Mechanism of cadmium biosorption from aqueous solutions using calcined oyster shells. (1st March 2015)

• Record Type: Journal Article
• Authors: Alidoust, Darioush; Kawahigashi, Masayuki; Yoshizawa, Shuji; Sumida, Hiroaki; Watanabe, Makiko
• Is Part Of: Journal of environmental management. Volume 150(2015:Mar.)
• Page Start: 103
• Page End: 110
• Publication Date: 2015-03-01
• Subjects: Cadmium hydroxide -- Ettringite -- Otavite -- Specific surface area -- Surface precipitation -- Waste shell calcination; Environmental policy -- Periodicals; Environmental management -- Periodicals; Environment -- Periodicals; Ecology -- Periodicals; 363.705
• DOI: 10.1016/j.jenvman.2014.10.032
• Languages: English
• ISSNs: 0301-4797

Abstract

Abstract: The physicochemical properties of oyster shell-derived adsorbents prepared by calcination at different temperatures were characterized by elemental analysis, specific surface area, particle size distribution, X-ray diffraction, and scanning electron microscopy. The pH value in natural oyster shell increased from 9 to 12.7 following calcination above 750 °C. All of the oyster shell-derived adsorbents exhibited a BET surface area that ranged from 1.8 to 64.6 m 2 /g. Clearly, the proportion of particles within the ranges 25–50 μm and 50–100 μm increased after calcination, regardless of calcination temperature. The adsorption equilibrium and kinetics of cadmium (Cd) were investigated, and the mechanisms of sorption discussed. Experimental equilibrium data were fitted to a Langmuir adsorption isotherm model. Most Cd adsorption occurred during the initial hours of contact time, and a pseudo-second-order kinetic model best fitted the adsorption process. Cd sorption profiles indicated an initial, low Cd sorption region (25.25–32.36 mg/g) that was associated with calcination temperatures of up to 650 °C for 2 h, and a second region that contributed to high Cd sorption from 750 °C, with the maximum sorption capacity reaching a value of 1666.67 mg/g at 900 °C. The high Cd-removal capacity of oyster shell-derived adsorbents above 750 °C is attributed to their enhanced specific surface area, their material porosity, the bulk precipitation of Cd hydroxide and otavite on shell fragments, the formation of ettringite as a secondary precipitate, and ion exchange via Ca ions. This study highlights the effectiveness of calcined oyster shells in Cd removal from highly contaminated water and wastewater. Highlights: An effective biosorbent was fabricated by thermally treating oyster shells. Calcination enhanced specific surface area and created a porous surface morphology. Calcined oyster shells at >750 °C increased Cd 2+ removal from aqueous solutions. Bulk precipitation of Cd(OH)2 and otavite was the main Cd 2+ uptake mechanism. Cd exchange with Ca 2+ and incorporation of Cd 2+ into ettringite also occurred.