An evaluation of waste gypsum-based precipitated calcium carbonate for acid mine drainage neutralization

Abstract

Precipitated CaCO(3) compounds recovered from pulped waste gypsum using some carbonate and hydroxide-based reagents were evaluated for their utilization in acid mine drainage (AMD) neutralization. The neutralization potentials, acid neutralization capacities and compositions of the CaCO(3) compounds were determined and compared with some commercial CaCO(3). It was observed that CaCO(3) recovered from waste gypsum using Na(2)CO(3) significantly neutralized AMD compared with commercial CaCO(3) and that recovered using both (NH(4))(2)CO(3) or NH(4)OH-CO(2) reagents. Moreover, a higher acid neutralization capacity of 1,370 kg H(2)SO(4)/t was determined for CaCO(3) recovered from waste gypsum using Na(2)CO(3) compared with an average of 721 and 1,081 kg H(2)SO(4)/t for ammonium-based CaCO(3) and commercial CaCO(3) respectively. The inorganic carbon content for the CaCO(3) recovered using Na(2)CO(3) and ammonium-based reagents of 49 and 34% respectively confirmed their observed neutralization potentials and acid neutralization capacities, while energy dispersive X-ray fluorescence suggested absence of major oxide impurities, with the exception of residual SO(4)(2-) and Na(2)O which still requires further reduction in the respective compounds.

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

“…Generally, neutralization of AMD using CaCO 3 normally results in pH ranging between 6 and 7 because of CO 2 buffering during CaCO 3 dissolution. However, AMD neutralization in which AMD pH as high as 8.0 was achieved has been reported (Zvimba et al 2012), and as such a final AMD neutralization pH slightly above 7 reported in this study is therefore not surprising. It is worth noting that the rate of Fe(II) oxidation during AMD neutralization over the 4 cycles improved significantly with increased suspended solids, of which 3.8, 5.8 and 11.1g/l of suspended solids were measured before cycles 2, 3 and 4 respectively.…”

“…However this short term interventions plan, although necessary at this stage, is not integrative enough to include opportunities for sludge beneficiation as a strategy to recover some costs associated with AMD neutralization. With opportunities for waste gypsum beneficiation and application having been recently reported (Zvimba et al 2011;Zvimba et al 2012), there is significant need to ensure the short term interventions plan is configured to allow subsequent beneficiation of sludge in order to provide a sustainable AMD solution.…”

2013 Atomic spectrometry update—A review of advances in X-ray fluorescence spectrometry

“…The XRF technique was used to characterise this nickelactivated metahalloysite and calcium silicate hydrate material and a mechanism for the photocatalytic oxidative degradation of organic pollutants was proposed. The use of precipitated CaCO 3 compounds recovered from pulped waste gypsum using some carbonate-and hydroxide-based reagents for the neutralisation of acid mine drainage was evaluated by Zvimba et al 212 EDXRF contributed to this study, which showed that this treatment was more effective than ammonium-based CaCO 3 and commercial CaCO 3 .…”