Society of African Journal Editors

Journal of Chemical Engineering and Materials Science

Comparison between mixing and shaking techniques during the destabilization-hydrolysis of the acid mine drainage (AMD) using Ca(OH)2 and Mg(OH)2

Authors: Ntwampe, I. O, Waanders, F. B, Bunt T. S. S. R.

Journal: Journal of Chemical Engineering and Materials Science

Acid mine drainage (AMD) is detrimental to both humans and the ecosystem, and contains sulphuric acid and heavy metals, which have to be removed by dosing the coagulants. A 200 mL sample of AMD, emanating from a mining area in South Africa was poured into 500 mL glass beakers or Erlenmeyer flasks and were dosed with 0.043 M Ca(OH)2, 0.043 M Mg(OH)2 and synthetic 0.043 M CaMg.2(OH)2 and treated in a jar test or shaking apparatus employing rapid agitation at 250 rpm for 2 min. Each batch of samples was allowed to settle for an hour after which the pH, conductivity and turbidity were measured. The results showed that the turbidity removal efficiency exhibited by Ca(OH)2 or Mg(OH)2, and synthetic CaMg.2(OH)2 dosage of a range 30 to 60 mL was identical all above 90%. Effective wastewater treatment is not necessarily dependent upon the pH but the ability of the coagulant to destabilize the double layer (high electronegativity) of the aqua-colloids coupled with optimal hydrolysis, precursor to adsorption. The Ca2+ and Mg2+ ions added to AMD sample do not only neutralize the solution, but also cause destabilization; whereas the anionic species (OH-) increases the pH of the system. The Ca2+ and Mg2+ ions in Ca(OH)2 and Mg(OH)2 added to AMD sample respectively did not only neutralize the solution, but also cause destabilization, whereas the unreacted OH- ions increase the pH of the system. The identical turbidity removal yielded by all reagents confirms that the CaMg2(OH)2 can be used as a replacement of CaMg(CO3)2. Turbidity removal in AMD sample with Ca(OH)2, Mg(OH)2 or CaMg.2(OH)2 dosages is of a physical nature as can be observed from the SEM images, showing sponge cake-like structure with dense flocs linked together.   Key words: Coagulants, shaking, agitation, settle, pH, turbidity.