Adsorptive separation of cadmium from aqueous solutions and wastewaters by riverbed sand Y.C. Sharma a, * , S.N. Kaul b , C.H. Weng c a Environmental Engineering and Research Laboratories, Department of Applied Chemistry, Institute of Technology, Banaras Hindu University, Varanasi 221 005, India b Department of Chemical Engineering, Bhartiya Vidyapeeth Deemed University, Pune 411 043, India c Department of Civil and Ecological Engineering, I-Shou University, Da-Hsu, Kaohsiung County 84008, Taiwan Received 15 September 2006; received in revised form 16 January 2007; accepted 20 January 2007 Riverbed sand for adsorptive separation of cadmium from waters and wastewaters. Abstract Application of riverbed sand for the adsorptive separation of cadmium(II) from aqueous solutions has been investigated. Removal increased from 26.8 to 56.4% by decreasing the initial concentration of cadmium from 7.5  10 5 to 1.0  10 5 M at pH 6.5, 25  C temperature, agitation speed of 100 rpm, 100 mm particle size and 1.0  10 2 NaClO 4 ionic strength. Process of separation is governed by first order rate kinetics. The value of rate constant of adsorption, k ad , was found to be 2.30  10 2 per min at 25  C. Values of coefficient of mass transfer, b L , were calculated and its value at 25  C was found to be 1.92  10 2 cm/s. Values of Langmuir constant were calculated. Values of thermodynamic parameters DG 0 , DH 0 and DS 0 were also calculated and were recorded as 0.81 kcal/mol, 9.31 kcal/mol and 28.10 cal/mol at 25  C. pH has been found to affect the removal of cadmium significantly and maximum removal, 58.4%, has been found at pH 8.5. Process can be used for treatment of cadmium(II) rich wastewaters. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Adsorptive separation; Cadmium(II); Riverbed sand; pH; Temperature 1. Introduction Metals are essential for industrial development of any na- tion. Like many other metallic species cadmium also occurs in earth’s crust but its occurrence in nature is comparatively feeble. It, however, exists in close association with zinc and is also found with copper and mercury in chemically com- bined forms (Kannan, 1995). Cadmium has variety of applica- tions. It is an important constituent for a number of alloys; it is frequently used in electroplating, NieCd batteries and paint pigments. Main sources of cadmium into aquatic systems are discharges of untreated industrial effluents from various appli- cations. Discharge of mining effluents and geological weather- ing are also recognized as sources of cadmium pollution in aquatic sources. Ingestion of cadmium in human body results in a painful disease ‘‘itai-itai’’, which results from chronic ex- posure to cadmium (Forstner and Wittman, 1979). Cadmium is a non-essential toxic metal and its health effects are well docu- mented (Fribarg et al., 1974; Hagino and Yoshioka, 1961). A number of methods are known for separation and re- moval of metallic species from aqueous solutions and waste- waters. These include ion exchange (Canet et al., 2002), coagulation, flotation (Zouboulis et al., 1997), precipitation (Esalah et al., 2000), and adsorption on activated carbons (McKay, 1979; Ramos et al., 1997; Huang and Ostovic, 1979; Huang and Wirth, 1982; Reed and Arunachalam, 1994). The above methods are cost intensive and their * Corresponding author. Tel.: þ91 542 2307025, þ91 9935616119; fax: þ91 542 2316428. E-mail address: y_sharma_2002@rediffmail.com (Y.C. Sharma). 0269-7491/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2007.01.014 Environmental Pollution 150 (2007) 251e257 www.elsevier.com/locate/envpol