Speciation of mercury in South African coals

Total mercury (Hg-TOT) concentrations were determined by inductively coupled plasma mass spectrometry (ICP MS) for South African Highveld coals. The distribution of Hg in coals was investigated using a four-stage sequential leaching protocol and isotope dilution/gas chromatography coupled to ICP MS (ID-GC-ICP MS). The results show that HgTOT ranged from 144 to 303 mu g kg(-1) with a mean of 199 +/- 26 mu g kg(-1), while HgTOT leached from coals using different solvents ranged between 103 and 310 mu g kg(-1) (mean: 218 +/- 60 mu g kg(-1)). Hg leaching rates of 53-78% were achieved in crushed coals. Hg-0, Hg2+, and CH3Hg+ were identified in all coals. CH3Hg+ in studied coals ranged between 0.1 and 0.4 (mean: 0.2) mu g kg(-1). GC ICP MS chromatograms also showed unknown Hg peaks which were identified as other organomercury species such as ethylmercury. Modes of occurrence of Hg in coals were variable with the organic-bound (37-40%) and the sulfide-bound (37-39%) being the dominant mercury forms. Increasing the HCl concentration in the used protocol increased the amount of Hg leached (16%) during this step.