CATION-EXCHANGE PROPERTIES OF HYDROTHERMALLY TREATED COAL FLY-ASH

Two samples of fly ash were treated for 2-48 h in 3.5 M NaOH at 100 de grees C. Powder XRD patterns of resulting products were obtained, and their CEC was determined. Zeolite P and/or hydroxysodalite formed duri ng the treatment from the glassy part of fly ash, while quartz gradual ly dissolved and mullite remained stable. Approximately 50% of fly ash could be converted to zeolites with the CEC of resulting products rea ching 2.5-3 mequiv/g. Concentrations of extractable B, Mo, and Se in f ly ash considerably decreased upon treatment. Adsorption isotherms of lead on treated fly ash suggested that at low initial lead concentrati ons and at pH lower than 6 precipitation of lead compounds is not like ly. A desorption experiment indicated ii incomplete reversibility at h igher concentrations, suggesting that part of the adsorption may not h ave been cation exchange related. Treated fly ash displayed high selec tivity for Pb2+ > Sr2+ > CU2+ > Cd2+ > Zn2+ > Cs+ in competition with Na+, especially at low concentrations of these cations, and was effect ive in removing Pb and Zn from industrial wastewaters. It was not sele ctive for Ni2+ and UO22+. In a column test, 160 bed vols of NH4+-conta minated fish-pond water was filtered through treated fly ash until NH4 + breakthrough occurred.