1-s2.0-089268759500048U-main

Minerdr Engineerin& Vol. 8, No. 8, pp. 859-870, 1995 Cotwtiebt Q 1995 Elsevier Science Ltd Pergamon

0892-6875(95)00048-8 Printed’i &at Britain. All rights reserved

0892-6875/95 [email protected]

ULTRAFINE TANTALUM RECOVERY STRATEGIES

P -_--___-iJ. .__I R.O. BUKTS,G.BORi~~Kt,S.K. YOUNG 1 and C. DEVFAUT

0 Tantalum Mining Corporation of Canada Limited, Box 2000, Lac du Bonnet, Manitoba, Canada ROE 1AO

t Tantalum Niobium International Study Centre, Rue Washington 40, 1050 Brussels, Belgium

(Received I August 1994; accepted 4 April 1995)

ABSTRACT

The Bernie Lake mine of the Tantalum Mining Corporation of Canada is the largest producer of tantalum concentrate, high purity spodumene, as well as cesium and rubidium ores, in North America. Tantalum is one of the “high-tech” materials, and some of its applications are briefiy discussed.

Tantalum recoveries have consistently been in excess of 70%, from ores grading less than 0. IT0 Tazi2> The prnnary target for increased recovery ts tn the ubra J#ne size ranges.

This paper discusses ultrafine recovery strategies which have been attempted, including flotation and “slime” gravity concentration devices such as Battles-Mozley Separators and Crossbelt Concentrators. Testwork has now been carried out on the new generation of fine gravity devices; centrifugal separators. Data from four such devices - Mozley Multigravity Separator, Kelsey Jig, Falcon concentrator and Knelson Concentrator - have been compared with the existing technology, which has resulted in modifications to the ftne tantalum recovery circuit.

Keywords, Gravity co~ncentration, tantalum, Tanco, centrifugal concentrators, Mozley MGS, Falcon Concentrator, Crossbeit Concentrator.

INTRODUCTION

Exploring for gold around the north shore of Bernie Lake in 1929, Jack Nutt found tin instead. In the resulting diamond drilling programme the blind Bernie Lake pegmatite was discovered. Its tin content was too low to be of interest, and its lithium content being of no value, the deposit lay dormant until the 1950’s, when the requirement for lithium brought renewed interest. At that time, not only the lithium, but also the cesium, rubidium, beryl and tantalum potential was discovered; however it was not until the tantalum capacitor had been developed that mining commenced.

Tantalum, a member of the refractory metals group, has a very high melting point (2,996OC) and density (16,600 kg/m3). In an oxidizing environment it forms a tough, adhesive, impermeable film which, when applied anodically has outstanding dielectric properties. Tantalum is very ductile, and it can be worked hot or cold; by reaction with carbon it forms a very stable carbide. These properties are the basis of all major applications of tantalum.

Presented at Minerals Engineering ‘94, Lake Tahoe, USA, September 1994

859

860 R. 0. BURT et (11.

Electronics. The electronics industry accounts for about 60% of annual tantalum production of about 3 million pounds, in the form of powder, wire, or furnace hardware for the production of tantalum capacitors.

The first applications of tantalum capacitors were for the military and aerospace fields, but today all rr\mnlltPr cvctemc electronic devices in telecormnunications, VCRs, radar and other commnrt l=ll=rtrnnir ‘“..Li.,-‘V’ ‘, “._......, rl-- _.VV...,..._ devices use tantalum capacitors. The automotive industry has become an important consumer of tantalum capacitors: their unique ability to withstand the substantial temperature fluctuations that occur under the hood of a car (from -5OOC to +8OOC) without deterioration make them the capacitor of choice.

The ability to sinter tantalum to predetermined sized anodes, the high purity of the powder and its unique porous structure allow very high values of capacitance, not only by weight, but also by volume. This is of critical importance in the ever increasing trend of miniaturisation, and has resulted in close to a threefold increase in tantalum capacitor shipments over the last eight years (from 3.57 billion units to 9.14 billion). Tne fastest growing is the small sized, su~ace mouniable, chip_ca~accitor,

Hard Metals. The addition of tantalum carbide, usually in conjunction with titanium carbide, to hard metals of the WC-Co type allows cutting of steel at significantly higher speeds, thereby improving economy of metal removal. Whereas small amounts of TaC (0.2-0.3%) were added as grain growth inhibitors to many hard metal grades, it is the special grades containing 3-8% TaC which account for the majority of 380,000 lbs of tantalum used in hard metals.

Equipment construction. Tantalum is one of the most corrosion resistant metals; such resistance is based on its formation of a tough, adhesive, impermeable oxide film. Its excellent ductility, high degree of thermal conductivity, good strength and rigidity permits construction of almost any type of equipment. Bayonet heaters, heat exchangers, tubing, coils, tantalum clad reaction vessels for highly corrosive environments (e.g. sulphuric acid) are the main products. Total inertness to human body fluids is responsible for its medical application as surgical staples, plates and others.

High temperature applications. Tantalum, doped with less than 100 ppm of silicon, yttrium or thoria to prevent grain growth, is used for the manufacture of furnace parts such as heat shields, trays, etc, which can be onerated at above 2000°C. Alloys with tungsten (9OTa-1OW and 97.5Ta-2,5W being the most -r------- P ---- ------ common) are stronger than pure tantalum at high temperatures and find their application mainly in aerospace.

Ballistics. The combination of high ductility and high density forms the basis for the recent application in anti-armour weapon systems, being used as a liner in the long, armour-piercing high kinetic energy penetrators.

Tantalum superalloys. The higher the operating temperature of a jet engine, the better its performance and * ̂ .... I*:..” F..,, ,F4Z”:,..,... IX, nnn..-..1nt:,.. ,.F :-....‘-:t:,, A :-...a.F-~+:,..” .-.* 4.a . . . . . ..*..I I. _.._ A....i-- ,c ,c;sulnllg l”rjl GlllLlrjrlL#y. lllci LIbbLJIIIUILIII”II “1 mlp”“L’Ki aiiu IIqJGLIGbLI”IIJ LLL LUG uy>ku ““UI,Ual,GS “1

normal polycrystalline metal structures limits metal strength at these high temperatures. The development of single crystal turbine blades is allowing the engine designer to significantly increase thrust to weight ratio with resultant increased fuel efficiency and reliability. Up to 12% tantalum is used in these single crystal alloys.

PREVIOUS STRATEGIES FOR FINES RECOVERY

Tlle Bemic iake orebody is a complex, zoned, pegmatite containing economic reserves of tantaium, iithium, cesium and rubidium. The major tantalum minerals present in the tantalum zone are wodginite, microlite, pseudoixiolite, simpsonite and tantalite: ranging in density from 6,500 to 7,200 kg/m3 and liberated essentially at 150 micrometres. Their response to gravity concentration is similar. Hence, for simplicity the various tantalum bearing minerals are collectively referred to as “tantalum” in this paper. Tantalum was essentially Tanco’s only product from 1969 to 1982, when poor markets resulted in the mine’s closure. Attention turned to the high grade, low iron spodumene reserves; mining of this commenced in 1984, and

Ultrafine tantalum recovery 861

Tanco is now the world’s largest producer of high grade spodumene concentrates. Cesium mining, which was carried out in, a desultory fashion prior to the mid 80’s is also increasing in importance. Tantalum mining recommenced in 1988, but was again shut down in 1992; however stockpiled tailings have been reprocessed in the summers of 1993 and 1994. Some tantalum is also recovered on an ongoing basis as a by-product from the spodumene circuit.

The original flow.sheet did not include any equipment for recovery of -30 micrometer tanta!um; this deficiency was soon realised and pilot plant testwork on a Denver-Buckmann table was carried out, but with little success. In 1975, the first slime plant was installed, with six Battles-Mozley Separators treating main plant tailing, screened at 50 micrometer, with the rougher concentrate being upgraded to 30% Ta,O, on two stages of Holman Tables. The second stage Holman tables were replaced by a Bartles Crossbelt concentrator in 1977, with tantalum flotation partially replacing the gravity circuit in 1980.

The float circuit was abandoned when the tantalum plant restarted after the 1983-8 closure, high operating cost and low concentrate grade making it less cost effective than a full gravity circuit. The slime plant feed preparation circuit was improved [l], enhancing performance. The slime plant flowsheet at the commencement of the current project is shown in Figure 1.

Various other concentration strategies for ultrafine tantalum recovery have been attempted on a bench scale, including high gradient magnetic separation and oil phase extraction: however, in neither case did the results warrant pilot scale testwork. The new generation of centrifugal separators gave the needed impetus to turn, once again to rese.arching gravity concentration devices.

Slime Plant Flowsheet, 1992

1 150 mm cyclones 2 Stokes Hydrosizer 3 Holman Tables w 4 Bartles-Mozley Separator 5 Mozley cyclones 6 Bartles Crossbelt Concentrators

Fig.1 Slime Plant Flowsheet, 1992

CENTRIFUGAL SEPARATION

The use of centrifugal force to increase the settling rate of particles has been successfully applied for many years, for classification in hydrocyclones, and for dynamic heavy medium separation.

Thp ~di~~t LWW~I rpntrifiloll ~+~itv rnn~~ntratnr wcx tm~ntd hv PP& in 1RQl r31 hd tdd~d~ littb I‘&” “_.IV.,I &.I.“..*. w-.1.. “..~.a 6’““‘J -.,..-w ..I. . ..“I I...” y”‘-“‘v.” YJ _“_.. . . . -v/l L’J, “I. ‘~....“...‘J . . . . . I was known of the technology in the west until about 20 years ago. However, centrifugal separators were developed in the (then) Soviet Union in the 1950’s and were also in use in China by 1960. The earliest

862 R. 0. BURT et ul.

scientific study into centrifugal separation was by Ferrara [3], who studied what has become known as Ferrara’s tube; a 20 mm diameter perspex pipe 1100 mm long rotating at up to 2,200 ‘pm. While results were very encouraging, the obvious mechanical difficulties inherent to the design mitigated against any commercial application.

Centrifugal concentrators can be divided into three basic types: vertical axis machines and their sub-set, centrifugal jigs, and horizontal axis machines.

Vertical Axis Units: All vertical axis units were originally developed for the recovery of fine alluvial gold. Typical devices include the Gilkey Bowl, the Knudsen Bowl Centrifugal Concentrator, the DTsS Refining Centrifuge and the Dual Hydrofuge Concentrator.

The Knelson Concentrator, first introduced as a semi-batch unit in 1982, has gone through several iterations of design, leading to the development of a continuous discharge machine [4]. All Knelson Concentrator models consist essentially of a conical drum with a series of parallel “Vee” shaped riffles. Centrifugal force ..,h;ph ot 3-n tn fCiI,-. C.C,I,PPC thn nnrt;rlm tn h- rlr;rmn tn thn hnt+r\m fif the Affl P” ;” ..n..+;nll.r n,.~...*s..,.~taA vv,1,~.,) LL% Lay &” vvg, CUU~UU %R.Y yuLu”Iuu b” VW UlllUl. C” UIU ““LL”l‘l “I UlL. 11111b5 ,a pumlllJ ~““,‘IE;IaLI~u

by hydrostatic water injected into the bedding to form a fluidised bed. The concentration mechanism can, therefore, best be likened to a hindered settling classifier [5,6]. It is almost exclusively used within gold grinding circuits, rather than for ultrafine recovery. Although Forssberg and Nordquist [7] suggest the ability of the Knelson to recover -37 pm particles is poor, Laplante suggests this may be a function of particle shape, rather than size [6].

Unlike the Knelson, the rotating drum of the Falcon concentrator is smooth walled and there is no back-flow of water. The drum is approximately twice the length of it diameter, tapering over the majority of its length, and paraiiei sided &se to the discharge, or top, of the drum, with a short inwardly tapering section at the very discharge. The batch unit tends to pack fairly quickly, unless well controlled; a continuous discharge unit has been developed which it is claimed will overcome this limitation [8]. Concentration mechanism has been likened to the Reichert Cone with high recovery and low enrichment ratio, and with the double- recovery peak first described by Harris [9]. Typical data indicates that the Falcon is best suited for the treatment of fine, dilute pulps. In gold circuits, therefore, it tends to be used on cyclone overflows; that is, more akin to Tanco’s requirement.

Centrifugal Jigs: The only known commercially available centrifugal jig is the Kelsey Centrifugal Jig. It is effectively a standard jig, wrapped into a cylinder and rotated on a vertical axis, and is more suited to fine sands than ultrafines. Development work utilized mineral sands; it was successfully applied in the pilot plant for a large, fine grained (-loo+50 l,trn) heavy mineral sands project in Australia, but no details are available. The first successful commercial installation was at the Renison tin mine in Australia [lo].

Horizontal Axis Units; Centrifugal separators are widely used in China, with reported applications not only for gold, but also for iron, tin and tungsten. They consist essentially of a tapered drum (3-loo taper) rotating at approximately 400-700 rpm. Reported capacity and performance of typical units are of the same order as the BM Separator [ 111.

The Mozley Multi Gravity Separator (MGS) “may be visualised as rolling the horizontal surface of a conventional shaking table into a drum, then rotating it” [ 121. The drum’s axis can be inclined to about 100: a sinusoidal shake is superimposed on the drum in an axial direction. The diameter of the drum tapers at lo increasing from the high (concentrate) end to the low (tailing) end. Feed enters the unit about half way down the cone. Heavies, which settle to the revolving drum, where they are moved counter-current to the flow by scrapers moving at a slightly higher speed than the drum, are subjected to a counter-current wash prior to being scraped out of the cone. Lights and water flow down the cone to a separate launder.

The pilot plant unit has one single, 470 mm (average) diameter drum; the mine scale unit has two horizontally opposed 1,220 mm (average) diameter drums to minimise vibration.

Unlike other centrifugal concentrators, the majority of the development work has been carried out on tin

Ultrafine tantalum recovery 863

ores, with excellent results especially in ultrafine recovery, including the replacement of flotation column

[131.

RRNCH SCAT I?. Tli!il.CTWnRK --..___ --rr-d- _--- ., -____

The flowstream chosen for bench scale testwork was the Bartles-Mozley Separator feed, typically 45% finer than 12 micrometres in size. A bulk sample was taken over a four week period. Half was sent to McGill University who carried out bench scale testwork on the Falcon and Knelson concentrator. Half to Carpco Inc. for testwork on the Kelsey Jig and Mozley MGS. During the sample collection period the Bartles-Mozley separators were fully sampled as a control. All analytical work was carried out by Tanco.

Results are summarised in Figure 2. Based on this, the Knelson Separator and the Kelsey Jig could be discounted from any further consideration. Both the Moziey iviGS and the Faicon out-performed the existing Bartles-Mozley selparators. Single pass MGS results were superior to the two pass Falcon test, and the MGS was, therefore, chosen for further, on stream, study and a unit was rented from Carpco Inc. Further laboratory scale testwork on the Falcon Concentrator was also carried out, at McGill University.

Compararison of slime separators

E n r I

i m a n t

R a

! 0

PILOT PLANT TESTWORK

As a result of other plant testwork, two circuitry changes were made for the 1994 tailings retreatment campaign. To improve classification in the slime plant the overflow of the primary 150 mm cyclones was diverted to the secondary bank of 150 mm cyclones. This had the desired effect of minimising tramp oversize passing to the Bartles Mozley Separators; however feedrate to the 12 Holman tables increased to close to 5 tonnes per hour which has probably slightly overloaded the tables. The Barties Moziey Separators were later replaced with a bank of Mozley 50 mm cyclones, upgrading of the Mozley cyclone underflow being effected by ‘two stages of Bartles Crossbelt concentrator. Typical size distribution of Holman table and Crossbelt concentrator feed is shown in Figure 3; even after “desliming”, the feed to the latter still contains close to 40% -10 micrometre material. Mozley cyclone overflow is 100% finer than 10 micrometre.

864 R.O. BURT et al.

Slime Plant size distributions

C U m

%

75

50

25

20 30

Size, micrometre Equivalent Quartz spheres

Fig.3 Slime Plant Size Distributions

The MGS separator was first tested in parallel with the Battles Crossbelt concentrators. Considering the fineness of the feed, the shortest stroke length (10 mm) was used throughout the test programme. Rotational speed, an increase of which will increase the centripetal force on the particles, was determined to be the critical control. Small increases of speed significantly increase recovery, while decreasing enrichment ratio (Figure 4); at low speed there is insufficient “g” force to pin the fines to the drum. Recovery decreases with excess drum speed; above the optimum speed it is probable that the increased axial flow toward the tailings launder becomes the dominant factor, rather than centripetal force [14], and fine material is peeled away from the bed. The sensitivity of the MGS to changes in drum speed is in agreement with Tucker and others [15]. Indeed the rate of change is so significant that it could have a detrimental effect on product consistency unless close control of the unit is maintained.

70

Effect of Drum Speed Crossbelt feed

10

I I '0 195 200 205

Drum rpm

Fig,4 Effect of Drum Sneed Crossbelt Peed -r--- _-_LL_--. Increasing the tilt of the axis of rotation results in a faster flow of pulp through the machine. To counteract this higher drum rotational speeds are required to achieve recovery.

Ultrafine tantalum recovery 865

On this exceedingly fine feed, feed characteristics are of major importance. Both excess solids flowrate and excess pulp density have a deleterious effect on unit performance (Figures 5 and 6); maintaining other parameters constant it would appear that recovery decreases essentially linearly with increased feedrate.

Effect of solids feedrate Crossbelt feed

75 6

l5 -@- Recowy -# Enrichment Ratio

0 I I I 1 0 15 30 45 60 75

feedrate kglhr

Fig.5 Effect of Solids Feedrate Crossbelt Feed

Effect of pulp density Crossbelt feed

60 5

R 40 -......................................... e C 0 30 _ V e

; 20 _ .._..._._._......._........................... \ .t.............................................. \ n

t L

10 -' ?? Recovery -1 . . . . . . .......i + Enrichment Ratio

\ 0 I I Cl 10 15 20 25

Feed % solids

Fig.6 Effect of Pulp Density Crossbelt Feed

The optimum recovery is of the order of 60%, which compares very favourably to the performance of the Crossbelt concentrator, with typical recovery of 2530%. Not only does the MGS recover finer material than the Crossbelt (Figure 7), it outperforms the Crossbelt throughout the whole size range. However, it should be noted that the Crossbelt is normally applied as a cleaner unit rather than as a rougher, and the relatively poor recovery throughout the size range may be related to feed grade.

866 R. 0. BURT et 01.

Recovery versus particle size Crossbelt Feed

t MGS

- Crossbell

0 10 20 30 Size, micrometre

40 50

Fig.7 Recovery Versus Particle Size Crossbelt Feed

A series of tests was also carried out on the Holman table feed, again treating drum speed as the main control. While recoveries can exceed 90% it is at the expense of enrichment; to achieve an enrichment in excess of 10, recovery is 67% (Figure 8); equivalent Holman table recovery is less than 40%. The ability of the MGS to recover fine tantalum particles more effectively than the Holman table is, again, a primary factor in it’s superior performance (Figure 9), although overloading of the Holman tables may have been a factor.

Performance of MGS Holman table feed

01 I I 10 165 170 175 180

Drum rpm

E n r I

m e n t

Fig.8 Performance of MGS Holman Table Feed

Ultrafine tantalum recovery

Recovery versus particle size Holman table feed

667

6

J 0 IO 20 30 40 50

Size, micrometre

Fig.9 Recovery Versus Particle Size Holman Table Feed

Additional testwork carried out with the Falcon concentrator at McGill University [ 161 confirmed the earlier results, showing that to achieve acceptable recovery, several passes through the unit are required. A series of tests at low and high flowrate treating a low and high quantity of feed showed that optimum performance resulted from treatment of a higher quantity of feed at a lower flowrate; nevertheless, three passes through the unit were required to achieve a recovery in excess of 35% (Figure 10). Falcon Concentrator feed had not been deslimed by the Mozley cyclones; hence a recovery of 35% compares fairly reasonably with that of the MGS. However, a fairer comparison is between the first stage of the Falcon, and the MGS: here there is little doubt that tbe MGS is superior. Comparing recovery by size (Figure 11) of the two units is a further indication of the superior performance of the MGS.

Three Stage Falcon Concentration 9

E n 6 r i C h m e

: 3

;t -k First r- * second

0 Third

0 25 50 75

Recovery %

Fig. 10 Three Stage Falcon Concentration

100

868 R. 0. BURT et (11.

Recovery versus particle size Falcon and MGS

0 I I I

0 10 20 30 40 size, micrometre

Fig.1 1 Recovery Versus Particle Size Falcon and MGS

FUTURE STRATEGY

With the circuitry changes that had been made, the total flowrate to the Crossbelt concentrators is now of the order of 0.5 tph, at a typical feed grade of 0.1% Ta,O,. Even if it is accepted that the increased recovery achieved by the MGS can be maintained during upgrading of the rougher concentrate, the potential increase in production of about 2,500 lbs/year of tantalum does not warrant the cost of replacing the Crossbelt concentrators with a Mozley MGS. However, the Holman table feedrate is of the order of 5 tph, grading of the order of 0.07% Ta,O,; as, on recycled tailings at least, the Holman table recovery rarely exceeds 35%, this flowstream has more potential for the MGS. Assuming that the increase in recovery achieved by the MGS can be maintained during upgrading to saleable concentrate grades, there is the potential to increase tantalum production by as much as 15,000 lbs per year. Even at current tantalum prices (US$25 per pound) the economics of the replacement of the Holman tables by the MGS is attractive, and will be seriously considered for future tails reprocessing campaigns.

A potential flowsheet incorporating the Mozley MGS is shown in Figure 12. While no testwork has to date been carried out on the upgrading of the rougher concentrate produced by the Mozley MGS, it is probable that performance of the Holman tables, with a much lighter loading, will improve and they will be suitable as MGS cleaner units, especially in closed circuit.

CONCLUSIONS

Thirty years ago, recovery of particles finer than 20 micrometres would be regarded as exceptional. The development of the Battles Mozley concentrator and Bartles Crossbelt concentrator in the ’60s and ’70s reduced the bottom size of effective recovery to about 15 micrometres.

However, the efficient recovery of ultrafine oxide minerals, such as tin and tantalum is the key to maximising plant performance, and the introduction of a range of centrifugal separators gives the opportunity to reduce the minimum size of recovery even further. Four such units were tested on an ultrafine tantalum ore from Tantalum Mining Corporation; two units (the Knelson Concentrator and the Kelsey Jig) were shown to be incapable of recovering the very fine particles.

Of the other two units, the Mozley MGS was shown to be clearly superior to the Falcon concentrator, as well as to the existing equipment at Tanco. The data would indicate that the MGS has pushed the bottom

Ultrafme tantalum recovery 869

size of effective recovery below 10 micrometres. As with any other fines concentrator, however, no centrifugal separator, Mozley MGS included, is capable of particularly high enrichment ratio concurrent with acceptable recovery: stage upgrading will continue to be required.

Economically, the rleplacement of the two Bartles Crossbelts by a Mozley MGS is not viable; however, there is economic justification to replace the 12 Holman fines tables with two Mozley Multi Gravity Separators.

Proposed Slime Plant Flowsheet

2

150 mm cyclones Stokes Hydrosizer ‘-) --.B Mozley MGS Holman Tables Mozley cyclones Bartles Crossbelt Concentrators

Fig. 12 Proposed Slime Plant Flowsheet

ACKNOWLEDGEMENTS

This project has been carried out as part of the Canada-Manitoba Minerals Development Agreement; funding has been shared by Tanco and the Federal and Provincial Governments of Canada and Manitoba.

All parties are duly acknowledged for their support.

REFERENCES

1.

2. 3.

4.

5.

6.

7.

Burt, R.O., Hallewell, M., Young, S.R. & Deveau, C., Aspects of Tantalum Concentrate at Tanco. Inter. Symp. on the Proc. of Complex Ores, Halifax: CIM Conf. of Metallurgists. August. 10 (1989). Peck, O.B.., US. Pat 444,619. (1891). Ferrara, G., A process of Centrifugal Separation Using the Rotating Tube. Proceedings 5th ht. Miner. Process. Cong. London: IMM, 173-184 (1960). Knelson, B. & Jones, R., A new Generation of Knelson Concentrators: a Totally Secure System goes on Line, Minerals Engineering 7, (2/3), 201-207 (1994). Burt, R.O., Gravity Concentration of Ultrafines - a Literature Review of Centrifugal Concentrating Devices. MDA Report, 22 (October 1992). Laplante, A.R., A Comparison of two Centrifugal Concentrators. Ann. Canadian Miner. Proc. Conf., Otta‘wa, 20 (1993). Forssberg, E. & Nordquist, T., Pilot Plant Trials of New Gravity Concentration Equipment. Minerals and Metall. Proc., 87-89 (May 1987).

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Laplante, A.R., Buonvino, M., Veltmeyer, A., Robitaille, J. & Naud, G., A Study of the Falcon Concentrator On Gold Recovery by Gravity McGill Short Course, 31 (May 1993). Harris, J.H., Serial Gravity Concentration: a new Tool in Mineral Processing Trans. Inst. Min. & Metall., 69, 85-94 (Dec. 1959). Beniuk, V.G., Vadeikis, C.A. & Enraght-Moody, J.N., Centrifugal Jigging of Gravity Concentrate and Tailing at Renison Limited. Minerals Eng., 7 (5/6), 577-589 (1994). Burt, R.O., assisted by Mills, C., Gravity Concentration Technology, Amsterdam: Elsevier Science Publishers BV, 607 (1984). Chan, B.S.K., Mozley, R.H. & Childs, G.J.C., The Multi-Gravity Separator (MGS) - a Mine Scale Machine. ~107-123 in Dowd, P.A. (ed.) Miner. Process. in the United Kingdom London: IMM. (1989). Turner, J.W.G. & Hallewell, M.P., Process Improvements for fine Cassiterite Recovery at Wheal Jane. 21pp Int. Symp. Processing Complex and Refractory Ores. CSM, Camborne. (1993). Chan, B.S.K. & Mozley, R.H., Enhanced Gravity Separation for the Benefication of Fines and Ultra-fines. Redruth: Richard Mozley Ltd., (1987). Tucker, P., Chan, S.K., Mozley, R.H. & Childs, G.J.C., Modelling the Multi Gravity Separator. XVI&h Inter. Miner. Proc. Gong. Dresden. 77-89 (1991). McGuiness, M. & Anonychuk, D., Recovery of Fine Gold and Tantalum Particles Using the Falcon Concentrator. Research Project, Course 306--41OB, McGill University Dept of Min and Metal1 Eng., 35 (1994).