The present invention provides a simple, facile and clean process route for the production of commercially potential sodium silicate precursor material from spent foundry sand through amenable hydrothermal method. The synthetic process route involves the depolymerization of fused crystalline mass of spent foundry sand using the solution of concentrated caustic soda over a period of 12 hours at 250 °C. The depolymerization of spent foundry sand and the formation of sodium silicate were ascertained from appropriate analytical techniques. The synthetic process route developed for the production of sodium silicate possesses number of special features with regard to the concentration of caustic soda, reaction time, temperature, work up methodology, yield and purity. The product sodium silicate resulted from spent foundry sand can be conveniently utilized for different household products and industrial applications, including the binding materials for the preparation of geopolymer concretes. This invention is considered as the novel method of industrial waste utilization and effective approach for solid waste management.