Modeling and optimization of removal of toluene from aqueous solutions using iron oxide nanoparticles by RSM method

Toluene is a dangerous pollutant in aqueous solutions that should be removed completely. In this paper iron oxide nanoparticles were employed for removing of toluene from aqueous solutions with initial concentration of 100 ppm by Fenton-Like process. Iron oxide nanoparticles synthesised from spent catalysts of Tabriz Petrochemical Styrene Unit using a ball mill. these nanoparticles were characterized by BET, XRD, XRF and FE-SEM analysis. The milling of spent catalysts was performed in dry ball mill. Dry ball milling of spent catalysts was carried out in presence of argon as an inert gas. Iron oxide nanoparticles with diameter about 18 nm were obtained after 4 hours by dry ball milling of spent catalysts using 15 balls with a diameter of 20 mm. The milling was performed at a rotation speed of 400 rpm.The results of BET analysis showed that specific surface of catalysts has increased more than 9 times with the milling of spent catalysts. XRD patterns showed that during dry milling, some of Fe3O4 has converted to Fe2O3. Due to the higher rate of reaction of Fe2O3 compared to the Fe3O4 in Fenton process, this conversion causes higher rate of toluene elimination from aqueous solutions. The crystal size of spent catalysts and synthesized iron oxide nanoparticles was calculated by Scherrer equation. The crystal size of spent catalysts and synthesized iron oxide nanoparticles were obtained 56.6 nm and 33.9 nm respectively which confirmed the results of BET analysis. The concentration of toluene in aqueous solutions was measured by Gas Chromatography (GC-Agilent 7890A) equipped with FID detector and HP-Plot Q column (30m × 0.530 mm× 40.0 μm) using liquid-liquid extraction by hexane. Hexane and samples were mixed with volume ratio of 1/10. Samples were injected to GC in volume of 1 micro liter by a syringe (Agilent). Experiments were performed at pH=3 and room temperature (25◦C) in a batch reactor in volume of 500 ml with a mechanical stirrer. Due to study of interaction between the parameters and determining the optimal conditions, experimental design was performed by RSM method. [H2O2]/[Catalyst], [H2O2]/[concentration of pollution] and time (min) were considered as efficient parameters on removing of toluene. Quadratic equation with high correlation coefficient fitted using RSM method. R2 and R2(adj) values of predicted model for removing of toluene in Fenton-Like process were obtained 99.14% and 98.37% respectively. The results showed that [H2O2]/[Catalyst] and [H2O2]/[concentration of pollution] have optimum ranges. The optimum ranges for [H2O2]/[Catalyst] and [H2O2]/[concentration of pollution] were obtained 0.36-0.5 and 4-5.5 respectively . Optimal values for [H2O2]/[Catalyst], [H2O2]/[concentration of pollution] and time (min) for removing of toluene in Fenton-Like process were obtained 0.460, 4.928 and 105.7 respectively. In optimum conditions for efficient parameters, complete removal of toluene by Minitab software was predicted. Experiments in the optimum conditions also confirmed the results of Minitab software. The results showed that spent catalysts of Tabriz Petrochemical which are considered as waste, have a good ability for activation of H2O2 and removing of toluene from aqueous solutions.