Most of the mineral matter was extracted from Illinois No. 6 coal, a representative bituminous coal, by first leaching it with a hot alkaline solution and then with a dilute mineral acid. The alkalis employed, in decreasing effectiveness, were: (1) NaOH, (2) Na2CO3, (3) NaHCO3. The results generally agreed with those obtained in leaching quartz, kaolinite, and iron pyrite individually under similar conditions. The quartz was solubilized by the stronger alkalis. Kaolinite was largely converted to sodium hydroaluminosilicates such as analcime, hydroxycancrinite, and natrodavyne. A portion of the iron pyrite was converted to hematite, the amount depending on alkali strength and temperature. The sodium hydroaluminosilicates and hematite were subsequently extracted by acid.
Available at: http://works.bepress.com/thomas-wheelock/28/