Minimization of Bauxite Residue Neutralization Products Using Nanofiltered Seawater

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• 作者：Sara J. Couperthwaite ; Dean W. Johnstone ; Mark E. Mullett ; Kelvin J. Taylor ; Graeme J. Millar
• 刊名：Industrial & Engineering Chemistry Research
• 出版年：2014
• 出版时间：March 12, 2014
• 年：2014
• 卷：53
• 期：10
• 页码：3787-3794
• 全文大小：462K
• 年卷期：v.53,no.10(March 12, 2014)
• ISSN：1520-5045

文摘

Currently, open circuit Bayer refineries pump seawater directly into their operations to neutralize the caustic fraction of the Bayer residue. The resulting supernatant has a reduced pH and is pumped back to the marine environment. This investigation has assessed modified seawater sources generated from nanofiltration processes to compare their relative capacities to neutralize bauxite residues. An assessment of the chemical stability of the neutralization products, neutralization efficiency, discharge water quality, bauxite residue composition, and associated economic benefits has been considered to determine the most preferable seawater filtration process based on implementation costs, savings to operations and environmental benefits. The mechanism of neutralization for each technology was determined to be predominately due to the formation of Bayer hydrotalcite and calcium carbonate; however, variations in neutralization capacity and efficiencies have been observed. The neutralization efficiency of each feed source has been found to be dependent on the concentration of magnesium, aluminum, calcium, and carbonate. Nanofiltered seawater, with approximately double the amount of magnesium and calcium required half the volume of seawater to achieve the same degree of neutralization. These studies have revealed that multiple neutralization steps occur throughout the process using characterization techniques such as X-ray diffraction (XRD), infrared (IR) spectroscopy, and inductively coupled plasma optical emission spectroscopy (ICP-OES).