Effect of Inorganic Anions on the Morphology and Structure of Magnesium Calcite

Abstract

Calcium carbonate was precipitated from calcium hydroxide and carbonic acid solutions at 25 degrees C, with and without addition of different magnesium (MgSO(4), Mg(NO(3))(2) and MgCl(2)) and sodium salts (Na(2)SO(4), NaNO(3) and NaCl) of identical anions, in order to study the mode of incorporation of magnesium and inorganic anions and their effect on the morphology of calcite crystals over a range of initial reactant concentrations and limited c(i)(Mg(2+))/c(i)(Ca(2+)) molar ratios. The morphology, crystal size distribution, composition, structure, and specific surface area of the precipitated crystals, as well as the mode of cation and anion incorporation into the calcite crystal lattice, were studied by a combination of optical and scanning electron microscopy (SEM), electronic counting, a multiple BET method, thermogravimetry, FT-IR spectroscopy, X-ray diffraction (XRD), and electron paramagnetic resonance (EPR) spectroscopy. In the systems of high initial relative supersaturation, precipitation of an amorphous precursor phase preceded the formation of calcite, whereas in those of lower supersaturation calcite was the first and only polymorphic modification of calcium carbonate that appeared in the system. The magnesium content in calcite increased with the magnesium concentration in solution and was correlated with the type of magnesium salt used. Mg incorporation caused the formation of crystals elongated along the calcite c axis and, in some cases, the appearance of new [011] faces. Polycrystalline aggregates were formed when the c(i)(Mg(2+))/c(i)(Ca(2+)) molar ratios in solution were increased. Addition of sulfate ions, alone, caused formation of spherical calcite polycrystalline aggregates.

Synthesis of Calcium Carbonate by Semicontinuous Carbonation Method in the Presence of Dextrans

“…Other important ways to influence on the PCC particle morphology are the use of magnetic field, 12,13 high pressure, 14,15 or a specific additive. [16][17][18][19][20][21][22] The paper industry uses a huge amount of calcium carbonate as a filler component. The more filler is applied, the cost of the final product is lower.…”

Co-Precipitation of Trace Metals in Groundwater and Vadose Zone Calcite: In Situ stablization of 90 Sr and Other Divalent Metals and Radionuclides in Arid Western DOE Sites

“…The predominantly rhombohedral morphology is consistent with the standard polyhedral prismatic form of calcite, (Deer et al, 1992) often precipitated without the presence of bacteria or organic macromolecules (Meldrum and Hyde, 2001;Braissant et al, 2003;Roque et al, 2004), which suggests the influence of B. Pasteurii surfaces and exudates on crystal morphology is somewhat limited. The stepped and rounded edges of crystals from both the B. Pasteurii and bacteria-free AGW (Figure 6) probably reflect the effect of inorganic ions within the precipitating solid, which have been shown to distort CaCO 3 mineral structures (Tracy et al, 1998;Raz et al, 2000;Kontrec et al, 2004;Kralj et al, 2004). Interestingly, the rhombohedral form with rounded stepped edges is very similar to mature calcite crystals precipitated from solutions containing urea and CaCl 2 in the presence of purified urease enzyme (Sondi and Matijevic, 2001).…”

Carbonate phases rich in magnesium in the Triassic limestones of the eastern part of the Germanic Basin

“…Apart from high-magnesium calcite, other carbonate minerals rich in magnesium also exist, such as protodolomite, ordered dolomite, huntite and magnesite (Table 7) (Böttcher et al 1997). The symmetry of high-magnesium calcite crystal is rhombohedral (Althoff 1977;Kralj et al 2004;Paquette and Reeder 1990;Wenk et al 1991), similar to the typical one for protodolomite. Dolomite of Muschelkalk limestones of the Polish part of the Germanic Basin have a stoichiometric value of MgCO 3 for dolomite, so it can be treated as ordered dolomite.…”

“…Structures of the crystal cell and chemical formulas of carbonate phases rich in magnesium are presented in Table 7. Some data placed in this table come from previous studies (Althoff 1977;Kralj et al 2004;Paquette and Reeder 1990;Stanienda 2013a;Titiloye et al 1998;Tsipursky and Buseck 1993;Wenk et al 1991). The chemical formula of low-magnesium calcite (low-Mg calcite) of the Lower Muschelkalk limestones is the same for the rocks of all beds (Stanienda 2013a).…”