Removal of Heavy Metals Using Bentonite Clay and Inorganic Coagulants

Heavy metals have always been defined as elements with a density higher than 5 g/cm3. They are regarded as serious wastewater contaminants with detrimental effect to human and environment. Their removal from wastewater poses a serious challenge as they require cost-effective reagent and treatment technique. About 200 mL solution of acid mine drainage (AMD) collected from the Western decant in Krugersdorp, South Africa was poured into five 500 mL glass beakers. Three different sets of experiments (employing mixing, shaking and no mixing) were conducted using a jar test and a shaker with 1.5 g bentonite clay, 20-60 mL of 0.043 M FeCl3 and Al2(SO4)3 and a flocculent of bentonite clay and FeCl3 dosage, respectively. The experiments were conducted without pH adjustment. The samples settled for 1 hour after which the pH, conductivity and turbidity were measured. The results show that a combination of bentonite clay and FeCl3 exhibits a better turbidity removal efficiency compared to the samples with bentonite clay, FeCl3 and AlCl3 respectively. The variation of the turbidity removal in the samples with mixing shaking and without mixing is insignificant, showing that destabilization-hydrolysis depends upon the strength of the reagent and the physicochemical properties of the solution. The results also show that hydrolysis occurs at low pH, indicating that it plays an insignificant role in destabilization. The SEM micrographs show that turbidity removal is a physical phenomenon.