Turbidity Removal Efficiency of Clay and a Synthetic af-PACl Polymer of Magnesium Hydroxide in AMD Treatment

In this study five 200 mL acid mine drainage (AMD) samples were treated with 5g clay (bentonite) alone or mixed with 0.1 M Al3+ in AlCl3 and 0.1 M Mg 2+ in Mg(OH)2 polymer. The AMD samples were poured into five 500 mL glass beakers and dosed with 5 g/L of clay in a jar test, (250 rpm for 2 minutes and reduced to 100 rpm for 10 minutes) and the samples were allowed to settle for 1 hour after which the pH, conductivity, turbidity, dissolved oxygen (DO) and oxidation reduction potential (ORP) were measured. In the next step, 200 mL of the supernatant was poured into five 500 mL glass beakers and dosed with a af-PACl (acid-free polyaluminiumchloride) polymer of 0.1 M Al3+ in AlCl3, mixed with 0.1 M Mg2+ in Mg(OH)2, and treated in a similar manner in a jar test, settled for 1 hour, after which similar measurements were conducted, depicted as experiment (A). Another similar set of experiments was conducted, where the AMD sample was dosed with a polymer of 5 g of clay, 0.1 M Al3+ in AlCl3 and 0.1 M Mg(OH)2 in a jar test. Similar measurements were conducted after 1 hour of settling, depicted as experiment (B). The results showed that the addition of the clay to the AMD sample as a reagent (A) or a polymeric component (B) does not affect the turbidity removal, but the rate of hydrolysis (pH changing pattern) and ORP are affected. The experimental results showed that there is a correlation between the ORP and the pH, and also showed that oxidation takes place during the destabilization-hydrolysis process. The results also showed that the conductivity plays a role during the destabilization-hydrolysis process, i.e. correlation between changing rate of the conductivity and the turbidity.