[MIS07-P04] Formation and transformation of amorphous magnesium carbonate in aqueous solution
Keywords:amorphous, magnesium carbonate, hydrous phase
Precipitation experiments were performed by mixing 0.2 M Na2CO3 and 0.2 M MgCl2 aqueous solutions. Immediately after mixing, white precipitates were formed. TEM observation showed these were fine particles of AMC of several tens of nanometers. TG-DTA revealed that its approximate chemical formula was MgCO3·2H2O. With the slurry stirred, this AMC transformed into needle crystals of nesquehonite(MgCO3·3H2O), one of the hydrated magnesium carbonates, via a solvent-mediated process. After that, dypingite (Mg5(CO3)4(OH)2·5H2O) particles of several micrometers were formed, while nesquehonite crystals dissolved. These results indicate that AMC forms as the precursor of nesquehonite and influences these transformation process into hydrated magnesium carbonates. The comparative consideration of the short-range structure between AMC and hydrated magnesium carbonates may lead to further understanding the formation process in the system of MgCO3-H2O.