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 ze olite. Zeolites could be readily synthesized from the glassy combustion res idues and showed potential for the removal of heavy metal ions. By the use of different temperatures and NaOH concentration, five different zeolites w ere obtained: Na-P1, faujasite, hydroxy sodalite, analcime, and cancrinite. The synthesized zeolites had greater adsorption capabilities for heavy met als than the original fly ash and natural zeolites. Na-P1 exhibited the hig hest 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 orde r of the radius of hydrated metal ion. The adsorption isotherm for lead by Na-P1 fitted the Freundlich rather than the Langmuir isotherm.