Removal of humic acid from aqueous solutions by a novel hydrogarnet/zeolite composite
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Removal of humic acid from aqueous solutions by a novel hydrogarnet/zeolite composite Hirotaka Maeda1 · Kazuya Suzumura1 · Toshihiro Kasuga1 Received: 1 June 2020 / Accepted: 24 September 2020 © Springer Nature Switzerland AG 2020
Abstract Removal of humic acid from aqueous solutions is pivotal to protect water from environmental and health concerns. Slurry consisting of silica gel, alumina, calcium hydroxide, and zeolite A was hydrothermally treated to prepare a hydrogarnet/ zeolite composite for humic acid removal from water. The amount of hydrogarnet formed and the partial disorder in the zeolite structure affected the porous properties of the composite. The zeolite content in the slurry influenced the humic acid adsorption capacity. The composite hydrothermally treated for 2 h showed improvement in higher humic acid adsorption capacity (9.0 mg g−1) than the composites hydrothermally treated for 6 and 24 h (7.4 and 5.9 mg g−1) based on the pseudo-second-order model. The adsorption capacity of the composite was related to its crystal phase and the lattice distortion of the hydrogarnet, not the amount of hydrogarnet formed. Keywords Humic acid removal · Composite · Hydrothermal · Zeolite · Hydrogarnet
1 Introduction Natural organic matter (NOM) present in water is formed via metabolic reactions and contains mainly humic substances, polysaccharides, and proteins. The contamination level of NOM in water is changed by the site and season [1]. High NOM levels in water can cause coloration and fouling of membranes used in ultrafiltration treatments for drinking water [2–5]. Removal of NOM from aqueous solutions by using adsorbents and coagulants [6, 7] is important, addressing aesthetic and health concerns. Many adsorbent types were reported to purify water containing humic acid (HA), which is one constituent of humic substances present in water [8, 9]. Zeolite-based materials are known to be HA adsorbents [10]. It was reported that a combination of zeolite with chitosan, cetylpyridinium bromide hydrate, and N,N-dimethyl dehydroabietylamine
oxide has improved HA adsorption capacity due to hydrophobic interactions and hydrogen bonds [11–13]. Using such a zeolite composite is a suitable approach to remove color resulting from the presence of NOM in water. Hydrogarnet (Ca3Al2(SiO4)3−x(OH)4x with x = 0–3) prepared by a hydrothermal treatment is a solid solution consisting of C a3Al2(OH)12 and C a3Al2(SiO4)3. It is a novel HA adsorbent that utilizes hydroxyl groups at the surface to interact with HA [14]. Zeolite dealumination is achieved by hydrothermal treatment and leads to an increase in the number of SiOH [15]. This supposes that a combination of hydrogarnet with zeolite by a hydrothermal treatment is one approach to provide HA adsorption sites, increasing its adsorption properties. In this study, composites were hydrothermally prepared by combining zeolites and hydrogarnet, and the HA adsorption abilities of the resulting composites were evaluated to
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