The application of silica gel synthesized from chemical bottle waste for zinc (II) adsorption using Response Surface Methodology (RSM)

The application of silica gel adsorbent synthesized from chemical bottle waste to remove zinc ions in the solution has been carried out. The synthesis of silica gel was carried out using alkaline fusion followed by sol-gel reactions. The chemical glass bottle container was made from borosilicate glass which was different from glass bottles for food and beverage that has been studied in previous studies. The Zn²⁺ adsorption was optimized using Box-Behnken Design (BBD). Box-Behnken Design was applied to study the optimum zinc ion removal and the input variables interaction. The input variables optimized were adsorbent dosage (1.0 - 2.0 g), initial zinc ion concentration in the solution (25 - 100 ppm), contact time (15 - 45 min), and pH (4 - 9). Response Surface Methodology (RSM) was applied to visualize the input variables' correlation to zinc ion removal. The optimum zinc ion removal was achieved at an adsorbent dosage of 2 g, initial concentration of 35 ppm, contact time of 45 min, and pH 8, which was 99.56%. The optimization of adsorption isotherm obtained that the adsorption follows the Langmuir isotherm model. The silica gel obtained was characterized using SEM-EDX and BET to obtain silica gel properties. The SEM-EDX showed a spherical shape of silica gel. Silica gel containing zinc (Zn) was observed from SEM-EDX after the adsorption process. A pore diameter of 42.098 nm and surface area of 297.083 m²/g were obtained from BET analysis of synthesized silica gel.