Brightness improvement studies on ‘kaolin based’ zeolite 4A

China clay or kaolin in which kaolinite (Al2O3 · 2SiO2 · 2H2O) is the principal mineral, can be a convenient raw material for the synthesis of zeolite 4A since the Si/Al ratio is ideally suited for the same. Zeolite 4A has been recognised as a substitute for sodium tri-polyphosphate (STPP), which is the traditional water softening agent in detergents. Zeohte 4A is generally produced from pure chemicals i.e. from a freshly prepared sodium aluminosilicate gel and hence the impurities are negligible. The clay based zeohte is inferior due to its lower brightness since the kaolin is invariably associated with colouring impurities such as micaceous, titanoferrous and ferruginous compounds. The transition metal ions (e.g. iron), above a particular level, not only reduce the brightness but also decompose the perbomtes which is an ingredient in certain detergent formulations. The present paper discusses ways to improve the brightness of zeolite 4A prepared from kaolin by the removal or masking of iron minerals at various levels of the process route.