Quantification and characterization of the sludge generated from synthetic acid mine drainage treatment using sodium ferrate (VI) as an advance oxidation process

A major problem in the active treatment of acid mine drainage (AMD) is the generation of large volumes of sludge through pH neutralization, oxidation of iron (II) and subsequent metal precipitation. The sludge settling rate, sludge volume index (SVI) and sedimentation process are ones of parameters identifying a good treatment of AMD. Sodium ferrate (VI) (Na2FeO4) is one reagent currently used to treat water 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 Na2FeO4-treated AMD sludge. This study aimed at characterizing and monitoring settling rate and densification process of synthetic AMD sludge after treatment with Na2FeO4. The results confirmed a complete removal of iron from the synthetic AMD due to high oxidation strength of ferrate (VI) in acidic medium (Eᵒ = 2.2V) and showed the presence of different minerals formed in the sludge after treatment. The concentrations of the sludge collected at different intervals were justified by the densification process and high density of the sludge was obtained after 25 minutes while high weight percent of iron was found at 10 min and Fe and O dominated other elements in the sludge. The study demonstrated very good settling properties of the sludge and the low SVI value ranging between 30 and 60 mL/g TSS.