SILICA EXTRACTION FROM BEACH SAND FOR DYES REMOVAL: ISOTHERMS, KINETICS AND THERMODYNAMICS
RASAYAN Journal of Chemistry
Beach sand is an abundant natural resource that contains silica minerals with many benefits. One of the uses of silica is to remove synthetic dyes that are toxic to biota in the environment. The goal of this research was to extract and characterize the silica from Bengkulu beach sand and to apply it as dyes adsorbent. The extraction of silica consisted of two steps that were potassium silicate formation and gel formation. The gel was formed by adding strong acid into a potassium silicate
... ium silicate solution. Silica's particle size and crystallinity were characterized using PSA and XRD, respectively. SEM-EDS was used to characterize the morphology and chemical composition of extracted silica. The effect of the different experimental settings, like pH, temperature, contact time, the concentration of dyes and adsorbent weight, on adsorption of dyes were monitored as well as the study of adsorption isotherms, kinetics, and thermodynamics. At equilibrium, synthetic dyes adsorption to silica suited to the Freundlich model producing correlation coefficients (R 2 ) of 0.853 and 0.976 for remazol blue and congo red, respectively. At optimum conditions, maximum adsorption capacities for remazol blue and congo red were 133 and 131 mg/g, respectively. The research implied that adsorption of dyes to silica fitted the pseudo-second-order model with thermodynamic values of ∆G°, ∆H°, and ∆S° were -4.04 to 2.19 kJ/mol, -13.53 to -4.726 kJ/mol, and 0.019 to 0.021 J/mol.K, respectively. By using these results, we resolve that the adsorption of dyes trends was exothermic and spontaneous. In addition, the reaction increases the system's entropy. This study emphasizes the potential of silica from the sand beach as a substitute economical adsorbent for the toxic dyes removal.