Arsenate removal from water by an alumina-modified zeolite recovered from fly ash

A cancrinite-type zeolite was synthesized from Class C fly ash by molten-salt method. The product (ZFA) was used as the adsorbent for the arsenate removal from water. The adsorption equilibriums of arsenate are investigated on various adsorbents. ZFA showed a higher adsorption capacity (5.1 mg g(-1)) than activated carbon (4.0 mg g(-1)), silica gel (0.46 mg g(-1)), zeolite NaY (1.4 mg g(-1)), and zeolite 5A (4.1 mg g(-1)). The relatively higher adsorption capacity of ZFA than zeolite NaY and 5A was attributed to the low Si/Al ratio and the mesoporous secondary pore structure of ZFA. However, it was found that the adsorption capacity of zeolites were generally lower than activated alumina (16.6 mg g(-1)), which is ascribed to the small pores in zeolite frameworks. The adsorption capacity of ZFA was significantly improved after loaded by alumina via a wet-impregnation method. The modified ZFA (ZFA-Al(50)) with the optimum alumina loading showed an adsorption capacity of 34.5 mg g(-1), which was 2.1 times higher than activated alumina. The Toxicity Characteristic Leaching Procedure (TCLP) leachability tests indicated that the spent ZFA and alumina-modified ZFA complied with the EPA regulations for safe disposal.