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 Ni²⁺ metal ions by solid tofu waste immobilized on silica surface. The isothermal adsorption model developed in this study revealed that a temperature of 27oC was required for the adsorption of Ni²⁺ metal ions in a batch system with pH = 6. Absorption model of Ni²⁺ ion followed BiLangmuir Model. The real adsorption capacity was between 0.478 mg/L to 4.750 mg/L. The Gibbs free energy for Ni²⁺ 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 Ni²⁺ 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 60oC) was used to determine the average enthalpy adsorption values for Ni²⁺ ions (111.092 KJ/mol). While the pH of zero charge potential (pHPCZ of adsorbent was 8.40) and the optimum pH for the adsorption of Ni²⁺ ion is 6.