Empirical Multicomponent Equilibrium and Film-Pore Model for the Sorption of Copper, Cadmium and Zinc onto Bone Char
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Empirical Multicomponent Equilibrium and Film-Pore Model for the Sorption of Copper, Cadmium and Zinc onto Bone Char CHUN-WAI CHEUNG, KEITH K.H. CHOY, JOHN F. PORTER AND GORDON MCKAY∗ Department of Chemical Engineering, Hong Kong University of Science and Technology, Clear Water Bay Road, Kowloon, Hong Kong SAR, China [email protected]
Received June 30, 2003; Revised September 14, 2004; Accepted November 3, 2004
Abstract. The adsorption of three metal ions onto bone char has been studied in both equilibrium and kinetic systems. An empirical Langmuir-type equation has been proposed to correlate the experimental equilibrium data for multicomponent systems. The sorption equilibrium of three metal ions, namely, cadmium (II) ion, zinc (II) ion and copper (II) ion in the three binary and one ternary systems is well correlated by the Langmuir-type equation. For the batch kinetic studies, a multicomponent film-pore diffusion model was developed by incorporating this empirical Langmuir-type equation into a single component film-pore diffusion model and was used to correlate the multicomponent batch kinetic data. The multicomponent film-pore diffusion model shows some deviation from the experimental data for the sorption of cadmium ions in Cd-Cu, Cd-Zn and Cd-Cu-Zn systems. However, overall this model gives a good correlation of the experimental data for three binary and one ternary systems. Keywords: film-pore diffusion, batch sorption, metal ions, bone char, multicomponent
Introduction Sorbent performance is the critical factor in the design and operation of an adsorption system. Bone char is a heterogeneous sorbent which is derived from the calcination of animal bone in the absence of air. This sorbent has been demonstrated to remove aluminum ions and iron ions from rural water in a pilot study (Lewis, 1995). Therefore, it is believed that bone char can be used to remove metal ions from wastewaters. Bone char, a mixed adsorbent containing around 10% carbon and 90% calcium phosphate, is mainly produced by the carbonization of bones. Structurally, the calcium phosphate in bone char is in the hydroxyapatite form Girgis et al. (1997). It has been shown that after the decarbonization of bone char it has little or no decolorizing power (Elliott, 1994), although the hydroxyapatite in bone char retains an adsorption ∗ To
whom correspondence should be addressed.
capacity to adsorb calcium salts (Killedar, 1991) and dissolved salts (Elliott, 1994). Therefore, bone char can eliminate either organic or inorganic species from their solutions. Bone char has traditionally been used to decolourize sugar solutions in the sugar refining industry for many years. Abdel Raouf and Daifullah (1997) reported that the bone char derived by heating the animal bone to 500–600◦ C could be used to remove fluoride from drinking water on a laboratory scale (Christoffersen et al., 1991; Larsen et al., 1993; Phantumvanit and LeGeros, 1997). In recent studies, bone char was used to adsorb the radioisotopes of antimony and europium ions from radioactive wa
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