Kinetic and thermodynamic study of thionine dye adsorption by peanut hull

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Abstract
In the present study, thionine dye was adsorbed on the surface of the peanut hull. Experiments were carried out by changing speed of agitation (50–300) rpm, time of contact (0–300) min, initial concentration of dye (10–50 mg/L), adsorbent dose (2–8 g/L), solution pH (2–12), and temperature (298–333 K) to evaluate their effect on the adsorption. The characterisation of the peanut hull was done by using XRF, FTIR and SEM. The optimum conditions were found as agitation speed = 200 rpm; time of contact = 300 min; initial dye concentration = 20 mg/L; adsorbent dose = 4 g/L; solution pH = 8 and temperature = 313 K. Equilibrium isotherm and kinetic models were studied to estimate their parameters and to predict adsorption capacity of peanut hull. Langmuir isotherm was found to be the best-fitted isotherm with R 2 of 0.992 and contributes the maximum adsorption capacity of 8.45 mg/g. Pseudo-first-order describes the kinetics with R 2 equal to 0.99. The change in enthalpy and entropy were also estimated from Gibbs’ free energy.

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