1. Introduction - Firenze University Press

Figure 2. Effect of Mg/Fe ratio of the Mg-silicate rocks on % Mg extraction. The figure on the left
shows results from both serpentinite and olivine rocks while the one on the right is for only
serpentinite rocks.
Table 4. Sensitivity analysis for the factors affecting Mg extraction by varying the conditions.
# Selected conditions
1
2
3
4
5
6
7
8
A>2.16 g/g, B≤1 g/g,
C>480 o C, D>60 min
A>2.16 g/g, B≤1 g/g,
C>440 o C, D>60 min
A>2.16 g/g, B≤0.67 g/g,
C>480 o C, D>60 min
A>2.16 g/g, B≤0.67 g/g,
C>440 o C, D>60 min
A>2.16 g/g, B≤1 g/g,
C>480 o C, D>25 min
A>2.16 g/g, B≤1 g/g,
C>440 o C, D>25 min
A>2.16 g/g, B≤0.67 g/g,
C>480 o C, D>25 min
A>2.16 g/g, B≤0.67 g/g,
C>440 o C, D>25 min
Factors Interactions
Mg/Fe (g/g)
A
S/AS (g/g)
B
238
T ( o C)
C
T (min)
D
AB
AC
AD
R 2
√ 27%
√ 31%
22%
25%
√ √ β √ 47%
√ √ √ 52%
√ √ √ 45%
√ √ √ 50%
√ and √ β represent positive and negative effect of the factors/interactions respectively. R 2 is the
regression coefficient obtained for each condition.
It is obvious from Fig. 2 that serpentinite rocks with a Mg/Fe ratio ≥ 2.16 show an exceptionally
(>2x) higher % Mg extraction than others. This was the reason why Mg/Fe ratio level was
benchmarked at > 2.16 (Table 4) in the sensitivity analysis. Given the information deductible from
Fig. 2, it was more interesting to understand the effects and interaction effects of the more reactive
minerals with Mg/Fe ratio > 2.16.
Our goal is to obtain a process condition that allows us to design a Mg extraction reactor that
operates at optimal reaction conditions. The reactor should be able to process different types of
serpentinite minerals with varying Mg/Fe ratios, minimal amounts of AS salt reagent (slightly less
than 1 g/g), temperatures < 440 o C and reaction time ≤ 60 min. The combination of parameters in
Table 4 which mostly suits this goal is condition 6 which also has the highest regression coefficient
(R 2 =52%). It is arguable that the R 2 value obtained is not sufficient enough to describe a process;
however, it is not surprising that a system as complicated as the one simulated here would give a