Thermodynamics of removal of cadmium by adsorption on an indigenous clay

Equilibrium and thermodynamic studies of the removal of cadmium by adsorption on an indigenous adsorbent, china clay, have been investigated. The results of effect of temperature and thermodynamic parameters confirm the process of removal to be exothermic in nature. The removal decreased from 80.3% to 51.3% by increasing the temperature from 30 to 50 °C at 5.10 × 10−5 M initial concentration of cadmium, 1.0 × 10−2 M NaClO4 ionic strength, 6.5 pH, 100 μm particle size and 100 rpm. Rate was found in decreasing pattern with increasing temperature and value of rate constant of the reaction, kad, was found to be 5.10 × 10−2 min−1 at 30 °C. Values of Langmuir's constants, ‘Qo’ and ‘b’ were also determined. Thermodynamic parameters namely enthalpy of adsorption, isosteric heat of adsorption, change in standard free energy, ΔG°, standard enthalpy, ΔH°, and standard entropy, ΔS° were determined.