Precipitation of nesquehonite from homogeneous supersaturated solutions

Abstract

The homogeneous (unseeded) precipitation of nesquehonite (MgCO 3 ·3H 2 O) was studied over the temperature range of 10-40 °C. Precipitation was triggered by the supersaturation created by mixing MgCl 2 solution (0.5-1.5 M) with Na 2 CO 3 solution in the same concentration range. The Meissner's method was adopted in the calculation of supersaturations during the MgCl 2 -Na 2 CO 3 reaction to monitor the precipitation. Solids were identified using X-ray diffraction (XRD) analysis and scanning electron microscope (SEM) images. In the temperature range of 10-40 °C, MgCO 3 ·3H 2 O with needle-like or gel-like morphology was precipitated. It was seen that the length, width and surface smoothness of the particles changed with reaction temperature and supersaturation. The supersaturation (S) was in the range of 1.09-58.68 during titration of Na 2 CO 3 solution. The dimension of the crystals increased with longer addition time (or lower initial concentration of reactant) at the same temperature. Slower addition via titration of 2 h followed by 2 h of equilibration at 40 °C proved successful in producing well developed needle-like MgCO 3 ·3H 2 O crystals of 30-50 µm long and 3-6 µm wide. MgCO 3 ·3H 2 O obtained were calcined to produce highly pure magnesium oxide (MgO) at 800 °C. The morphology of MgO was similar to that of their corresponding precursors.

Solubility of the hydrated Mg-carbonates nesquehonite and dypingite from 5 to 35 °C: Implications for CO2 storage and the relative stability of Mg-carbonates

“…Both nesquehonite and dypingite are readily formed during reaction of Mg-rich minerals with CO 2 at ambient temperatures, with nesquehonite tending to form at greater than atmospheric pCO 2 or evaporative conditions (Königsberger et al, 1999;Power et al, 2007;Xiong and Lord, 2008;Zhao et al, 2010;Schaef et al, 2011;Harrison et al, 2013a), and dypingite favored under atmospheric pCO 2 (~400 ppm) and microbially-mediated conditions (Power et al, 2007;Wilson et al, 2010;Mavromatis et al, 2012;Shirokova et al, 2013;Harrison et al, 2013a;McCutcheon et al, 2016). In addition to their natural occurrence and use for CO 2 storage, hydrated Mg-carbonates have prompted interest due to their potential formation in engineered Mg(OH) 2 /MgO barriers for nuclear waste storage (Xiong and Lord, 2008;Xiong, 2011), and the precipitation of nesquehonite from MgCl 2 brines has been investigated as a way to exploit Mg resources from salt lakes (Dong et al, 2008;Wang et al, 2008;Cheng et al, 2009;Cheng and Li, 2009), and as a precursor for high purity MgO production (Cheng et al, 2009;Wang and Li, 2012). This broad interest in nesquehonite has inspired a number of studies regarding its thermal stability (Lanas and Alvarez, 2004;Hales et al, 2008;Vágvölgyi et al, 2008;Ballirano et al, 2010;Jauffret et al, 2015;Morgan et al, 2015), nucleation kinetics (Cheng and Li, 2010;Zhao et al, 2013), its tendency for solid-solution with transition metals (Hamilton et al, 2016), and the impacts of temperature, saturation state, and fluid composition on nucleation and crystal morphology and size (Zhang et al, 2006;Wang et al, 2008;Cheng et al, 2009;…”

“…In addition to their natural occurrence and use for CO 2 storage, hydrated Mg-carbonates have prompted interest due to their potential formation in engineered Mg(OH) 2 /MgO barriers for nuclear waste storage (Xiong and Lord, 2008;Xiong, 2011), and the precipitation of nesquehonite from MgCl 2 brines has been investigated as a way to exploit Mg resources from salt lakes (Dong et al, 2008;Wang et al, 2008;Cheng et al, 2009;Cheng and Li, 2009), and as a precursor for high purity MgO production (Cheng et al, 2009;Wang and Li, 2012). This broad interest in nesquehonite has inspired a number of studies regarding its thermal stability (Lanas and Alvarez, 2004;Hales et al, 2008;Vágvölgyi et al, 2008;Ballirano et al, 2010;Jauffret et al, 2015;Morgan et al, 2015), nucleation kinetics (Cheng and Li, 2010;Zhao et al, 2013), its tendency for solid-solution with transition metals (Hamilton et al, 2016), and the impacts of temperature, saturation state, and fluid composition on nucleation and crystal morphology and size (Zhang et al, 2006;Wang et al, 2008;Cheng et al, 2009;Ding et al, 2016). Robie and Hemingway (1972; determined its standard heat capacity, standard entropy, and standard enthalpy of formation.…”

Ab initio thermodynamics of magnesium carbonates and hydrates in water-saturated supercritical CO2 and CO2-rich regions

“…Under ambient conditions, magnesium and carbonate ions will precipitate exclusively as hydrates (barringtonite MgCO 3 2H 2 O, nesquehonite MgCO 3 3H 2 O, and lansfordite MgCO 3 5H 2 O) or basic hydroxides (hydromagnesite Mg 5 (CO 3 ) 4 (OH) 2 4H 2 O), artinite (Mg 2 (CO 3 )(OH) 2 3H 2 O), dypingite (Mg 5 (CO 3 ) 4 (OH) 2 5H 2 O), and several more basic carbonates analogous to dypingite but with additional water molecules. (Cheng and Li, 2009;Hales et al, 2008;Hänchen et al, 2008;Langmuir, 1965;Montes-Hernandez et al, 2012;Sandengen et al, 2008) Up to 325 K in magnesium bicarbonate solutions, nesquehonite will precipitate; at 325 K or above in vacuum or aqueous solution, nesquehonite will transform to hydromagnesite. (Davies and Bubela, 1973) Botha and Strydom (Botha and Strydom, 2001) systematically investigated the impact of temperature, pH, and drying temperature on the products of CO 2 sparging of brucite, and determined that conditions could easily be tailored to synthesize nesquehonite, hydromagnesite, or another unidentified hydrated basic carbonate (likely dypingite).…”

Reactive magnesia cement

“…The produced nesquehonites with those from different reactions, e.g. Wang et al (2008) and Cheng and li (2009) are also being compared. The work is also performing carbon footprint calculations for these processes and comparing them with the processes from a number of the other initiatives above (Hassan, forthcoming).…”