Abstract:In this study five 200 mL acid mine drainage (AMD) samples were treated with 5g clay (bentonite) alone or mixed with 0.1 M Al 3+ 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 Al 3+ in AlCl3, mixed with 0.1 M Mg 2+ 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 Al 3+ 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.Keywords: mixing, disperse, turbidity, multivalent, pH, turbidity IntroductionConventional wastewater treatment using inorganic coagulants is a common practice because aluminium, one of the reagents utilized in the process is in abundance and has also exhibited desirable effectiveness in the wastewater treatment. On the other hand, the use of polymeric flocculants over inorganic polyelectrolytes, such as poly-aluminium complexes, gives significant advantages when the water has a high concentration of suspended solids; the concentration of the polymeric flocculent is lower, the resulting sludge is more compact and there is less coagulant left in the water after treatment (Stoll, 2013). However polymeric flocculants are not always used in a rational way for optimal flocculation due to the natural fluctuations and heterogeneity of the water composition (e.g., pH, ionic composition), suspended particle concentration and corresponding physicochemical properties (e.g., sizes, shapes, surface charges). The main objective in the present study is to investigate the impact of the polymer which contains clay and Mg(OH)2 with FeCl3 on the destabilization-hydrolysis process for an AMD sample. An improved understanding of the interaction mechanisms between flocculants and the suspended material is also often necessary. Since most of the flocc...

Heavy metals have always been defined as elements with a density higher than 5 g/cm 3. 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 FeCl 3 and Al 2 (SO 4) 3 and a flocculent of bentonite clay and FeCl 3 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 FeCl 3 exhibits a better turbidity removal efficiency compared to the samples with bentonite clay, FeCl 3 and AlCl 3 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.

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