Investigation of zeolite scales formed in the Bayer process

Synthetic sodium aluminosilicate Bayer refinery scale has been prepared in 8 and 4.2 M sodium hydroxide solutions at four temperatures in the temperat ure range 80-240 degreesC. The effect of different anions (CO32-, OH- SO42- , Cl- and C2O42-) and varying anion concentrations (10(-2)-10(-1) M) on the type of aluminosilicate phase formed has also been investigated. These syn thetic phases have been compared with industrial scale formed in different parts of low and high temperature Bayer processing plants. Synthetic and pl ant scales were both characterised using powder X-ray diffraction, IR spect roscopy and SEM. The plant scale crystallises as two different zeolitic alu minosilicate phases, depending on the temperature in the area of the plant. This behaviour has been shown to closely mirror the formation of synthetic scale in sodium hydroxide solutions containing the carbonate anion. The la rge concentration of organic ions present in Bayer liquor appear to have li ttle effect on the type of scale formed and are relatively insignificant in promoting scale formation. (C) 2000 Elsevier Science B.V. All rights reser ved.