Modeling equilibrium data for cd (ii) adsorption by peat using non-linear regression analysis

The Romanian peat was used as low-cost adsorbent to remove Cd(II) ions from aqueous solutions. The cadmium adsorption capacity of the peat was studied as a function of the solution pH (3-5.5) and temperature (293 333 K). Adsorption capacity was found to increase with the pH increasing and temperature decreasing and attained a maximum value of 27.9 mg/g at pH = 5 0.1 (acetate buffer) and 293 K. In addition, various thermodynamic parameters such as free energy change (.G0), enthalpy change (.H0), entropy change (.S0) along with isosteric heat of sorption (.Hx) were calculated. The adsorption of Cd (II) ions by peat was found to be a spontaneous and exothermic process, which is governed by electrostatic interactions (physisorption). FT-IR analysis of the peat before and after Cd (II) sorption suggests electrostatic attraction between cadmium cations and negatively charged COO- groups present on the peat surface.