Abstract
Nowadays scientific and technological advances have allowed to Mankind to improve the life-style, but in this way, other problems have appeared. Currently, environmental problems are one of the most important. Many countries have developed a large number of environmental laws with the purpose of reducing human and industrial effects in the environment. In this work, a valorization procedure is developed for one of the most important wastes generated during aluminum recycling, namely, saline slag, finding that the final solids can be used for environmental applications. The procedure is divided into two steps: 1) recovery of aluminum from various slag fractions, and b) the use of recovered aluminum in the synthesis of two zeolites, namely, 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 than 0.4 mm and other lower than 0.4 mm. The fraction <0.4 mm was treated under reflux conditions with NaOH or CsOH solutions of different concentrations. The extraction liquor contained aluminum and alkali metal cations; thus after adding the necessary amount of Si, hydrothermal synthesis was carried out at 200 °C for 24 hours, obtaining the zeolitic materials. The solids were characterized by powder X-ray diffraction, thermal analysis, FT–IR spectroscopy, element chemical analysis and electron microscopy. The results of the first step showed that a high percentage of Al (~ 44 wt.%) in the fraction <0.4 mm, can be recovered. The results of the second step indicated that crystalline analcime and pollucite zeolites can be hydrothermally synthesized from extractions liquors and a source of Si, being the only phases detected by PXRD. Acknowledgements. MINECO and ERDF (financing, MAT2016-78863-C2-R). Junta de Castilla y León (formation programs, AJ and AM). Santander Bank (AG).
Highlights
Aluminum properties, such as corrosion resistance, low melting point (660 °C) or low density (2.70 g/cm3) [1] make it an ideal material for many applications
The results of the second step indicated that crystalline analcime and pollucite zeolites can be hydrothermally synthesized from extraction liquors and a source of Si, the zeolites being the only phases detected by powder X-ray diffraction
Analcime and pollucite zeolites can be synthesized from aluminum saline slag
Summary
Aluminum properties, such as corrosion resistance, low melting point (660 °C) or low density (2.70 g/cm3) [1] make it an ideal material for many applications. This element can be recycled and reused without losing its properties. The recycling process requires less energy than primary aluminum production (Bayer and Hall–Héroult processes [2,3,4]) but other wastes are generated, the most important is the so-called Salt Cake or Saline Slag. Raw saline slag contains various aluminum species (metallic Al, Al(OH), different phases of Al2O3, etc.) forming aggregates of different sizes and can be managed in different ways [2, 6,7,8,9,10]
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