This research paper reports the removal of heavy metal ions from mine effluents using the gum karaya (GK)-grafted poly(acrylamide-co-acrylic acid) incorporated iron oxide magnetic nanoparticles (Fe 3 O 4 MNPs) hydrogel nanocomposite [i.e., GK-cl-P(AAm-co-AA)/ Fe 3 O 4 hydrogel nanocomposite] and inorganic coagulants such as polyferric chloride (af-PFCl), Al 2 (SO 4 ) 3 , FeCl 3 and Mg(OH) 2 . The Fe 3 O 4 MNPs were incorporated in the matrix of the hydrogel polymer of Gk-cl-P(AAm-co-AA) through the free radical graft co-polymerization technique using N,N 0 -methylene-bis-acrylamide as the cross-linking agent. The graft co-polymerization of the P(AAm-co-AA) with Gk and the successful incorporation of the Fe 3 O 4 MNPs within the hydrogel polymer matrix was evidenced using different characterization techniques such as FTIR, XRD, SEM and TEM. The performance of coagulants was evaluated by considering parameters such as turbidity removal, pH correction, metal removal and settling time. It was observed that the monomeric inorganic coagulants had a relatively poor performance compared to the organic coagulant, i.e., GK-cl-P(AAm-co-AA)/Fe 3 O 4 hydrogel nanocomposite. Most of the coagulants achieved maximum turbidity removal in the range of 67-99.5 %, but the hydrogel nanocomposite showed the greatest reactivity by achieving the fastest floc formation rate and shortest optimum sedimentation time of 5 min (100 % removal in 5 min). The removal of metal followed the order Pb 2? [ Cr 6? [ Ni 2? with an optimum settling time of 15 min; more often, Ni 2? was poorly removed (B23.2 % removal after 15 min) from acidic mine water samples. Therefore, the synthesized hydrogel nanocomposite has shown great potential as a flocculant and adsorbent for the removal of suspended particles as well as heavy metal ions and can be used to improve the quality of mine effluents prior to discharge in the environment.

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The physicochemical treatment was employed to treat acid mine drainage (AMD) in the removal of turbid materials using clay only (exp A) and a combination of clay, FeCl3 and Mg(OH)2 (exp B) to form a polymer. A 5 g sample of clay (bentonite) was added to 1.2 L of AMD and treated in a jar test at 250 rpm for 2 min and reduced to 100 rpm for 10 min. A 200 mL sub-sample from the 1.2 L mother liquor was poured into five 500 mL glass beakers, and 20 mL dosages of a polymer of 0.1 M Fe(3+) in (FeCl3) and 0.1 M Mg(2+) in (Mg(OH)2) was added to the beakers. The samples were allowed to settle for 1 h, after which the supernatant was analyzed for pH, total suspended solids (TSS), dissolved oxygen (DO) and oxidation-reduction potential (ORP) (exp A). A similar set of experiments was conducted where 200 mL of the AMD sample was poured into 500 mL glass beakers and (20-60 mL) dosages of a combination of 5 g clay, 0.1 M Fe(3+) (FeCl3) and Mg(2+) (Mg(OH)2) polymer was added and similar mixing, settling time and measurements were conducted (exp B). The polymers used in exp A exhibited TSS removal efficiency (E%) which was slightly lower compared with the polymer used in exp B, above 90%. Clay has a high TSS removal efficiency in the treatment of the AMD, indicating that adsorption was a predominant process in exps A and B. The scanning electron microscope (SEM) micrographs of the AMD sludge of both exps A and B, with a rigid and compacted structure consisting of dense flocs surrounded by the smaller flocs bound together, corroborate the fact that adsorption is a predominant process.

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.

Acid mine drainage collected from the western decant in South Africa was treated in a series of small-scale laboratory experiments. 200 mL of the sample was poured into five 500 mL glass beakers using flocculants formed by mixing size-optimized 1.5 g of bentonite clay with 3.5 g saw dust and 1.0 g of Na3PO4 in triplicates (experiment A). Four similar sets of control experiments were conducted using the same amount of bentonite clay and saw dust with varying Na3PO4, contents in AMD treatment; the rationale being to determine the efficiency of Na3PO4 (experiments B, C and D). The results show that conductivity has an influence in the removal of the turbid materials. The removal efficiency of toxic metals using a flocculant containing 220 μm bentonite clay particle size and 0.012 or 0.25 M of Na3PO4 is higher than 96% when compared to that of the samples dosed with a flocculant containing 0.05 M Na3PO4, which is less than 91%. The flocculent also showed optimal removal efficiency of both turbid materials and toxic metals, i.e. removal efficiency within a range 96.5–99.3%. The flocculants containing 0.025 M Na3PO4 showed optimal removal efficiency of turbidity, colour, toxic metals and natural organic compounds.