Raw materials
Mineração Catalão, Aerial view of Catalão plant (Ruy George Fischer)
The primary mineral from which niobium is obtained is known as pyrochlore. The world's largest deposit is located in Araxá, Brazil and is owned by Companhia Brasileira de Metalurgia e Mineração (CBMM). The reserves are enough to supply current world demand for about 500 years, about 460 million tons. The mining of weathered ore, running between 2.5 and 3.0% Nb2O5, is conducted by simple open pit mining without the need for drilling and explosives. Approximately 85 to 90% of the niobium industry obtains its niobium ores from sources other than those associated with the mining of tantalum-containing ores.
Another pyrochlore mine in Brazil is owned and operated by Mineração Catalão de Goias and contains 18 million tonnes at 1.34% niobium oxide. The third major deposit of pyrochlore being actively mined is the Niobec Mine in Quebec, Canada, owned by Camet Metallurgy, with reserves of 18 000 tonnes.
In all three facilities, the pyrochlore mineral is processed by primarily physical processing technology to give a concentrate ranging from 55 to about 60% niobium oxide.
These three companies produce about 85% of the world's demand for niobium products, with most of that output being in the form of ferro-niobium with a nominal 60% niobium oxide content, for making high-strength, low-alloy steel.
Columbite, a mineral with a ratio of Nb2O5:Ta2O5 ranging from 10:1 to 13:1, occurs in Brazil, Nigeria, and Australia, also other countries in central Africa. Niobium is recovered when the ores are processed for tantalum.
Niobium is also found, in very small quantities, in the slags produced from the smelting of some tin ores.
Extraction/refining
Cambior, Ferroniobium production (Rachelle Bergeron)Two separate processing schemes are utilized for niobium production. Those companies that mine pyrochlore convert the niobium oxide units into HSLA ferro-niobium through the aluminothermic reduction process or by reduction in an electric arc furnace. CBMM has installed capacity for the production of a high purity oxide that can be used to produce vacuum grade ferro- and nickel-niobium as well as niobium metal ingots via electron beam refining.
The use of columbite and tantalum-bearing ores, such as tantalite, as feedstocks results in the necessity to process these materials chemically as described in the tantalum section. The purified niobium-containing process stream is generally converted to niobium hydroxide by the introduction of ammonia, followed by washing, filtration, and calcining to the oxide. Purities exceeding 99.99% can be achieved.
Niobium oxide (Nb2O5) is generally the starting chemical for the production of other compounds, such as niobium chloride (NbCl5), niobium carbide (NbC), or lithium niobate (LiNbO3). Niobium metal is produced by the aluminothermic reduction of the oxide followed by electron beam refining. Niobium powders can be produced by the reduction of potassium niobium heptafluoride (K2NbF7) with sodium, or by the reduction of niobium oxide with magnesium.
The various metallurgical products are generally produced from electron beam or vacuum arc melted niobium ingot. Double and triple melt ingots achieve a very high level of purification with respect to metallics and interstitial elements. Ingots are used to produce niobium alloys such as niobium-1% zirconium, niobium-titanium, C-103, Inconels, and others.
Several capacitor manufacturers are developing capacitors using niobium metal powder or niobium oxide, and these models are gradually being brought to the market.
