Abstract
Several passive and active treatment approaches are available for dealing with Acid Mine Drainage (AMD). Despite a range of newly emergent techniques for the treatment of AMD, pH control using low-cost neutralizing reagents has been the most common and economical technique for the treatment of AMD. Thereby, owing to their widespread availability, ease of use, and cost effectiveness, active treatment techniques utilizing calcium-based reagents (particularly limestone) are considered the prime choice for treating AMD. Limestone is a well-known option worldwide for AMD neutralization thanks to its easy availability, low cost, and excellent efficiency. Generally, acidity is reduced by the presence of CaCO3 and alkalinity (i.e., HCO−3) is increased. pH can be increased from 2.5 to 7.5 by using limestone as a treating agent, resulting in the precipitation of heavy metals, which can then be removed by precipitation and sorption. Wargal limestone, a well-known limestone from the Salt Range, Indus basin, Pakistan, has high potential for neutralization and treatment of PTEs present in mine water or AMD. After selecting a suitable neutralization material at pilot scale, two different filters were designed using selected Wargal limestone: Filter 1 A (Oxic-based, Vertical bed-type Wargal Limestone Filter) and Filter 1 B (Anoxic-based Vertical bed-type Wargal Limestone Filter with Compost). The pH of the AMD under study was elevated from 2.5 to 7.65 and 7.60, respectively, in uncoated and coated media of limestone. Although the neutralization potential decreased over time, as an overall phenomenon the Ca concentration and net alkalinity (280–360 mg/L) were increased with the removal of metals such as Fe, Cu, Pb and Mn. The respective removal efficiency of these metals was 98%, 99%, 99% and 60%, with a threshold residence time of 5 h. in all columns of the developed filters.
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