A chronological study on formation mechanism of nesquehonite from nanoparticles to grown crystals and its application in nanoparticle synthesis

Abstract

Abstract Nesquehonite or hydrated magnesium carbonate is an ideal precursor for the production of magnesium compounds. One of the most important industrial routes for the synthesis of Nesquehonite is the reaction of MgSO4 (or MgCl2), existing in natural or desalination brines with Na2CO3. During this reaction, the viscosity (and other bulk properties) of the slurry dramatically increases after 20–40 min induction period. Such a surge of viscosity is important for the reactor engineers, as it may damage the driving motor. The current study was undertaken to 1: Elucidate the formation mechanism of the Nesquehonite crystals and its induction period, and 2: Propose a method for the production of nano MgCO3 by stopping the formation reaction in its early stage. By simultaneous monitoring of the microstructure and bulk properties using SEM, XRD, FTIR, Raman, TGA, and Rheometry, the following formation mechanism was suggested: The nano-sized nuclei of “MgCO3·3H2O” are formed, nearly instantaneously after contacting the reagents. Those nanoparticles need an induction period to form the sheet-like intermediate. Large crystals are then formed quickly through stacking of the intermediate sheets, or their horizontal extension. Glycine capping agent, that stabilizes nanoparticles and deters their merges, slows down the formation of the aforesaid intermediate. Lowering the initial supersaturation of MgCO3, on the other hand, alters the size of the nanoparticles, but does not affect the formation kinetics of “Sheet-like intermediate → Final crystals” transformation. Simultaneous usage of capping agent and spray dryer seems to be an ideal method for the production of nano MgCO3 from the aforesaid reaction.