Geologic Occurrence: Boron is predominantly organically bound in coals with some B also bound in minerals, especially illite, kaolinite, montmorillonite 1. Boron has also been found in coals in the mineral tourmaline 2. Boron is the only element effected by the rank of the coal. Boron content decreased with increased rank as measured by volatile matter (moisture, mineral-matter-free basis) through high volatile bituminous rank and remained low through medium volatile and low volatile rank in West Virginia coals. Stratigraphic and geographic B distribution was related only to coal rank. Boron averaged 20.1 ppm in West Virginia coals on a whole coal basis and did not correlate with ash yield, total sulfur, pyritic sulfur or other trace elements, but did correlate with volatile matter on a moisture, mineral-matter-free basis.
Economic Impact: Coal may be used to manufacture nuclear-grade graphite used as a moderator in nuclear reactors, where boron content is critical and must be less than 2 ppm 3, 4 . Boron in coke may also influence the mechanical strength of steel 1. Boron is used as borax in water softeners, and in glass making 5.
Environmental Impact: Boron is retained in fly ash of coal combustion. Leachates from fly ash may contain enough B to contaminate ground water, also B leaching from fly ash may also be suitable as a soil amendment 5.
References:
1. Swaine,
D.J., (1990)
2. Finkelman,
R.B., (1981)
3. Hutcheon,
J.M., (1953)
4. Winter,
R., Leibnitz, E. and Otto, F., (1963)
5. CRC
Handbook of Chemistry and Physics
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