Dissolution of iron sulfates from pyritic coal waste

Reactions governing the oxidation of pyritic coal waste at the earth's surface are discussed. Water quality associated with a disposal site receiving pyritic coal refuse or spoil usually depended upon the method of disposal and on whether saturated or unsaturated conditions prevailed. Previous studies examining the acid potential of coal refuse under aerobic nonequilibrium leaching conditions have been reported. Results of simulated long term changes in water quality from coal wastes placed in a saturated zone are reported. Coal refuse from an abandoned refuse pile exposed to weathering for over 50 years was extensively leached with deionized water in a modified Soxhlet apparatus. Analyses of leachate for pH, cationic and anionic composition were performed following a 3 month and 6 month leaching period. Data presented show that leachate was acidic after a 6 month period indicating a constant generation of acidity. Following leaching of the most soluble ferric and ferrous solid phases it is suggested that there is a long term release of iron species and aluminium ions to solution permitting oxidation of pyrite. Results of leachate analysis show that a fundamental change in solid phase properties occurred, with removal of relatively soluble sulphate and carbonate ions leaving control of cation and anion concentrations to the more stable primary and secondary minerals. It was concluded that the long term geochemistry of the waste/water system changed with leaching of the solid phase.