Conversion Of Coal Fly Ash Research Articles

Conversion of coal fly ash into zeolite and heavy metal removal characteristics of the products

Fly ash obtained from a power generation plant was used for synthesizing zeolite. Zeolites could be readily synthesized from the glassy combustion residues and showed potential for the removal of heavy metal ions. By the use of different temperatures and NaOH concentration, five different zeolites were obtained: Na-P1, faujasite, hydroxy sodalite, analcime, and cancrinite. The synthesized zeolites had greater adsorption capabilities for heavy metals than the original fly ash and natural zeolites. Na-P1 exhibited the highest adsorption capacity with a maximum value of about 1.29 mmole Pb g-1 and had a strong affinity for Pb2+ ion. The metal ion selectivity of Na-P1 was determined as: Pb2+> Cu2+> Cd2+> Zn2+, consistent with the decreasing order of the radius of hydrated metal ion. The adsorption isotherm for lead by Na-P1 fitted the Freundlich rather than the Langmuir isotherm.

Study of the pre-crystallization stage of hydrothermally treated amorphous aluminosilicates through the composition of the aqueous phase

A detailed study of the parameters and phases involved in the pre-crystallization of the hydrothermal conversion of coal fly ash to zeolites has been performed. The study has also been extended to pumice, a natural glassy aluminosilicate.Dissolution of the main components, their concentration ratio in the solution phase, the re-precipitation in the form of an amorphous gel from which evolves zeolite crystals, and the compositions, occurrence times and degrees of completeness of the gel and zeolite crystals have been found to be strongly interrelated and all influenced by the temperature and alkali–metal content of the treatment.In the case of coal fly ashes, the halt occurring in the conversion to zeolites some time after its beginning has been shown to be due to the mullitic phase located inside the ash particles and containing most of the total aluminium content of the ashes. In contrast to the external amorphous phase, this phase is insoluble at the experimental conditions suitable for the conversion treatment.