1. Introduction - Firenze University Press

HEAT
Fig. 1. Scheme and main reactions of the magnesium silicates’ carbonation process. Adapted from
[15]
2. Aspen Plus ® simulations – Mineralisation of serpentine with
flue gas
2.1. Aspen Plus ® model – Hitura’s (Finland) serpentine
The ÅA CSM process was simulated using Aspen Plus® Software. The model follows the same
scheme as the ones presented in earlier publications [12,16-17] but differs on the CO2 inlet stream
of the carbonation step and on the source of heat supplied to the endothermic stages.
The S-DECOMP block represented in the Aspen Plus model (Figure 3) simulates the Solid/Solid
extraction reactor. It operates at 440ºC and atmospheric pressure. Experimental results, on
Portuguese samples, show that the presence of water greatly enhances the rate of magnesium
extraction and lowers the temperature by ≈50°C compared to reacting dry matter. [16-17].
In this block, AS is mixed with Hitura’s serpentinite (86% Mg3Si2O5(OH)4, 13% FeO, 1% CaSiO3)
and water at a ratio of 3:2:1. In the simulations 80% of Magnesium 1 , 60% of iron and 100% of
calcium are assumed to be extracted.
It is expected that, under the referred operating conditions, the following reactions occur:
Mg3Si2O5(OH)4 + 3 (NH4)2SO4 = 3 MgSO4 + 2 SiO2 + 6 NH3 (g) + 5 H2O (g) (R1)
FeO + (NH4)2SO4 = FeSO4 + 2 NH3 (g) + H2O (g) (R2)
1 Although experimental results with Hitura’s samples so far had a maximum of 74% of Mg extraction.
105