172 † To whom correspondence should be addressed. E-mail: aghaemi@iust.ac.ir Korean J. Chem. Eng., 30(1), 172-180 (2013) DOI: 10.1007/s11814-012-0113-1 INVITED REVIEW PAPER Characterization of Ag(I), Co(II) and Cu(II) removal process from aqueous solutions using dolomite powder Ahad Ghaemi* ,† , Meisam Torab-Mostaedi**, Shahrokh Shahhosseini*, and Mehdi Asadollahzadeh** *Department of Chemical Engineering, Iran University of Science and Technology, P. O. Box 16765-163, Tehran, Iran **Nuclear Fuel Cycle Research School, Nuclear Science and Technology Research Institute, P. O. Box 14155-1339, Amirabad, Tehran, Iran (Received 12 January 2012 • accepted 9 July 2012) Abstract -Dolomite, a natural adsorbent, was used for removal of Ag(I), Cu(II) and Co(II) from aqueous solutions. Adsorption parameters including pH, temperature and contact time have been investigated to obtain adsorption mech- anism. The results of experiments showed that adsorption of the metal ions increased by increasing pH values up to 5.5. The adsorption process was initially fast. Equilibrium isotherm data were analyzed using Langmuir, Freundlich and Dubinin-Radushkevich isotherm models. Maximum adsorption capacity of Ag(I), Cu(II) and Co(II) was 1.34, 1.63 and 2.84 mg/g at 20 o C, respectively. Kinetic models including Lagergren first-order and pseudo-second-order were used to test kinetic data. The results showed that pseudo-second-order has good agreement with experimental data. Thermodynamic parameters of the process were also investigated at different temperatures. The negative values of Gibbs free energy and enthalpy changes for Ag(I), Cu(II) and Co(II) indicated the spontaneous and exothermic nature of the adsorption process. Key words: Dolomite, Ag(I), Cu(II), Co(II), Adsorption Isotherm INTRODUCTION Contamination of heavy metal ions in water supplies has increased over the last years as a result of over population and expansion of industrial activities. Metal ions pollution has a harmful effect on biological systems and does not undergo biodegradation. There- fore, the elimination of toxic metal ions from aqueous solutions is very important from environmental, economical and protection of public health points of view [1,2]. Several treatment technologies such as adsorption, solvent extrac- tion, precipitation, membrane filtration and ion exchange have been developed to remove the metal ions from aqueous solutions. Among these techniques, adsorption is a more useful, feasible and practical method for metal ion removal than are other processes [3-8]. In the adsorption technique, different natural and synthetic ad- sorbents were used to remove metal ions [9-14]. Synthetic adsor- bents such as activated carbon have been used widely in wastewater treatment applications throughout the world. In spite of their pro- lific use, synthetic adsorbents remain an expensive material, since higher the quality of these adsorbents, the greater their cost [15]. Therefore, this situation makes it no longer attractive to be widely used in small-scale industries because of cost inefficiency [16,17]. Due to the problems mentioned previously, research interest into the production of alternative adsorbents to replace the costly syn- thetic adsorbents has intensified in recent years. Attention has been focused on the various adsorbents which have metal-binding capac- ities and are able to remove unwanted heavy metal ions from con- taminated water at low cost. Because of their low cost and local availability, natural materials are classified as low-cost adsorbents. There are many different natural minerals such as perlite, zeolite, chitosan and clay or certain waste products from industrial opera- tions such as fly ash, coal and oxides of minerals which have high adsorption capacity and can remove metal ions from effluents at reasonable costs [18-21]. On the other hand, natural sorbents are widely used in water and sewage purification, ammonia and heavy metal ion removal, ion exchange in radioactive wastewater treatment, removal of oil pol- lution from water and adsorption of other components from liquid and gaseous phases [22,23]. Clay minerals are considered very im- portant adsorbents in natural water systems because of their high surface area combined with the structural and pH dependent charge developed on their surfaces. Low-cost adsorbents are still needed and these should be easily regenerated or disposed of without sub- stantial environmental impact. A review of more than 70 natural and synthetic adsorbents and their potential uses for metal ions re- moval has been reported [24]. The aim this study was to investigate the adsorption potential of Iranian dolomite as a low-cost adsorbent in the removal of Ag(I), Cu(II) and Co(II) ions from aqueous solution. Adsorption experi- ments were performed at different conditions to determine the opti- mum parameter values for the maximum adsorption of Ag(I), Cu(II) and Co(II) ions from aqueous solutions. The Langmuir, Freundlich and Dubinin-Radushkevich (D-R) models were used to describe equilibrium isotherms. The adsorption mechanisms of Ag(I), Cu(II) and Co(II) onto dolomite were also evaluated in terms of kinetics and thermodynamics. EXPERIMENTS 1. Adsorbent Characterization The dolomite sample used in this study was supplied from Tabriz