Elemental Modes of Occurrence in an Illinois #6 Coal and Fractions Prepared by Physical Separation Techniques at a Coal Preparation Plant
Journal Article
·
· International Journal of Coal Geology
In order to gain better insight into elemental partitioning between clean coal and tailings, modes of occurrence have been determined for a number of major and trace elements (S, K, Ca, V, Cr, Mn, Fe, Zn, As, Se, Pb) in an Illinois No.6 coal and fractions prepared by physical separation methods at a commercial coal preparation plant. Elemental modes of occurrence were largely determined directly by XAFS or Moessbauer spectroscopic methods because the concentrations of major minerals and wt.% ash were found to be highly correlated for this coal and derived fractions, rendering correlations between individual elements and minerals ambiguous for inferring elemental modes of occurrence. Of the major elements investigated, iron and potassium are shown to be entirely inorganic in occurrence. Most (90%) of the iron is present as pyrite, with minor fractions in the form of clays and sulfates. All potassium is present in illitic clays. Calcium in the original coal is 80-90% inorganic and is divided between calcite, gypsum, and illite, with the remainder of the calcium present as carboxyl-bound calcium. In the clean coal fraction, organically associated Ca exceeds 50% of the total calcium. This organically-associated form of Ca explains the poorer separation of Ca relative to both K and ash. Among the trace elements, V and Cr are predominantly inorganically associated with illite, but minor amounts (5-15% Cr, 20-30% V) of these elements are also organically associated. Estimates of the V and Cr contents of illite are 420 ppm and 630 ppm, respectively, whereas these elements average 20 and 8 ppm in the macerals. Arsenic in the coal is almost entirely associated with pyrite, with an average As content of about 150 ppm, but some As ({approx} 10%) is present as arsenate due to minor oxidation of the pyrite. The mode of occurrence of Zn, although entirely inorganic, is more complex than normally noted for Illinois basin coals; about 2/3 is present in sphalerite, with lesser amounts associated with illite and a third form yet to be conclusively identified. The non-sulfide zinc forms are removed predominantly by the first stage of separation (rotary breaker), whereas the sphalerite is removed by the second stage (heavy media). Germanium is the only trace element determined to have a predominantly organic association.
- Research Organization:
- Brookhaven National Laboratory (BNL) National Synchrotron Light Source
- Sponsoring Organization:
- DOE - OFFICE OF SCIENCE
- DOE Contract Number:
- AC02-98CH10886
- OSTI ID:
- 1020090
- Report Number(s):
- BNL--95939-2011-JA
- Journal Information:
- International Journal of Coal Geology, Journal Name: International Journal of Coal Geology Journal Issue: 1 Vol. 78; ISSN IJCGDE; ISSN 0166-5162
- Country of Publication:
- United States
- Language:
- English
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