Concentration of Tantalum and Niobium R.O. Burt Tantalum Mining Corporation of Canada Ltd., P.O. Box 2000, Lac du Bonnet, Mb. Canada CONTENTS Page ABSTRACT 36 1. INTRODUCTION 36 2. MINERALOGY AND ORE 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 mineral processing of tantalum and Tantalum and niobium do not occur in the niobium ores forms part of the chain which free state; they occur almost exclusively in extracts ore from the ground and converts the complex oxide minerals, often in solid solution contained metals into a useable state. This paper with a variety of other elements, such as tin, briefly examines the various tantalum and titanium, thorium and uranium. 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. Tantalite (Mn Fe)4 (Ta Nb)8 024 Microlite (Na.Ca)2Ta206 (O.OH.F) 1. INTRODUCTION Wodginite 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 metal, Columbite (Fe.Mn) (Nb.Ta)2 06 compounds or finished products is little different. Pyrochlore (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 microlite 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 pegmatite /3/ in Western Australia. 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 China, 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 Brazil 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 Thailand /9/; some niobium by-product is being dredging. also recovered from these operations. Mining of both primary weathered pegmatites By far the largest amount of niobium is and alluvials is also carried out on a very small produced as pryochlore from carbonatite deposits, scale in various parts of the world, 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 sodium and calcium 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.