Insights into the direct carbonation of activated lizardite: the identification a poorly reactive amorphous Mg-rich silicate phase

Abstract

This work aims to shed light on the yet unanswered question regarding the limited carbonation yield of activatedlizardite via direct carbonation. Two amorphous Mg-rich silicate phases were identified upon activation. A rapid and complete carbonation of a highly reactive amorphous silicate phase was observed under moderately low pressure and temperature conditions (50-120 °C, 6 bar). Carbonation of this phase yielded to the formation of carbonates and a Si-rich passivating phase. On the other hand, the other amorphous silicate phase remained unaltered upon carbonation, fixing a significant amount of Mg within its disordered structure. The presence of poorly reactive intermediate Mg-rich silicate and Si-rich phases might be responsible for the yet unanswered relatively low carbonation efficiencies obtained via direct carbonation of activated lizardite. These limiting factors are considered to reduce the carbonation yield significantly more than the nucleation of forsterite during thermal activation. Analogous experiments carried with different meta-serpentines yielded the formation of distinct carbonate phases. The different distribution of highly and poorly-reactive amorphous phases among the different activated materials might have played an important role in the accelerated formation of magnesite (which was observed to occur once hydromagnesite formation reached a steady state) and the transformation of nesquehonite to dypingite-like phases.