Removal of salicylic acid by adsorption on activated carbon : A kinetic study
A.Nageswara Raoa*, B.Sivasankarb , V.Sadasivamb a Department of Chemistry, Sathyabama University, Chennai-600 119, Tamil Nadu, India b Department of Chemistry, Anna University, Chennai-600 025, Tamil Nadu, India
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Abstract A commercially available activated carbon has been tested as an adsorbent for the removal of salicylic acid from aqueous solutions. The effect of system variables such as pH of the solution, contact time, adsorbent dosage, solute concentration and temperature has been studied. The percentage removal of salicylic acid is found to increase with an increase in salicylic acid concentration.…show more content… Rapid uptake of organics was observed during the initial stage of contact and 50 % removal was observed within first 20 minutes and equilibrium time was around 60 minutes. A series of experiments were undertaken for varying initial salicylic acid concentration ranging from 13.8 to 22.1 mg/L. The removal of salicylic acid was found to increase from 1.28 to 1.83 mg/g by increasing the concentration from 13.8 to 22.1 mg/L at temperature 30 oC and pH 7.0 as shown in Fig.1. This shows that the removal of salicylic acid is highly concentration dependent. The removal curves were found to be smooth and continuous indicating the formation of monolayer coverage of the adsorbate on the outer surface of the…show more content… Q0 and b are Langmuir isotherm constants. The linear plot of Ce versus Ce / qe yielded a straight line showing the applicability of Langmuir isotherm as shown in Fig. 5. The values of Langmuir constants calculated are given in Table 1. From the experimental data the decrease in the value of ‘b’ with an increase in temperature from 30 to 50 ºC indicates that the reaction is exothermic. The equilibrium parameter RL is represented as follows12 ( Eq. 3 ). 1 RL = ─────── ………………….. ( 3 ) 1+ bC0
Where b is the Langmuir constant and C0 is the initial concentration of salicylic acid. The RL value of 0.55 obtained for the initial concentration of 13.8 mg/L at 30 0C is in the range of 0>RL<1 and shows that adsorption is favourable12.
The Freundlich adsorption isotherm is given by the expression ( Eq. 4 ). 1 log qe = log K + —— log Ce .................. ( 4