Abstract
Abstract 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 flocculant 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.
Highlights
South Africa is one of the countries rich in mineral resources such as gold, coal, uranium, steel and diamond
The concentration of the acid mine drainage (AMD) sample was of a complex nature in order to elevate reactivity rate after the dosage with a flocculant characterized by porosity, ionic exchange, intercalation, selectivity and sorption
The performance of a reagent in the removal of toxic metals was typically influenced by the electrical conductivity (EC) and ionic strength attributed to the complexity of the sample, both determining the destabilization-hydrolysis process, resulting in high adsorption capacity
Summary
South Africa is one of the countries rich in mineral resources such as gold, coal, uranium, steel and diamond. Just as industrial wastewater is normally purified and re-used for essential or auxiliary processes, AMD can be treated through physico-chemical immobilization of toxic metals employing. Research studies continued to explore some other mixed technologies, but the problem associated with costs still remains a challenge (Gitari et al 2006, 2011; Nermen et al 2009; Buzzi et al 2011; Kopf et al 2013). It was after various methods involving commercial reagents and new technologies showed unsuccessful outcomes that some other types of reagents such as waste materials and natural resources were investigated. Bentonite clay has very reactive constituents, which provide it with net negative charge (Oladipo & Gazi 2014)
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