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

Precipitated CaCO₃ 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 CaCO₃ compounds were determined and compared with some commercial CaCO₃. It was observed that CaCO₃ recovered from waste gypsum using Na₂CO₃ significantly neutralized AMD compared with commercial CaCO₃ and that recovered using both (NH₄)₂CO₃ or NH₄OH-CO₂ reagents. Moreover, a higher acid neutralization capacity of 1,370 kg H₂SO₄/t was determined for CaCO₃ recovered from waste gypsum using Na₂CO₃ compared with an average of 721 and 1,081 kg H₂SO₄/t for ammonium-based CaCO₃ and commercial CaCO₃ respectively. The inorganic carbon content for the CaCO₃ recovered using Na₂CO₃ 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 SO₄²⁻ and Na₂O which still requires further reduction in the respective compounds.