Synthesis and thermodynamic data of acetate-containing giorgiosite – a novel hydrated magnesium carbonate

Organic additives play important roles in enhancing the formation of Mg‑carbonates and reaction kinetics in MgO-based cements. However, little is known about the influences of organics on the formation pathways of carbonate phases and whether organo-modified Mg‑carbonates exist. We found that acetate can be involved in the formation of a new hydrated magnesium carbonate phase containing acetate: Mg 5 (CO 3 ) 3.25 (OH) 2 (CH 3 COO) 1.5 ·5H 2 O. In this work, the solubility product (log K s0 ) of this phase was reported for the first time, while we also re-calculated the log K s0 of artinite. This acetate-containing giorgiosite is rather stable at low temperature but artinite Mg 2 (OH) 2 (CO 3 )(H 2 O) 3 and amorphous magnesium carbonates were observed at 20 °C while hydromagnesite Mg 5 (CO 3 ) 4 (OH) 2 ·4H 2 O, hydrated carbonate brucite (HCB) and amorphous magnesium carbonates were present at 50 and 80 °C. The work enables the potential of using organic additives in steering the reaction and formation of carbonates for better efficacy of carbon utilization and reactions in MgO-based cements.