Amending highly acidic blowdown sludge by direct addition of beneficiated alumina refinery residue

Amending highly acidic blowdown sludge by direct addition of beneficiated alumina refinery residue

This paper examines the relationship between sulfuric acid plant blowdown sludge and alumina refinery residue. Specifically, the research focuses on the neutralization of high levels of acidity in blowdown sludge (i.e., pH <1.0) and the reduction of leachable mercury (average 17.0 mg/L), a major contaminant in this type of industrial sludge at >19,000 mg/kg or 1.9%, using a modified form of alumina refinery residue, also called bauxite residue. Ten experiments on three different types of blowdown sludge were carried out to determine the potential role beneficiated alumina refinery residue might play in neutralizing acid and sequestering leachable mercury into non-bioavailable forms.

Results from the study indicate that while all ten treatments either partially or completely neutralized
acid and reduced leachable mercury by an average of 68%, only one was successful in reducing mercury to <0.1 mg/L. These findings suggest that alumina refinery residue may be useful in sequestering heavy metals in other forms of industrial solids, sludges and filter cakes.

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