RESEARCH ARTICLE Arsenic removal characteristics of natural Mn-Fe binary coating on waste filter sand from a water treatment facility Young-Soo Han 1,2 & Seol-Hee Kim 3,4 & Jeong-Yun Jang 3,5 & Sangwoo Ji 3 Received: 2 April 2021 /Accepted: 19 July 2021 # The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2021 Abstract In this study, the arsenic (As) removal characteristics of a Mn–Fe binary coating formed on waste sand filter of an acid mine drainage treatment facility are investigated. Owing to the Mn–Fe binary coating forming on the surfaces of the sand grains, its potential for arsenic removal, particularly As(III), was evaluated and characterized through batch experiments and x-ray absorp- tion spectroscopy. Sorption isotherms reveal that the Mn–Fe binary coating exhibits comparable removal efficiencies for As(III) and As(V) under low initial As concentrations. However, at higher initial As(III) and As(V) concentrations, the As(III) removal efficiency increases because of newly formed active adsorption sites from reductive dissolution of Mn. The oxidation of the As(III) and reduction of the Mn oxide phases are verified through As K-edge and Mn K-edge X-ray absorption near edge fine structure analysis. The outstanding As(III) removal efficiency of the Mn–Fe binary coating suggests synergy of Fe- and Mn- oxides, highlighting a potential application for this coating system. The natural formation of binary coating through acid mine drainage treatment reported in this study indicates that similar coating can form naturally in other environments, thus, providing plausible natural attenuation processes for arsenic immobilization. Keywords Mn-Fe binarycoating . Filter sand . As(III)oxidation . As(V)adsorption . Mn oxide reduction . Arsenicimmobilization Introduction Arsenic is a highly toxic metalloid, and Fe oxides are among the most effective adsorbents for its removal from solutions. The affinity of As to Fe oxides is high for As(V), an oxidized form of inorganic As, with insufficient effectiveness for ad- sorption of As(III), a reduced form. To improve the As(III) removal efficiency, oxidation of As(III) as a step preceding As(V) adsorption has been suggested in many studies (Tournassat et al. 2002; Lafferty et al. 2011; Schacht and Ginder-Vogel 2018). As(III) oxidation is conventionally achieved using chemical oxidants such as chlorine, potassium permanganate, and persulfate or catalyzed oxidation such as the Fenton reaction, metal-activated, and photocatalytic sys- tems (Xu et al. 2016). Conversely, Mn oxides have been suggested as effective As(III) oxidants in natural and engineering systems (Deschamps et al. 2003; Han et al. 2011; Ying et al. 2012; Wu et al. 2018). In fact, Mn oxides reduce As mobility by oxidizing As(III) to the less toxic As(V) and concurrently provide adsorption sites, especially for As(V) (Lafferty et al. 2011). Manganese arsenate precipitation has also been pro- posed as an As removal process involving As(III) oxidation (Tournassat et al. 2002). Using evidence from the Mn K-edge X-ray absorption near edge structure (XANES) analysis, Tournassat et al. (2002) indicated that the precipitate was an As–Mn solid mixture with chemical composition resembling Responsible Editor: Ioannis A. Katsoyiannis * Sangwoo Ji swji@kigam.re.kr 1 Department of Environmental Engineering, Chungnam National University, 99 Daehak-ro, Yuseong-gu, Daejeon 34134, Republic of Korea 2 Department of Environmental and IT Engineering, Chungnam National University, 99 Daehak-ro, Yuseong-gu, Daejeon 34134, Republic of Korea 3 Geologic Environment Division, Korea Institute of Geoscience and Mineral Resources, 124 Gwahak-ro, Yuseong-gu, Daejeon 34132, Republic of Korea 4 Division of Environmental Science and Ecological Engineering, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 02841, Republic of Korea 5 Department of Earth Resources and Environmental Engineering, Hanyang University, Seoul 04763, Republic of Korea Environmental Science and Pollution Research https://doi.org/10.1007/s11356-021-15580-0