Detailed studies have been carried out on the distribution of organic functional groups and inorganic species
in as-received (ar) and acid-washed (aw) brown coals using elemental analysis, energy dispersive X-ray analysis
(SEM-EDX), X-ray photoelectron spectroscopy (XPS), and Time-of-flight−secondary ion mass spectrometry
(TOF−SIMS). Surface concentrations of the various carbon groups, organic oxygen, and inorganic hydroxide
were obtained using XPS, but oxygen from clay and quartz, if present, interfered with organic oxygen
determinations for the coals. A comparison of ar and aw coals using XPS and SEM-EDX is provided in terms
of inorganic and organic sulfur groups. Chloride in these coals is present mainly as acid extractable forms, but
small amounts of chloride in the organic matrix were indicated by the elemental analysis of ultra low-ash
coals. TOF−SIMS fragments from brown coals were indicative of polymers consisting mainly of single aromatic
groups linked by hydrocarbons with carboxyl and phenol functional groups. Sulfur fragments were from inorganic
sulfur, thiols, organo-sulfates, and S−N−organic species. Numerous fragments containing organically bound
chloride were observed. Fragments of the inorganic species Na, Mg, Al, Si, K, Ca, Ti, Cr, Fe, Mn, Ni, Cu, and
Ga were also observed. Environmentally undesirable species, particularly from organo-sulfur and organo-chloride groups in brown coal, are likely to emerge from processes that heat coal−water mixture.