Reaction dynamics of bentonite clay, FeCl3, Al2(SO4)3 and Na2CO3 dosage in AMD using varying dispersion techniques

Abstract

200 mL solution of acid mine drainage (AMD) sample was collected from Krugerdorp gold mine in South Africa. The samples were poured into five 500 mL glass beakers, and varying volumes of 0.043 M of FeCl3, Al2(SO4)3, Na2CO3, and 2.0 g of bentonite clay were added respectively. The samples settled for 1 h, after which the pH and turbidity were measured. Second and third similar sets of experiments were conducted using five 500 mL glass beakers and Erlenmeyer flasks respectively, treated in a jar test or a shaker; at 250 rpm for 2 min respectively, similar settling and measurements were conducted. A fourth similar set of experiments was conducted dosing the samples with a combination of 2.0 g bentonite clay and Na2CO3 (flocculent) using 250 rpm rapid mixing between 20 and 60 s, 1 h settling and measurements. Turbidity removal of the samples dosed with a flocculent is lower than that of the samples with dosage of other reagents. The turbidity/heavy metals removal of the samples treated with mixing, shaking and without mixing is relatively identical. Turbidity of the samples without mixing of pH adjustment was also low. The SEM micrographs show that turbidity removal is a physico-chemical phenomenon.