Organo-Modified Vermiculite: Preparation, Characterization, and Sorption of Arsenic Compounds

Abstract

Among the various technologies tested for removing the anionic species resulting from arsenic contamination, sorption methods have received unflagging interest. Being potential sorbent materials, clay minerals modified by cationic surfactants are often examined for this purpose. Among the clay minerals tested, information regarding sorption properties of expanded vermiculite modified with surfactants is scarce. Therefore, the present study aims to prepare organo-vermiculites modified with hexadecyltrimethylammonium (HDTMA) and benzyldimethylhexadecylammonium (HDBA) at surfactant concentrations of 0.5, 1.0, and 2.0 cation exchange capacity. Modified sorbents were identified and characterized using the analytical methods that can determine phase composition and textural properties of the samples. The sorption of As(III) and As(V) as a function of initial pH value, initial concentration of As(III, V), and initial dosage of sorbent was investigated. The results show that HDTMA and HDBA affect the properties of raw vermiculite. For instance, increase in the concentration of surfactants is often accompanied by a change in interlayer space or textural properties of vermiculite. It was observed that tested organo-minerals adsorbed As(V) to a greater extent compared to As(III). Various analytical studies were carried out and the results revealed the successful synthesis of organo-vermiculite. Moreover, the study also showed that the structure of organo-vermiculite has a significant impact on the uptake of As(III) and As(V) anions.In the last decades, various technologies for removing As from contaminated water have been investigated, such as oxidation, coagulation, ion exchange, precipitation, membrane filtration, biological treatment, and sorption [9][10][11]. However, most of these methods have drawbacks, including high costs, deficient removal, generation of waste products, or high reagent and energy requirement. Among the methods mentioned earlier, adsorption seems to be the most effective method [1,12]. For removal by adsorption technique, activated carbon, metal-organic frameworks, zeolites, bog iron ores, water treatment residuals, and activated alumina have been proven to be promising adsorbents for arsenic removal [13][14][15][16][17].Clay minerals are low-cost and nontoxic sorbents. Raw clays are able to sorb cations owing to their negatively charged surface; however, they display low sorption efficiency for negatively charged contaminants such as arsenic [18]. Nevertheless, clays can be chemically modified by organic surfactants, which change the charge on the clay surface from negative to positive [19]. The organo-clays are hydrophobic materials that can effectively sorb anions and organic compounds. Modified kaolinite, montmorillonite, and illite are the most popular clay minerals that are used as sorbents [20][21][22]. However, only a few studies have focused on using organo-vermiculites to sorb anions [23,24].Vermiculite is a 2:1 phyllosilicate mineral having a sandwiched structure with two tetrahedral shee...

Expanded vermiculite-filled flexible polymer composites

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