Vertical Roller Mill - Great Wall. Vertical roller mill is mainly used for grinding raw meal, clinker, GGBFS(Ground Granulated Blast Furnace Slag), iron ore, limestone, coal powder, coke powder, coal gangue, fly ash, volcanic ash, gypsum, calcite, pyrophyllite, quartz, clay, sandstone, bauxite and other processing industry related to metal and non-metal mine