Synthesis and Properties of Zeolites from Coal Fly Ash

Abstract

Previous attempts to use fly ash as a soil amendment have had limited success because of its low nutrient value, low cation exchange capacity (CEC), and elevated levels of toxic trace elements. However, treating fly ash with NaOH or KOH at an elevated temperature converts the ash into zeolite minerals and solubilizes the toxic trace elements, which are removed in the base solution. The CEC of the untreated fly ash was <100 mmolC kg-1 but increased to over 3000 mmolC kg-1 when heated for 3 days at 100 °C in 3 M NaOH. The dominant zeolites formed at 100 °C in NaOH were zeolite Na-Pl and zeolite P-C, and at temperatures of 150−250 °C, the mineralogy changed to zeolite X and pectolite. In KOH at 100 °C, zeolite K-G (potassium chabazite) was formed. The fly ash zeolites had a high affinity for K+, Ca2+, and NH4 +, although attempts to use the treated ash to remove NH4 + and heavy metals from wastewater and electroplating wastes were only partially successful. Potential uses of the treated ash were limited due to the high pH that resulted from the dissolution of the zeolite minerals. At pH 4 and pH 5, the rate of fly ash zeolite dissolution was 1000 times faster than most aluminosilicate minerals. Attempts to produce a zeolitic material with NH4OH or fluorides were not successful.

Formation of linde F zeolite by KOH treatment of coal fly ash

“…6) Amrhein et al reported that Ψ-chabazite (K-G zeolite; K2Al2SinO2n+4·xH2O) was formed when FA was treated with 3 mol dm -3 KOH in a capped Teflon tube at 100°C for 3 d. 7) Murayama reported similar results, 8) in which Ψ-chabazite was formed by the treatment of FA with 2 mol dm -3 KOH in an autoclave at 120°C for 24 h. It is, however, still unclear how FA-derived zeolite phases change depending on synthetic conditions of the KOH hydrothermal treatment. In the present study, the effects of synthetic conditions of the KOH treatment on the formation of FA-zeolite were examined.…”

Zeolite Formation from Coal Fly Ash and Its Adsorption Potential

“…9, 10 The addition of reaction promoters such as sodium hydroxide (NaOH) and/or potassium chloride (KCl) to enhance the reaction activity in forming zeolite and to improve the adsorption properties by increasing the surface area of synthesized zeolite is quite common. 9,10,13,14 Often the resulting zeolite has negatively charged functional groups on the surface, offering potential sorption applications particularly for the sequestration of cationic metals. 15 In this work, the synthesis of zeolite from the CFA obtained from one of the actual coal-fired combined power plants in Thailand was investigated.…”

Study on the Adsorption Properties of Ni(II) by Linde Typr/.ee F(K) Zeolite

“…Because of the environmental problems presented by the fly ash, considerable research has been undertaken on the subject worldwide. The utilization of fly ash as a low-cost adsorbent and zeolite synthesis for the removal of heavy metals has been studied in several literatures [8][9][10]. Fly ash was found to have a higher adsorption capacity for Cd(II), as Fly ash obtained from the combustion of poultry litter was also utilized as an adsorbent for the removal of Cr(III) from aqueous solution [11].…”