Laboratory weathering studies of coal refuse

Coal refuse samples from Staunton, Illinois, were continuously leached in soxhlet extractors at 97, 65, 55 and 45°C for up to 192 hr. An identical refuse sample was leached once a week for 11 weeks using a humidity cell at approximately 25°C. Leachate collected from the soxhlet and humidity cell apparatus was analysed for pH, EC, SO₄, Fe, Mn, Al and total acidity.The data indicate that concentrations of SO₄, Fe and Mn increased rapidly as the leaching temperature in the soxhlets increased. Soxhlet extractors removed virtually all soluble Fe and Mn species within 64 hr of leaching. A comparison of the leachate characteristics of the low-temperature soxhlet and humidity cell showed that the soxhlet removed 50% more total Fe and SO₄ for the complete leaching cycle. Pyrite oxidation in the soxhlet extractors was observed near the end of the extraction sequence, but pyrite oxidation in the humidity cell was masked by the release of soluble iron sulphates. Thus, the origin of leachate acidity in the humidity cell could not be distinguished between the soluble mineral phase and the acidity resulting from the oxidation of pyritie minerals.The results of this experiment suggests that the use of the soxhlet extractor for leaching coal refuse may produce a faster and more accurate representation of water quality impacts than would the use of the humidity cell. Long-term leaching studies must be completed to further clarify the role of both these leaching methods for predicting water quality impacts.Contribution of the Land Reclamation Program at Argonne National Laboratory, Argonne, Illinois 60439.