Models, Kinetics, and Thermodynamics for The Adsorption of Ni2 + Metal Ions by Solid Tofu Waste Immobilized on Silica’s Surface

This research aimed to study the models, kinetics, and thermodynamics for the adsorption of Ni 2+ metal ions by solid tofu waste immobilized on silica surface. The isothermal adsorption model developed in this study revealed that a temperature of 27 o C was required for the adsorption of Ni 2+ metal ions in a batch system with pH = 6. Absorption model of Ni 2+ ion followed BiLangmuir Model. The real adsorption capacity was between 0.478 mg/L to 4.750 mg/L. The Gibbs free energy for Ni 2+ ions adsorption was 2159.57 J/mol within the initial concentration range of about 5,10,20 and 30 ppm and -7769.27 J/mol in the initial concentration range about 40 and 50 ppm. The order of the adsorption kinetics for Ni 2+ ions were second order for a concentration range of about 5-50 ppm. The thermodynamic study of adsorption carried out at temperature variations (from 30 to 60 o C) was used to determine the average enthalpy adsorption values for Ni 2+ ions (111.092 KJ/mol). While the pH of zero charge potential (pH PCZ of adsorbent was 8.40) and the optimum pH for the adsorption of Ni 2+ ion is 6.