Hydrophobic dolomite sorbent for oil spill clean-ups: Kinetic modeling and isotherm study

A low-cost chemical hydrophobic sorbent was synthesized by the dip-coating method. The sorbent was characterized using different methods, including TGA, FTIR, XRD, SEM, and Zeta potential. The removal of unconventional oil from water by palmitic acid-modified dolomite was investigated by batch adsorption after varying pHs (1-9), contact times (5-80 min), adsorbent dosage (0.1-0.7 g mL(-1)), initial oil concentration (3000-7000 ppm), salinity (0-0.1 g mL(-1)) and different temperatures (299 and 309 K). TGA analysis revealed the increase in maximum oil sorption capacity of sorbent from about 64 to 498 mg g(-1) (Dilbit) and 98 to 530 mg g(-1) (Bakken oil) in the oil-water mixture. The kinetic studies showed that pseudo-second kinetic (PSO) model described unconventional oil sorption on hydrophobic sorbents in a much better manner than other models in term of R-2 values indicating that the overall rate of the oil sorption process might be controlled by a strong chemical reaction between oil molecules and active sites on the surface of sorbent. However, the obtained values of free energy estimated from Dubinin-Radushkevich (D-R) isotherm model were 7.57 and 7.833 KJ mol(-1) for the sorption of Dilbit and Bakken oil, respectively, which indicated strong physical nature of unconventional oil sorption on the studied sorbent. PSO model is not the only rate-limiting step and other mechanisms may control the rate of sorption, as all of them may be operating simultaneously. The external mass transport of sorbate and external film diffusion in this sorption system was very fast in comparison with the intraparticle diffusion and adsorption. For both tested oils, the isotherm studies revealed that the experimental data agreed with Sips, Toth, Temkin, and Freundlich models due to the highly heterogeneous systems.