Alumina extraction from fly ash by the MgO sintering method: Waste reduction and utilization

L. Zhao, Q. Sun, B. Wang, X. Wang, Y. Xiao, G. Yu, X. Liu, Z. Zhang
National Institute of Clean-and-low-carbon Energy (NICE), CN

Keywords: alumina extraction, fly ash, MgO sintering, waste reduction, waste utilization

Summary:

In recent years, many methods for the alumina extraction from fly ash have been tested, developed and demonstrated in China. Generally, alkali sintering methods are more easily deployed than acid leaching methods, but it is also apparent that alkali sintering methods produce more waste of little value. The fact is that, in conventional alkali sintering methods, CaO is usually added in the formula besides soda, so that CaO•SiO2 or 2CaO•SiO2 is formed in the sintering process, resulting accordingly in a large amount of waste. In this patented process, MgO is added to replace CaO in the formula, and it has been found that the sintering temperature can be significantly decreased by 100-200 oC. At the same time, much less extraction residue is produced because MgO•SiO2 (100) has a lower molecular weight than CaO•SiO2 (116) or 2CaO•SiO2 (172). The replacement of CaO by MgO reduces the output of extraction residue, spares a lot of energy in the sintering process, and causes no detrimental effect on the alumina extraction from fly ash. As a raw material for quality products such as heat insulator and paints, MgO•SiO2 can be more efficiently used than CaO•SiO2 or 2CaO•SiO2.