Synthesis of pollucite and analcime zeolites by recovering aluminum from a saline slag

ABSTRACT This work describes a valorization procedure for one of the most important wastes generated during aluminum recycling, namely, saline slag. This procedure was divided in two steps: a) recovery of aluminum or its compounds in various fractions, and b) the use of one of those fractions in the synthesis of two zeolites: analcime (NaAlSi2O6·H2O) and pollucite (CsAlSi2O6·nH2O). Saline slag was ground, sieved (1 mm), washed and separated into two fractions of different sizes, one larger and another smaller than 0.4 mm. The fraction smaller than 0.4 mm was treated under reflux conditions with NaOH or CsOH solutions. The extraction liquor contained aluminum and alkali metal cations; after adding the necessary amount of Si, hydrothermal synthesis was carried out, obtaining the zeolitic materials. Characterization of the solids obtained was carried out by powder X-ray diffraction, thermal analysis, FT–IR spectroscopy, element chemical analysis and electron microscopy. The valorization procedure proposed in this work showed that a high percentage of Al (close to 45 wt.%) can be recovered from the fraction smaller than 0.4 mm and that the liquors extracted with NaOH or CsOH can be used as a source for the hydrothermal synthesis (200 oC for 24 h) of two zeolites of the analcime family, obtaining in both cases pure and crystalline solids.