NIOBIUM (COLUMBIUM) AND TANTALUM 



445 



rary allocation controls were applied to the use of 

 these metals, and some concentrates were airlifted 

 to help alleviate the shortage which could not be 

 met by domestic production. The increased need for 

 these metals was caused by the increased use of 

 niobium in high-temperature steel alloys and the 

 use of tantalum as a catalyst in the manufacture 

 of synthetic rubber. 



A se(;ond period of critical shortage occurred in 

 the early 1950's during the Korean conflict when 

 niobium-bearing steel alloys were required in the 

 greatly increased manufacturing of jet engines. At 

 this time the United States instituted a guaranteed 

 purchase program that promoted exploration, dis- 

 covery, and production of niobium in both domestic 

 and foreign deposits. The program resulted in the 

 discovery of numerous large low-grade carbonatite 

 deposits and some large placer deposits. One of these, 

 the Bear Valley, Idaho, placer deposit, has been the 

 site of the dominant and the only significantly large- 

 volume niobium-tantalum production in the United 

 States. This production ceased in 1959 because gov- 

 ernment purchase contracts were fulfilled at that 

 time. 



In the subsequent 10 years, production and con- 

 sumption of niobium and tantalum generally fol- 

 lowed the trend in production of steel which showed 

 a general gradual increase, and niobium-tantalum 

 consumption of the United States accounted for the 

 largest proportion of the world production. How- 

 ever, during the last few years prior to 1972, as 

 illustrated in figure 53, this relation has changed 

 markedly, with the U.S. consumption of niobium, 

 though increasing, greatly overshadowed by the 

 much greater rate of increase in world production. 

 The increased rate of world production is attributed 

 to the rapidly expanding use of niobium in the manu- 

 facture of high-strength low-alloy steels by modem 

 steel-manufacturing facilities in Japan and Western 

 Europe. 



ENVIRONMENTAL PROBLEMS 



Mining operations for niobium and tantalum have 

 no known unique features that affect the environ- 

 ment differently from the mining of many other 

 ores. Open-pit mining of carbonatites presents the 

 problems of large excavations and extensive waste 

 disposal which in populated regions are offensive to 

 view and may affect local property values. Placer 

 mining and dredging of niobium-tantalum minerals 

 requires the restoration of placered ground and also 

 requires the application of measures to control the 

 added mud and silt in the draining streams. Niobium- 

 tantalum minerals themselves are not pollutants. 



and drainage waters from mines should not be de- 

 grading to the environment. 



Niobium and tantalum are not hazardous metals; 

 stack exhaust fumes, gases, and dust from extrac- 

 tion plants are easily controlled and offer no known 

 health hazards or uncontrollable environmental 

 problems. 



GEOLOGIC ENVIRONMENT 



GEOCHEMISTRY 



Niobium is a chemical element with atomic num- 

 ber 41 and atomic weight 92.91 ; tantalum has atomic 

 number 73 and atomic weight 180.95. In nature both 

 elements consist almost entirely of single isotopes 

 Nb"' and Ta'" (Strominger and others, 1958), with 

 Ta'^" accounting for only 0.01 percent of that ele- 

 ment (Evans and others, 1955; White and others, 

 1955). 



Niobium and tantalum have strong geochemical 

 coherence; that is, they are closely associated and 

 found together in most rocks and minerals in which 

 they occur. Great preponderance of one element over 

 the other rarely occurs in some rocks such as nephe- 

 line syenite (niobium-rich) or lithium-bearing peg- 

 matites (tantalum-rich). The principal reasons for 

 coherence are similar ionic radii and identical 

 valence states (Nb+^ =0.69 A and Ta+^ =0.68 A). 

 Both elements are lithophilic, showing strong affinity 

 for oxygen and being enriched in the earth's crust 

 (Rankama and Sahama, 1950). Niobium is also en- 

 riched in some carbonatites and kimberlites that are 

 considered to be of mantle derivation. 



The crustal abundance of niobium is considered 

 by modern estimates to be about 20 ppm (parts per 

 million) and of tantalum, to be about 2 ppm (sum- 

 marized by Parker and Fleischer, 1968). The abun- 

 dance is variable both in members of the same rock 

 type in different localities and in different rock types. 

 In general, however, lowest values of niobium and 

 tantalum are found in some ultramafic rocks (not 

 related to alkalic complexes) and some of the highest 

 values of niobium are found in alkalic granites, 

 nepheline syenites and related ultramafic rocks, peg- 

 matites, and carbonatites. Highest contents of tan- 

 talum occur in albitized granites and pegmatites 

 that are late-stage differentiates of granitic batho- 

 liths. Worthy of note is the fact that many carbona- 

 tite niobium deposits have very low contents of 

 tantalum. 



The small amounts of niobium and tantalum that 

 are dispersed in ordinary magmatic rocks are chiefly 

 present as "camouflaged" elements in iron- and iron- 

 titanium-bearing minerals, to a certain extent in 

 zirconium minerals, and rarely as discrete minerals 



