Abstract
In this work, various physicochemical characteristics, e.g., surface properties and mineralogical compositions, of five clays collected from different sites in the Al-Hasa oasis in Saudi Arabia have been investigated. Analysis of the mineralogical compositions of the clays in the study by X-ray diffraction indicated the coexistence of palygorskite, montmorillonite, illite, kaolinite, chlorite, calcite and quartz in different percentages. Thermogravimetric analysis indicated that all studied clays exhibited dehydroxylation temperatures higher than 470 °C. On the other hand, pore size distribution analysis of clays from N2 adsorption indicated the presence of micro- and narrow mesopores (of 1.3–2.8 nm). Furthermore, the capability of the different clays for removal of Pb (II) from aqueous solution has been studied. The adsorption process was described through the Langmuir, Freundlich, Temkin and Dubinin–Radushkevich models. The Langmuir model was the most suitable compared to the other models in the case of palygorskite- and montmorillonite-rich clays. However, the Temkin model better represented the adsorption process of Pb (II) on calcite-rich clay. The clay sample with 61.0 wt% of palygorskite was found to be the most effective at removing Pb (II), with a maximum removal capacity of 74.07 mg/g at pH 6, with a contact time of 6 h and at 25 °C. Generally, the adsorption mechanism of lead over all the studied clays followed the pseudo-second-order kinetics. On the other hand, the catalytic activity of clays in the study has been tested in methanol conversion. The acidic clays, those containing high amounts of montmorillonite, showed higher selectivity to ethylene, viz., 78.9%, with a methanol conversion of 39.1% at 350 ° C and 0.1 MPa.
Highlights
Several sources of clays are available in the Saudi Arabia, and so numerous studies have been conducted to characterize them and to investigate their potential uses [1,2,3,4,5,6]
Al-Hasa oases are situated between the rock desert of As Summan plateau in the west and sand dunes covering the adjoining plain in the east
It is well known that clays are widely used in many industrial applications such as ceramic, paper, paint, barrier, catalyst, and adsorbent applications, etc. [7,8,9]
Summary
Several sources of clays are available in the Saudi Arabia, and so numerous studies have been conducted to characterize them and to investigate their potential uses [1,2,3,4,5,6]. Saudi Arabia is geologically divided into four distinct and extensive terrains, (Figure S1). To the best of our knowledge, no extensive study has been conducted to investigate the surface and physicochemical characteristics of Al-Hasa clays and their potential uses in the literature. Reuse of wastewater resources from industrial processes is a strategic aim in Saudi Arabia. Heavy metals, especially lead, are the common contaminants of wastewater, collected as residues from petroleum industries
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