Roberto Villas-Bôas reports that thorium reserves within monazite were mined from beaches in Prado, south of Bahia, Brazil, beginning in 1886 by John Gordon. This monazite was exported to European markets, mainly, but not only, to Austria and Germany for the manufacture of the Auer gas lamp net bags. In fact, Brazil was the biggest player in the thorium (Th) markets until 1915, when surpassed by India, and until 1945, when alternatively India and Brazil disputed the first rank of Th production. In 1955, the Brazilian resources (identified domestic monazite quantities (in situ)), were roughly estimated as shown in Table 8.
By 1942, a chemical processing plant to process monazite was built by ORQUIMA S.A., an industry located in the city of São Paulo; this operation was devoted to the manufacture of rare earths oxides, becoming a major exporter to the United States. Monazite-rich sands were also mined and beneficiated at the SUPRA/SULBA plant in Buena beach, Rio de Janeiro, until 1960. From this processing an inventory of about 2,000 t of mixed thorium chlorides, known as TORTA 2, is stockpiled at the INB’s (Indústrias Nucleares do Brazil) Caldas Mine in Minas Gerais.
It is well known that by the mid-1960s the Mountain Pass mine in California, United States (case study G) came into full production and then dominated global rare earth element production. The Mountain Pass operation led global supply of rare earth elements until 1985, when China began its large-scale production of rare earths. By 2002, China dominated the market of rare earths oxides, while further setting thorium apart from rare earth element production. With almost no demand for thorium, this resulted in little geological exploration for thorium. However, due to a recent rebirth in research towards thorium-based nuclear reactors, Thorium-containing deposits may experience some increasing demand and a new evaluation of thorium deposits is needed.
The principal thorium containing deposits and types in Brazil are listed in the IAEA – Thorium Deposits database [34]; references are given in this database.
New rare earths ore deposits that might be of interest for their thorium content were recently (2013) registered and approved by the Brazilian National Department of Mineral Production (DNPM) [35].
Thorium resource estimates are based on limited sampling and extrapolations, thus considered as estimates at the lowest level of geological confidence. Using UNFC-2009 as a classification system, these deposits might be classed generally as 3, 3, 3, except for the Buena mine, which previously had estimates at higher levels of confidence.
Mina Buena – Classification of the case study by UNFC-2009
As a monazite mine for REEs, the Mina Buena, or Buena mine of INB (Figure 9), is classified as shown in Table 9; that is:
E1.2 “Extraction and sale is not economic on the basis of current market conditions and realistic assumptions of future market conditions, but is made viable through government subsidies and/or other considerations.”
F1.1 “Extraction is currently taking place.”
G1+G2 “Quantities associated with a known deposit that can be estimated with a high level of confidence” (proven reserves) (G1) and “with moderate level of confidence” (probable reserves) (G2).
Non Commercial Project
Development Unclarified (If Th is recovered because Th reactors become a reality)
Source: Brazilian Minerals Yearbook, AMB, 2010 [36].
* Proven and probable monazite and ThO2 resources based on an estimated total of 1,292,282 t of monazite sands resources in situ, at Buena Mine, São Francisco de Itabapoana, Estado do Rio de Janeiro.
The Buena mine of Indústrias Nucleares do Brasil located in northeast Rio de Janeiro (21°24´36”S, 41°00´18”W)
Note: This was the only REE-producing mine in Brazil. The ore body is beach placer monazite-rich sand. The mine has been in standstill since the Chinese boom of rare earth production [39]; it reopened operations with stockpiled ore in 2011 [40]. On the other hand, there is no current market for thorium as a commodity. However, the large monazite resources represent a potential future source of thorium if needed or desired [37].
Mining in Buena was conducted in a very simple, logical and rational way: first, soil rich in organic matter was removed and stored for reclaiming purposes; second, overburden was then shovelled off; third, shovelling continued, which extracted the monazite-rich ores (ancient beach sands); fourth, trucks transported the ores to the physical beneficiation plant located nearby (Figure 10); fifth, concentrates and wastes were produced; and sixth, reclamation of the mined area was performed.
A two-step physical beneficiation process was performed, along with site reclamation:
- Humphrey´s spirals concentrate the “heavy minerals” part of the “monazite sands”, producing a concentrate consisting of monazite, ilmenite, zirconite and rutile. Waste products from this operation – paleo seashore sands – were returned for the concomitant reclaiming operations.
- Concentrates from step one were subjected to electromagnetic, electrostatic and further gravimetric operations to produce cleaner concentrates. The overall ore recovery was 85 per cent for the heavy minerals.
- Reclamation was performed concomitantly, transporting the waste materials from the concentrations steps 1 and 2 described above to fill the mining trenches then cover the fill with the separated and stored upper soil from operation 1.
In fact, the Buena mine has been working since 2011 from stockpiled ores and is currently planning for closure [38]: Stockpile/Year (t) 2011 2012 2013
Monazite
An estimate [38] of remaining stockpiles for zirconite/rutile, 10,000 t; ilmenite, 50,000 t; and monazite, 7,000 t; thus, still classified as E(1.2), F(1.1), G(1+2).
Conclusion
UNFC-2009 allows a better understanding of the availability of Brazilian thorium resources and reserves and certainly is a valuable tool to future planning of thorium nuclear energy uses as well as REE deposits.
Figure 10 S-X extraction, semi-commercial plant in 1992-1993 (extracting La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Y)
Source: [37].
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