Coal Ash By-Product from Shanxi Province, China, for the Production of Portland-Calcium Sulfoaluminate

Abstract

Twenty bulk samples were collected from ponded coal combustion ash in Shanxi Province, China, as part of an investigation of their beneficiation potential. The samples were shipped to the University of Kentucky, where they were chemically analyzed. The samples were highly consistent in chemistry, falling within the ASTM C-618 class F compositional range. The particle size of the ponded ash was relatively coarse, with only ,7% by weight on average, falling below 200 mesh (75 mm) particle size. The bulk of the material (.80%) was within 50 by 200 mesh (equivalent to 300 by 75 mm). X-ray diffraction investigation combined with microscopy indicated that the agglomeration was probably due to the presence of small amounts (i.e., ,3.5%) of gypsum. The utilization potential of the ash was assessed in light of its characteristics and location. The presence of sulfate and relatively high alumina concentration, which averaged ,37%, suggested that it may serve as an important ingredient in the fabrication of a Portland–calcium sulfoaluminate (CSA) hybrid cement. Portland-CSA hybrid clinkers were successfully produced from this ponded ash when mixed with hydrated lime, gypsum, fluorite, and bauxite. The raw mixture was fired at 1250uC for 60 minutes twice (sample D) and consisted of approximately 40% alite (C3S), 21% belite (C2S), 3% ferrite (brownmillerite or C4AF), 32% CSA (ye’elimite, Klein’s compound, or C4A3SO3), and no free lime by weight.