1. Introduction - Firenze University Press

comparatively low R 2 . The results reported here contain tests performed on the reaction of solids
(solid state reaction) with multivariate parameters. Solid state reactions are less predictable than
those involving other states/phases. We assume that not all the factors contributing to Mg extraction
have been identified and studied. Some other factors like particle size difference between the
reacting Mg-silicate mineral and AS salt, heat and mass transfer, geometry and size of the reactants
and their containers may affect solid/solid reactions. These are the main subjects of ongoing
investigation as we embark on the next stage - pilot scale development.
3.2.2 Effect of amount of reagents (S/AS ratio)
By varying S/AS ratio of the tests between ≤0.67 g/g and ≤1 g/g, its effect on the extent of Mg
extraction was evaluated. For conditions 5-8 (Table 4), at 95 % (α = 0.05) significance level, S/AS
ratio has a significant positive effect on Mg extraction. The results obtained show that an increase in
S/AS salt ratio above both the level of 0.67 g/g or 1 g/g does not significantly affect Mg extraction
beyond a reaction time of 60 min (see conditions 1 to 4 in Table). In other words, a change in the
amount of AS salt reagent levels is more important when the reaction time is less than 60 min.
Increasing S/AS salt from low (-1) to high (+1) levels results in a 10% point increase in Mg
extraction. The effects of S/AS ratio, those of the parameters and their interactions can be visualized
from Fig.3 which is plotted for condition 6.
Figure 3.Main effects and interaction for Mg extraction under Condition I
3.2.3 Effect of reaction temperature and time
The effect of reaction temperature is not important under most of the conditions evaluated, but
shows negative dependence on Mg extraction above 480 o C (condition 4 in Table 4).
Figure 4. Effect of temperature (left) and time (right) on Mg extraction
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