A non-immersed induction conductivity system for controlling supersaturation in corrosive media: The case of gibbsite crystals agglomeration in Bayer liquors

Agglomeration of gibbsite AI(OH)(3) crystallites is an important stage of the Bayer process, aiming at increasing the initial size of the particles. In the present work, a semi-continuous crystallizer working at constant and imposed supersaturation, and equipped with an automatic withdrawal system was developed to study the agglomeration of gibbsite crystals in supersaturated Bayer liquors. The liquor conductivity was measured using an induction conductivity system placed around the crystallizer, the conductivity relation being used to work at constant supersaturation. Using this system allowed one to work with both a small crystallizer and a highly corrosive and abrasive suspension of gibbsite in a five molar caustic soda solution at 70 degrees C. Analyses of the withdrawals were carried out with an Elzone particle counter, in order to draw N(t)/N(0)=f(t) plots, representing the decrease of crystal number with time, due to agglomeration.