Neutralization of Acid Mine Drainage using thermally treated chromite mining waste

Abstract

In this study, two different mining waste streams were combined in the context of circular and green economy. Acid mine drainage (AMD) is considered to be the main environmental issue of the corresponding industry due to its acidic nature and high concentration of heavy metals. On the other hand, a large volume of tailings is produced during chromite mining and beneficiation processes. These tailings are mainly ultrabasic rocks, namely, serpentine and olivine. Despite not posing a significant environmental concern, they need to be properly managed. This work aimed to evaluate the AMD treatment (neutralization and metal removal) by the chromite mining tailings, contributing to sustainable practices within the mining industry. As experimental material, field samples of ultrabasic rocks were obtained, sieved, homogenized, and thermally upgraded (700^oC). Artificial AMD was synthesized to simulate real conditions, and the homogenized material was tested under batch and column setups to determine its neutralization efficiency. According to the results, the AMD was successfully neutralized by the upgraded ultrabasic rock. In detail, an equilibrium pH value of 7.9 was achieved by applying a liquid-to-solid ratio of 12.5 after 1 h of reaction time. Regarding the continuous flow column setup, neutralization was obtained by applying an empty bed contact time equal to 30 min. The heavy metal removal efficiency was mainly dependent on their solubility and experimental duration. Even if most of them presented high removal rates, magnesium concentration increased since it was leached from the upgraded ultrabasic rock to the aquatic phase.