Minerals columbite

A research project concentrated on columbite minerals to the left and on platinum ores to the right (Figure 29.1), oughtto locate the elements 43 and 75 and make a discovery possible. 

Gr. Tantalos, mythological character, father of Niobe) Discovered in 1802 by Ekeberg, but many chemists thought niobium and tantalum were identical elements until Rowe in 1844, and Marignac, in 1866, showed that niobic and tantalic acids were two different acids. The early investigators only isolated the impure metal. The first relatively pure ductile tantalum was produced by von Bolton in 1903. Tantalum occurs principally in the mineral columbite-tantalite. 

The menstmum niobium—carbide process (7) utilizes either columbite [1310-23-2] mineral concentrates or ferroniobium as starting materials. A low level of TaC in soHd solution with NbC commonly occurs, as Ta and Nb occur together in ores. The properties of NbC are given in Table 1. The grayish brown NbC powder is used in cemented carbides to replace TaC. TaC—NbC soHd solutions that have 3 1, 2 1, 1 1, and 1 2 ratios and the corresponding ternary and quaternary soHd solutions with TiC and WC are common. 

In the same year that del Rio found his erythronium, C. Hatchett examined a mineral which had been sent to England from Massachusetts and had lain in the British Museum since 1753. From it he isolated the oxide of a new element which he named columbium, and the mineral columbite, in honour of its country of origin. Meanwhile in Sweden A. G. Ekeberg was studying some Finnish minerals and in 1802 claimed to have identified a new element which he named tantalum because of the difficulty he had had in dissolving the mineral in acids. It was subsequently thought that the two elements were one and the same, and this view persisted until at least 1844 when H. Rose examined a columbite sample and showed that two distinct elements were involved. 

Pressure-induced phase transitions in the titanium dioxide system provide an understanding of crystal structure and mineral stability in planets interior and thus are of major geophysical interest. Moderate pressures transform either of the three stable polymorphs into the a-Pb02 (columbite)-type structure, while further pressure increase creates the monoclinic baddeleyite-type structure. Recent high-pressure studies indicate that columbite can be formed only within a limited range of pressures/temperatures, although it is a metastable phase that can be preserved unchanged for years after pressure release Combined Raman spectroscopy and X-ray diffraction studies 6-8,10 ave established that rutile transforms to columbite structure at 10 GPa, while anatase and brookite transform to columbite at approximately 4-5 GPa. 

Niobium and tantalum are rare elements. The content of niobium and of tantalum in the Earth s crust is lxl0"3 and 2x1 O 4 wt. %, respectively [21]. Niobium and tantalum are encountered in nature together, mostly in the form of oxides that are derived from orthoniobic (orthotantalic), metaniobic (metatantalic) and pyroniobic (pyrotantalic) acids. The main minerals are listed in Table 2, which reveals that the most important source of tantalum and niobium is tantalite-columbite, (Fe,Mn)(Nb,Ta)206. 

The electrostatic separation method is the exclusive choice in some specific situations, for example in the cases of rutile and ilmenite deposits. These deposits generally contain minerals of similar specific gravities and similar surface properties so that processes such as flotation are unsuitable for concentration. The major application of electrostatic separation is in the processing of beach sands and alluvial deposits containing titanium minerals. Almost all the beach sand plants in the world use electrostatic separation to separate rutile and ilmenite from zircon and monazite. In this context the flowsheet given later (see Figure 2.35 A) may be referred to. Electrostatic separation is also used with regard to a number of other minerals. Some reported commercial separations include those of cassiterite from scheelite, wolframite from quartz, cassiterite from columbite, feldspar from quartz and mica, and diamond from heavy associated minerals. Electrostatic separation is also used in industrial waste recovery. 

Literature on flotation of gold, PGMs, rare earths and various oxides is rather limited, compared to literature on treatment of sulphide-bearing ores. As mentioned earlier, the main problem arises from the presence of gangue minerals in the ore, which have flotation properties similar to those of valuable minerals. These minerals have a greater floatability than that of pyrochlore or columbite. In the beneficiation of oxide minerals, finding a selectivity solution is a major task. 

Niobium minerals, especially columbite, are also associated with other valuable minerals, such as tantalum, zircon and rare earth minerals. Pyrochlore and a mixture of pyrochlore and columbite have different origins, and therefore, beneficiation of pyrochlore and columbite are different from that of the mixed tantalum niobium ores. In actual plant practice, the treatment process is significantly different from that used for mixed niobium tantalum ores. This is due to the fact that the beneficiation process is largely determined by the nature of gangue minerals present in the ore. In most cases, the beneficiation process applicable for pyrochlore ore cannot be successfully applied for beneficiation of tantalum/ niobium ores. 

The major minerals contained in pyrochlore-containing ores are pyrochlore, columbite and sometimes ilmenorutile to a lesser extent. Table 22.1 shows pyrochlore minerals present in pegmatite and carbonatite ores. 

Ta/Nb minerals often occur as impurities in ilmenite, rutile, cassiterite, wolframite and perovskite, most of which contain REE. Because tantalite and columbite have similar chemical properties, they often replace each other, and are usually found as isomorph mixtures. Tantalum and niobium can also be found as separate minerals. Tantalite and microlite are primary sources of tantalum. 

Figure 23.1 Effect of level of sodium oleate on recovery of tantalite, columbite and associated gangue minerals.

Sodium alkyl sulphonate is also a collector for tantalite and columbite at a pH below 3.0 (Figure 23.2). At a pH above 3.0, flotation recovery of tantalite and columbite decreased rapidly. This collector was not selective towards gangue minerals, such as tourmaline and garnet. 

Cationic flotation of tantalite columbite has also been studied on several ore types that contain tourmaline, feldspar and muscovite as the major gangue minerals [3], The effect of aliphatic mono-amine on flotation of Ta/Nb is presented in Figure 23.3. 

The ore used in this example contained a mixture of pyrochlore and columbite as the major niobium minerals. The tantalum is mainly associated with columbite. The major gangue minerals present in this ore were soda and potassium feldspars with small amounts of mica and quartz. Beneficiation of this ore using cationic flotation, normally employed for flotation of niobium, was not applicable for this particular ore, since most of the mica and feldspar floated with the niobium and tantalum. The effect of amine on Ta/Nb flotation is illustrated in Figure 23.9. The selectivity between Ta/Nb and gangue minerals using a cationic collector was very poor. 

Euxenite is a titanotantalum/niobium-containing mineral and has a complex formula (Table 24.1) with variable chemical composition. It is usually found in sand deposits together with monazite, xenotime, zircon, beryl, columbite and other minerals. 

In a number of cases, the REO from the yttrium group contains significant amounts of pyrochlore and/or tantalum columbite. Both minerals usually float with the zircon and REO minerals. 

Columbite-tantalite minerals, 17 134-135 Columbium, 17 132. See also Niobium (Nb) Columnar phase, of liquid crystalline materials, 15 96... 

Occurrence. The most important minerals are pirochlore (NaCaNb206F) and those of the columbite-tantalite series (Fe/Mn)(Nb/Ta)206 with various metallic ratios. 

Niobium is the 33rd most abundant element in the Earths crust and is considered rare. It does not exist as a free elemental metal in nature. Rather, it is found primarily in several mineral ores known as columbite (Fe, Mn, Mg, and Nb with Ta) and pyrochlore [(Ca, NaljNbjOg (O, OH, F)]. These ores are found in Canada and Brazil. Niobium and tantalum [(Fe, Mn)(Ta, Nbl Og] are also products from tin mines in Malaysia and Nigeria. Niobium... 

Niobium has a rather confusing history, starting in 1734 when the first governor of Connecticut, John Winthrop the Younger (1681—1747), discovered a new mineral in the iron mines of the New England. He named this new mineral columbite. Although he did not know what elements the mineral contained, he believed it contained a new and as yet unidentified element. Hence, he sent a sample to the British Museum in London for analysis. It seems that the delivery was mislaid and forgotten for many years until Charles Hatchett (1765-1847) found the old sample and determined that, indeed, a new element was present. Hatchett was unable to isolate this new element that he named columbium, which was derived from the name of Winthrop s mineral. 

Tantalum is the 51st most abundant element found on Earth. Although it is found in a free state, it is usually mixed with other minerals and is obtained by heating tantalum potassium fluoride or by the electrolysis of melted salts of tantalum. Tantalum is mainly obtained from the following ores and minerals columbite [(Fe, Mn, Mg)(Nb, Taj O ] tantalite [(Fe, Mn)(Ta, Nb)jOJ and euxenite [(Y, Ca, Er, La, Ce, U, Th)(Nb, Ta, Tij OJ. Tantalums ores are mined in South America, Thailand, Malaysia, Africa, Spain, and Canada. The United States has a few small native deposits but imports most of the tantalum it uses. 

British mineralogist Charles Hatchett Soft metal found in the mineral columbite, along with iron and manganese combined with germanium it forms an excellent high-temperature superconductor. 

The element was discovered in 1925 by Walter Noddack, Ida Tacke Noddack, and 0. Berg. They detected it by x-ray examination of platinum ores. X-ray studies also showed its occurrence in columbite and other minerals. It was named after the German river Rhine, called Rhenus in Latin. In 1929, Walter and Ida Noddack produced Ig of rhenium metal from 660 kg of Norwegian molybdenite. 

Rhenium does not occur alone in nature in elemental form. It is found in trace quantities in a number of minerals such as columbite, gadolinite, molybdenite, tantalite, wolfranite, and many platinum ores. Its average concentration in earth s crust is 0.0007mg/kg. 

Tantalum is never found in nature in free elemental form. The most important mineral is columbite-tantalite (Ee,Mn) (Nb,Ta)206. Tantalum also is found in minor quantities in minerals pyrochlore, samarskite, euexenite, and fergusonite. The abundance of tantalum in the earth s crust is estimated as 2 mg/kg. 

Tantalum pentoxide is obtained as an intermediate in extracting tantalum from the columbite-tantalite series of minerals. Also, the oxide can be made by heating Ta metal in oxygen or air at elevated temperatures. 

The discovery on which his fame rests was announced before the Royal Society on November 26, 1801, in a paper entitled Analysis of a Mineral from North America containing a Metal hitherto Unknown (3). This mineral, now known as columbite, is a black rock found in New England, and the specimen Hatchett analyzed had an interesting history. 

---