Nesquehonite Precipitation Kinetics in an MSMPR Crystallizer of the MgO–CO2–H2O System Issued from Activated Serpentine Carbonation

Abstract

For the first time, continuous nesquehonite precipitation was investigated. The context of this study is indirect aqueous carbonation. The precipitation was operated in a mixed suspension-mixed product removal (MSMPR) crystallizer. The investigated temperature was 40 °C, but the study also covered 50, 60, and 65 °C for comparison purposes. In a continuous mode, the nesquehonite grains obtained are a perfect spherical assemblage of needles instead of the individual needles usually obtained in batch mode. During precipitations in the MSMPR crystallizer, growth dispersion was noticed when supersaturation values were greater than 20. Growth dispersion is attributed to the high density of dislocation screw sites induced by high supersaturation. Meanwhile, for the idealized MSMPR tests, the linear growth rate varied from 1.11 × 10^–8 to 2.22 × 10^–7 m·s^–1. Volumetric growth rates varied from 5.13 × 10^–17 to 2.63 × 10^–15 m³·s^–1. Primary nucleation varied from 8.06 × 10⁰⁴ and 7.02 × 10⁰⁵ number·m^–3·s^–1. Finally, the agglomeration kernel varied from 3.38 × 10^–11 to 6.94 × 10^–8 m³·number^–1·s^–1. The growth of the crystals is a limited transport growth. It is also found that agglomeration suppresses primary nucleation. In addition, agglomeration is negatively affected by high solid density due to attrition.