AN IMPROVED METHOD FOR EXTRACTING SULFATE FROM BITUMINOUS COALS USING FORMIC-ACID

In connection with the determination of sulfate S, the sulfur mass balance for four bituminous coals was determined using different extraction procedures, including use of 1 M and 4.8 M HCl under nitrogen and under air, and at room temperature, 95 degrees C and boiling point. Since HCl extractions yielded poor S mass balances (as low as 83%), acid extraction with formic acid was also evaluated, Extractions with formic acid gave better S mass balances than those obtained using HCl, and the sulfate S yields agreed with those measured by the ASTM D-2492 HCl procedure. S-34/S-32 ratios determined by stable sulfur isotope mass spectrometry demonstrated that formic acid extraction was more selective for sulfate sulfur than the more rigorous HCl extractions.