Zeolite synthesis from pre-treated coal fly ash in presence of soil as a tool for soil remediation

The study reports the synthesis of zeolites from pre-treated coal fly ash in presence of a natural agricultural soil. The synthetic process of zeolites formation in soil was studied for a period of 6 months at 30 and 60 °C. The synthesis of zeolite P (zeolite belonging to the Gismondine series) and zeolite X (zeolite belonging to the Faujasite series) was observed for the first time directly in soil in the presence of organic matter (2.4% C) and several mineral phases. Zeolites were characterized and quantified by means of XRD and SEM-EDX analysis. Moreover, correlations between Si/Al molar ratio in solution, curing temperature and the type of synthesized zeolite were found. A Si/Al ratio lower than 1 and higher curing temperatures favored the synthesis of zeolite P, while a Si/Al higher than 1 and lower curing temperatures drove the synthesis preferentially towards zeolite X. The results obtained in the present research could be useful for a better comprehension and long-term assessment of the physical and chemical processes which are at the basis of many solidification/stabilization (S/S) soil remediation technologies for the stabilization of heavy metals or for the catalytic degradation of organic pollutants.