Solar-grade silicon microparticles have been prepared by a two-stage technique consisting of a combustion process in a SiO(2)+alpha Mg (alpha is the mole number of Mg) system in an inert atmosphere and the hydrometallurgical treatment of the combustion product. It has been shown that the refining behavior of the metallic impurities from combustion-synthesized silicon (CS-Si) is better than that of metallic impurities from metallurgical-grade silicon (MG-Si) since CS-Si particles have a unique microporous network structure, which makes the hydrometallurgical treatment process very efficient. Inductively coupled plasma (ICP) analysis results indicate that silicon of purity greater than 99.99% can be obtained by the developed technique. The principle of the hydrometallurgical purification of CS-Si is discussed in the context of particle morphology and a comprehensive explanation for porous structure formation is provided. (C) 2010 Elsevier B.V. All rights reserved.