Mining, Ore Preparation and Niobium-based Materials Production at Araxä, Brazil O. de Souza Paraiso Fo, Rafael de Fuccio Jr. and E.W. Betz Companhia Brasileira de Metalurgia e Mineraqao Corrego da Mata, Caixa Postal 8 - CEP 38180, Araxä - MG, Brazil CONTENTS Page ABSTRACT 120 LOCATION 120 HISTORY 120 GEOLOGY AND MINERALOGY 121 ORE RESERVES 122 MINING THE ORE 124 CONCENTRATOR 125 A. Crushing the Ore 125 B. Grinding 126 C. Magnetic Separation 126 D. Desliming 127 E. Flotation Circuit 128 F. Filtering 128 G. Tailing Disposal and Concentrator's Water Supply 129 LEACHING PROCESS 129 STANDARD FERRONIOBIUM PRODUCTION 132 NIOBIUM OXIDE 133 HIGH PURITY NIOBIUM FERRO ALLOYS 133 NIOBIUM METAL 134 SPECIAL OXIDES FOR OPTICS, CERAMICS AND CATALYSTS 136 OTHER PRODUCTS 136 A. FeNbC 136 Β. Niobium Pentachloride, NbCls 137 REFERENCES 137 119 Vol. 11, Nos. 1-4, 1993 Mining, Ore Preparation and Niobium-based Materials Production at Araxä, Brazil ABSTRACT south of the city of Araxä in the state of Minas Gerais. Fig. 1 shows the map of Brazil and the The pyrochlore deposit of Araxä, Brazil, is location of Araxä, about 400 air kilometers widely recognized today as the world's largest north of the city of Säo Paulo and approximately know niobium reserve. This mineral deposit, 550 air kilometers northwest of Rio de Janeiro. which represents more than 70 percent of the world's economically extractable known reserves, has been mined by CBMM HISTORY (Companhia Brasileira de Metalurgia e Mineracga) since the beginning of the 1960's The presence of pyrochlore in Araxä and, for those thirty years has supplied more carbonatite was first identified in 1954 by the than 60 percent of the world niobium eminent Brazilian Geologist, Professor Djalma consumption. Guimaraes, who had at an earlier date The purpose of this paper is to describe confirmed the presence of significant phosphate CBMM's present exploration of the Araxä values in the deposit/1 / . deposit, its ore preparation and production of Aerial photography, geological mapping and ferroniobium. radiometric surveys, both ground and aerial, Besides standard ferroniobium, CBMM has were carried and to define the extent of the recently commenced production at Araxä of pyrochlore mineralization with its unique vacuum-grade ferroniobium, vacuum grade concentrations of niobium. nickel niobium, and pure metal, as well as Beneficiation studies of the Araxä pyrochlore niobium oxide in different grades of purity, deposit began in 1958 when a 50-ton sample of ranging from the high purity grade for ore was sent to the United States for evaluation. metallurgical applications to especially pure During 1959, beneficiation studies conducted oxides for optical chemical and electronic on site in Araxä were successful in producing a applications. concentrate containing 55 to 60 percent Nb2Os, with a total recovery of between 60 to 80 percent of the niobium values in the ore. LOCATION In March 1960, construction was started on the first beneficiation plant, with a treatment CBMM's niobium deposit Is found in the capacity of 500 tons of ore per day; initial Araxä carbonatite complex, located about 6 km production of concentrates began in April, 1961. SÄO PAULO , - • J RIO DC JANEIRO Fig. 1: Arexä Mine Location 120 Ο. de Souza Paraiso Fo, R. de Fuccio Jr. and E.W. Belz High Temperature Materials and Processes Between 1961 and 1965, the company had predominate in these carbonatites: niobium in difficulties with various impurities in the Araxä, Cataläo I and II, apatite, a source of concentrate, the most significant being silicon, fertilizer phosphate in Araxä, Tapira and phosphorus and sulfur. These difficulties were Cataläo I; and titanium in Tapira, Cataläo I. overcome by reducing phosphorus in a caustic Serra Negra, Salitre I and II. Other less soda leaching plant, built in 1964. important mineralizations of vermiculite, barite, Finally, by 1965 it became possible to meet magnetite and rare earth minerals also occur, all the specifications for steelmaking grade but are not yet commercially exploited. ferroniobium. The Araxä complex, approximately circular in Later in the 1970's customer attention shape and about 4.5 km in diameter, is shifted to the relatively high lead content in distinguished by the unique extent of its CBMM's ferroniobium. The company, therefore, niobium mineralization, with an average content developed a new concentrate treatment process higher than 2.5 percent Nb2Os and isolated involving high temperature calcination with mineralized zones containing up to 5 percent calcium chloride to volatilize lead chloride, Nb2Os. followed by a hydrochloric wash to dissolve The main geological features of the phosphorus and sulfur. carbonatite, comprise the precambrian rocks of Production of ferroniobium from leached and the Araxä Group arched in a domic structure by calcined concentrate, produced by either the the alkaline intrusion which occurred during caustic soda or the calcium chloride process, the Upper Cretaceous period. began in 1965, using the established The Araxä complex is emplaced in quartzitic aluminothermic reduction process, and at rocks with some interbedded schists, which are present, the majority of CBMM's supply of overlain by a unit of biotite muscovite schists niobium is in the form of ferroniobium. At and chloride muscovite schists with some present, no pyrochlore concentrates are interbedded quartzites. The predominant exported by CBMM for production of quartzitic unit is in contact with the Araxä ferroniobium by other converters. complex, forming a complete ring surrounding In January 1980, CBMM developed the the intrusion. capacity to produce high grade niobium oxide in The high niobium concentration of the large quantities. The oxide plant's nominal deposit, located in the central part of the capacity is 2,400 tons per year of niobium oxide chimney, is the result of deep weathering and a (the equivalent of more than 5 million pounds), strong residual enrichment of the original making this product extensively available for the carbonatite rock. In the pyrochlore mineralized world market. zone, also circular in shape and approximately Finally, during 1981, CBMM developed a 1,800 m in diameter, this weathering reaches process and constructed a plant to produce depths of more than 100 meters, and in some especially pure grades of niobium oxide for places more than 200 meters before fresh rock optical and electronic applications. is encountered. Potential constraints on availability of Although the fresh carbonatite rock is also niobium in higher purity forms have thus been known to contain niobium mineralization, only dissipated, which could in turn stimulate the lateritic weathered mantle, the result of the interest for additional uses. residual enrichment of the deposit, is included in the ore reserves. The ore is capped by a layer of dark red overburden, grading less than 0.4 GEOLOGY AND MINERALOGY percent Nb2Os and varying in thickness from 0.5 meter to more than 40 meters. The Araxä carbonatite is part of an important The delineation between overburden and the alkaline district where the presence of ore zone is easily distinguished due to the sharp carbonatites has been established in seven transition in color, from the dark red of the complexes. These complexes are known as overburden to the light brown of the ore, this Tapira, Araxä. Salitre I, Salitre II, Serra Negra, being an important feature to locate contact Cataläo I and Cataläo II. between overburden and ore during the mining Several important mineralizations operations. 121 Vol. 11, Nos. 1-4, 1993 Mining, Ore Preparation and Niobium-based Materials Production at Araxä, Brazil The ore is composed principally of the substitute for niobium. minerals geothite, limonite, magnetite, barite, The specific name of the niobium-bearing monazite, ilmenite, gorceixite, quartz and the mineral in the Araxä ore is pandaite, a niobium mineral pandaite, a bariopyrochlore. pyrochlore in which Na*1 and Ca*2 are virtually The average mineralogical composition of the absent and have been partly replaced by Ba+2 in in-place ore is shown in Table 1/2/. the A positions of the crystal lattice. The Niobium occurs in the mineral pandaite, chemical analysis of the mineral corrected for which is essentially a complex hidro-oxide of impurities is given in Table 2. niobium, barium, titanium, rare earths of the The name pandaite, in honor of the Panda cerium group, and thorium. The ore is Hill carbonatite in Africa where this niobium radioactive due to the presence of thorium mineral was first identified, was given by Jager (0.12% in the ore) in the pandaite and monazite et al., in 1959 to those minerals of the minerals. pyrochlore group in which Ba*"2 predominates The pyrochlore group has the general over all other ions occupying the A positions of formula: A2.mB206(0,0H,F)1.1>pH20 where A is the crystal lattice/4/. More recently, the represented primarily by sodium and calcium chemical designation bariopyrochlore was and Β primarily by niobium to yield the usually- recommended as a replacement for the name cited theoretical formula, NaCaNb2Oe (OH,F)/3/. Pandaite by the IMA Commission, but Pandaite Appreciable amounts of thorium, lead, trivalent is still in common use/3/. rare earths, zirconium, and uranium, may substitute for sodium and calcium in the A positions of the crystal lattice. In the Β ORE RESERVES positions of the crystal lattice, appreciable amounts of tantalum, titanium and iron, may Since the early days of its discovery, the TABLE I AVERAGE MINERALOGICAL COMPOSITION OF THE ORE % Weight Pandaite (Bariopyrochlore) 4,6 Limonite, Goethite (Fe203.nH20) 35,0 Barite (BaS04) 20,0 Magnetite (Fe204) 16,0 Gorceixite (Ba, Ce)(AI, Fe)3(P04)2(0H)5.H20 5,0 Monazite (CeP04) 5,0 Ilmenite (FeTi03) 4,0 Quartz (Si02) 5,0 Others 5,4 122 Ο. de Souza Paraiso Fo, R. de Fuccio Jr.