Reactivity of Fe salts in the destabilization of acid mine drainage employing mixing and shaking techniques without pH adjustment

• Investigate the treatment of acid mine drainage without pH adjustment.
• Compare coagulation in the AMD with FeCl3 or af-PFCl of Ca(OH) or Mg(OH) polymers with mixing and shaking.
• Compare turbidity removal in the corresponding samples when AMD is dosed with the metal salts or polymer using the two techniques.
• Observed the correlation between turbidity removal and pH in AMD without pH adjustment.

Ferric chloride and Fe-sulphates are commonly Fe-salts used in water treatment, and the iron ionizes to form Fe3 + or Fe2 + when reduction occurs. A volume of 200 mL acid mine drainage (AMD) sample was poured into five 500 mL glass beakers or Erlenmeyer flasks and dosed with salts such as FeCl3, Fe2(SO4)3 and FeSO4 respectively. The samples were treated in a jar test and shaken respectively, then settled for 1 h, after which the pH, conductivity and turbidity were then measured. Another similar set of experiments was conducted in a jar test where the jars were rotated at 100, 150, 200, 250 and 300 rpm for 2 min, after which the samples settled for 1 h and the same measurements were conducted. A third, similar set of experiments was conducted at a rotating speed of 250 rpm for 30, 60 and 90 s, and then settled for 1 h and the same measurements were conducted. Although the Fe-salts are both divalent and trivalent, the turbidity removal values of the treated AMD samples do not differ significantly. The turbidity in the AMD samples with 90 s rapid mixing is slightly higher than in the samples with 30 and 60 rapid mixing. The SEM image of the sample with 90 s rapid mixing showed scattered agglomerates which indicates that rupturing occurred. Although there was no pH adjustment done on AMD sample before treatment, the pH and conductivity showed a direct relationship with the turbidity.

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