Thesis (M.Sc.)--Chulalongkorn University, 2013

Rice husk ash (RHA), a material mainly composed of silica of more than 90 % by weight, was applied to study the sorption because it has high surface area due to its high porosity. In this study, sorbents were prepared by combining RHA and magnetic particles as composites and coated with polystyrene for oil adsorption. The sorbents could be separated from the contaminated sources using an external magnetic force due to the incorporation of magnetic particles. The composites were synthesized using co-precipitation of ferric iron (Fe³+), ferrous iron (Fe²+) to form Fe₂O₃in presence of RHA. The RHA/Fe₂O₃composite was coated by polystyrene (PS)in order to increase their surface hydrophobicity. The important variables affecting the oil adsorption are the amount of magnetic particles and polystyrene on RHA surface. RHA/Fe₃O₄–PS composites were successfully prepared and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray analysis (EDX), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and atomic absorption spectrometry (AAS). After preparing the magnetic particles on RHA surfaces using various quantities of Fe₃O₄ particles ranging from 10-20 %weight of Fe₃O4 to weight of RHA, the composites were divided into two classes of size, i.e. 1-75 and 75-150 µm. The results showed that the composites with 10% of starting magnetic particles had the highest specific surface area of 492 and 545 m2/g for 1-75 and 75-150 µm composites, respectively. RHA/Fe₃O₄ composites were then modified with waste polystyrene foam of various weight percent ranging from 5–20 %weight of polystyrene to weight of RHA/Fe₃O₄ composites. The results showed that the composites with 10% polystyrene had the highest oil adsorption capacity of 10.3 and 12.5 g/g for 1-75 and 75-150 µm sorbents, respectively.