Extraction of iron and calcium from low rank coal by supercritical carbon dioxide with entrainers

Iron and calcium were extracted from low rank coal with supercritical carbon dioxide and methanol, ethanol, acetic acid, acetyl acetone, ethanol and acetic acid, or acetyl acetone and water entrainers at 313.2 K and 15.0 MPa. The low rank coal used in this study was Berau coal from Indonesia. The addition of methanol, ethanol, or acetic acid entrainers in supercritical carbon dioxide showed very limited effect on enhancement of the recovery rates of Fe. The recovery rates of Fe from dried coal by supercritical carbon dioxide with acetyl acetone were low, however, the addition of acetyl acetone with water in supercritical carbon dioxide remarkably enhanced the recovery rates of Fe. Water seems to play an important role in extracting Fe from coal with supercritical carbon dioxide and acetyl acetone. On the other hand, the extraction rates of Ca with supercritical carbon dioxide and water, methanol, ethanol, and acetyl acetone entrainers were very low. The addition of acetic acid with or without water in supercritical carbon dioxide slightly enhanced the recovery rates of Ca. The addition of acetic acid with ethanol in supercritical carbon dioxide remarkably enhanced the recovery rates of Ca. The effect of carbon dioxide flow rate and coal particle size on the recovery rates of Fe were examined. The recovery rate of Fe increased with increasing carbon dioxide flow rate and with decreasing particle size of the low rank coal. (C) 2006 Elsevier B.V. All rights reserved.