Calcium Carbonate in Waste Flooring for Neutralization of Acid Rock Drainage

Acid rock drainage (ARD) was successfully neutralized in this study using carpet tiles. Most polyolefin-based carpet tiles contain over 65% of finely ground calcium carbonate (CaCO₃) powder by weight in the compound-blended and extruded backing structure; therefore, using them for neutralization is an innovative way to reuse a difficult-to-recycle complex and abundant product. The overall neutralization efficiency potential was calculated at 40% based on the density, purity, and surface images that display the domains of CaCO₃ on the tiles. The carpet backing increased the mean of proton activity of AMD collected from a single acidic stream point within the Pinkerton Run tributary near Pittsburgh, PA from 3.3 to 6.1 over the span of four hours in batch-method experiments at CaCO₃ loading levels of 0.1 g/L and overall surface area exposure of 229 mm²/mL. Hot acidity levels decreased from 90 to less than 10 mg CaCO₃/L, and below detection limits after 20 h of neutralization. The treated and neutralized AMD sample contained 80 mg/L more calcium than the untreated, non-neutralized control, demonstrating the dissolution of CaCO₃ from the carpet tile.