Sodium carbonate alkali-treated coal

Various bituminous coals were demineralized by an experimental two-step leaching process in which the ball-milled 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. 

What became known as the Leblanc process was actually several interrelated processes. Salt was first reacted with sulphuric acid in a cast-iron pan, then in a reverberator furnace (in which heat was apphed from a flame blown from a separate chamber, not in direct contact with the salt), to produce saltcake (sodium sulphate), with hydrochloric acid released as a waste gas. Saltcake was used to make sodium carbonate, or roasted with limestone (calcium carbonate) and coal or coke to produce black ash. This mixture of sodium carbonate, calcium sulphide, sodium sulphide, hme, salt, carbon, and ash could be treated further with hot water to produce impure sodium carbonate in solution, evaporated into soda crystals (washing soda), or heated to yield anhydrous sodium carbonate. The latter, in turn, could be reacted with lime to made caustic soda (sodium hydroxide), the strongest commercial alkali then available. 

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