minerals Article The Treatment of Acid Mine Drainage Using Vertically Flowing Wetland: Insights into the Fate of Chemical Species Beauclair Nguegang 1, * , Vhahangwele Masindi 1,2 , Titus Alfred Makudali Msagati 3 and Memory Tekere 1   Citation: Nguegang, B.; Masindi, V.; Msagati, T.A.M.; Tekere, M. The Treatment of Acid Mine Drainage Using Vertically Flowing Wetland: Insights into the Fate of Chemical Species. Minerals 2021, 11, 477. https://doi.org/10.3390/min11050477 Academic Editor: Carlito Tabelin Received: 26 February 2021 Accepted: 23 April 2021 Published: 30 April 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Environmental Science, College of Agriculture and Environmental Sciences (CAES), University of South Africa (UNISA), P.O. Box X9, Florida 1710, South Africa; masindivhahangwele@gmail.com (V.M.); tekerm@unisa.ac.za (M.T.) 2 Magalies Water (MW), Scientific Services (SS), Research & Development (R&D) Division, Erf 3475, Stoffberg Street, Brits 0250, South Africa 3 Institute of Nanotechnology and Water Sustainability, College of Science, Engineering and Technology (CSET), University of South Africa (UNISA), P.O. Box 392, Florida 1710, South Africa; msagatam@unisa.ac.za * Correspondence: demenvc@gmail.com Abstract: In this study, the treatment of acid mine drainage (AMD) using vertically flowing wetland was explored. The wetland was enriched with Vetiveria zizanioides as a decontaminating media and soil as the substrate. Water was percolated through the substrate and the throughput samples were collected and characterized every five days for a period of 30 days. The obtained results revealed a tolerant index of 1.03 for Vetiveria zizanioides, and a net reduction of metals and sulfate. The removal efficacy of chemical species was observed to obey the following order: Fe (71.25%) > Zn (70.40%) > Mn (62%) > Al (56.68%)> SO 4 2− (55.18%) > Ni (35%) > Cu (18.83%). The removal of chemical species was further aided by the used substrate, and this could be attributed to the accumulation of chemical species on the soil through precipitation, adsorption, and phyto-retention. As such, it could be deduced that the substrate plays a significant role in the removal of metals, while the grass and external factors accounted for the rest of the chemical species attenuation. The translocation assessment revealed that the distribution of chemical species was observed to be predominant in the roots, except manganese, which was transferred in the shoot (67%). The XRF, XRD, FTIR, and SEM-EDS analysis revealed the presence of AMD chemical species in the substrate and the grass components, hence confirming that the plants are playing a huge role in the removal of contaminants from AMD. The PH REdox EQuilibrium (in C language) (PHREEQC) geochemical model confirm that metals existed as di-and-trivalent complexes in AMD. Lastly, available metals were precipitated as metals hydroxides and oxy-hydrosulfates by the substrate. In light of the obtained results, vertically flowing wetland could be used for the passive treatment of AMD, and it will play a huge role in active and abandoned mines. However, prolonged assessment should be undertaken to understand its performance over a notable period of time. Keywords: acid mine drainage; vertically flowing wetland; treatment; phytoremediation; Vetiveria zizanioides 1. Introduction Over many decades, the mining of gold and coal has played an indispensable role in the economy of any given country. The latter has been widely used for its high colorific value for power generation, while gold has been used for jewelry [1]. Despite their enor- mous socio-economic benefits, mining has been associated with numerous environmental problems, such as land destruction and the generation of acid mine drainage (AMD), among others [2,3]. Due to the nature and magnitude of its ecological impacts, AMD has been a topical issue that has been troubling the mining industry over the years [4,5]. In particular, during the mining of coal and gold, the associated sulfide-bearing minerals such as pyrite and arsenopyrite which are embedded in the surrounding geology and stratas get Minerals 2021, 11, 477. https://doi.org/10.3390/min11050477 https://www.mdpi.com/journal/minerals