Competitive Removal of Heavy Metals from Aqueous Solutions by Montmorillonitic and Calcareous Clays

Abstract

A batch sorption method was used to study the removal of few toxic metals onto the Late Cretaceous clays of Aleg formation (Coniacian-Lower Campanian system), Tunisia, in single, binary and multi-component systems. The collected clay samples were used as adsorbents for the removal of Pb(II), Cd(II), Cu(II) and Zn(II) from aqueous solutions. Results show that the natural clay samples were mainly composed of silica, alumina, iron and magnesium oxides. N 2 -adsorption measurements indicated mesoporous materials with modest specific surface area of <71 m 2 /g. Carbonate minerals were the most influencing parameters for heavy metal removal by natural clays in both single and multi-element systems. The affinity sequence was Pb(II)>Cu(II)>Zn(II)>Cd(II) due to the variable physical properties of the studied metals. The maximum adsorption capacity reached 131.58 mg/g in single systems, but decreased to <50.10 mg/g in mixed systems. In single, binary and muti-element systems, the studied clay samples removed substantial amounts of heavy metals, showing better effectiveness than the relevant previous studies. These results suggest that the studied clay samples of the Late Cretaceous clays from Tunisia can be effectively used as natural adsorbents for the removal of toxic heavy metals in aqueous systems.

Adsorption of copper and zinc onto natural clay in single and binary systems

“…The stretching bands near 1,435.34, 871.67, and 711.60 cm -1 , found in the original sample, were assigned to calcite, but disappeared after the removal of carbonate minerals by acid treatment (Sdiri et al 2010(Sdiri et al , 2011. Detailed mineralogical, geological, and spectroscopic characterization of the studied clay samples can be found in Sdiri et al (2011Sdiri et al ( , 2012b.…”

“…The obtained FTIR spectra of the bulk (RS and RY) and the decarbonated (TS) clay samples showed the stretching vibrations of the surface hydroxyl groups (Si-Si-OH, or Al-Al-OH) near at 3,694.94 and 3,619.73 cm -1 . The other vibration at 1,635.34 cm -1 was attributed to the bending of adsorbed water (Sdiri et al 2011(Sdiri et al , 2012b. The stretching bands near 1,435.34, 871.67, and 711.60 cm -1 , found in the original sample, were assigned to calcite, but disappeared after the removal of carbonate minerals by acid treatment (Sdiri et al 2010(Sdiri et al , 2011.…”

“…Hereafter, we use the abbreviations RS and TS to refer to original and treated clays, respectively. To clarify the effects of carbonates on the adsorption process, additional smectitic clay (RY), collected from the Gabes area, was used for comparative purposes (Sdiri et al 2011(Sdiri et al , 2012b.…”

“…This was expected because of the higher precipitation pH (pH 6.8) for zinc carbonates; therefore, lower solubility constant (K sp = 1.4 9 10 -11 at 25°C) (Al-Degs et al 2006). Sdiri et al (2012b) mentioned that carbonaceous materials have high affinity to Cu(II) and Pb(II) due to their enhanced relative binding strength. As for RY clay, the removal efficiency was lower than the original RS clay because of the small amounts of carbonate (Table 1).…”

“…Those studies were limited to the adsorption of single metals, despite the fact that contaminated wastewaters contain more than one pollutants [e.g., Pb(II), Cd(II), Cu(II), and Zn(II)] that have to be removed before the final discharge in the receiving ecosystems. The Coniacian-Lower Campanian clays of the Aleg formation, Tunisia, showed high adsorptive capacities for heavy metal (Sdiri et al 2011(Sdiri et al , 2012b. While most sorption studies that are conducted on clays usually start by the removal of non-clay minerals (e.g., carbonate minerals, and quartz) in order to concentrate the clay minerals and improve the sorption properties of the adsorbent (Al-Degs et al 2006), the effects of carbonates impurities have not been studied in details.…”