Sorption Properties and Adsorption Kinetics of Cd²⁺ Ions on Silica Derived from Rice Husk

Abstract

This study provides a comparative analysis of the adsorption efficiency and structural characteristics of silica (SiO₂) sorbents derived from rice husk for the removal of Cd²⁺ ions. Two types of sorbents were examined: the thermally synthesized SiO₂ (650) sample and the purified SiO₂ clean (650) sample obtained through an alkaliprecipitation method. According to the results of elemental analysis, the sample obtained by the thermal method contained 85.7% SiO₂, and when purified by the alkaline precipitation method, it contained 100% SiO₂. Experimental findings revealed that the sorption capacity of SiO₂ (650) was 7.38 mg/g, while that of SiO₂ clean (650) reached 7.46 mg/g. Both sorbents achieved equilibrium within 10-30 min, with removal efficiencies of 96.7% and 97.7%, respectively. Kinetic analysis demonstrated that the adsorption behavior of Cd²⁺ ions follows the pseudo-secondorder model (R² > 0,999), indicating a predominant chemisorption mechanism. The enhanced performance of the SiO₂ clean (650) sorbent is attributed to its higher number of active surface sites. Overall, silica sorbents synthesized from rice husk represent environmentally safe, accessible, and economically efficient materials for the purification of heavy-metal-contaminated water. The outcomes of this research provide a foundation for further improvement of rice-husk-derived sorbents, enhancement of their adsorption capacity, and potential expansion into industrialscale applications.