In this work, a heating stage microscope and a thermogravimetric analyzer were adopted to explore behaviors of char-slag/ash transition during CO2 gasification of rice straw (RS) and Neimeng lignite (NM). Effects of demineralized treatment and various gasification temperatures on the char-slag/ash evolution process were studied. Both RS and NM particles exhibited shrinkage particle form at a moderate reaction temperature (1000 degrees C). The variation of the existential state of K with char-slag/ash transition could well explain the reactivity differences between RS raw char and demineralized char. Compared to RS raw char, NM raw char showed a more significant flow of molten slag at 1350 degrees C, which accounted for the high inhibitory effects at the late stage of NM raw char gasification. There is a threshold conversion (x = 0.9) during the evolution processes of NM char samples to NM slag/ash at 1200 degrees C and 1350 degrees C, while this threshold value is only existing at 1000 degrees C for RS char gasification. (C) 2017 Elsevier Ltd. All rights reserved.