LAUSR

Abstract Control of the morphology of carbonate crystals plays an indispensable role in mineralization process. We investigated the relationship between HPMC concentration and different molar ratios of Mg/Ca on the carbonate crystallization by monitoring crystal polymorph, crystal size, and morphology. In this experiment, the total molars of [Mg2+] and [Ca2+] were 50 mM. The results demonstrated that different molar ratio of Ma/Ca primarily can help different morphology form in multidimensional spline space, for instance, lens-like calcite, spindle shaped aragonite and polyhedron nesquehonite. Moreover, the metastable aragonite phase of CaCO3 can come into being with the existence of HPMC. Meanwhile, the Mg2+ would inhibit the growth of calcite and facilitate the production of the aragonite when the Mg2+ concentration is lower than 25 mM in solution. With increasing the molar ratio of Mg/Ca, the nesquehonite precipitation would be induced when the magnesium concentration is sufficiently high. The nesquehonite grew along the same (4 0 0) orientation in that the HPMC can be controlled by the basic units during the aggregation and reorientation process. The results of polarizing microscope also provided forceful support for the crystal growth mechanism. The thermodynamical stable phase of anhydrous calcium carbonate (CaCO3) was nucleated preferentially after the combination between Ca2+ and CO32−, then, the Mg2+ can bond with the oxygen atoms in HPMC due to electrostatic adherence and combine with CO32− and H2O to form a nesquehonite crystal phase. The results illustrated that the extent of binding affinity during HPMC with Ca2+ or Mg2+ was suggested to be in connection with the reconstructuring process and the morphology of final carbonate crystals.