Hydromagnesite Precipitation Kinetics in a Mixed-Suspension-Mixed-Product Removal Crystallizer of the MgO–CO₂–H₂O System Issued from Activated Serpentine Carbonation

Abstract

The precipitation kinetics of hydromagnesite (Mg5(CO3)4·(OH)2·4­(H2O)) in a MgO–CO2–H2O medium issued from a carbonation solution has been studied in a continuous mode via a mixed-suspension-mixed-product removal crystallizer. The carbonation solution is a result of the carbonation procedure of serpentine mining wastes and CO2 gas flux. The main precipitation temperature for the study was 80.0 °C. For comparative purposes, 82.5, 85.0, and 90.0 °C were also studied. Relative supersaturation was calculated via the Davies model using PHREEQC software. Kinetics parameters of linear and volumetric growth rate, nucleation rate, and the agglomeration kernel were determined for each temperature. Both the linear and volumetric growth orders were estimated to be, respectively, 0.92 and 0.91 via the correlation of empirical equations, indicating limited transport growth. The growth rate increases with temperature and supersaturation. The nucleation rate increases with the volumetric growth rate. The magma density of the solution is found to have a negative impact on the grain size if the residence time exceeds 2700 s. The mean grain size of this study is at least 1.5 times larger than those previously reported in the literature.