Fe(II) oxidation during acid mine drainage neutralization in a pilot-scale sequencing batch reactor

• Published in: Water science and technology Vol. 68; no. 6; pp. 1406 - 1411
• Main Authors: ZVIMBA, J. N, MATHYE, M, VADAPALLI, V. R. K, SWANEPOEL, H, BOLOGO, L
• Format: Journal Article
• Language: English
• Published: London International Water Association 01.01.2013; IWA Publishing
• Subjects: Acid mine drainage; Analysis methods; Applied sciences; Batch reactors; Beneficiation; Bioreactors; Calcium carbonate; Calcium Carbonate - chemistry; Cost recovery; Cycles; Dumping; Exact sciences and technology; Ferric hydroxide; General purification processes; Gold; Gypsum; Hydraulic retention time; Hydrogen-Ion Concentration; Hydroxides; Industrial Waste; Iron; Iron - chemistry; Kinetics; Landfills; Mine drainage; Mining; Natural water pollution; Neutralization; Ocean dumping; Oxidation; Oxidation-Reduction; pH effects; Pollution; Pollution abatement; Pollution prevention; Reaction kinetics; Reactors; Recovery; Removal; Retention; Retention time; Scale (corrosion); Sequencing; Sequencing batch reactor; Sewage; Sludge; South Africa; Suspended particulate matter; Suspended solids; Waste disposal sites; Waste Disposal, Fluid - methods; Wastewaters; Water pollution; Water treatment and pollution; South Africa; Bioreactor; Sequencing batch reactor; Industrial waste water; Iron II; Fe(II) oxidation; Oxidation; Water pollution; Acid mine drainage; Biological purification; Neutralization
• ISSN: 0273-1223; 1996-9732
• DOI: 10.2166/wst.2013.389

This study investigated Fe(II) oxidation during acid mine drainage (AMD) neutralization using CaCO3 in a pilot-scale Sequencing Batch Reactor (SBR) of hydraulic retention time (HRT) of 90 min and sludge retention time (SRT) of 360 min in the presence of air. The removal kinetics of Fe(II), of initial concentration 1,033 ± 0 mg/L, from AMD through oxidation to Fe(III) was observed to depend on both pH and suspended solids, resulting in Fe(II) levels of 679 ± 32, 242 ± 64, 46 ± 16 and 28 ± 0 mg/L recorded after cycles 1, 2, 3 and 4 respectively, with complete Fe(II) oxidation only achieved after complete neutralization of AMD. Generally, it takes 30 min to completely oxidize Fe(II) during cycle 4, suggesting that further optimization of SBR operation based on both pH and suspended solids manipulation can result in significant reduction of the number of cycles required to achieve acceptable Fe(II) oxidation for removal as ferric hydroxide. Overall, complete removal of Fe(II) during AMD neutralization is attractive as it promotes recovery of better quality waste gypsum, key to downstream gypsum beneficiation for recovery of valuables, thereby enabling some treatment-cost recovery and prevention of environmental pollution from dumping of sludge into landfills.