WHAT IS THE KINETIC ORDER OF DESILICATION?
Jones, F. and Smith, P.
Desilication of liquor is an important process in the digestion of bauxite, particularly with respect to its ability to influence the silica remaining in the liquor to precipitation and, ultimately, in the gibbsite product. Not surprisingly therefore, desilication kinetics is an area of considerable interest. A common desilication rate equation from the literature is:
d[SiO2]/dt = k([SiO2]t – [SiO2]eq)n
in which the order (n) has various values ranging from 1 through to 3. Can all these values be correct and why, as some authors have found, is n a function of the seed added?
This paper tries to shed some light on the inconsistencies found in the literature and presents new desilication data at low and moderate seed charges. We find that use of this equation does lead to the situation where n is a function of surface area added. However, how can this be physically interpreted? In this paper we discuss the kinetic equation, where its use is valid and whether it is suitable to describe the desilication reaction at all. In addition, we present results of DSP seeding on desilication and show that the behaviour is challenging our understanding of the desilication process.