Adsorption of silver from aqueous solution onto raw vermiculite and manganese oxide-modified vermiculite

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Abstract

In this work, the manganese oxide-modified vermiculite (Mn-MV) was prepared from raw vermiculite (RV) and characterized chemically and morphologically. The adsorption surface of RV was increased about 10 times after the modification due to the increase in negative charge onto the sorbent surface. The adsorption performance of RV and Mn-MV sorbents in the removal of silver (Ag(I)) ions from aqueous solution was examined using batch method. The effects of initial pH of solution, contact time, adsorbent concentration, initial silver ion concentration, modifying agent concentration and temperature of solution on the adsorption efficiency were investigated systemically. The maximum adsorption capacity of RV and Mn-MV sorbents was found as 46.2 and 69.2 mg g−1, respectively. The calculated adsorption energy (9.6 kJ mol−1) from the Dubinin–Radushkevich (D–R) model indicated that the adsorption process onto modified sorbent was taken place mainly by chemical ion exchange. A 95% portion of the Ag(I) ions adsorbed was desorbed successfully from the sorbent surface by using 0.5 M 10 mL HCl. The Mn-MV sorbent had good reusability performance after 10 adsorption–desorption cycles. The calculated thermodynamic parameters showed that the adsorption of Ag(I) onto Mn-MV sorbent process was feasible, spontaneous and exothermic. The kinetic evaluation also suggested that the adsorption process followed well the pseudo-second-order kinetic model.

Graphical abstract

The manganese oxide-modified vermiculite (Mn-MV) was prepared from raw vermiculite (RV) and characterized chemically and morphologically. The effects of initial pH of solution, contact time, adsorbent concentration, initial silver ion concentration, modifying agent concentration and temperature of solution on the adsorption efficiency were investigated systemically. The maximum adsorption capacity of RV and Mn-MV sorbents was found as 46.2 and 69.2 mg g−1, respectively. A 95% portion of the Ag(I) ions adsorbed was desorbed successfully from the sorbent surface by using 0.5 M 10 mL HCl. The prepared Mn-MV sorbent had good reusability performance after 10 adsorption–desorption cycles. The calculated thermodynamic parameters showed that the adsorption process was feasible, spontaneous and exothermic. The kinetic evaluation also suggested that the adsorption of Ag(I) onto Mn-MV sorbent followed well the pseudo-second-order kinetic model.

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Highlights

► The modified sorbent (Mn-MV) was prepared by manganese oxide modification of raw vermiculite (RV). ► Adsorption capacity of RV and Mn-MV was found to be 46.2 and 69.2 mg/g at pH 4, respectively. ► The results indicated that the prepared Mn-MV sorbent is a promising sorbent in the removal of Ag(I) from aqueous solutions.

Introduction

Industrial effluents frequently include significant quantities of heavy metal ions that cause danger for living population if they are discharged to environment without sufficient treatment [1]. Heavy metal pollution in water and soil increases along with the enlargement of industrial activities [2]. Therefore, the remediation of heavy metal ions from industrial wastewaters using low cost-sorbents is always of great interest [3], [4], [5], [6], [7].

Silver is one of the precious metals that have significant roles in many parts of human life [8]. Silver is exist as combined with copper or lead minerals in nature [9]. The major utility area of silver in industry is the manufacture of photographic film. Moreover, it is a functional raw material in development of mirroring, electroplating, catalyst, antimicrobial materials, batteries and, coinage, medication industries due to its excellent properties such as malleability, ductility, electrical and thermal conductivity, photosensitivity and antimicrobial [10]. Thus, silver ion pollution in wastewaters is caused by these industrial activities. The contact with soluble silver compounds may create some toxic effects such as liver and kidney damage, irritation of the eyes, skin, respiratory, and intestinal tract, and changes in blood cells [11], [12]. The World Health Organization (WHO) and the US Environmental Protection Agency (EPA) classified soluble silver ions as hazardous substance in water systems and limited its concentration level in drinking waters to be 100 μg L−1 [13]. So, there is a requirement to develop an effective way for the elimination of silver ions from aqueous solutions. A variety of techniques such as ion exchange [14], [15], electrolysis [16], membrane separation [17], biosorption [18] have been used for the remediation of silver ions from different pollution sources. The initial costs for the equipment and operation of these techniques are usually high [19]. On the other hand, adsorption method has also been widely used for retrieval of silver ions because of its several advantages such as simplicity, quickness and appropriateness. Several new adsorbents, including activated carbon [20], chelating resins [21], polymeric materials [22], micro- and nano-sized functional spheres [23], [24], colloidal carbon nanospheres [8] have been investigated for elimination of silver ions from aqueous solutions. However, such type sorbents are not economically feasible for actual wastewater treatment. An adsorbent must be ecofriendly, cost-effective industrially viable, and efficient in the removal of different toxic metals. For this reason, it is essential to look for low-cost adsorbents that could replace synthetic ion exchange resins or other expensive materials. A lot of efforts have been spent to increase the variety of inexpensive and environmentally friendly adsorbents such as fly ash [25], [26] and clay minerals [10], [27], [28], [29] used in the elimination of silver ions from aqueous solutions.

In recent years, some novel metallic oxides or composite oxides (MnO2, Al2O3, Fe2O3, TiO2, Fe3O4, MnFe2O4 have gained a rising awareness since they are particularly functional in the removal of different heavy metal ions from wastewaters [30], [31], [32], [33], [34]. Also, manganese oxide (MnO2)-loaded adsorbents has attracted much interest as a result of its specific physical and chemical properties [35]. However, it is difficult to be performed individually due to its easy agglomeration and poor dispersion properties [36]. Therefore, in recent times, there has been a rising attention for new type MnO2-modified adsorbents, such as MnO2-coated bentonite [37], MnO2-coated zeolite [38], MnO2-coated sand [39], δ-MnO2-loaded weak basic anion exchange resin D301 [40], δ-MnO2-loaded graphene [36], MnO2-dispersed in cellulose gel beads [41], MnO2-deposited diatomite [42].

Vermiculite consists of unit layers with two silica tetrahedral sheets attached to a central magnesium octahedral sheet [43]. Vermiculite has characteristics of a stable negative charge, great surface area, and intensive reactive surface sites. Moreover, it is exist abundantly, easily provided and inexpensive material (e.g.: approximately 0.5 $/L in Turkish markets). These advantageous properties make it suitable adsorbent for heavy metal removal from wastewaters [44], [45]. The purpose of this work was to investigate the adsorption potential of raw vermiculite (RV) and MnO2-modified vermiculite (Mn-MV) in the removal of Ag+ from aqueous solution. Here, MnO2 was selected as modifying agent due to the following facts: (i) Since it ionizes at low pH, it carries larger net negative charge in solution in relation to other oxides like SiO2, TiO2, Al2O3, and FeOOH [46]. (ii) It can be high loaded to silica-based surfaces [47]. (iii) The surface area of a silica-based adsorbent can be increased noticeably by MnO2 modification [37], [42], [47]. In addition, to the best of our knowledge, a detailed research report about silver ions sorption onto RV and Mn-MV sorbents is not available in literature. The influences of initial pH, initial metal concentration, adsorbent concentration, modifying agent concentration, contact time, and temperature of solution on the adsorption efficiency were studied systemically. The reusability performance of the modified sorbent was also investigated. In addition, the experimental data were examined by evaluating the adsorption isotherms, thermodynamics and kinetic parameters.

Section snippets

Adsorbents and reagents

The RV sorbent was obtained from Agrekal Company (Antalya-Turkey). According to the data supplied by the manufacturer company, the chemical composition of super fine grade RV (size: below 2 mm) is follow: 38–46 wt.% SiO2, 16–35 wt.% MgO, 10–16 wt.% Al2O3, 6–13 wt.% Fe2O3, 1–5 wt.% CaO, 1–6 wt.% K2O, 1–3 TiO2, 8–16 H2O and 0.2–1.2 wt.% the others. Moreover, all chemicals used in the batch adsorption experiments and modifying process were analytical reagent grade.

Preparation of manganese oxide-modified vermiculite (Mn-MV)

Manganese chloride (MnCl2) and sodium

Characterization of raw and modified materials by BET and SEM analyses

The amount of MnO2 loaded to the sorbent surface was determined to be 0.25 g per mass unit (g) of vermiculite. Several researchers reported different results about the amount of Mn or MnO2 deposited onto various adsorbent surfaces. For example; 5.46 mg Mn/g-sand [39], 90 mg Mn/g-D301 [40], 0.71 g MnO2/g-cellulose [41], 0.38 g MnO2/g-diatomite [47], 0.18 g MnO2/g-acrylic fibers [48], 0.35 g MnO2/g-diatomite [50]. These results indicated that the depositing ability of MnO2 depends on the surface

Conclusions

In this work, the adsorption potential of Mn-MV sorbent in the removal of Ag(I) ions from aqueous solution was investigated using batch method. The experimental results indicated that initial pH of solution, contact time, adsorbent concentration, initial metal ion concentration, temperature of solution and MnO2 concentration used in modification were found to be efficient in the removal of Ag(I) ions from aqueous solution using Mn-MV sorbent. A considerable improvement in adsorption capacity of

Acknowledgements

Authors thank Altınay Boyraz (Erciyes University, Technology Research & Developing Center) for SEM analysis. Authors also thank Güngör Şahinoğlu due to his helping in some studies. Dr. Mustafa Tuzen thanks Turkish Academy of Sciences for financial support.

References (63)

  • M. Akgul et al.

    Micropor. Mesopor. Mater.

    (2006)
  • N.A. Öztaş et al.

    Micropor. Mesopor. Mater.

    (2008)
  • Y. Zeng et al.

    Micropor. Mesopor. Mater.

    (2010)
  • E. Eren et al.

    J. Hazard. Mater.

    (2008)
  • X. Song et al.

    J. Hazard. Mater.

    (2011)
  • M.A. AbdEl-Ghaffar et al.

    Hydrometallurgy

    (2009)
  • H. Ghassabzadeh et al.

    J. Hazard. Mater.

    (2010)
  • H.Y. Huo et al.

    Chem. Eng. J.

    (2009)
  • M. Hosoba et al.

    Anal. Chim. Acta

    (2009)
  • N. Lihareva et al.

    Micropor. Mesopor. Mater.

    (2010)
  • B. Pollet et al.

    Ultrason. Sonochem.

    (2000)
  • A.R. Ladhe et al.

    J. Membr. Sci.

    (2009)
  • Z. Lin et al.

    Spectrochim. Acta A

    (2005)
  • B. Volesky

    Hydrometallurgy

    (2001)
  • X. Lu et al.

    Chem. Eng. Sci.

    (2010)
  • M. Akgül et al.

    Micropor. Mesopor. Mater.

    (2006)
  • H. Yang et al.

    J. Hazard. Mater.

    (2008)
  • H.K. Tamura et al.

    J. Colloid Interface Sci.

    (1997)
  • Y.M. Ren et al.

    J. Hazard. Mater.

    (2008)
  • X.Y. Hou et al.

    Colloid Surf. A: Physicochem. Eng. Aspects

    (2010)
  • K. Wu et al.

    Chem. Eng. J.

    (2012)
  • S.S. Tripathy et al.

    J. Colloid Interface Sci.

    (2005)
  • Z. Khan et al.

    Interface Sci.

    (2005)
  • Y.M. Ren et al.

    Chem. Eng. J.

    (2011)
  • E. Eren et al.

    J. Hazard. Mater.

    (2009)
  • R.H. Han et al.

    J. Hazard. Mater.

    (2006)
  • L.J. Dong et al.

    J. Environ. Sci.

    (2010)
  • M.A.M. Khraisheh et al.

    Chem. Eng. J.

    (2004)
  • P.K. Pandey et al.

    Bioresour. Technol.

    (2009)
  • S.H.R. Davies et al.

    J. Colloid Interface Sci.

    (1989)
  • T. Mathialagan et al.

    J. Hazard. Mater.

    (2002)
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