Calcium and magnesium were removed from a brown coal and two subbituminous coals by treating with CO2 dissolved in water under a pressure of 600 kPa. The results were compared with treatment in a hydrochloric acid solution. Removal of calcium was significantly dependent on the chemical form of calcium in the coals. Calcium removal from Wandoan and Taiheiyo coals was about 50% after CO2 treatment of 12 h, but only 10% for Morwell brown coal. The effects of pH and coal:water ratio on calcium removal were explained by a new model based on ion exchange equilibrium. When the content of carboxyl groups in Morwell and Wandoan coals was decreased by mild preheating, calcium and magnesium removal was greatly increased. Preheating also improved the oil yield in direct coal liquefaction.
All Science Journal Classification (ASJC) codes
- Chemical Engineering(all)
- Fuel Technology
- Energy Engineering and Power Technology
- Organic Chemistry