Heavy metals and sulfate removal from acid mine drainage using steel mill slag in a rotational mixing device

Abstract

The steel mill slag (SMS) production in converter furnaces is one of the main by-products generated during steel production. This waste material is usually composed of different metal oxides that include basic cations such Ca, Mn, and Mg. These cations can favor alkalinity and a heavy metals removal when they are partially dissolved in a contaminant solution such as acid mine drainage (AMD). This work aims to study the potential use of SMS produced in converter furnaces in the mining-steel region of Boyacá- Colombia as an alternative to pre-treat AMD produced by coal mining in the zone. The SMS were separated into two particle sizes by screening, and these were put in contact with AMD samples in a rotational mixing system for 36h. The pH, total Fe (Fe²⁺, ³⁺), SO₄^2-, and heavy metals concentration were analyzed at 0h, 12h, 24h, and 36h time intervals. The final results show that SMS produced in the region is an optimal low-cost alternative to treat AMD, allowing complete heavy metals removal in the firsts 12h of treatment. Furthermore, Fe and SO₄^2- removal were observed, reaching 99.9% and 85%, respectively, at 36h. The application of rotational mixing allows complete mixing between AMD and SMS, reducing the possible precipitates adhesion on the surface, limiting the reactivity losses. This mixing treatment device favors a continuous use, avoiding the application of cleaning stages that could be required in the future for optimal functioning.