BACKGROUNDSodalite has been commonly employed as a photochromic material, and low Si/Al ratio sodalite is theoretically suitable for hydrogen storage. Consequently, a green and energy-saving synthetic route towards sodalite from inexpensive sources is highly desirable. Oil shale ash is a fly ash by-product produced from oil shale and has been used to synthesize NaA and zeolite X. In this paper, oil shale ash was selected as raw material to synthesize hydroxysodalite. RESULTSThe highly crystallized hydroxysodalite was synthesized by hydrothermal reaction without any pretreatment. The binary crystallization phase diagram was obtained. The optimum reactant molar ratio, hydrothermal reaction temperature, and time are as follows: 10Na(2)O:2SiO(2):75H(2)O, 180 degrees C, 24h. The synthesized hydroxysodalite was further characterized by scanning electron microscopy. CONCLUSIONHigh purity and well-crystallized hydroxysodalite was successfully synthesized from oil shale ash without pretreatment. Relatively high molar ratios of Na2O/SiO2 as well as low molar ratios of H2O/Na2O favour the formation of hydroxysodalite. (c) 2014 Society of Chemical Industry