Heat-treated gilsonite as an efficient natural material for removing toluene: A Box-Behnken experimental design approach

Heat-treated Gilsonite (HT-Gil) has been used for the adsorptive removal of toluene from wastewater. Characterization of the sample was carried out by utilizing appropriate standard test methods. The FT-IR spectrum indicates the presence of long aliphatic chains and aromatic rings. FE-SEM imaging is employed for investigating the surface morphology, the grain size of the sample and confirms the irregular shape of the HT-Gil with different particle size distributions. Determination of chemical properties and elemental composition of the sample was conducted according to several ASTM tests along with XRF analysis. Also, TGA experimental results revealed the thermal stability of the sample up to 350 °C. Optimization of adsorption parameters, including temperature (A: 5-45 °C), pH (B: 4-9), and contact time (C: 20-90 min) was performed by BBD. The results showed that the maximum adsorption capacity of 69.1% was achieved in the optimum condition containing 5 °C, pH 9, and 90 min. The spent adsorbent also has acceptable adsorption efficiency (62.12%) after four thermal regeneration cycles. Moreover, the results of equilibrium data were in accordance with the Freundlich isotherm model (R2 = 0.9531) and imply the non-uniformity of the adsorbent surface that is in line with those found previously in the literature.