Removal of Rhodium (III) from Aqueous Solution by Na- and K-Treated Clinoptilolites Ömer Saltabaş & Murat Teker & Aslı Döver & Eylem Serpil Atay Received: 24 January 2011 /Accepted: 13 June 2011 /Published online: 25 June 2011 # Springer Science+Business Media B.V. 2011 Abstract The clinoptilolite which was modified with sodium and potassium chloride was found to have adsorption capacity for rhodium. To evaluate the adsorption capacity and characteristics, the effects of solution pH, dose of clinoptilolite loading, contact time, temperature, and initial rhodium concentration were investigated in a batch mode. Adsorption was decreased with the increasing temperature for both modified clinoptilolites. The Langmuir and Freundlich adsorption models were used for mathematical description of the adsorption equilibrium. Equilibrium data were fitted to the Langmuir model in the concentrations of 2– 60 mg l -1 at 293 and 313 K. Based on the Langmuir isotherm plots, the maximum adsorption capacity value was calculated to be 0.415 mg g -1 at 293 K. Various thermodynamic parameters such as ΔG°, ΔH°, and ΔS° were evaluated with results indicating that this system was an exothermic spontaneous reaction and kinetically suited to the pseudo-second-order model. Keywords Adsorption . Clinoptilolite . Rhodium . Isotherm 1 Introduction Many toxic heavy metals have been discharged to the environment as industrial wastes, causing serious soil and water pollution. Various physicochemical and biological methods were studied for metal removal. Adsorption techniques are seen as an alternative and the most effective physical process for removal of heavy metals. Recent progress in treatment technolo- gy of metal-containing wastewater has led to the development of finding low-cost, renewable, locally available botanic material (Songkroah et al. 2004), bacteria (Pethkar and Paknikar 2003), larva shells (Gyliene et al. 2002), clays (Ajmal et al. 2001; Brigatti et al. 2000; Lam et al. 2007; Lin and Juang 2002), ion exchanger (Panayotova et al. 2007), or agricultural wastes (Donia et al. 2007; Fiol et al. 2006; Sciban et al. 2007; Srivastava et al. 1989; Teker et al. 1999, 1997) for the removal of metals. Some of the adsorbent materials had been used for rhodium sorption from wastewater, which included sulfate- reducing bacteria (Ngwenya and Whiteley 2006) and some anion exchanger (Alam et al. 1998a, b). In the last years, utilization of natural zeolites to control the pollution due to the effluents polluted with heavy metal ions has increased. Natural zeolites have ion exchange capability to remove metal ions, and this property makes zeolites favorable for wastewater treat- ment. Basically, zeolites are naturally occurring crystal- line aluminosilicates consisting of a framework of tetrahedral molecules, linked with each other by shared oxygen atoms and containing exchangeable alkaline and Water Air Soil Pollut (2012) 223:411–419 DOI 10.1007/s11270-011-0869-7 Ö. Saltabaş (*) Ceha Jewellery & Chemistry Co., Molla Fenari Mah., Gazi Sinan Paşa Sok, No: 18/1, Cağaloğlu-Fatih, 34420 Istanbul, Turkey e-mail: omer_saltabas@hotmail.com M. Teker : A. Döver : E. S. Atay Department of Chemistry, Sakarya University, 54100 Sakarya, Turkey