The wet disposal of ash, from the coal-fired thermal power plants, involves its mixing with water and its impoundment in the ash ponds or lagoons. This causes the interaction of ash and the alkalies present in it with water over a period and the formation of ash zeolites (i.e. zeolitization of the ash) takes place. In order to simulate such ash-water interactions, alkali activation of a typical lagoon ash, from India, has been conducted. Investigations have been conducted to identify the effect of zeolitization of the ash on its physical, chemical and mineralogical characteristics. Such studies are essential to explore the possibility of application of the lagoon ash, and the zeolitized ash, for various environmental applications, viz. retention and removal of heavy metals from the industrial sludge.