Physicochemical characterization and toxicity of coal fly ash leaching from a thermoelectric power plant and its final disposal as geopolymers

The study aimed to characterize the physicochemical properties of carbon fly ash (CFA) from a thermoelectric plant in Mexico. The ultimate goal was to find a responsible way to dispose of the CFA and reduce pollution. The CFA were spherical particles ranging from 0.4 to 100 µm in size, with an average size of 22.7 µm. XRF analysis revealed the primary chemical constituents to be 59% SiO₂, 26% Al₂O₃, 7% Fe₂O₃, and 3% CaO. The XRD analysis showed mullite and quartz crystalline phases. The study also evaluated the leaching of CFA using the Toxicity Characteristic Leaching Procedure. The results showed that the metals As, Cd, Zn, Cu, Ni, and Co were present in decreasing order of concentration. To reduce the mobility of heavy metals traces, the study explores the consolidation of ashes through a geopolymerization reaction in an alkaline medium, achieving an efficient reaction for precipitation hydrated amorphous alkaline aluminosilicate.