Removal of diazinon from aqueous solutions by the adsorption process of activated carbon produced from rice husk and enhanced with ultrasonic waves

Background: The World Health Organization (WHO) has classified diazinon as a dangerous chemical for human health and the environment. This research aimed to remove diazinon from aqueous solutions using the enhanced adsorption process with ultrasonic waves. Methods: The adsorbent was prepared from rice husk after acid washing, and was placed in a furnace under nitrogen gas at a temperature of 700 °C for 2 hours. The effects of pH, initial diazinon concentration, adsorbent dose, contact time, and the combined effect of ultrasonic waves were investigated. The concentration of diazinon was measured by ultraviolet spectrophotometry at a wavelength of 247.5 nm. Results: In this study, the pHpzc of the adsorbent was determined to be 9. The highest removal efficiency (RE) was obtained at a pH of 8, adsorbent dosage of 2 g/L, and diazinon concentration of 20 mg/L. With the increase of the contact time, the RE increased, and maximum RE was obtained up to 78% at 60 minutes. The RE of diazinon using a combination of adsorption with ultrasonic waves increased up to 90%. In this study, with four recovery stages of the spent adsorbent, approximately 4% of the RE decreased. The equilibrium data were studied using Langmuir, Freundlich, and Temkin isotherms. Moreover, kinetic studies were evaluated by pseudo-first-order (PFO) and pseudo-second-order (PSO) models. The results indicated that the Langmuir isotherm and PSO model had the most agreement with the experimental data. Conclusion: Application of this adsorbent with ultrasonic waves can be effective in removing diazinon from agricultural and pharmaceutical effluents containing diazinon.