterials

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Papers presentedat the Recyclingof MetalliferousMaterialsconference,organizedbyThe Institutionof MiningandMetallurgyandheldin Birmingham,England,from23to 25April,1990

296 mm x 208 mm, 333 pagesPublished in May, 1990

ISBN 1 870706 18 8Price £42.00

Orders, with remittance, should be addressed to:The Institution of Mining and Metallurgy, 44 Portland Place, London W1 N 4BRTelephone: 071-580 3802 Telex: 261410 IMM G Fax: 071-436 5388

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