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

Abstract

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 Ca 2+ and Mg 2+ 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 Ca 2+ and Mg 2+ 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 OHions 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(CO 3) 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.

Study of the Processes in Acid Mining Drainage Wastes During Its Neutralisation With Sodium Hydroxide

“…By water stabilisation we mean that there are virtually no visible changes in AMD after standing for a long time 20 . We have previously shown that when water stands still, pH decreased, turbidity increased, and schwertmannite precipitated 21,22 . It has been proved that such changes are the result of the transition of iron(II) to iron(III) (Ref.…”

Influence of Sodium Phosphate Salts with Different Chain Length on the Flotation Behavior of Magnesite and Dolomite

“…It can be concluded that the metal sites of the two minerals are very small, and the number of broken bonds is the same, indicating that the difference in the crystal chemistry of the two minerals is mainly reflected in the surface Ca and Mg activity. Phosphate interacts with Ca or Mg through ionic bonds, and the action strength is related to the electronegativity difference between the phosphate group and Ca (or Mg) [17]. Among them, the electronegativity of Ca and Mg are 1.0 and 1.2, respectively.…”

“…Moreover, the electronegativity of the phosphate group is greater than that of O (3.5). Therefore, the electronegativity difference between Phosphate interacts with Ca or Mg through ionic bonds, and the action strength is related to the electronegativity difference between the phosphate group and Ca (or Mg) [17]. Among them, the electronegativity of Ca and Mg are 1.0 and 1.2, respectively.…”

The removal of turbidity and toxic metals in the AMD using a combination of saw dust, bentonite clay and synthetic CaMg.2(OH)2

“…toxic metals, total dissolved and suspended (TSS and TDS), organic and inorganic matter, odour and colour producing substances are the main attributes to problems associated with its treatment. Various technologies such as adsorption, precipitation, bioremediation, distillation, reverse osmosis, carbon nanotubes, Fenton's reagent, wet oxidation, advanced oxidation, coagulation-electro oxidation (McCurdy et al 2004;Swartz et al 2004;Ghaly et al 2006;Ntwampe et al 2013;Skousen 2014;Chen et al 2015;Liu et al 2015;Mackie & Walsh 2015;Ntwampe et al 2015a, Walsh 2015Demers et al 2017;Ntwampe et al 2017;Neelaveni et al 2019). Different types of the reagents (organic or inorganic coagulants, metal hydroxides, biomass wastes, minerals, etc.)…”