Abstract
A major problem in the active treatment of acid mine drainage (AMD) is the generation of large volumes of sludge through pH neutralization and subsequent metal precipitation. The sludge typically contains a low concentration of solids, resulting in associated handling and disposal difficulties. Anhydrous ammonia is one reagent commonly used to neutralize AMD due to its quick reaction rate, easy implementation, and relatively low chemical and operational costs. However, very limited information is available in the literature related to the detailed characterization and dewaterability of ammonia-treated AMD sludge. In this study, sludge was collected from an AMD treatment facility where ammonia neutralization was used. The sludge characteristics included high pH and alkalinity, high total Fe and Al, elevated sulfate, and low solids content (0.72 ± 0.24%). Coagulants and flocculants were not effective in reducing the settled sludge volume. Based on filtration tests, ammonia-treated AMD sludge demonstrated relatively good dewaterability in terms of specific resistance to filtration (SRF). Sludge cake containing 4.5–6.3% solids were obtained using vacuum filtration at a vacuum of 50.8 kPa (15-inch Hg). The appropriate immersion time was 60 s for a vacuum filter, and sludge cakes of 6.2% solids and a yield of 3.04 kg/m2h were achieved. Overall, the belt filter press showed the best performance in improving total solids content in the sludge cakes, where concentrations of ∼10% solids were achieved.
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