Fly ash samples from the Bayswater and Eraring power plants, located in New South Wales, Australia, were used in a preliminary study on zeolite synthesis by hydrothermal treatment with sodium hydroxide under various conditions. The treated¯y ash was tested for the ability to remove lead ions from aqueous solution. Both¯y ashes were partially converted to zeolite. The zeolites formed under the experimental conditions were zeolite Na-P1 and sodalite octahydrate for the Bayswater ash and phillipsite, zeolite X, zeolite Na-P1 and sodalite octahydrate for the Eraring ash. The type of zeolite formed was dependent on the treatment time and sodium hydroxide concentration. In the case of the Bayswater ash, zeolite Na-P1 was formed by treatment with 4 mol dm À3 NaOH for 48 h while treatment with 5 mol dm À3 NaOH for 96 h produced sodalite octahydrate at the expense of zeolite Na-P1. In the case of the Eraring ash, phillipsite was formed following treatment with 3 mol dm À3 NaOH, zeolite X and zeolite Na-P1 were formed following treatment with 4 mol dm À3 NaOH and sodalite octahydrate was formed following treatment with 5 mol dm À3 NaOH. A maximum cation exchange capacity of $400 meq/100 g was achieved by both treated ash samples. Treatment of a solution with a lead ion concentration of 120 ppm using 0.5 g of both treated ash samples (S/L ratio = 0.25 g/100 cm 3 ) achieved complete removal in 5 min, whereas treatment with 0

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