Origin and assessment of acid leachate formation fromsulphur-bearing industrial by-products

Abstract: This study is focused on two industrial by-products, Blast Furnace Slags (BFS) and Pyrite cinders (PC). The BFS which comes from the north of Sweden has been suspected to be the source of occasional occurences of acidity observed in leachates emerging from the material when disposed in road basement. Acid leachates polluted with high concentrations of As and Cu were collected at the base of a provisory landfill containing PC in the vicinity of the old factories. In the BFS, chemical analyses indicated that reduced S are present and, if oxidised, could be a potential source of acidity. However, the sequential chemical extraction showed large amounts of Ca and Mg in BFS which are assumingly linked to instable alcalic oxides and silicates. They can be dissolved in water and neutralise any acidity produced. Hence, the material in itself cannot be judged to be acid-producing. Acid assessment (Acid Base Account) is not applicable to BFS unless it is adapted to silicate buffering materials. .In the PC, pyrite was observed by XRD and other sulfides linked with Zn and Cu were indicated using sequential chemical extraction. Jarosite was observed by XRD and confirmed by the extraction. In PC, As seems to be associated with the reducible fraction (oxides) and Cu with the oxidizable fraction (sulfides). Acid assessment indicated a high acid producing capacity for PC but the method has to be adapted to sulphates which were shown to constitute an important fraction of the S present in the material. The sequential extraction procedure has to be adapted to a high amount of crystallized hematite present in PC. A longer extraction time in oxalic acid is recommended.