Effective fluoride adsorption by aluminum oxide modified clays: Ethiopian bentonite vs commercial montmorillonite

Abstract

ABSTRACT. This study focuses on the chemical modification of Ethiopian bentonite and commercial montmorillonite with aluminum oxi-hydroxide (AO) for the purpose of defluoridation from aqueous solution. The chemical modification was achieved by preparing AO-modified adsorbents at different pH values. The adsorbent materials were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF) and point of zero charge (PZC). From the modified adsorbents, AO-Mont at pH 5 (AO-Mont 5) showed a slight shift of d001 at 2θ = 7.5º reflection toward the lower angle 2θ = 7.0º as a result of the Al2O3 insertion into interlayer space. The elemental composition from XRF further showed the increment of Al content accompanied with a decrease in the exchangeable cations in the modified samples and higher content of Al was observed in AO-Mont 5. In addition, the PZC initially 8.5 and 2.5 for raw bentonite and montmorillonite clays were increased to 10 and 8.5 in AO-Bent 5 and AO-Mont 5, respectively. Adsorption of fluoride on these modified adsorbents was studied as a function of preparation pH, contact time, solution pH and co-existing anions. AO-Mont prepared at pH 5, which contained higher content of Al resulted better fluoride removal performance. AO-Bent 5 and AO-Mont 5 have shown five and nine fold increase in fluoride removal capacity, respectively as compared to their respective unmodified clays. The experimental data fitted well with Freundlich adsorption isotherm model which indicated that the surface of the adsorbent is heterogeneous and adsorption of fluoride followed a multilayer sorption. Hence AO-modified Bent and Mont adsorbents prepared at pH 5 can be considered as potential adsorbents for defluoridation from drinking water.

Environmental uses of zeolites in Ethiopia

“…One of the collaborative projects developed in the north region of the country, yielded several zeolitic phases and at least one highly-pure large deposit of stilbite could be identified [18]. Besides, we have devoted large efforts in adding value to other Industrial Minerals, such as Bentonite [19][20][21] and Kaolinite [22,23], with known deposits at early stages of exploitation. On our side, we analyzed the samples and evaluated potential applications that could justify their commercial exploitation.…”

Applicability of Clay/Organic Clay to Environmental Pollutants: Green Way—An Overview

“…This was the phenomenon in which Langmuir monolayer adsorption was studied layer by layer. In the same year, the removal of heavy metals, phenols, fluorides, and dyes was studied by Almasri [82], Li et al [83], Xu et al [84], Dessalegne et al [85], and Belbel et al [86].…”

“…This was the phenomenon in which Langmuir monolayer adsorption was studied layer by layer. In the same year, the removal of heavy metals, phenols, fluorides, and dyes was studied by Almasri [82], Li et al [83], Xu et al [84], Dessalegne et al [85], and Belbel et al [86]. In 2020, Choi and Shin [96] and Luis Malvar et al [97] modified montmorillonite with hexadecyltrimethylammonium and octadecylamine for phenol removal.…”

Effect of synthesized carbon quantum dots on the photocatalytic properties of ZnO

“…Owing to the complexity of the different types of pollutants, the implementation of simple, fast, effective, and low-cost treatment techniques of these pollutants in wastewater remains a major challenge. To contain this plague, several techniques such as adsorption [5], biosorption [6], and coagulation [7] are used. However, these wastewater treatment methods transfer the pollution from an aqueous phase to a new phase, leading mostly to a formation of concentrated sludge, thus creating secondary pollution.…”