Kinetic Study of Erbium Ion Adsorption on Activated Charcoal from Aqueous Solutions
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Kinetic Study of Erbium Ion Adsorption on Activated Charcoal from Aqueous Solutions RIAZ QADEER Pakistan Atomic Energy Commission, P.O. Box 1611, Islamabad, Pakistan Received March 23, 2004; Revised October 26, 2004; Accepted January 3, 2005
Abstract. The kinetics of the adsorption of erbium ions on activated charcoal from aqueous solutions has been studied in the temperature range of 10 to 40◦ C. It was observed that the diffusion of erbium ions in to the pores of activated charcoal controls the kinetics of the adsorption process, and the values of intra-particle diffusion rate constant, kd (g/g · min1/2 ) were evaluated as 0.7 × 10−3 to 1.6 × 10−3 in the temperature range studied. Various thermodynamic parameters H , G and S were also computed from values of the equilibrium constant K C . The results showed that the adsorption of erbium ions on activated charcoal is an endothermic process. Keywords:
activated charcoal, erbium ions, adsorption, kinetics, aqueous solutions
Introduction
Experimental
The time dependence study of metal ions adsorption on solids provides valuable information about the adsorption process and its mechanism. Generally, the adsorption process can be broken down into three consecutive steps: transport of the metal ions to the adsorbent; the adsorption process itself i.e., the formation of the adsorption bond; and transport of metal ions to the deeper layer of the adsorbent. The rate of each of these steps is dependent on many factors such as agitation of solution, the state of metal ions in solution, age of the solution, concentration of metal ions and temperature etc. (Benes and Majer, 1980). The adsorption of erbium ions is important for pre-concentration for use in nuclear and metallurgical industries. Due to its thermal neutron absorption cross section (168 b) and high melting point (1529◦ C), erbium along with other material is used to make nuclear control rods. Earlier reports have dealt with the adsorption of erbium ions on molybdenum surface (Shakirova et al., 1990) and resin (Yuan et al., 1996), but no data are available on its adsorption on activated charcoal. This communication reports the results of a temperature dependence study of erbium ion adsorption on activated charcoal from aqueous solutions.
Materials The chemicals used in this study were erbium nitrate (Rare Earth Product, 99.999%) and a commercial activated charcoal (M/S British Drug House BDH; item No. 33032). The B.E.T. surface area, determined by nitrogen adsorption, was found to be 980 ± 10 m2 /g. The porosity and pore volume were found to be 75.75 ± 2% and 1.43 ± 0.12 cm3 /g respectively, and average particle size was 3.7 ± 0.2 µm.
Instruments An energy dispersive X-ray fluorescence (EDXRF) spectrometer, XR 500 from Links System, U.K., equipped with an 860 analyzer, a Si (Li) detector and an X-ray tube K5012 with tungsten anode, was used for measuring the erbium ions concentration in solution with an error of ±1.5%. A Hetofrig shaker from Heto Birkerod, Denmark was used for temperature controlled adsorptio
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