A Kinetic study of leaching of coal pyrite with nitric acid

Abstract

The leaching of coal pyrite with nitric acid has been investigated. The temperature ranged from 313 to 363 K, and the concentration of nitric acid was varied from 0.154 to 1.54 mol/l. A coal sample of 50 grams was leached in a reactor containing 500 ml of solution in an open system. It was observed that the leaching reaction could remove 47 pct of the pyrite sulfur in seven minutes and 88 pct in 30 minutes at 343 K with 1.54 mol/l of nitric acid. The reaction order with respect to hydrogen and nitrate ion activity was found to be first order. The activation energy for the initial stage of the reaction was determined to be 14.7 K cal/mol (61.5 kJ/mol). A mathematical model was developed on the basis of mixed kinetics (reaction zone model) to explain the leaching rates. Good agreement between experimental rate data and predicted rate curves by the developed model was obtained. Ultimate analysis was used to determine the extent of nitration of the leached coal. This nitration was found to be insensitive to the reaction temperature and acidity of the solution.