Effect of Temperature on Phase Transformation and Leaching Behavior of Acid Mine Drainage Sludge

Abstract

A large amount of sludge is generated from the neutralization of acid mine drainage (AMD) in Japan, which may cause severe environmental problems. This study showed there is potential to reuse such sludge in ceramic materials by thermal treatment. We sampled and characterized two types of iron-rich Japanese AMD sludge. Their phase compositions in the temperature range of 900–1200°C were identified by X-ray diffraction. α-Fe₂O₃ was the main crystalline phase in all sludge samples after thermal treatment. This can be used in ceramic enamels, porcelain bodies, and ferrite ceramics production. The results of leaching tests using acetic acid solution and distilled water as extraction fluids suggested that the stability of AMD sludge can be increased to a certain degree by thermal treatment; however, amorphous aluminosilicates formed by Al and Si impurities at lower temperatures weakened its stability. The enhanced mobility and volatilization of As impurity by thermal treatment also limits the application of AMD sludge. Applications that are insensitive to Al and Si impurities and products with higher arsenic stability are required when using sludges with high contents of impurities.