An empirical model for adsorption thermodynamics of copper (II) from solutions onto illite clay-batch process design
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The copper causes important health problems risk when it exists at high concentrations in drinking waters and daily feeds. Therefore, in this study, copper adsorption from solutions onto illite clay was investigated in batch mode as a function of the initial solution pH (3-6), temperature (30-60 °C) and ionic strength (0-0.1 mol/L-1 NaCl). The equilibrium was attained within 24 hours. Optimum conditions were determined as pH 6, temperature 60 °C and 0 mol/L-1 NaCl concentration. The isotherm data followed the S-class isotherm. The reason of this S-class isotherm was either solute-solute attractive forces at the surface causing cooperative adsorption or a competing reaction such as complexation with a ligand. Mathematically, the isotherm data were explained with the sum of several single Freundlich models. Also, the thermodynamic parameters of the process were calculated. Positive values of Gibbs free energy change (δG°) indicated that the adsorption process was unspontaneous. As the enthalpy change (δH°) had positive value for all the parameter intervals, copper adsorption was concluded to be physical and endothermic process. The positive entropy values indicated that the randomness at solid-liquid interface increased with concentration decrease. Maximum copper adsorption capacity of illite clay was calculated at 60 oC as 1.823×10-5 mol/g. Furthermore, an empirical model was developed to determine the thermodynamic parameters of the process and operation conditions of the batch reactor as follows.