Efficiency of a flocculent consisting of bentonite clay and fly ash for the removal of pollutants in AMD

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 flocculants-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 a 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.