Suspended particles (SPs) were separated from an FCC Slurry Oil (SLO) via centrifugation with the aid of toluene-dilution. Further solvent extraction of SPs with CS2/toluene (50 V/V%) mixed solvent would generate solvent extraction insolubles (SEINS) and solubles (SES). They were sent for a series of chemical and structural characterizations, respectively, in the hope of providing clues to address issues from sedimentation and clarification processes. It was found that SPs were composed of catalyst fragments and organic substances wrapped around them, serving as a shield. The characterizations from TEM and XPS strongly suggested that the outer surface of SEINS was sufficient in oxygen-containing sites (organic functional groups and aluminosilicate), while the outer surface of SPs was not. High oxygen content and almost same nitrogen content of SES, comparable with that of asphaltenes, were detected through XPS characterization. This rationalized the strong adsorption of SES on SEINS in the form of a tedious solvent extraction process. A new structure of SPs has thus been described on the basis of these characterizations. Design sedimentation experiments verified the SPs' structure. Furthermore, the experiments offered a promising way for acquiring high clarification efficiency with rather low usage of sinking agent through solvent pretreatment. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.