Behavior of Quartz, Kaolinite, and Pyrite during Alkaline Leaching of Coal

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

Chemical Cleaning of Coal with Hot Alkaline Solutions

Various bituminous coals were demineralized by an experimental two-step leaching process in which the ballmilled coals were first treated with a hot alkaline solution and then with a dilute mineral acid. Different alkalis and acids were studied to determine their relative effectiveness. In addition, the effects of alkali concentration, treatment temperature, and treatment time were evaluated. Under the best conditions, the process reduced the ash content of the coals by 85-90% and the total sulfur content by 70-90%. As the temperature of the alkaline treatment was raised from 150 to 345°C, the removal of sulfur increased greatly whereas the recovery of organic matter declined. When a 1 M sodium carbonate solution was employed for the treatment, the recovery of organic matter was 91-97% for various coals treated at 250°C and 79-89% for the same coals treated at 300°C

Behavior of Quartz, Kaolinite, and Pyrite during Alkaline Leaching of Coal

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.Reprinted (adapted) with permission from Mineral Matter and Ash in Coal, Chapter 34, pp 462–472. Copyright 1986 American Chemical Society.</p

Behavior of Quartz, Kaolinite, and Pyrite during Alkaline Leaching of Coal

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.Reprinted (adapted) with permission from Mineral Matter and Ash in Coal, Chapter 34, pp 462–472. Copyright 1986 American Chemical Society.</p

Chemical Cleaning of Coal with Hot Alkaline Solutions

Various bituminous coals were demineralized by an experimental two-step leaching process in which the ballmilled coals were first treated with a hot alkaline solution and then with a dilute mineral acid. Different alkalis and acids were studied to determine their relative effectiveness. In addition, the effects of alkali concentration, treatment temperature, and treatment time were evaluated. Under the best conditions, the process reduced the ash content of the coals by 85-90% and the total sulfur content by 70-90%. As the temperature of the alkaline treatment was raised from 150 to 345°C, the removal of sulfur increased greatly whereas the recovery of organic matter declined. When a 1 M sodium carbonate solution was employed for the treatment, the recovery of organic matter was 91-97% for various coals treated at 250°C and 79-89% for the same coals treated at 300°C.Reprinted (adapted) with permission from Fossil Fuels Utilization, Chapter 3, pp 30–41. Copyright 1986 American Chemical Society.</p