Manufacture of a High Temperature Structural Insulator (HTSI) Using Electrofilter Powders Generated in the Bayer Process

Electrofilter powder (EP) is a residue generated in large amounts during the calcination of aluminium hydroxide in the Bayer process. The production of high temperature structural insulator (HTSI) using EP is proposed. Different tests were made using different proportions of the starting materials, although the optimal mixture contained (in wt%) 52% EP, 14.7% silica fume (or quartz), 12% refractory aluminous cement and 21.3% water. Besides, 900 cm3 of polystyrene flakes were added to the mixture to promote a fine structure of pores. The brick was formed using manual mixing and vibration compacting in silicone molds. Then, it was dried at 100°C for 24 h, and after that, subjected to pre-sintering by heating up to 1050°C, and finally it was sintered at 1400° or 1450°C for 2 h. At the end of the process, the brick comprised 63% mullite, 24% anorthite and 13% corundum, with the following properties: density values within 0.75 and 0.80 g.cm−3, thermal conductivity values within 0.25 and 0.29 W.m−1.K−1, compressive strength values higher than 3.5 MPa, total porosity in the range 75–79% and overheat stability at 1400°C for 24 h with no appreciable dimensional changes.