Thermochemistry of Hydrotalcite-like Phases Intercalated with CO₃^2-, NO₃^-, Cl^-, I^-, and ReO₄^-

Abstract

The enthalpies of formation of hydrotalcite-like phases containing Mg and Al and intercalated with NO3 -, Cl-, I-, ReO4 -, or CO3 2- were determined using high-temperature oxide melt and room-temperature acid solution calorimetry. The relative stability of phases bearing the various anions was gauged by comparing the enthalpy of formation from the single-cation components (Δf H scc). Trends relating Δf H scc to the nature of intercalating anions (halides, NO3 -, and CO3 2-) show small stabilization from the mechanical mixtures of single-cation components. The aim of this study was to relate the enthalpy of formation to the nature of interlayer bonding in hydrotalcite-like compounds (HTLCs) bearing various anions, to uncover trends in the relative aqueous solubilities of these phases. The entropy of formation of these compounds was estimated using an approximation based on third-law entropy measurements for the compound Mg0.74Al0.26(OH)2(CO3)0.13·0.39H2O which were performed in a previous study. This approximation for the third-law entropy was combined with the enthalpy data from our calorimetric measurements performed in this work in order to calculate the standard-state free energy of formation for the HTLCs. The solubility products for the compounds investigated in this study were calculated from these free energies of formation and were used in geochemical calculations. The results of these calculations support our previous hypothesis that carbonate-intercalated HTLCs are less soluble than phases bearing other anions such as nitrates and halides. We suspect that the solubilities of HTLCs bearing anions other than carbonate may correspond to the solubilities of single-cation phases bearing the same anions.

Reversible hydration and aqueous exfoliation of the acetate-intercalated layered double hydroxide of Ni and Al: Observation of an ordered interstratified phase

“…Calorimetric measurements show that CO 3 2 À ions in the solid state have near zero hydration enthalpy [35].…”

Synthesis, characterization and stability properties of Cl-bearing hydrotalcite-pyroaurite solids

“…[1][2][3][4][5][6][7] and especially due to their anion-exchange properties (substitutions of I − , Br − , Cl − , OH − , CO 3 2− , SO 4 2− , Fe(CN) 6 4− , carboxylates, sulfonates or dicarboxylates C n H 2n (CO 2 − ) 2 , etc.) [8][9][10][11][12][13][14][15]. The anion-exchange properties of LDHs with general formula [M II…”

“…However, the understanding of the retention properties, behavior of LDHs in aqueous environment and finally, applying these substances for geochemical modeling at conditions of nuclear repositories are hampered by scarce information on their thermodynamic and solubility properties. The problem of retrieving thermodynamic data and predicting stability of LDHs have been recently touched only in a few studies [8,[17][18][19][20]. This work on the synthesis, characterization of a particular case of big LDH family, namely, chloride-bearing hydrotalcite (Htlc) Mg 3 Al(OH) 8 Cl·nH 2 O -pyroaurite (Pyr) Fe(II) 3 Al(OH) 8 Cl·nH 2 O solids because they have been identified as characteristic secondary phase components in corrosion products under repository conditions of disposed nuclear fuel elements [4,21].…”

“…The problem of retrieving thermodynamic data and predicting stability of LDHs have been recently touched only in a few studies [8,[17][18][19][20]. This work on the synthesis, characterization of a particular case of big LDH family, namely, chloride-bearing hydrotalcite (Htlc) Mg 3 Al(OH) 8 Cl·nH 2 O -pyroaurite (Pyr) Fe(II) 3 Al(OH) 8 Cl·nH 2 O solids because they have been identified as characteristic secondary phase components in corrosion products under repository conditions of disposed nuclear fuel elements [4,21]. Using various experimental techniques (X-ray powder diffraction, infrared spectroscopic measurements, thermogravimetric analysis, scanning electron microscopy, energy dispersive X-ray spectroscopy), the primary objective was to ascertain the presence of a continuous solid solution series between hydrotalcite and pyroaurite (i.e., isostructural substitution of Mg by Fe(II)).…”

Azo dye removal from aqueous solution by organic-inorganic hybrid dodecanoic acid modified layered Mg-Al hydrotalcite

“…and anions (Cl − , SO 4 2− , etc.) have been usually introduced to tailor the structures and properties of HTC [10][11][12]. Recently, some organic anions have also been intercalated into the layers of HTC to modify the hydrophobic environment and obtain higher exchangeable capacity for organic pollutants by ion exchange method and calcination-rehydration method [13][14][15][16].…”