The existing states of impurities in carbide slag were investigated which can be a good guide for impurity removal by physical methods. The calcium phase and the impurities wrap each other made it hard to research impurities. Therefore an acid chemical dissociation method was firstly proposed via plotting Eh-pH-diagram of the Ca(OH)(2), CaCO3, MgSiO3, Al2SiO5, Fe3O4 and H+ system. The optimum dissociation condition (pH = 4.0) was deduced from Eh-pH-diagram and verified by X-ray diffraction, X-ray fluorescence spectrum and morphology analysis. Morphological and elemental chemical analyses of the dissociated residues revealed the existence of Si in the form of SiO2. Fe and C existed as isolated particles of Fe3O4 and carbon respectively. Al and Mg were existed in the form of silicates such as Al2SiO5 and MgSiO3. Si, Al and Mg always appeared together in the carbide slag, providing a possibility for their integral removal. (C) 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).