Buffering copper tailings acid mine drainage : modeling and testing at Fushë Arrëz flotation plant, Albania

The beneficiation process of sulfide ores has the inevitable consequence of generating huge amounts of tailings highly enriched in sulfur, thus inducing acid mine drainage (AMD) and the release of potentially toxic elements. The aim of the work was to define the most suitable procedures for buffering acid drainage waters through the addition of commercial CaCO3 paste, provided by UNICALCE. High- and low-pyrite tailing samples were collected at the copper enrichment plant of Fushe Arrez (Northern Albania copper mining district). They were used for leaching and buffering tests, whose leachates and precipitation products were characterized by ICP-MS, chromatographic, XRD and TEM analyses. In addition, a geochemical model was developed in order to predict the pH trend of the leachate as a function of the addition of CaCO3. The results show the good buffering capacity of CaCO3, accurately predicted by the geochemical model. A drastic reduction in metals in the solution can be easily attained for low-pyrite samples, whereas high amounts of buffering agent are required to reach similar metals concentration reduction in high-pyrite. Precipitates are dominated by oxyhidroxides, followed by sulfates and hydrosilicates, but TEM showed also the presence of nanocrystalline and amorphous phases.