This study aims to calculate the removal efficiency (%RE) of metals and sulphate and the constant rate of sulphate reduction from acid mine drainage (AMD) based on passive treatment principles named permeable reactive barrier (PRB) in batch test prior column test. Three media mixtures containing a variety of domestic sewage sludge (SE), mess hall compost (CO), cocopeat (CP), and fly ash (FA) were simulated. All reactive materials are solid waste from other operating units. M1 and M2 were contains organic and inorganic waste, M3 was only contain organic waste. The AMD was collected from a copper mining waste rock dump of which contained high sulphate, metals, and low pH. Batch tests were conducted in a series of glass bottles in an anaerobic chamber, and sub-samplings were taken on days 0, 7, 14, and 28. At the end of treatment, it indicated that M1 mixture resulting in the highest sulphate (SO4 2-) removal (44%), highest alkalinity generation of 1431 mg/L (as CaCO3) and %RE of Al, Cd, Co, Cu, Fe, and Zn were expected to be 100%, Ni 82%, Se 57%, and Mn 98%. Additional of FA for treatment such in M1 and M2 releasing more As in the final result compare to M3 that only contain organic substrates. The primary mechanism controlling the reaction from the M1 was a combination of sulphide precipitation enhanced by Sulphate Reducing Bacteria (SRB) activities supported by pH buffering and hydroxide precipitation. The sulphate reduction mechanism assumed to be the first-order reaction with highest rate constants found as 0.0208 d−1 from M1 reactors, 0.0144 d−1, 0.0161 d−1 for M2 and M3 respectively.
Containing sulphates and heavy metals, acid mine drainage (AMD) should be managed strategically to mitigate and control the migration of the contaminants to the downstream area. Conventional treatment techniques such as using lime to increase pH levels and metal precipitation or using imported material are usually inefficient and unsustainable. The AMD treatment investigated in this study uses the permeable reactive barrier (PRB) technique to enhance bacterial sulphate reduction and metal sulphide precipitation. The AMD treated is seepage water from industrial mining waste rock dump. This study aims to calculate the removal efficiency percentage of reactive materials to reduce contaminants in a batch test. Reactive materials used were organic waste generated locally i.e. domestic sewage sludge (SE), municipal compost (CO), cocopeat (CP), and the inorganic waste material is fly ash (FA) from a coal-firing power plant. A batch test was conducted in 56 days in an anaerobic chamber using nitrogen gas to support an anaerobic environment during subsampling. Mine water used in this test has a low pH level of 3.2, alkalinity (as CaCO3) < 1 mg/L, high sulphate 3280 mg/L, and contains Fe 46 mg/l, Al 54 mg/L, Cu 2.3 mg/L and Zn 3.4 mg/L. The test result at day 56 from using individual reactive material shows increased pH levels to 6.9; 5.6; 3.7; and 11.6 for sewage (SE), compost (CO), cocopeat (CP), and fly ash (FA), respectively. Alkalinity was increased to 1450 mg/L (SE), 323 mg/L (FA), 15 mg/L (CO), 1 mg/L for CP. The highest sulphate removal was measured in 85% from addition of FA. Sulphate removed from organic material reactor were 52% by (SE), 17% by (CO), 20% by (CP). %RE of dissolved metals (Al, Cd, Co, Mn, Ni, Fe, Cu, Zn), from SE reactor was 80%, CO reactor 80%, CP reactor 52%, FA reactor 94%. Oxidation-Reduction Potential (ORP) was measured to determine reducing conditions. ORP were measured at -551 mv, 255 mv, 156 mv, and -113 mv for SE, CO, CP and FA respectively. SE has the potential to remove metals and favour reducing conditions for sulphide precipitation at medium pH levels. Meanwhile, metal precipitation from addition of FA is mainly due to hydroxide precipitation at high pH levels. FA was able to decrease the most sulphate due to ion adsorption.
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