The extraction of sulfate sulfur from coals by organic acids

Determination of sulfate sulfur in coal has been done by using organic acid s, namely: acetic acid, oxalic acid and tartaric acid. The results have bee n compared with those of the ASTM HCl method. It is found that 0.5 M tartar ic acid is a suitable reagent by which sulfate sulfur can be effectively ex tracted. Minor increases of sulfate sulfur in the tartaric acid extraction over that of HCl extraction may be correlated with the solubility of sulfat e minerals which seem to be unleached with the mineral acid. This has been verified by studying the solubilities of gypsum and pyrite in the tartaric acid solution. Increased solubilities of gypsum and of sulfate obtained fro m pyrite have been found as the concentration of tartaric acid is increased . The variation of sulfate sulfur content in the extractions of 0.5 M tarta ric acid and 4.8 M HCl is not significant. As the mineral acid could degrad e the organic sulfur (which can affect its determination, calculated by dif ference), the use of tartaric acid is strongly recommended for the determin ation of sulfate sulfur in coal. (C) 1999 Elsevier Science B.V. All rights reserved.