Zeolites are crystalline hydrated alumino silicates with a framework of an indefinitely extending three dimensional network of sulphate and aluminate ion tetrahedrons linked to each other by sharing oxygen, enclosing cavities occupied by cations as well as water molecules, both of which have considerable freedom of movement permitting certain exchange and reversible dehydration. The most important property of zeolite is its adsorption characteristics and it can act as molecular-sieve i.e. it can separate particles based upon difference in the molecular sizes of the materials to be separated. It can also selectively adsorb or reject molecules based on differences in shape and other properties such as polarity. These characteristics of zeolite have resulted in its principal use as water softening agent in detergent industry and other sectors.

In the commercial production of detergents the principal raw materials are "active material" and "phosphate builders". The sodium tripoly phosphate (STPP) is mostly used as phosphate builder in detergent industry. However, in recent years there has been an upsurge of interest in the builder Zeolite-A for the detergent industry. The most important resin is the increased awareness and concern about the polluting effect on the environment by the phosphate builders used in most of the detergents all over the world. Legislative measures were also enacted in many countries to stop or curtail the use of phosphate builders detergents. This has led to the development and use of Zeolite-A as phosphate substitute.

PROCESS

Sodium Aluminate liquor is dissolved in calculated quantity of water and required quantity of caustic soda is added to obtain required Na2O:Al2O3 ratio.Sodium silicate is dissolved in calculated quantity water and here also caustic soda is added to attain the required Na2O : SiO2 ratio.

Sodium aluminate and sodium silicate solutions are then reacted under controlled conditions to obtain a Gel. The Gel is heated for the formation of complex- composition known as Zeolite- A. The filtrate containing caustic soda is partly recycled and partly can be sold as by- product. The water in filter- cake is removed by compressed air. The wet cake is dried, pulverised and packed in HDPE woven bags.