Oil Spill Treatment Using Magnetic Fe-biochar Composites Derived from Spent Coffee Grounds

Abstract

Fe-biochar composites were prepared by treating spent coffee grounds (SCG) with FeCl₃·6H₂O and pyrolyzing them at 500 ℃. The basic physical and chemical characteristics of the Fe-biochar composites were analyzed, and their capacity to remove oil spills was evaluated. The C content of the magnetic Fe-biochars tended to decrease slightly as the concentration of the pretreatment FeCl₃·6H₂O solution increased; however, the content of other elements-H, N, S, and O was not much different. The BET specific surface area of the Fe-biochar composites did not considerably differ among the composites prepared with different pretreatment concentrations. Analysis using SEM and EDS showed that Fe chemical compounds were well present and distributed on the surface of the Fe-biochars. The engine oil removal test results at temperatures of 5 ℃ and 25 ℃ showed that the concentration of the pretreatment solution should be at least 0.1 M when manufacturing Fe-biochar composites to apply for oil removal. There was little effect of initial pH on oil removal by the Fe-biochar composites. The adsorption kinetics analysis of engine oil, waste engine oil, and diesel oil by the Fe-biochar pretreated with 0.1 M FeCl₃·6H₂O solution(MCB-0.1M) showed that the pseudo-first order kinetics model was more suitable than the pseudo-second order kinetics model. The isothermal adsorption characteristics of MCB-0.1M showed a better level of fit for the Langmuir model relative to the Freundlich model for all three types of oils, and the Langmuir maximum adsorption capacity for engine oil, waste engine oil, and diesel oil was 4.59 g/g, 4.21 g/g, and 2.53 g/g, respectively. The results obtained in this study showed the great capacity of the SCG-based magnetic Fe-biochar composites made by the pretreatment with FeCl₃·6H₂O, for oil spills removal. The results also showed the high application potential of the Fe-biochar composites for effective oil spills removal using magnetic fields.