Indian Journal of Chemistry Vol. 41A, June 2002, pp. 1212-1216 Silica enriched faujasitic zeolite-Y from flyash S U Meshram, S S RayaJu' , K N Munsht & M Z Hasan National Environmental Engineering Research Institute, Nehru Marg , Nagpur 440 020, India Received 3 October 2001; revised 19 February 2002 Various process modifications to enrich silica in zeolite-Y have been carried out by increasing substantially the Si0 2 IAI 2 0 3 ratio from 1.8-2.0 to 2.5-3.0 with consequent increase in thermal stability. Some new phases of zeolites have been observed with improved silica alumina ratio up to 3.0 to 3.5. Crystallinity has been monitored by XRD analysis, ranging from 70-99 % for different samples A process has been developed for the synthesis of zeolite-Y from flyash, which has been patented internationally 1 ,2 and reported elsewhere 3 . The process details for the synthesis of zeolite-Y with Si0 2 /AI 2 0 3 for various optimised conditions has been reported 3 . Also some attempts 4 .5 have been made to synthesize faujasitic type zeolites from flyash but not much work has been reported for the synthesis of siliceous zeolite-Y from flyash. There are also some reports available on synthesis of zeolite A from flyash 6 • 7 . Also recently synthesis of pure phases has been reported by few workers 8 . 9 . In this note attempts made to improve Si0 2 /AI 2 0 3 ratio of flyash based siliceous zeolite-Y have been reported. Experimental Flyash sample was collected from hopper of electrostatic precipitator at Koradi Thermal Power Plant, which is using sub-bituminous coal for power generation. The chemical composition of flyash is SiOf 58-60%, Ah03: 25-28%, Fe203: 5-7%, CaO: 3-5%, MgO : 0.3-0.5%, trace metals: 0.01-0.05 %, loss on ignition (LOI): 5-6 %. The other chemicals used were from E Merck (99.5% pure). The standard zeolite-Y was procured from Contekka, Sweden. The basic process developed by National Environ- mental Engineering Research Institute (NEERI) for *Department of Chemistry, Nagpur University, Nagpur 490 010, India, synthesis of FAZ-Y have already been discussed in details elsewhere 3 . The modification incorporated in the process to increase the silica content in zeolites includes acid treatment, alum treatment, EDTA chelation, silica enrichment and pressure digestion. Acid treatment of flyash Flyash was subjected to different concentration of acid treatment to sol ubi lise the amorphous alumina and thus increase the silica content of the system. The flyash was treated with hydrochloric acid of different strengths, 1 N, 6 N, 8 N, and concentrated HCI at about 100 to 1l0°e. The acid treated flyash was cooled and filtered. The solid product was then washed with water and dried at about 11O-120°e. However, it was observed that during acid treatment some portion of iron oxide also get dissolved in 8 N HCI which helps to improve the optical brightness of the product. The acid treated flyash so obtained was subjected to fusion with caustic soda followed by agitation of alkaline alumino-silicate gel and hydrothermal crystallization 3 . Alum treatment In this case, the flyash being used was sieved and iron was removed magnetically and subjected to aforereferred fusion step. The alumino-silicate gel obtained after fusion step was treated with alum solution, Ah(S04h.16H 2 0 of different strength i.e. 2.5, 5, and 10% solution. Subsequent steps are similar to that of aforereferred process. EDTA -chelation The solid F AZ-Y obtained as per the aforereferred process was treated with calcium chloride (CaCh). The F AZ-Ca Y so obtained was mixed with EDTA solution (5-6 g/30-40 ml of water) for about Ih . The reaction mixture was then refluxed for about 8-10 h at 100-11O°e. Silica addition The alumino-silicate gel was supplemented with 5% commercially available silica source i.e ., m- sodium silicate and reactive silica. Pressure digestion The alumino silicate gel so obtained was subjected to pressure digestion in autoclave by adding structure