Abstract

The seawater neutralization process is currently used in the alumina industry to reduce the pH and dissolved metal concentrations in bauxite refinery residues through the precipitation of Mg, Al, and Ca hydroxide and carbonate minerals. This neutralization method is very similar to the co-precipitation method used to synthesize hydrotalcite (Mg<sub>6</sub>Al<sub>2</sub>(OH)<sub>16</sub>CO<sub>3</sub>.4H<sub>2</sub>O). This study looks at the effect of temperature on the type of precipitates that form from the seawater neutralization process of Bayer liquor. The Bayer precipitates have been characterized by a variety of techniques, including X-ray diffraction (XRD), Raman spectroscopy, and infrared spectroscopy. The mineralogical composition of Bayer precipitates largely includes hydrotalcite, hydromagnesite, and calcium carbonate species. Analysis with XRD determined that Bayer hydrotalcites that are synthesized at 55 °C have a larger interlayer distance, indicating that more anions are removed from Bayer liquor. Vibrational spectroscopic techniques have identified an increase in hydrogen bond strength for precipitates formed at 55 °C, suggesting the formation of a more stable Bayer hydrotalcite. Raman spectroscopy identified the intercalation of sulfate and carbonate anions into Bayer hydrotalcites using these synthesis conditions.

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