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Home , Microlite, Niobium, Pyrochlore, Tantalum

Concentration of and

R.O. Burt

Tantalum Corporation of Ltd., P.O. Box 2000, Lac du Bonnet, Mb. Canada

CONTENTS Page

ABSTRACT 36 1. INTRODUCTION 36 2. MINERALOGY AND DEPOSITS 36 3. MINING 37 4. GRAVITY CONCENTRATION METHODS 37 5. FLOTATION 43 6. FUTURE PROSPECTS 46 REFERENCES 47

35 Vol. 11, Nos. 1-4, 1993 Concentration of Tantalum and Niobium

ABSTRACT 2. MINERALOGY AND ORE DEPOSITS

The processing of tantalum and Tantalum and niobium do not occur in the niobium forms part of the chain which free state; they occur almost exclusively in extracts ore from the ground and converts the complex , often in solution contained into a useable state. This paper with a variety of other elements, such as , briefly examines the various tantalum and , and . While close to fifty niobium minerals that are processed for the tantalum and niobium bearing minerals have recovery of the contained values, and introduces currently bee identified /l/, only six tantalum and the two major concentration routes: gravity three niobium minerals are of economic concentration and flotation. significance (Table 1). Some flowsheets of operating plants are provided, which typify these processes. The paper TABLE 1 also comments on possible future processing Important minerals of tantalum and niobium routes that may, in time, become commercially employed. (Mn Fe)4 (Ta Nb)8 024

Microlite (Na.Ca)2Ta206 (O.OH.F) 1. INTRODUCTION Mn4 (Sn Ta,Ti,Fe)4 (Ta Nb)8 032

Simpsonite AL4 (Ta.Nb)3 (0,0H,F)I4 The production of metals is the result of the Stiblotantalite SbTa04 cooperative effort of various disciplines; mine; +3 Struverite fn,Ta,Fe )3 Oe concentrator; smelter; refinery; fabricator. The manufacture of tantalum and niobium , (Fe.Mn) (Nb.Ta)2 06 compounds or finished products is little different. (Ca,Na)2 Nb2 06 Raw ore from the mine has first to be processed to Bariopryochlore (Ba,Sr)2 (Nb.Ti)2 (O.OH)7 a concentrated mineral form, which, in its turn, must be converted into the metal or the oxide, Tantalite and columbite are end members of which finally is fabricated Into the finished article. an isomorphous series, as are and A typical tantalum bearing ore contains piyochlore. approximately 1 kg of tantalum in every tonne of Primary tantalum ore deposits are almost ore: niobium ores of the order 6-30 kg of niobium exclusively zoned pegamites, which are usually per tonne. This is far too low a content for the relatively small, and higher grade: the major such metallurgist to be able to economically convert the deposits, where mining is ongoing, are the Tanco minerals to metal without some form of pregmate /2/, Manitoba, Canada and the Wodgina concentration of the mineral into a smaller, much /3/ in Western . Another higher grade fraction. This mineral processing potentially significant pegmatite, in Wycoming, stage forms the subject of this paper. U.S.A. is of lower grade but higher tonnage /4/. In

36 R.O. Burl High Temperature Materials and Processes the Soviet Union and in , much of the those used for the mining of the majority of other tantalum produced is from apogranites, albitites minerals, any differences that do exist being the and griesens /5/· result of the scale operations.

The majority of tantalum is, however, Mining of primary ores requires either recovered as a co-product or by-product from tin underground, or open pit, mining. Tanco's Bernic mining, either in the mineral form, or as a by- Lake tantalum mine and Niobec's niobium mine product from the tin smelter. Such deposits are are examples of the former, the Wodgina pegmatite often much larger, and the tantalum lower grade. is typical of the latter. Outcropping ores which

The Greenbushes pegmatite /6/ in Western Aus- have weathered to the point of kaolinization can tralia, the Mibra mine /7/ and Paranapenama's be mined with front-end loaders, or by hydrau-

Pitinga deposit /8/, both in are typical of co- licing. The weathered cap of the Greenbushes product tantalum: tin mining, the latter also hav- pegmatite is such an orebody, as is the Araxa mine ing a significant niobium content. By-product of CBMM. The mining of alluvials can be accom- tantalum is recovered from many of the alluvial tin plished by a variety of methods, the most common mines in /9/; some niobium by-product is being dredging. also recovered from these operations. Mining of both primary weathered

By far the largest amount of niobium is and alluvials is also carried out on a very small produced as pryochlore from deposits, scale in various parts of the , with little with approximately two thirds of the world's mechanization. Individual output is small. Collec- production coming from the Araxa mine /10/ of tively these small operations make up an impor-

Companhia Brasileira de Metalurgica e Mineracao tant sector of the tantalum mining scene: however

(CBBM) in Brazil; here the and in their impact on overall niobium production is the crystal lattice have been replaced by barium, much less significant. to form bariopyochlore. The majority of the remainder comes from the Catalao mine / ll/, also 4. GRAVITY CONCENTRATION METHODS in Brazil, and Niobec's St. Honore deposit /12/,

Quebec, Canada. Gravity concentration - the separation of two Not only is the genesis of the two elements or more minerals as a result of differences in their significantly different, so are the major mineral specific gravity - is, next to hand picking, the recovery processes. Tantalum is separated from oldest form of mineral processing, with its ores by gravity concentration: niobium, on the archaeological evidence of it's widespread use well other hand is separated by flotation. over two thousand years ago. To this day, more

minerals are processed by gravity concentration

3. MINING than any other process, including flotation. Nevertheless, its major application is currently in

The methods employed for the mining of coal processing, and most metals are processed tantalum and niobium ores are little different to by flotation.

37 Vol. 11, Nos. 1-4, 1993 Concentration of Tantalum and Niobium

Tantalum is one of the exceptions. Apart TABLE 2 from a short-lived attempt at tantalum flotation by Typical recovery by gravity concentration Tanco in the early eighties /13/, gravity at different size ranges concentration has remained the only commercially applied process for tantalum Type Size Range Recovery concentration /14/, although some by-product Coarse + 1 mm 90-95% columblte is also produced by gravity methods. Sands -1+01mm 85-95% This section will, therefore, primarily deal with Fine Sands -0.1-+0.05mm 70-90% tantalum processing. Fines -0.05+0.01mm 50-70% Gravity concentration is most effective when Ultrafines -0.01mm 5-30% separating liberated particles, thereby maximizing the differences in specific gravity. The overall size liberated and any ultrafine particles will have range of particles that can be treated by gravity percolated out of the deposit - very high recoveries concentration is larger than with any other are, therefore common. Weathered deposits will be process. The practical size range is 500 mm to partially liberated; the extent of weathering 0.005 mm. However, no item of gravity determining the amount of crushing and grinding concentration equipment can efficiently handle required prior to concentration. this whole size range, and different types of For efficient gravity concentration, some form equipment have been developed to handle of feed preparation is essential. For rough different size ranges. Fig. 1 shows the effective size concentration, or preconcentratlon of alluvials, range of some gravity concentration units. this may simply involve rejection of oversize, and Recovery of heavy minerals by an item of removal of ultrafines. However, for final equipment will depend on many factors, including concentration and concentration of finer sizes, particle size, degree of liberation, particle shape, more complex feed preparation of material into etc; efficiency decreases with decreasing particle fairly small size ranges is required. size (Table 2) and increases with increasing Screening is effective at coarser size (+ liberation. 0.5mm), but is less effective at finer sizes; further- Primary ores require crushing and grinding to more, except in low tonnage situations, fine liberate the tantalum exacerbating, the fineness of screening becomes prohibitively expensive. many of the mineral assemblages, resulting in Screening is therefore used mainly in grinding incomplete recovery - much of the complexity of a circuits, to minimize overbreak, and in simple typical tantalum concentrator is related to the sizing of coarser fractions. effort expended attempting to improve this Classification is more common in feed recovery. Alluvial ores, on the other hand, are by preparation circuits. For single size separations, their very nature completely or almost completely hydrocyclones, sand cones and rake or spiral

38 R.O. Burt High Ύemperature Materials and Processes

classifiers, are used. Such units are also used for though it is the most efficient process available in desliming - the rejection direct to waste of the coarser sizes) nor Reichert cones have found untreatable material - and as preliminary sizers favour in the tantalum industry. To date the new prior to multiple sizing units such as hydrosizers. range of centrifugal separators have not been

These latter are ideal units for the separation of incorporated in tantalum concentrating circuits; long range feed for subsequent treatment on however, it is likely that in time they will be. shaking tables. Particles settle in a series of Concentrates produced in the gravity plant chambers against an upcurrent of water, such may require final clean-up to separate the various upcurrent decreasing in successive chambers; the heavy mineral values from each other. This is effect of a relative specific gravity of values and especially so where tantalum is a by-product in tin waste is enhanced, improving subsequent concentration, such as in the South-East Asian treatment. alluvlals. Typical minerals that report to such

Of the units shown in Fig. 1. jigs and sluices gravity concentrates, apart from the tantalum are commonly used for primary concentration of minerals and cassiterlte, can Include, ; alluviale or weathered pegmatites, as these units ; ; garnets; xenotime; ; are capable of treating fairly long size range feeds. monazite; sulphide minerals; and

Spirals, shaking tables, Bartles-Mozleys and ; and even some precious metals, as well

Crossbelts are commonly utilized for concentra- as some entrained lights, such as quartz /15/. The tion of primary ores, and for clean-up or rougher majority of these various minerals are themselves concentrates; these units treat smaller size range often of economic value; efficiency of separation is feeds. Neither heavy medium separation (even therefore paramount, and throughput is generally

STATIC DYNAMIC Heavy Medium WATER ONLY -I JIGGING Stratification SLUICE BOX REICHERT CONE Flowing PINCHED SLUICE film SPIRAL SHAKING TABLE BARTLES- MOZLEY Shaking CROSSBELT PNEUMATIC JIG AIR TABLE Other CENTRIFUGAL

Fig. 1 Effective size range of gravity concentration equipment

39 Vol. 11, Nos. 1-4, 1993 Concentration of Tantalum and Niobium

low. Clean-up can be carried out wet, dry, or a Typical concentrating plants combination of both, using a variety of processes, The following section considers only those which Include sizing, further gravity concentration, plants where tantalum is the primary product, or sulphide flotation, magnetic electrostatic is a co-product with tin; it does not consider plants separation. This is carried out in the "tin shed", a which are essentially tin concentrators, where by- shore based plant Incorporating several of these product tantalum or niobium Is produced In the stages: final separation of by-products, including clean-up stage, or after smelting. tantalum minerals may be carried out in "among" Primary ore: Alluvials and elulvals adjacent to the plants, such as that shown In Fig. 2. Wodgina orebody, in Western Australia have been Over fifty percent of the tantalum produced is mined since 1905; mining and processing of the as a by-product from the tin smelting industry; tin, main pegmatite commenced in 1990 with the along with its by-products, is concentrated on commissioning of a 100,000 tpa concentrate late dredges, or in smaller gravel pump plants, by 1989 Fig. 3/17/. gravity concentration followed by clean-up in tin Mine ore Is crushed In a two stage plant and sheds. The tin with associated tantalum and ground In closed circuit closed with DSM screens niobium is smelted by standard technology; the in a grate discharge ball mill to 0.5 mm. Screen tantalum and niobium reports to the slag, from undersize is treated on a four-stage spiral circuit, which they are recovered by hydrometallurgical to produce a final 40% Ta205 concentrate; roughly methods beyond the scope of this paper /16/. 60% of the tantalum is recovered in this circuit. Classifier Shaking Table Lanchute Drier High Intensity Magnetic Separator Induced Roll Separator Pneumatic Table

Casslterite

Struvcrite

Fig. 2. Typical Amang plant, South-East Asia

40 R.O. Burt High Temperature Materials and Processes

Feed η λ 1 1 mm Sieve Bend 2 Ball Mill 3 Rougher spirals 4 Cleaner Spirals 5 Recleaner spiral 6 Middling Spirals 7 0.6mm Sieve Bend F3 4 8 Cyclone 9 Scavenger Spirals 5 Tail 10 Rougher Tables 11 Middling Table 12 Cleaner Table 13 Recleaner Table T 1 Cone

Fig. 3 Tantalum concentration plant at Wodgina, Western Australia

Spiral circuit tailings are rescreened at 0.45 philosophy, but with the more complex nature of mm (the final liberation size of the tantalum), the ore, and the longer life of the operation, the oversize returning to the ball mill. Undersize Is circuitry is more sophisticated, Fig. 4 /18/. The cycloned at 75 μιη In a stub-cyclone, sands being major differences are in the secondary circuits, scavenged In a final bank of spirals. Cyclone after the spiral concentration stage. overflow Is treated on a bank of twelve Holman Four spigot hydrosizers and cyclones are tables, with rougher concentrate being upgraded used to split the -250 μηι ground product into a on a further table. Table middlings are also total of six size fractions. Hydrosizer spigots are re tabled. The table circuit accounts for a further treated on four banks of Concenco triple deck 15% of the tantalum, resulting in an overall tables, cyclone underflow on Holman slime tables recovery approaching 75%. Apart from low and cyclone overflow on Bartles-Mozley intensity magnetic separation, to remove grinding Separators. Rougher concentrates from each , no further treatment of gravity concentrates section are upgraded on tables or Crossbelt Is currently carried out. concentrators, with Table 3 showing a typical

The flowsheet at Tantalum Mining metallurgical balance. Corporation of Canada follows a similar Kaolinized Ores: The Greenbushes pegmatite is

41 Vol. 11, Νos. 1-4, 1993 Concentration of Tantalum and Niobium

3 mm Tyspeed Screen Ball Mill 2 mm A-C screen GEC Spiral circuit Sieve Bend 0.25 mm Derrick Screen 150 mm Cyclones Holding Tank Bartles-Stokes Hydrosizer Concenco Rougher Tables Holman Fine Sand Tables Screw Classifier 100 mm Cyclones Deister Hydrosizer Deister Cleaner Table Spiral Holman & Yun-tin Tables Bartles-Mozley Separators 50 mm Cyclones Cleaner Crossbelt Concentrator Recleaner Crossbelt Low Intensity Magnet Filter Pans Drier

Fig. 4 Tantalum Mining Corporation of Canada; tantalum plant

TABLE 3

Typical metallurgical balance: Tantalum Mining Corporation of Canada

Product Wt. tpd %Ta206 Dist.

Coarse Concentrate 0.66 37.0 35.0

Sand concentrate 0.35 40.0 20.0

Fine Concentrate 0.19 38.0 12.0

Slime Concentrate 0.11 30.0 5.0

Tailing 698.8 0.03 28.0

Feed 700 0.10 100.0

highly weathered, to the point of kaolinization; on plants. Consequently, whilst it's primary the other hand, it contains a larger suite of heavy treatment plant is relatively simple, its minerals than either of the primary tantalum retreatment plant is much more complex /19/.

42 R.O. Burt High Temperature Materials and Processes

The primary, or clay plant Fig. 5 consists of Ta205) and (25% Ta205) degradation followed by two stages of jigging, with concentrates, and an ilmenite reject. Greenbushes

Jig tailing fines being upgraded on spirals. is unique amongst tantalum producers In that It

Rougher concentrate is retreated in the Mineral has its own on-site pyrometallurgical and hydro-

Dressing plant. Fig. 6, as is rougher concentrate metallurgical plants to produce tin metal, from a tailings reprocessing plant; it will also, tantalum and tantalum intermediates. eventually, treat rougher concentrates from the proposed hard-rock mine. The mineral dressing 5. FLOTATION plant consists of both wet and dry sections; the former upgrading rough concentrates with gravity Pyrochlore minerals Eire the major source of concentration and low intensity magnetic niobium; they are amenable to cationic flotation, separation. The dry section utilizes air tables, using amines as collector. magnetic and electrostatic separation to produce Unlike sulphide flotation, oxide flotation is separate (72% Sn02), tantalite (42% very susceptible to deleterious fractions in the ore.

Feed 1 Trommel 2 Vibrating Screen 3 Autogenous Mill 4 Cyclone 5 Rougher Jig 6 Cleaner Jig 7 Spiral 8 2 mm Stationary Screen 9 Scavenger Spiral Circuit

ΗΙς.ι Grade Cone

Medium Grade Cone

Low Grade Cone

Fig. 5 Greenbushes clay plant

43 Vol. 11, Nos. 1-4, 1993 Concentration of Tantalum and Niobium

High Grade Cone

Low Grade Cone Classifier Shaking Tables Low intensity magnet Screen Roll Holding tank Drier Kason multi-deck Screen Pneumatic Table Induced Roll Magnet Roll High Tension Separator Electrostatic Plate Separator High Intensity Magnetic Separator

llmenlte Tantailte Casslterite

Fig. 6 Greenbushes mineral dressing plant

The presence of slimes Is a serious impediment, Flotation concentrates generally require and their removal is, therefore, essential prior to further treatment, as their quality is unacceptable commencement of flotation. Slimes removal used for succeeding processing to ferroniobium. to result in significant losses, especially with Sulphide flotation followed by a hydrochloric weathered ores such as at Araxa, as much of the leach is carried out by Niobec; a roast-leach at pyrochlore reports to the line to ultraflne size Araxa. range. The development of efficient, small diameter, cyclones, has permitted effective Typical concentrating plants: desliming as fine as 5 μηι, thereby minimizing losses In the desliming stage. Likewise, excess The flowsheet of the Niobec orebody Is magnetite is deleterious to flotation and its typical of primary niobium processing, Fig. 7 /12/. removal by magnetic separation is mandatory. Crushed ore, grading 0.66% Nb205, is ground in Carbonates, which are present in primary ore, closed circuit with screens and a screw classifier must also be removed, by a pre-flotatlon stage to 95%-200 μπι, flowed by desliming at 10 μπι by prior to pyrochlore flotation. banks of 250 mm and 100 mm cyclone in series.

44 R.O. Burt lligh Temperature Materials and Processes

Feed 1 Rod Mill ' —r 2 Sieve Bends 3 Screw Classifier 4 Ball Mill τ^τ 5 Desiiming Cyclones 4 -J 6 Conditioner 7 Carbonate Flotation - coarse 8 Carbonate Flotation - fine 9 Low Intensity Magnetic Separation 10 Pyrochlore Flotation - rougher 11 Pyrochlore Flotation - cleaner 12 Pyrochlore Flotation - recieaner 13 Sulphide Flotation Μ KZI Cone to filtering & drying 14 Thickener 15 Leach tanks

Fig. 7 Niobium concentration at Niobec, Canada

Deslimed ore is subjected first to carbonate xanthates at a pH of 10.5, and an acid leach. flotation followed by further desiiming which also Overall recoveiy at Niobec is 61-63%. removes hard water emanating from the carbonate Ore grade at Araxa is approximately 3%

flotation stage; finally magnetite is removed by low Nb205 /20/ significantly higher than at Niobec. intensity magnetic separation, prior to pyrochlore The flowsheet Fig. 8 /21/ has some significant flotation. Approximately 40-45% of the feed differences, due to the different mineralogy of the weight is removed prior to pyrochlore flotation, associated minerals. There is no carbonate with a loss of only 15-20% of the niobium. flotation at Araxa; however, the magnetic Pyrochlore flotation upgrades the ore from separation stage rejects 10-25% of the ore.

1.0-1.2% Nb205 to 40-45%; it consists of roughing Desiiming is carried out at 5 μπι using banks of followed by six stages of cleaning, with the pH 381, 100 and 25 mm cyclones in series. Flotation being reduced in each bank, from 6.5 in the of the coarse fraction (the underflow from the 381 roughers to a pH of 2.8 in the sixth cleaner bank. and 100 mm cyclones) consists of roughing Final flotation concentrates are further upgraded followed by four stages of cleaning, at a pH of 2.5- by two stages of sulphide flotation, using 3.5. Only two stages of cleaning are used in the

45 Vol. 11, Νos. 1-4, 1993 Concentration of Tantalum and Niobium

feed 1 Ball Mill 2 20 inch Cyclones 3 Low Intensity Magnetic Separators 4 15 inch Cyclones 5 Scrubber ό 4 inch Cyclones 7 25 mm Cyclones 8 Conditioners 9 Rougher Flotation 10 Thickener 11 Cleaner Flotation (4 stages) 12 Rougher Flotation-fines 13 Cleaner Flotation-fines

Fig. 8 Araxas concentration plant, Brazil

circuit floating the 25 mm cyclone underflow. tantalum and niobium ores in existing plants

Filtered flotation concentrate is trucked to using current state of the art technology. Some

the plant, where it is first calcined, at new prospects that have been examined require

800-900°C with CaCl2, followed by an acid leach either a substantial increase in the price of the

with 5% HCl. The phosphorous, lead and sulphur product to render them economic, or require the

content of the final product are significantly development of new technology to unlock the

reduced, and calcium is substituted for barium in complex mineralogy.

the crystal lattice. In the former category are the Wyoming

These two flowsheets highlight the signi- tantalum deposit, and the large, low grade deposit

ficant amount of desliming that is required to in , as well as the niobium-tantalum

facilitate effective niobium flotation. This can be resources of /22/. However, it is the

compared with the various tantalum flowsheets in latter category that intrigue the adventurous

the previous section, where little to no desliming mineral processor.

takes place. In Canada, the Thor Lake deposit was first

studied for its tantalum potential, then for its rare

6. FUTURE PROSPECTS earth potential, and latterly for its beryllium potential. The ultrafine nature of the tantalum

This paper has outlined the processing of defied existing technology, as well as such

46 R.O. Burl High Temperature Materials and Processes potential processes as , oil- a -, Mining Journal Mar. 31, p. 254 (1989). extraction and high Intensity magnetic separation. 4 WOUDEN, M.L. and CHATMAN, M.L., SME

In Australia, the Mount Weld carbonatite /23/ Annual Meeting, preprint 91-43 (1991). and the Toongl project /24/ are both complex rare 5 GAINES, R.V., in International Symposium on earth-tantalum-niobium deposits with complex Tantalum and Niobium, Brussels: T.I.C. metallurgy. In both cases, the deposits are being (1988). primarily considered for their rare earth potential, 6 HATCHER, M.I. and BOLITHO, B.C., in with the low grade tantalum and niobium of Granitic Pegmatites In Science and Industry, secondary Importance. However, with an "inferred" edited by P. Cerny, Miner. Assoc. Can., resource of 150 million tonnes of 0.034% of Ta205 Winnipeg, p. 513-25 (1982). and 273 million tonnes of 0.9% Nb205, the former 7. -, T.I.C. Bulletin, BO, April (1987). deposit Is vast. In both cases, however, current 8 -, T.I.C. Bulletin, 51, Aug. (1987). mineral processing technology is unsuitable for 9 CHADWICK, J.R., World Mining, Oct. p. 69 the concentration of the tantalum and niobium, (1983). and hydrometallurgical processing is being 10. -, Mineracao Metalurgica, 50 479 (Aug/Sept), considered. p. 54-58 (1986) (in Portuguese).

However, considering the relatively low cost 11. STUART, H., T.I.C. Bulletin, 52, Nov. (1987). concentration of tantalum by gravity methods, the 12. RODRIGUE, M. and BISS, R. in International ore reserves at the currently operating niobium Symposium on Tantalum and Niobium, plants, and the known but unexploited lower grade Brussels: T.I.C. pp. 163-195 (1988). deposits that can be concentrated by current 13. BURT, R.O., FLEMMING, J.. MILLS, C. and technology, commercial exploitation of low grade, HAMONIC, F. XIV Inter. Miner. Proc. Cong. complex resources requiring novel, and relatively Toronto: CIM. paper IV-12 (1982). costly processing, is unlikely in the near future, 14. BURT, R.O. in International Symposium on unless it can be subsidized by the value of the rare Tantalum and Niobium, Brussels: T.I.C., pp. earths they contain. 125-162 (1988).

15. HASBI HASSAN, A.B., in Beneficiation oj Tin REFERENCES and Associated Minerals Ipoh: SEATRAD

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Cerny and F. Saupe, pp. 27-79. Berlin: 17. -, T.I.C. 31st General Assembly (1990).

Springer-Verlag (1989). 18. BURT, R.O., in The AusIMM 1989 Annual

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FERGUSON, R.B., GRICE, J.D., MACEK, J.J. pp. 95-102 (1989).

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11(3), pp. 591-734 (1972). Engineering 2(3), pp. 299-320 (1989).

47 Vol. 11, Nos. 1-4, 1993 Concentration of Tantalum and Niobium

20. ΡΕΝΑ, F.E., Bull #18, Dept. Nat. Prod. Miner. 23. DUNCAN, RK., T.l.C., 31st General Assembly.

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48