Green synthesis of silica nanoparticles from rice husk for chromium (vi) removal from leather tannery wastewater

Abstract

This study was aimed to explore the green synthesis of silica nanoparticles from rice husk for efficient adsorption of chromium (VI) from tannery wastewater. Rice husk, an abundant agricultural waste, was utilized to produce the silica nanoparticles through an eco-friendly approach. The rice husk-based silica nanoparticles were synthesized using precipitation method. Their surface morphology, elemental composition, functional groups and crystallinity were determined using SEM, FTIR and XRD respectively. The effect of four factors on the removal efficiency was also investigated. These factors that included; initial chromium (VI) concentration (10-140 mg/L), PH (1-8), adsorbent dosage (0.1-8 g/L) and contact time (10 -100 minutes) and the process were optimized using RSM-CCD. Using this optimization technique, 31 experiments were conducted and the response modeled using a quadratic equation as function of the variables. The optimal values of the variables were determined to be 28.05 mg/L, 1, 8 g/L and 100 minutes for initial chromium (VI) concentration, PH, adsorbent dosage and contact time respectively. The removal efficiency at these conditions was 83% and 75% with stock solution and real tannery wastewater respectively. The significance of each of the terms in the model was evaluated using the probability of error value (p values), ANOVA p values and R-sq. P-values less than 0.050 showed that the terms were significant. From the analysis of variance, p value of 0.009 for the model, p 0.001 for linear effects implying considerable significance and R-sq. 75.74%. The adsorption isotherms performed showed that the adsorption process followed Freundlich model since it had a higher R-sq (0.97242) than Langmuir.