Abstract
Batch adsorption studies were carried out to evaluate the Pb 2+ adsorption capacities of three different fired clay soils with different particle size distributions. Adsorption efficiency was observed to increase with an increase in clay content. Adsorption efficiencies of the fired clay soils were also influenced by the firing temperature, the solution’s acidity, initial Pb 2+ concentration, shaking time and adsorbent dose. Adsorption of Pb 2+ by the clay soils was observed to increase linearly from pH 1 to 5 and then remained nearly constant at higher pH values. The adsorption of Pb 2+ was observed to increase sharply with Pb 2+ for the lower initial concentrations (5 to 10 mg/L), while a modest increase in Pb 2+ adsorption was found from 10 to about 50 mg/L, a concentration at which maximum removal was attained. The Langmuir and Freundlich adsorption models were applied to the adsorption data and the Langmuir model represented the adsorption process better than the Freundlich model, with correlation coefficients (R 2 ) ranging from 0.97 to 0.99. The adsorption capacities (qm) calculated from Langmuir for the adsorption of Pb 2+ by S 3F , S 2F and S 1F were found to be 17.3, 15.9, and 11.2 mg/g, respectively. Key words : Adsorption, fired clay soils, isotherm, adsorption kinetics, sand, silt, particle size.
Highlights
Lead is known to be one of the most toxic contaminants, even at very low concentrations
The surface areas of the fired clay soils, very low relative to those of activated carbon adsorbents (500 to 1400 m2/g) which are used for various adsorption purposes, are fairly high relative to other adsorbents such as wheat bran (8.65 m2/g) (Bulut and Baysal, 2006), natural clay (26.90 m2/g) (Njoku et al, 2011) and vanadium mine tailing (42.39 m2/g) (Shi et al, 2009), and cottonseed hull charred at 350 (4.7 m2/g) and 650°C (34 m2/g) (Uchimiya et al, 2011)
This may be attributable to the higher specific surface area (SSA) and cation exchange capacity (CEC) possessed by the soil with higher clay content relative to the one with lower clay content
Summary
Lead is known to be one of the most toxic contaminants, even at very low concentrations. Due to the fact that these waste water purification methods require high capital, high operating costs and often generate chemical sludge, which itself is a disposal problem, the feasibility of using various low-cost locally available adsorbents has been investigated for the removal of Pb2+ ions from waste water (Bulut and Baysal, 2006; Malakootian et al, 2009; Li et al, 2007; Qaiser et al, 2009). Clays are among the various locally available materials that are used for the removal of Pb2+ and other various heavy metals from aqueous solutions (Njoku et al, 2011; Talaat et al, 2011; Mbadcam et al, 2011; Inglezakis et al, 2007; Sar et al, 2007; Nassem and Tahir, 2001; Shi et al, 2009; Eba et al, 2010). In the Abbreviations: S1, Clay soil 1; S2, clay soil 2; S3, clay soil 3; S1F, fired clay soil 1; S2F, fired clay soil 2l; S3F, fired clay soil 3
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