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

Abstract

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.

Sequencing batch reactor technology for landfill leachate treatment: A state-of-the-art review

“…This might be attributed to the lower temperature (25 o C) and the composition of the raw wastewater treated in the pilot system, compared with the operating conditions of the lab-scale SBR system (Kornaros, Marazioti, & Lyberatos, 2008). Findings revealed that it takes 30 min to completely oxidize Fe(II) in a pilotscale SBR, and with further optimization of SBR operation the number of cycles required to achieve acceptable Fe(II) oxidation can be reduced (Zvimba, Mathye, Vadapalli, Swanepoel, & Bologo, 2013).…”