Although oxidative precipitation by potassium permanganate is a widely recognised process for manganese removal, research dealing with highly contaminated acid mine drainage (AMD) has yet to be performed. The present study investigated the efficiency of KMnO4 in removing manganese from AMD effluents. Samples of AMD that originated from inactive uranium mine in Brazil were chemically characterised and treated by KMnO4 at pH 3.0, 5.0, and 7.0. Analyses by Raman spectroscopy and geochemical modelling using PHREEQC code were employed to assess solid phases. Results indicated that the manganese was rapidly oxidised by KMnO4 in a process enhanced at higher pH. The greatest removal, that is, 99%, occurred at pH 7.0, when treated waters presented manganese levels as low as 1.0？mg/L, the limit established by the Brazilian legislation. Birnessite (MnO2), hausmannite (Mn3O4), and manganite (MnOOH) were detected by Raman spectroscopy. These phases were consistently identified by the geochemical model, which also predicted phases containing iron, uranium, manganese, and aluminium during the correction of the pH as well as bixbyite (Mn2O3), nsutite (MnO2), pyrolusite (MnO2), and fluorite (CaF2) following the KMnO4 addition. 1. Introduction The oxidation of sulphide minerals exposed to oxygen and water produces acid effluents commonly referred to as acid mine drainage (AMD), described in detail elsewhere [1]. Although the generation of acid drainage is a natural phenomenon, mining activities can dramatically increase its production due to the large amounts of material usually exposed. In addition to its main characteristics (e.g., high acidity and sulphate levels), AMD features extensive chemical diversity, including metals such as iron, aluminium, and manganese in elevated concentrations [2]. These effluents are potentially hazardous to the environment. However, technologies available to deal with AMD are either unsuitable or costly [3]. Furthermore, practices are fairly exclusive and varying significantly from one site to another, which characterises several problems in terms of the implementation of available methodologies. In Brazil, for instance, as a consequence of high contents of manganese in the soil, the concentration of this metal in AMD can be up to 150 times the limit of 1.0？mg/L recognised by CONAMA Resolution 430 (Brazilian legislation) [4]. However, the majority of studies performed so far have addressed the removal of manganese from waters with low contamination such as drinking water (e.g., [5–8]). The management of AMD with exceptionally high
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