Heavy Metal Adsorption by Functionalized Clays

Abstract

Organic ligands containing the thiol (-SH) metal-chelating functionality were either grafted to the external surface silanol groups of sepiolite or introduced in the interlayers of montmorillonite, and the resulting functionalized clays were characterized and assayed as adsorbents for Hg(II), Pb(II), and Zn(II) ions from solution. Sepiolite was functionalized by covalently grafting 3-mercaptopro-pyltrimethoxysilane (MPS) to the surface tSi-OH groups of the clay, whereas montmorillonite was functionalized by replacement of the interlayer inorganic cation (Na + ) by 2-mercaptoethylammonium (MEA) cations. These clayorganic ligand systems were selected to minimize the congestion of the internal porosity of the clays, which has recently been shown to be the main obstacle to heavy metal adsorption by functionalized clays. Infrared spectroscopy and elemental analyses demonstrated the presence of the organic ligands in the modified clays. X-ray diffraction analysis indicated the organic cations (MEA) occupied the interlayers of montmorillonite. N 2 specific surface area measurements suggested that much of the surface area of montmorillonite and sepiolite remained accessible upon functionalization and that the organic ligand kept the montmorillonite interlayers open. The functionalized clays adsorbed most of the Hg(II) ions present in solution up to saturation and were also good adsorbents of Pb(II) at low metal ion concentrations (i.e., <0.02 mM). They were, however, less effective toward Pb(II) and Zn(II) at high metal ion concentrations. The presence of NaNO 3 or Ca(NO 3 ) 2 as background electrolytes at concentrations ranging from 0.001 to 0.1 M did not alter the great adsorption capacity of functionalized sepiolite for Hg(II). The results show that clay functionalization can be optimized by matching clay structure with a suitable reactive (i.e., fibrous clay with a graftable ligand or expandable clay with an exchangeable cationic ligand) and minimizing the gallery volume taken up by the organic ligand, thus improving the performance of the functionalized clay as adsorbent of heavy metals from solution.

Research progress of novel adsorption processes in water purification: A review

“…Among all the approaches proposed, adsorption is one of the most popular methods and is currently considered as an effective, efficient, and economic method for water purification. The adsorbents used include activated carbon (Nouri et al, 2002;Pereira et al, 2003), clay minerals (Celis et al, 2000;Abollino et al, 2003), zeolites (Oliveira et al, 2004), metal oxides (Wu et al, , 2005Zhang et al, 2007a), agricultural wastes (Robinson et al, 2002), biomass (Loukidou et al, 2003) and polymeric materials (Atia et al,2003).…”

Effect of salinity and temperature on the adsorption of Hg(II) from aqueous solutions by a Ca‐montmorillonite

“…Conversely, Celis et al . [8] did not find a significant difference between adsorption of mercury in the presence of up to 0.1 M NaNO 3 (8.5 g L − 1 ) and the adsorption measured in the absence of the electrolyte. On the other hand, Echeverría et al .…”

“…Because of the physical and chemical characteristics of clay minerals, such as large surface area, moderate to high cation exchange capacity and high negative surface charge, these materials can act as concentrators of trace elements in aquatic ecosystems [6], and can play an important role in controlling the background levels of such trace elements in sediments [7]. In addition, other features of these materials include their common occurrence in soils and sediments from most ecosystems and low cost [8]. Hirst [7] suggested that clay minerals concentrate trace elements in the sequence: montmorillonite > vermiculite > illite = chlorite > kaolinite.…”

Review on the Removal of Metal Ions from Effluents Using Seaweeds, Alginate Derivatives and Other Sorbents

“…bentonite, kaolinite, montmorillonite, wollastonite) (CELIS et al, 2000;PRADAS et al, 1994), human hair and teeth (HELAL et al, 2002;TAN et al, 1985), leaf mould (SHARMA and FORSTNER, 1994), sand (AWAN et al, 2003), metal oxides (Al, Fe, Mn -oxides) (BAILEY et al, 1992;TRIVEDI andAXE, 2001), vermicompost (PEREIRA andARRUDA, 2003), xanthate (FLYNN et al, 1980;JAWED and TARE, 1991), and zeolites (e.g., clinoptilolite and chabazite) (GENÇ-FUHRMAN, 2007;LEPPERT, 1990;KALLO, 2001;OLIVEIRA et al, 2004).…”