In this paper, a novel technique combined light-electronic microscopy and computer imaging trace was used for visualization of the sedimentation of micron iron oxide particles in a customized micro-reactor. Micron iron oxide particles were recovered from the cinder of sulfuric acid production by sedimentation separating and hydraulic, rating. Effects of particle size, shape and surface roughness on the sedimentation velocity were investigated. For irregular-shape particles, the sedimentation velocity and the geometric parameters of the particles were measured by the imaging trace technique. A correction coefficient (c) was used to modify the Stokes equation. In this study, the relationship between the correction coefficient and the equivalent diameter (d(p)) was found to be linear: c = 0.6272 - 0.0298d(p), for iron oxide particles with equivalent diameter 4-22 mu m. (c) 2006 Elsevier Inc. All rights reserved.