Abstract
Abstract Acid mine drainage was collected from the western decant in Krugersdorp, South Africa, to conduct a series of laboratory tests using 200 mL of AMD in five beakers dosed with increasing bentonite clay and decreasing pulverised fly ash respectively (flocculent-A) to establish accurate FA:BC dosing ratio. Two similar sets of experiments were conducted using a combination of bentonite clay and fly ash demineralized with distilled water (flocculent-B) and the other samples with tap water (flocculent-C). The pH, electrical conductivity (EC), turbidity and toxic metals were analyzed before and after experiments, i.e. As, Co, Zn and Pb, and treated in a jar test at 250 rpm for 2 min and reduced to 100 rpm for 10 min, allowed to settle for 1 hour after which the measurements were conducted. Turbidity removal of the samples of flocculent-A was slightly lower (72.5–75.1%) compared to that of flocculent-B and C (95.3–97.3%). On the other hand, FA:BC of 3:1 showed the highest turbidity removal. Toxic metals removal (85.9–94.8%) in the samples with flocculent-B and C is also higher compared to that of flocculent A. The SEM micrographs of the samples with flocculent-B and C showed large flocs indicating optimal sorption.
Highlights
Acid mine drainage (AMD) has globally been identified as a serious human and environmental hazard, in areas in the neighbourhood of operating and ceased mining operations
Following the pH changing trend (Figure 1), it is evident that the buffering effect is attributed to the basic condition by the presence of carbonates when reacting with sulphides in the AMD
The objective of this study was to determine the effect of fly ash when mixed with bentonite clay for the removal of pollutants present in AMD
Summary
Acid mine drainage (AMD) has globally been identified as a serious human and environmental hazard, in areas in the neighbourhood of operating and ceased mining operations. Its detrimental effect is attributed to high sulphide content resulting from minerals when rocks are exposed to oxidizing conditions mostly in coal and gold (Finkelman 2007), including copper mining and chemical industry. Sulphide minerals present in the AMD play an enormous role in environmental degradation through the sulphide oxidation process (Giere et al 2006). Pyrite (FeS2) and pyrrhotite (FeS) are sulphide species commonly found in coal (Kuyucak et al 2006). Their existence in AMD is attributed to oxidization during exposure to oxygen in an aqueous medium to form ferrous ions and sulphuric acid. A process which occurs underground where mining takes place and overflows to the surface after heavy rainfall in the form of acid water, termed AMD
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