Zeolite production from waste kaolin-containing materials

Conversion of the kaolin-rich fraction of Florinas (Sardinia) sand into zeolite was studied. After a preliminary study on the original waste material to obtain, through a suitable sieving, a further increase of the kaolinite content and, through chem. and/or thermal treatments, an improvement of its reactivity, an exploratory systematic investigation on the hydrothermal transformation of the obtained products as a function of nature and concn. of the alk. contact soln., solid-to-liq. ratio, temp., and reaction time was carried out. The obtained products, characterized by x-ray, chem., and microscope analyses, were (a) zeolites A, P, and X, besides sodalite, in a sodium environment and (b) zeolite F and chabazite in a potassium environment. Further research was focused on the synthesis of zeolite A, presenting the advantage of good transformation yields and notable chances of application, demonstrating that it is possible to perform a near-quant. conversion of the reactive starting material into zeolite A, provided the raw material is previously purified from the quartz, feldspar, and muscovite impurities