Preparation of various color ultramarine from zeolite A under environment-friendly conditions

The ultramarine analogs of various colors have been prepared by calcination (mostly at 800 °C) of the mixtures of zeolite A and sodium polysulfides or elemental sulfur and sodium carbonate. The color and structure of the products depend very much on alkalinity of the mixture. Low alkalinity leads to green products with retained LTA structure. Blue products with SOD structure are attained at high alkalinity. Alkalinity affects also the weight loss on heating (i.e. emission of volatile compounds) as well as the amount of salts removed on washing.