Thermodynamic and Kinetic Study of Diazinon Adsorption by Rice Bran from Aqueous Solution

Abstract

This study investigates the removal of diazinon from aqueous solutions using rice bran as a bio-adsorbent in both its raw and modified forms within a discontinuous adsorption system. Key parameters influencing surface adsorption were systematically examined, including adsorbent pretreatment, particle size, concentration, temperature, and pH. The experimental design utilized the Taguchi method to assess the effects of these parameters at four distinct levels. The findings revealed that the optimal conditions for maximum adsorption—achieving an efficiency of 80.42%—occurred with rice bran pretreated with 0.5 M sodium hydroxide, an adsorbent concentration of 4 g/L, a pH of 5, a particle size of 40 mesh, and a temperature of 30 °C. Isotherm analyses indicated that the Langmuir isotherm model best represented the experimental data, while kinetic studies suggested that the pseudo-second-order model provided the most accurate fit. The thermodynamic analysis demonstrated that the adsorption process is spontaneous (ΔG°ads < 0) and exothermic (ΔH°ads< 0). Additionally, scanning electron microscopy (SEM) was employed to examine the structural characteristics of the adsorbent surface before and after treatment.