Contents lists available at ScienceDirect Environmental Research journal homepage: www.elsevier.com/locate/envres Aluminosilicate-catalyzed electrochemical removal of ammonium cation from water –kinetics and selectivity. Ahmed Enmili a , Frédéric Monette a , Chakib Yahiat a , Makram Amor a , Ali Hedhli b , Abdelkrim Azzouz a,b,* a École de Technologie Supérieure, Montréal, Québec, H3C 1K3, Canada b University of Quebec at Montreal, Department of Chemistry, Montréal, Québec, H3C 3P8, Canada ARTICLE INFO Keywords: Ammonium-rich wastewaters Electrochemical treatment Zeolites Clinoptilolite Electro-catalysis Aluminosilicates ABSTRACT Aluminosilicate-catalyzed electrochemical decomposition of ammonium cation (NH 4 + ) in water was in- vestigated using NH 4 + -saturated clinoptilolite and copper-nickel electrodes in the presence of different salts and acidic species. The results showed beneficial roles of chloride anion and moderately acidic media. NH 4 + ad- sorbed by the zeolites was converted with a 98% selectivity into nitrogen. The process was found to obey zero- order kinetics in the presence of clinoptilolite and a first order process when NaCl is added. Beneficial buffering effects of the zeolite and acidic species were registered. Clinoptilolite turned out to act as both catalyst and NH 4 + reservoir. These results allow envisaging effective and waste-free technology in treating NH 4 + -rich aqueous effluents through total electroconversion into nitrogen using low cost aluminosilicates. Clay minerals, soils, sludges and natural water turbidity are potential catalysts for this purpose. 1. Introduction The presence of high amounts of nitrogen-containing compounds (N-compounds) in aqueous effluents is known to produce eutrophica- tion of aquatic media. This leads to excessive growth of aquatic plants and decay in oxygen content with negative impacts on biodiversity. One of these N-compounds is ammonium cation. The latter originates from wide variety of sources such as natural and artificial fertilizers, in- dustrial and urban nitrogen-rich wastewaters (Erisman et al., 2007; Liu et al., 2005; Lord et al., 2002; Schröder et al., 2004). This also causes a major environmental issue that resides in the pollution of aquatic media. More or less satisfactory attempts to remove ammonia from do- mestic and industrial wastewaters have been made through biological processes and others (Peng and Zhu, 2006; Langwaldt, 2008; Leyva- Ramos et al., 2010; Mook et al., 2012). Almost total removal of am- monia can be achieved by materials exhibiting cation exchange capa- city (CEC) (Widiastuti et al., 2011). The most commonly used are or- ganic resins and aluminosilicates. On aluminosilicates (AS), the CEC is strongly depending on the particle size and accessible specific surface area, which determine the contribution of the permanent charges arising from the Al atoms and that of the temporary charges resulting from silanol protonation-deprotonation. The temporary charges, in turn, are narrowly dependent on the pH level, ammonium concentra- tion and possible presence of competing cations (Widiastuti et al., 2011). Zeolites are expanded AS structures displaying appreciable CEC, and the SiO 2 /Al 2 O 3 ratio, framework type and pore size play key-roles in this regard (Ribeiro et al., 2013). These features are key criteria for using specific zeolite structure according to the targeted application (Maia, 2002). Among the wide variety of zeolites tested so far, chaba- zite and clinoptilolite have shown interesting performances for this purpose (Langwaldt, 2008; Leyva-Ramos et al., 2010; Widiastuti et al., 2011; Rahmani et al., 2004; Lahav and Green, 1998; Qiu et al., 2010; Wang et al., 2016; Malovanyy et al., 2013). However, clinoptilolite is the most abundant of more than 40 types of natural zeolites that turned out to be of great interest for environmental purposes (Ming and Boettinger, 2001; Ming and Dixon, 1987). Ion exchange imposes a regeneration of the adsorbents, which are usually treated with aqueous NaCl or NaOH solutions (Langwaldt, 2008; Leyva-Ramos et al., 2010; Widiastuti et al., 2011; Rahmani et al., 2004; Lahav and Green, 1998; Wang et al., 2016). However, re- generation requires operating time, reagents, energy consumption and often leads to a secondary pollution. Biological regeneration could be a more interesting alternative (Lahav and Green, 1998; Qiu et al., 2010; Wu et al., 2008; He et al., 2007; Almutairi and Weatherley, 2015), but https://doi.org/10.1016/j.envres.2020.109412 Received 10 May 2019; Received in revised form 12 March 2020; Accepted 19 March 2020 * Corresponding author. E-mail address: azzouz.a@uqam.ca (A. Azzouz). Environmental Research 185 (2020) 109412 Available online 21 March 2020 0013-9351/ © 2020 Elsevier Inc. All rights reserved. T