Adsorption of ruthenium ions on activated charcoal: influence of temperature on the kinetics of the adsorption process

Adsorption of ruthenium ions on activated charcoal: influence of temperature on the kinetics of the adsorption process first-author †E-mail:drriazqadeer@yahoo.com †E-mail:drriazqadeer@yahoo.com drriazqadeer@yahoo.com Pakistan Atomic Energy Commission, Islamabad, Pakistan Pakistan Atomic Energy Commission, Islamabad, Pakistan Influence of temperature on ruthenium adsorption on activated charcoal from 3 mol/L HNO 3 solutions was investigated in the temperature range of 288 K to 308 K. It was observed that the rise in temperature increases the adsorption of ruthenium ions on activated charcoal and follows the kinetics of first order rate law with rate constant values 0.0564–0.0640 min −1 in the temperature range of 288 K to 308 K respectively. The activation energy for the adsorption process was found to be 1.3806 kJ/mol. Various thermodynamics quantities namely Δ H , Δ S and Δ G were computed from the equilibrium constant K C values. The results indicated a positive heat of adsorption, a positive Δ S and a negative Δ G . Ruthenium Activated charcoal Adsorption Kinetics Thermodynamic parameters Nitric acid solution INTRODUCTION 1 Time dependence study of metal ions adsorption on solids provides valuable information on the adsorption process and its mechanism. Rate of metal ions adsorption process is dependent on a number of factors such as agitation of the solution, the state of metal ions in solution, concentration of metal ions and temperature (Benes and Majer, 1980 1980 ). Temperature is the parameter generally ignored in most adsorption studies (Bangash and Hanif, 1992 1992 ; Afzal et al., 1993 1993 ; Atun and Kilislioglu, 2003 2003 ; Esumi et al., 2004 2004 ; Ko et al., 2004 2004 ). 106 Ru ( t ½ =386 d) is an important radioisotope in the nuclear industry and its adsorption on solid is important for purification, trace metal analysis and waste treatment. This paper reports results of our investigation of temperature’s influence on the kinetics of ruthenium ions adsorption on activated charcoal from 3 mol/L HNO 3 solution. Activated charcoal is used due to its well known adsorptive characteristics and radiation stability (Qadeer and Hanif, 1994 1994 ). The results are important in relation to the recovery of ruthenium ions. Some workers studied the adsorption of ruthenium on various solids/substrate (Legin and Kuznestsov, 1974 1974 ; Qian and Yang, 1986 1986 ; Che et al., 1987 1987 ; Jiang and Anson, 1992 1992 ; Kavan et al., 1993 1993 ; Lin et al., 1993 1993 ; Chen et al., 1993 1993 ; Vrublevs’ka et al., 1999 1999 ; Lazarin and Sernaglia, 1999 1999 ). Only few data are available on its adsorption on graphite/carbon (Che et al., 1987 1987 ). These studies were investigated from different points of view. MATERIALS AND METHODS 1 The chemicals used in this study were ruthenium (III) chloride (MERCK, product No. 119246), a commercial activated charcoal (M/S British Drug House BDH; Item No. 33032, BET surface area 980 m 2 /g) and nitric acid (MERCK, Product No. 100441). Adsorption measurements were carried out via batch technique. Accordingly, 10 ml of ruthenium solutions of known concentration in 3 mol/L HNO 3 were added to 50 ml glass reagent bottles and shaken with 0.1 g of dry activated charcoal in a thermostat shaker, the temperature of which was pre-adjusted to a desired value. After a predetermined time, each solution was filtered through Whatman filter paper No. 40 (Circular, 14.0 cm). The first 2–3 ml portion of the filtrate was rejected because of the adsorption of ruthenium ions on the filter paper. The concentration of ruthenium ions in measuring filtrate was determined by means of a wavelength dispersive X-rays fluorescence spectrometer (Siemens SRS200) and was corrected for losses due to adsorption on the walls of the glass bottles by running blank experiments (i.e., without activated charcoal added). The amount of ruthenium ions adsorbed on the activated charcoal was computed using the following relation: Amount adsorbed (g/g)=( C o − C t ) V / W where C o is the initial concentration of ruthenium ions solution (g/L); C t the concentration of ruthenium ions in solutions (g/L) at time t ; V the volume of the solution taken (L) and W the weight of the activated charcoal taken (g). RESULTS AND DISCUSSION 1 Investigations were conducted to ascertain the time required to reach equilibrium between ruthenium ions and the activated charcoal as a function of temperature. This study involved shaking of 10 ml of a solution containing 5×10 −3 g/L of ruthenium in 3 mol/L HNO 3 with 0.1 g of activated charcoal for different time intervals from 2 to 100 min at temperatures of 288 K to 308 K. Fig. 1 1 represents the variation of ruthenium ions adsorption on activated charcoal with shaking time. This figure indicates that initially the amount of ruthenium ions adsorbed increases rapidly, but then the process slows down and subsequently attains a constant value after 80 min i.e., when adsorption equilibrium is established. The slow adsorption is explained by the diffusion of ruthenium ions into the pores of the activated charcoal. Fig. 1 1 also shows that the general time dependence of the ruthenium ions adsorption process is essentially independent of temperature. However, the temperature variations influence the amount of ruthenium ions adsorption, which increases with the rise in the adsorption temperature. This is because at higher temperature, the diffusion of ruthenium ions through the charcoal pores is faster and can proceed to a larger extent (Qadeer and Hanif, 1994 1994 ). The Lagergren equation (Lagergren, 1898 1898 ) employed for studying the rate constant of the process of ruthenium ions adsorption on activated charcoal is in the form: log( q e − q t )=log q e − K ads t /2.303 where q e is the amount of ruthenium ions adsorbed per gram of activated charcoal at equilibrium; q t is the amount of ruthenium ions adsorbed at time t and K ads is the rate constant for ruthenium ions adsorption (min −1 ). The linear plot of log( q e − q t ) versus t , Fig. 2 2 , shows the appropriateness of the above equation and subsequently the first order nature of the process involved. The values of the rate constant K ads were calculated from the slopes of the afore-mentioned curves and are given in Table 1 1 . The activation energy for the ruthenium ions adsorption process was determined from the slope of a linear plot of ln K ads versus 1/ T and was found to be 1.3806 kJ/mol. Temperature (K) K ads (min −1 ) 288 0.0640 298 0.0619 308 0.0564 The adsorption of ruthenium ions on activated charcoal can be expressed as: $${\text{S}} + {\text{M}}\underset{{k_2 }}{\overset{{k_{\text{1}} }}{\longleftrightarrow}}{\text{S}} - {\text{M}}$$ where S is the activated charcoal; M is the ruthenium ions; k 1 and k 2 are the rate constants for the adsorption and desorption processes, respectively. The equilibrium constant, K C can be calculated as: K C = k 1 / k 2 = C M,AC / C M,SN where C M,AC and C M,SN are the equilibrium concentrations of ruthenium ions on activated charcoal and in solutions, respectively. Mathematically, these concentrations can be expressed as: C M,AC = C Mi ( F ) and C M,SN = C Mi (1− F ) where C Mi is the initial concentration of ruthenium ions and F is the fractional amount of adsorption at equilibrium. On substituting the values of C M,AC and C M,SN into the Eq.( 4 4 ), it becomes: K C = F /(1− F ) The values of the equilibrium constant ( K C ) for the adsorption of ruthenium ions on activated charcoal were calculated at different temperatures at equilibrium time (i.e. 80 min). The variation of K C with temperature is shown in Fig. 3 3 showing that K C values increase with increase in adsorption temperature, thus implying a strengthening of the adsorbate-adsorbent interactions at higher temperatures. This also indicates that the ruthenium ions dehydrate considerably at higher temperature before adsorption and thus their size during adsorption is smaller yielding higher K C values (Qadeer et al., 1995 1995 ). The thermodynamic quantities such as Δ G , Δ H and Δ S of ruthenium ions adsorption on activated charcoal were calculated using the following relations: ln K C =−Δ H /R T +constant Δ G =−R T ln K C Δ S =(Δ H −Δ G )/ T where Δ H , Δ G , Δ S and T are the enthalpy, Gibbs free energy, entropy and temperature in K respectively; R is the gas constant (8.314 J/(mol·K)). Value of Δ H was computed from the slope of the linear variation of ln K C with the reciprocal of temperature, 1/ T (Fig. 4 4 ) according to Eq.( 8 8 ). The estimated Δ H value for the present system was 34.1642 kJ/mol. This value matches fairly well with the Δ H value determined by Chen and coworkers for the adsorption of ruthenium on resin as 22.59 kJ/mol (Chen et al., 1993 1993 ). The values of the free energy of specific adsorption, Δ G and entropy Δ S at various temperatures were calculated by using Eq.( 9 9 ) and Eq.( 10 10 ) respectively and are listed in Table 2 2 . The positive value of Δ H shows that the adsorption of ruthenium ions on activated charcoal is an endothermic process. A possible explanation of the endothermic process is given by Qadeer et al.( 1993 1993 ). The values of Δ G are negative at 298 K and 303 K as expected for a spontaneous process. The decrease in Δ G value with increasing temperature reveals that adsorption of ruthenium ion on activated charcoal becomes better at higher temperature, because ruthenium ions are more readily de-solvated. The positive value of Δ S reveals the increased randomness at the solid-solution interface during the fixation of the ruthenium ion on the active site of the adsorbent. Since the adsorption process is endothermic; it follows that under these conditions the process becomes spontaneous because of the positive entropy change. Temperature (K) Δ H (kJ/mol) Δ G (kJ/mol) Δ S (kJ/(K·mol)) 288 34.1642 0.3838 0.1172 298 34.1642 −0.6478 0.1168 308 34.1642 −1.4492 0.1156 References M Afzal , SM Hasany , H Ahmad , F Mahmood . Adsorption studies of cerium on lead dioxide from aqueous solutions . J Radioanal Nucl , 1993 . 170 309 - 319 . . Adsorption studies of cerium on lead dioxide from aqueous solutions G Atun , A Kilislioglu . Adsorption behavior of cesium on montmorillonite-type clay in the presence of potassium ions . J Radioanal Nucl Chem , 2003 . 258 605 - 611 . . Adsorption behavior of cesium on montmorillonite-type clay in the presence of potassium ions MA Bangash , J Hanif . Sorption behavior of cobalt on illitic soil . Waste Management , 1992 . 12 29 - 39 . . Sorption behavior of cobalt on illitic soil P Benes , V Majer . Trace Chemistry of Aqueous Solutions , 1980 . Elsevier Scientific Publishing Co. , 207 - 213 . . Trace Chemistry of Aqueous Solutions CM Che , KY Wong , FC Anson . Effects of electrode surface pretreatments on the electrochemistry of a macrocyclic dioxoruthenium (VI) complex . J Electroanal Chem Interfacial Electrochem , 1987 . 226 211 - 226 . . Effects of electrode surface pretreatments on the electrochemistry of a macrocyclic dioxoruthenium (VI) complex Y Chen , J Wu , N Wang . Study on the sorption mechanism of 4-amino-triazole resin for Ru(IV) . Guijinshu , 1993 . 14 1 - 6 . . Study on the sorption mechanism of 4-amino-triazole resin for Ru(IV) K Esumi , M Ichikawa , T Yoshimura . Adsorption characteristics of poly(amodoamine) and poly(propelene imine) dentrimers on gold . Colloid & Surfaces A: Physiochem Eng Aspects , 2004 . 232 249 - 252 . . Adsorption characteristics of poly(amodoamine) and poly(propelene imine) dentrimers on gold R Jiang , FC Anson . Association of electroactive counterions with polyelectrolytes. 4. Coordinative binding of ruthenium EDTA to poly(4-vinylpyridine) . J Phys Chem , 1992 . 96 452 - 458 . . Association of electroactive counterions with polyelectrolytes. 4. Coordinative binding of ruthenium EDTA to poly(4-vinylpyridine) L Kavan , B O’Regan , A Kay , M Graetzel . Preparation of titania (anatase) films on electrodes by anodic oxidative hydrolysis of titanium trichloride . J Electroanal Chem , 1993 . 346 291 - 307 . . Preparation of titania (anatase) films on electrodes by anodic oxidative hydrolysis of titanium trichloride I Ko , JY Kim , KW Kim . Arsenic speciation and sorption kinetics in As-hematite-humic acid system . Colloid & Surfaces A: Physiochem Eng Aspects , 2004 . 234 43 - 50 . . Arsenic speciation and sorption kinetics in As-hematite-humic acid system S Lagergren . Bil. K. Sven. Vatenskapasad. Handl. , 1898 . 24 . Bil. K. Sven. Vatenskapasad. Handl. AM Lazarin , RL Sernaglia . Adsorption of H[Ru(III)Cl 2 (H 2 EDTA)] complex on modified silica gel surface with [3-(2-aminoethyl)aminopropyl] trimethoxysilane in ethanol solution . Quim Nova , 1999 . 22 342 - 344 . . Adsorption of H[Ru(III)Cl2(H2EDTA)] complex on modified silica gel surface with [3-(2-aminoethyl)aminopropyl] trimethoxysilane in ethanol solution VK Legin , YV Kuznestsov . State of ruthenium in natural waters . Chem Abstract , 1974 . 82 144703X . State of ruthenium in natural waters R Lin , T Onikubo , K Nagai , M Kaneko . Investigation of tris(2,2’-bipyridine) ruthenium/nafion film coated on electrodes studied using in situ cyclic voltammetry and photoluminescence . J Electroanal Chem , 1993 . 348 181 - 188 . . Investigation of tris(2,2’-bipyridine) ruthenium/nafion film coated on electrodes studied using in situ cyclic voltammetry and photoluminescence R Qadeer , J Hanif . Kinetics of zirconium ions adsorption on activated charcoal from aqueous solutions . Carbon , 1994 . 32 1433 - 1439 . . Kinetics of zirconium ions adsorption on activated charcoal from aqueous solutions R Qadeer , J Hanif , M Saleem , M Afzal . Surface characterization and thermodynamics of Sr 2+ , Sm 3+ , Gd 3+ , Th 4+ and UO 2 2+ on activated charcoal from aqueous solution . Colloid Polym Sci , 1993 . 271 83 - 90 . . Surface characterization and thermodynamics of Sr2+, Sm3+, Gd3+, Th4+ and UO22+ on activated charcoal from aqueous solution R Qadeer , J Hanif , I Hanif . Uptake of thorium ions from aqueous solutions by molecular sieves (13X Type) powder . J Radioanal Nucl Chem , 1995 . 190 103 - 112 . . Uptake of thorium ions from aqueous solutions by molecular sieves (13X Type) powder D Qian , L Yang . Effects of surface adsorption of ruthenium (3+) and other cations on photoelectrochemical properties of n-indium phosphide . Wuli Huaxue Xuebao , 1986 . 2 444 - 451 . . Effects of surface adsorption of ruthenium (3+) and other cations on photoelectrochemical properties of n-indium phosphide TYa Vrublevs’ka , LV Vrons’ka , OYa Korkuna , NM Matviychouk . Adsorption concentration of platinum metal by clinoptilolite . Adsorpt Sci Technol , 1999 . 17 29 - 35 . . Adsorption concentration of platinum metal by clinoptilolite 10.1631/jzus.2005.B0353 2004-11-13 2004-12-23 2005-04-10 2022-01-05 Copyright © 2005, Journal of Zhejiang University Science 2005 Journal of Zhejiang University-SCIENCE B (Biomedicine and Biotechnology) 05 6B