Neutralization of acid mine drainage using the final product from CO2 emissions capture with alkaline paper mill waste

In this study, experiments were conducted to investigate the applicability of low-cost alkaline paper mill wastes as acidity neutralizing agents for treatment of acid mine drainage (AMD). Paper wastes include a calcium mud by-product from kraft pulping, and a calcite powder from a previous study focused on sequestering CO2 by carbonation of calcium mud. The neutralization process consisted of increase of pH by alkaline additive dissolution, decrease of metals solubility and precipitation of gypsum and poorly crystallized Fe-Al oxy-hydroxides/oxy-hydroxysulphates, which acted as a sink for trace elements to that extent that solutions reached the pre-potability requirements of water for human consumption. This improvement was supported by geochemical modelling of solutions using PHREEQC software, and observations by scanning electron microscope and X-ray diffraction of reaction products. According to PHREEQC simulations, the annual amount of alkaline additive is able to treat AMD (pH 3.63, sulphate 3800 mg L−1, iron 348 mg L−1) with an average discharge of about 114 and 40 L s−1 for calcium mud and calcite powder, respectively. Likewise, given the high potential of calcium mud to sequester CO2 and of resulting calcite powder to neutralize AMD, paper wastes could be a promising solution for facing this double environmental problem.