Kaolin waste dumps contain a huge volume of material that cannot be commercialized due to the presence of variable amounts of iron minerals, which impart a yellowish color to the kaolin. Elimination of iron from kaolin using either a chemical or a biological method was the aim of this study. The chemical leaching of iron from kaolin was carried out using response surface methodology to optimize the reaction conditions. Time was found to be the most influential variable, although oxalic acid must be present to leach 32% of the iron. Biological leaching was also assayed for 14 days using a Bacillus strain. The results of bacterial leaching of iron from kaolin showed <1% iron elimination.

Kaolin wastes from the Capim and Jari regions (Brazil) were used to produce sodalite under the same conditions used in the Bayer process, in order to control its formation when necessary. Of the two kaolin source materials, the kaolinite from the Jari region was more reactive in the synthesis of sodalite, which is attributed to the low degree of structural order of this clay mineral which increased its reactivity. At a temperature of 150°C and with a Na/Al ratio of 2, although the kaolinite did not react completely, sodalitewas the primary reaction product. An increase in the temperature to 200°C provoked the complete reaction of the kaolinite only for the products in which carbonate and sulfate were used. With a Na/Al ratio >2 and for both of the temperatures, the kaolinite reacted completely to form sodalite.

Ultramarine pigments were synthesized successfully from Na-A zeolite derived from kaolin waste. Na-A zeolite encapsulates the sulfur species formed and which act as chromophores, which circumvents their oxidation and the subsequent liberation of high levels of toxic gases during the reaction. Different Na-A zeolite matrices with various grain sizes (fine to coarse) were mixed with sulfur and sodium carbonate in various proportions to study the influence of these variables on the pigments’ colours and hues. After calcination at 500°C for 5 h, the products were characterized by X-ray diffraction, X-ray fluorescence and Raman spectroscopy and were classified by the Munsell system (colour and hue). Products with colour ranging from blue to green with various hues were obtained. Both colour and hue were affected by the amount of additives and by the particle size.