Chemical reactivity between CaCO3 and Ca(OH)2 in acid mine drainage (AMD) with mixing and shaking techniques during the destabilization-hydrolysis of the AMD

Abstract

The acid mine drainage (AMD) was poured into five 500 ml glass beakers. The samples were dosed with synthetic af-PFCl of Ca(OH) 2 and af-PFCl of CaCO 3 polymers respectively. The samples were treated in a jar test and a shaker at 250 rpm for 2 min, and thereafter were allowed to settle for an hour after which the pH, conductivity and turbidity (TSS) were measured. A similar second set of experiments was conducted by placing the samples in a shaker at 250 rpm for 2 min, after which three measurements were conducted after 1, 2 and 6 h. Similar third and fourth set of experiments was conducted dosing the AMD with 0.043 M of Ca 2+ in Ca(OH) 2, and 0.043 M Ca 2+ in CaCO 3 respectively. A fifth set of experiment was conducted by dosing the AMD sample with 0.021 and 0.043 M Ca 2+ in Ca(OH) 2 respectively and treated in a jar test, shaker and without mixing. The synthetic acid free PFCl of Ca(OH) 2 or CaCO 3 exhibited a high TSS removal efficiency. Both polymers also show a similarly identical TSS removal efficiency, which depict Fe 3+ ions as the principal role player during destabilization-hydrolysis. Effective sedimentation of the turbid materials in the AMD sample with af-PFCl polymers of both Ca(OH) 2 or CaCO 3 occurs after 2 h of settling. The TSS removal values in the AMD sample which were treated in a shaker at 200 rpm are slightly lower than those treated in a jar test at 200 rpm. The residual TSS values in the AMD samples stirred at 350 rpm during rapid mixing are slightly higher compared to those stirred at 200 rpm rapid mixing.