Reactive Barriers for Mine Waters Treatment: an Approach using Alternative and Nature-Based Materials

Abstract

This work aims to minimize Acid Mine Drainage impact on two mining areas located in the Iberian Pyritic Belt (IPB), a volcanogenic massive sulfide (VMS) province of high historical importance regarding the mining exploration activities. Both the Caveira mine (Grândola, Portugal) and the Trimpancho mining complex (Spain), located on opposite sites s of the Portuguese South Zone, ceased operations in the 1960s. Since then, the l region has been under the impact of acid drainage from waste piles, left in aerial exposure with poor coverage, without supervision, which releases potential toxic elements (PTEs) to waterways adjacent to the mining areas, subsequently leading to the dissemination of these PTEs to more distant lands, causing scattered contamination. In a first step, bench -scale tests have been conducted to evaluate the best conditions ofenvironmental remediation of both mining areas, by applying mining water samples, , in contact with different wastes and materials such as paper, marble and limestone sludge, iron oxides, clays and industrial activated charcoal. In this first step, it was verified that paper sludge had a great potential on pH increment, since a composed mining water with pH of 1.64 increased to 6.23 in 10 days of contact, in a proportion of 1g of geomaterial for 50mL of mining water. Analysis of 18 water samples from Caveira and other 18 from Trimpancho, collected in February 2023 showed extremely high values of As, Fe, Cu, Pb, and Zn with peaks of 200.6 mg/L, 1249.6 mg/L, 10.7 mg/L, 1.7 mg/L and 69.6 mg/L, respectively, in Caveira’s mining waters, and 855.9 mg/L, 708.1 mg/L, 53.7 mg/L, 0.3 mg/L and 509.4 mg/L, in Trimpancho’s mining waters. The highest values are associated to pH of ~1,22 (Caveira) and ~2,33 (Trimpancho). Furthermore, In addition, we tested the removal of heavy metals through column tests, with different combinations of geomaterials and waste, simulating reactive barriers, in order to verify which set is most effective for containing and remediating these acidic drainage waters rich in toxic metals. These laboratory-scale tests showed thatthe three sludges and the industrial activated charcoal, proved to be the most suitable materials for heavy metal retention, such as As, Fe, Cu, Pb, and Zn, in both regions. Also, due to the diversity of PTEs, there is geochemical competition between geomaterials versus chemical elements, so a multilayered reactive barrier shows to be the most suitable way for future applications in a large scale treatment out in the field, while attempting water remediation.