Phase-mineral and chemical composition of coal fly ashes as a basis for their multicomponent utilization. 2. Characterization of ceramic cenosphere and salt concentrates

The phase-mineral and chemical composition of ceramic cenosphere (CCCs) and water-soluble salt (WSCs) concentrates recovered from five fly ashes (FAs) produced in four large Spanish thermo-electric power stations was characterized. The CCCs and WSCs were isolated by sink-float separation in water and evaporation of the water-soluble solutions leached from FAs, respectively. The CCCs recovered are in the range 0.2–1.1% and their phase-mineral composition (in decreasing order of significance) commonly includes aluminosilicate glass, calcite, mullite, quartz, cristobalite, char, plagioclase, K-feldspar, dolomite, gypsum, and Fe oxides. The CCCs are enriched in Al, Ca, Ce, Co, Rb, Se and Sr in comparison with the FAs. The WSCs isolated are in the range 0.2–0.6% and their phase-mineral composition (in decreasing order of significance) normally includes gypsum, calcite, bassanite, inorganic amorphous matter, anhydrite, alunite, halite, opal, zeolite, dolomite, ankerite and jarosite. The WSCs are abundant in S and Ca, to a lesser extent in Al, Si, Na, K, Mg, Cl, Fe, P and Ti, and contain trace elements such as Cs, Li, Mn, Ni, Sn and Sr with ppm level, and As, Ba, Cr, Cu, Ge, Mo, Pb, Rb, Sb, Se, V, Zn and Zr with ppb level. Most of the elements studied are depleted and only Ca, Cl, K, Na and S are enriched in WSCs in comparison with the FAs. Significant proportions of Ca, Cl, Na and S (2–29%), and to a lesser extent of Al, Cs, K, Mg, P, Si, Sn and Ti (0.1–1%) were leached from the initial elemental contents in FAs. Some genetic features, properties, possible environmental concern and potential utilization directions related to the CCCs and WSCs are also discussed.