Solubility Product

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Mason B Tomson - One of the best experts on this subject based on the ideXlab platform.

  • the temperature and ionic strength dependence of the Solubility Product constant of ferrous phosphonate
    Langmuir, 1998
    Co-Authors: Stephen J Friedfeld, Shiliang He, Mason B Tomson
    Abstract:

    A new compound with implications in scale and corrosion control has been isolated and its Solubility measured under varying conditions of temperature and ionic strength from 25 to 75 °C and from 1 to 3 M ionic strength. Ferrous phosphonate was formed using the phosphonate nitrilotris(methylene phosphonic acid) (NTMP) and was found to have the stoichiometry Fe2.5HNTMP. Using a complexation and speciation model, the stability constants for the complexation of iron(II) with phosphonate were calculated, and the Solubility Product constant was derived for each temperature and ionic strength; at 25 °C and 1 M ionic strength, Ksp = 10-31.2. The temperature (T, K) and ionic strength (I, M) dependence of the negative logarithm of the ferrous phosphonate Solubility Product constant (pKsp) was determined to be:  pKsp = 39.54 − 6.14I1/2 + 2.18I − 1315/T. In simulated calculations using actual field data to compare iron and calcium phosphonates independently, ferrous salts were predicted to form in all instances and m...

  • the temperature dependence of the Solubility Product constant of vivianite
    Geochimica et Cosmochimica Acta, 1994
    Co-Authors: Amal Alborno, Mason B Tomson
    Abstract:

    Abstract Vivianite Fe3(PO4)2 · 8H2O is an important phosphate mineral in many natural and environmental aquatic systems. Yet, the Solubility Product constant of vivianite has been determined only at room temperature. A new apparatus has been designed to facilitate the study of redox sensitive elements. Using this apparatus the Solubility Product constant of vivianite has been determined from 5 to 90°C. The equilibrium aqueous model MINTEQA2 used for data interpretation assumes the formation of all possible aqueous complexes. The temperature dependence of the negative logarithm of vivianite Solubility (pKsp) Product can be described between 5 to 90°C by pKsp = −234.205 + 12,242.6/T + 92.510 log10T, where T is temperature in Kelvin, yielding log Ksp = −35.767 ± 0.076 at 25°C. Using this expression, the calculated values of ΔG°, ΔH°, ΔS°, and ΔC°p at 25°C and 0.969 atm total pressure are 204.1 kJ mol−1, 5.05 kJ mol−1, −667.8 J K−1 mol−1, and −769 J K−1 mol−1, respectively.

Pascale Benezeth - One of the best experts on this subject based on the ideXlab platform.

  • experimental determination of the Solubility Product of dolomite at 50 253 c
    Geochimica et Cosmochimica Acta, 2018
    Co-Authors: Pascale Benezeth, Ulfniklas Berninger, N Bovet, Jacques Schott, Eric H Oelkers
    Abstract:

    Abstract The ‘dolomite problem’, the scarcity of present-day dolomite formation near the Earth’s surface, has attracted much attention over the past century. Solving this problem requires having reliable data on the stability and kinetics of formation of this mineral. Toward this goal, the Solubility of natural dolomite (CaMg(CO3)2) has been measured from 50 to 253 °C in 0.1 mol/kg NaCl solutions using a hydrogen electrode concentration cell (HECC). The obtained apparent Solubility Products (Kapp-sp-dol), for the reaction: CaMg(CO3)2 = Ca2+ + Mg2+ + 2CO32−, were extrapolated to infinite dilution to generate the Solubility Product constants for this reaction (Ksp°-dol). The derived equilibrium constants were fit and can be accurately described by log10 Ksp°-dol = a + b/T (K) + cT (K) where a = 17.502, b = −4220.119 and c = −0.0689. This equation and its first and second derivatives with respect to T were used together with corresponding aqueous species properties to calculate the revised standard state thermodynamic properties of dolomite at 25 °C and 1 bar, yielding a Gibbs energy of formation ( Δ f G 298.15 ∘ ) equal to −2160.9 ± 2 kJ/mol, (log10 Ksp°-dol = −17.19 ± 0.3); an enthalpy of formation ( Δ f H 298.15 ∘ ) of −2323.1 ± 2 kJ/mol, an entropy ( S 298.15 ∘ ) of 156.9 ± 2 J/mol/K and heat capacity ( C p 298.15 ∘ ) of 154.2 ± 2 J/mol/K (uncertainties are 3σ). The dolomite Solubility Product derived in this study is nearly identical to that computed using SUPCRT92 (Johnson et al., 1992) at 200 °C, but about one order of magnitude higher at 50 and 25 °C, suggesting that dolomite may be somewhat less stable than previously assumed at ambient temperatures.

  • hydromagnesite Solubility Product and growth kinetics in aqueous solution from 25 to 75 c
    Geochimica et Cosmochimica Acta, 2014
    Co-Authors: Pascale Benezeth, Quentin Gautier, Vasileios Mavromatis, Jacques Schott
    Abstract:

    Abstract Hydromagnesite Mg5(CO3)4(OH)2·4H2O is the most widespread form of hydrated Mg-carbonate minerals. To better understand the factors controlling the precipitation of hydrated Mg-carbonates, we measured hydromagnesite Solubility Product at 25 and 50 °C and its growth rate between 25 and 75 °C, using natural hydromagnesite from a cave as seed material. The Solubility Products values derived in this study, Ksp–Hmgs = −37.08 ± 0.50 and −38.90 ± 0.54 at 25 and 50 °C, respectively, are in the upper range of published values. Hydromagnesite growth rate normalized to the BET surface area at 8 ⩽ pH ⩽ 10 is consistent with the direct and reversible attachment of the reactants at the solid surface being rate-limiting. It may be described by: R Hmgs = A 0 · e - Ea / RT ( Ω Hmgs 1 / 5 - 1 ) where A0, the pre-exponential factor, and Ea, the activation energy, are equal to 5.12 × 10−7 mol/cm2/s and 45.5 ± 9 kJ/mol, respectively, and ΩHmgs stands for the saturation state of the solution with respect to hydromagnesite. Comparison of hydromagnesite growth rates with recently published magnesite growth rates (Saldi et al., 2009, 2012) show that: (1) hydromagnesite apparent growth activation energy is lower by more than 100 kJ/mol compared to the activation energy for magnesite obtuse step advancement, and (2) hydromagnesite growth rate constant extrapolated to 90 °C is 2.5 orders of magnitude higher than corresponding magnesite growth rate constant. Thus, our results confirm the long-standing hypothesis that the slow dehydration kinetics of the Mg2+ cation is responsible for the sluggish magnesite formation at low temperature, and that the kinetic barrier for hydromagnesite growth is much lower. Nevertheless, simulation of hydromagnesite and magnesite growth rates as a function of solution composition at 50 and 90 °C, and pH 7 and 9 reveal that, because of its much higher Solubility, hydromagnesite would grow more quickly than magnesite in natural or industrial environments only at 50 °C and pH 9. This is consistent with the formation of hydromagnesite during the surface alteration of ultramafic rocks.

  • experimental determination of the Solubility Product of magnesite at 50 to 200 c
    Chemical Geology, 2011
    Co-Authors: Pascale Benezeth, Giuseppe D Saldi, Jeanlouis Dandurand, Jacques Schott
    Abstract:

    Abstract Accurate knowledge of magnesite thermodynamic properties over a wide range of temperatures is crucial for characterizing mineral stabilities in the system MgO–CO2–H2O and for modeling carbon dioxide fate in important natural and industrial processes. However, available databases, especially for its Solubility Product, are sparse and contradictory, leading to considerable uncertainties in the calculation of chemical equilibria and phase transformations among carbonates. In this study, the Solubility of synthetic magnesite was investigated from 50 to 200 °C in 0.1 mol kg− 1 NaCl solutions and in some cases under constant CO2 partial pressure (4–30 bars) both by means of a hydrogen electrode concentration cell (HECC) and a traditional batch Ti-reactor. The obtained apparent Solubility Products (Qsp-mgs) were extrapolated to infinite dilution to generate the Solubility Products (Ksp°-mgs), allowing calculation of the thermodynamic properties of magnesite. Of all the temperature functions tested, the equation giving a reliable fit of our data in the investigated temperature range (50–200 °C) has the following form: log10Ksp°-mgs = a + b / T (K) + cT (K) with: a = 7.267, b = − 1476.604 and c = − 0.033918. Based on this equation and its first and second derivatives with respect to T, we were able to derive values at 25 °C, 1 bar for magnesite thermodynamic functions: ΔfG298.15o = (− 1026.48 ± 2) kJ mol− 1 (log10Ksp°-mgs = − 7.80 ± 0.3), ΔfH298.15o = (− 1111.75 ± 2) kJ mol− 1, S298.15o = (60.00 ± 2) J mol− 1K− 1, and Cp 298.15o = (75.91 ± 2) J mol− 1K− 1 (uncertainties are 3σ).

  • Solubility Product of siderite feco3 as a function of temperature 25 250 c
    Chemical Geology, 2009
    Co-Authors: Pascale Benezeth, Jeanlouis Dandurand, Jeanclaude Harrichoury
    Abstract:

    Abstract The Solubility of natural siderite was investigated from 25 to 250 °C in 0.1 mol kg − 1 NaCl aqueous solutions using a hydrogen-electrode concentration cell, which provided continuous in situ measurement of hydrogen ion molality. Iron(II) was analyzed by a revised Ferrozine-spectrophotometric method. The obtained apparent Solubility Products ( Q sp-siderite ) were extrapolated to infinite dilution to generate the Solubility Products ( K sp°-siderite ), allowing calculation of the thermodynamic properties of siderite. Of all the temperature functions tested, the equation giving a reliable fit of our data in the investigated temperature range (25–250 °C) has the following form: log 10 K sp°-siderite  =  a  +  b  ∙ ( T / K ) +  c  ∙ ( T  /  K ) − 1  +  d  ∙ log 10 (T  /  K ) with: a  = 175.568, b  = 0.0139, c  = − 6738.483 and d  = − 67.898. Based on this equation and its first and second derivatives with respect to T , we were able to derive values for the Gibbs energy of formation: Δ f G 298.15 o  = (− 680.71 ± 2) kJ mol − 1 , enthalpy of formation: Δ f H 298.15 o  = (− 749.59 ± 2) kJ mol − 1 , entropy: S 298.15 o  = (109.54 ± 2) J mol − 1 K − 1 and heat capacity: C p 298.15 o  = (83.26 ± 2) J mol − 1 K − 1 of siderite (uncertainties are 3 σ ). The values of Δ f G 298.15 o and Δ f H 298.15 o are in very good agreement with the values reported by Robie et al. [Robie, R.A., Haselton, H.T. Jr., Hemingway, B.S., 1984. Heat capacities and entropies of rhodochrosite (MnCO 3 ) and siderite (FeCO 3 ) between 5 and 600 K. Am. Mineral. 69, 349–357] and Chai and Navrotsky [Chai, L., Navrotsky, A., 1994. Enthalpy of formation of siderite and its application in phase equilibrium calculation. Am. Mineral. 79, 921–929], respectively. The density model [Anderson, G.M., Castet, S., Schott, J., Mesmer, R.E., 1991. The density model for estimation of thermodynamic parameters of reactions at high temperatures and pressures. Geochim. Cosmochim. Acta 55, 1769–1779] reproduced correctly our experimental data and allowed the extrapolation of the siderite Solubility Product up to 350 °C by using our values of the Gibbs energy and enthalpy of formation of siderite combined with its entropy and the heat capacity equation given by Robie et al. [Robie, R.A., Haselton, H.T. Jr., Hemingway, B.S., 1984. Heat capacities and entropies of rhodochrosite (MnCO3) and siderite (FeCO3) between 5 and 600 K. Am. Mineral. 69, 349–357].

Andrew R Felmy - One of the best experts on this subject based on the ideXlab platform.

  • pupo4 cr hyd Solubility Product and pu3 complexes with phosphate and ethylenediaminetetraacetic acid
    Journal of Solution Chemistry, 2010
    Co-Authors: Dean A Moore, Andrew R Felmy, Kevin M Rosso, Harvey Bolton
    Abstract:

    To determine the Solubility Product of PuPO4(cr, hyd.) and the complexation constants of Pu(III) with phosphate and EDTA, the Solubility of PuPO4(cr, hyd.) was investigated as a function of: (1) time and pH (varied from 1.0 to 12.0), and at a fixed 0.00032 mol⋅L−1 phosphate concentration; (2) NaH2PO4 concentrations varying from 0.0001 mol⋅L−1 to 1.0 mol⋅L−1 and at a fixed pH of 2.5; (3) time and pH (varied from 1.3 to 13.0) at fixed concentrations of 0.00032 mol⋅L−1 phosphate and 0.0004 mol⋅L−1 or 0.002 mol⋅L−1 Na2H2EDTA; and (4) Na2H2EDTA concentrations varying from 0.00005 mol⋅L−1 to 0.0256 mol⋅L−1 at a fixed 0.00032 mol⋅L−1 phosphate concentration and at pH values of approximately 3.5, 10.6, and 12.6. A combination of solvent extraction and spectrophotometric techniques confirmed that the use of hydroquinone and Na2S2O4 helped maintain the Pu as Pu(III). The Solubility data were interpreted using the Pitzer and SIT models, and both provided similar values for the Solubility Product of PuPO4(cr, hyd.) and for the formation constant of PuEDTA−. The log 10 of the Solubility Product of PuPO4(cr, hyd.) [PuPO4(cr, hyd.) \(\rightleftarrows\)\(\mathrm{Pu}^{3+}+\mathrm{PO}_{4}^{3-}\)] was determined to be −(24.42±0.38). Pitzer modeling showed that phosphate interactions with Pu3+ were extremely weak and did not require any phosphate complexes [e.g., PuPO4(aq), \(\mathrm{PuH}_{2}\mathrm{PO}_{4}^{2+}\), \(\mathrm{Pu(H}_{2}\mathrm{PO}_{4})_{2}^{+}\), Pu(H2PO4)3(aq), and \(\mathrm{Pu(H}_{2}\mathrm{PO}_{4})_{4}^{-}\)] as proposed in existing literature, to explain the experimental Solubility data. SIT modeling, however, required the inclusion of \(\mathrm{PuH}_{2}\mathrm{PO}_{4}^{2+}\) to explain the data in high NaH2PO4 concentrations; this illustrates the differences one can expect when using these two different chemical models to interpret the data. Of the Pu(III)-EDTA species, only PuEDTA− was needed to interpret the experimental data over a large range of pH values (1.3–12.9) and EDTA concentrations (0.00005–0.256 mol⋅L−1). Calculations based on density functional theory support the existence of PuEDTA− (with prospective stoichiometry as Pu(OH2)3EDTA−) as the chemically and structurally stable species. The log 10 value of the complexation constant for the formation of PuEDTA− [\(\mathrm{Pu}^{3+}+\mathrm{EDTA}^{4-}\rightleftarrows \mathrm{PuEDTA}^{-}\)] determined in this study is −20.15±0.59. The data also showed that PuHEDTA(aq), \(\mathrm{Pu(EDTA)}_{4}^{5-}\), Pu(EDTA)(HEDTA)4−, Pu(EDTA)(H2EDTA)3−, and Pu(EDTA)(H3EDTA)2−, although reported in the literature, have no region of dominance in the experimental range of variables investigated in this study.

  • the Solubility Product of nauo2po4 xh2o determined in phosphate and carbonate solutions
    Radiochimica Acta, 2005
    Co-Authors: Andrew R Felmy, Zheming Wang
    Abstract:

    The Solubility Product of NaUO2PO4.xH2O was determined in phosphate containing solutions at low pCH+ values in the absence of carbonate and at higher pCH+ values in the presence of carbonate. NaUO2PO4.xH2O exhibited very low solubilities (~10-7 M in U) over a broad range of hydrogen ion concentrations, NaNO3 concentrations and in the absence of added carbonate. Time Resolved Laser Fluorescence Spectroscopy (TRLFS) analysis of non-carbonate solutions outside of the acidic region revealed the presence of complex mixtures of aqueous U(VI) hydroxyl or phosphate species and uranium phosphate nanoparticles. The presence of the nanoparticles made it impossible to accurately calculate a Solubility Product for NaUO2PO4.xH2O in the absence of carbonate and at higher pCH+ values. Therefore in order to increase the concentration of U(VI) in solution and thereby verify the Solubility Product calculated from the most acidic samples, we systematically introduced know concentrations of carbonate, which resulted in the formation of U(VI) carbonate complexes. Development of an accurate aqueous thermodynamic model for the aqueous U(VI) carbonate complexes then allowed calculation of a Solubility Product for NaUO2PO4.xH2O in the higher pH samples which was in good agreement with the values for the more acidic samples.

  • the formation of sr silicates at low temperature and the Solubility Product of tobermorite like sr5si6o16 oh 2 5h2o
    American Mineralogist, 2003
    Co-Authors: Andrew R Felmy, Marvin J Mason, Paul L Gassman, David E Mccready
    Abstract:

    The Formation of Strontium Silicates at Low Temperature and the Solubility Product of Tobermorite like Sr5Si6O16(OH)2 5H20

  • thermodynamics of the u vi ca2 cl oh h2o system Solubility Product of becquerelite
    Radiochimica Acta, 2002
    Co-Authors: Andrew R Felmy, Nancy J Hess, Virginia L Legore, David E Mccready
    Abstract:

    The Solubility of synthetic becquerelite (Ca(UO 2 ) 6 O 4 (OH) 6 .8H 2 O) was determined in 0.02, 0.1, and 0.5 M CaCl 2 solutions and at pC H + values ranging from approximately 4 to 11. The presence of becquerelite in equilibrated samples was confirmed by a combination of techniques involving X-ray diffraction, total chemical composition, and analyses of Solubility data. The Solubility data were interpreted using Pitzer's aqueous thermodynamic model and the thermodynamic data for U(VI) species available in the literature. The log of the Solubility Product for becquerelite [Ca(UO 2 ) 6 O 4 (OH) 6 .8H 2 O+14H + ⇄ Ca + + 6UO 2 2+ + 18H 2 O] was determined to be 41.4′0.2. This value is similar to the values previously reported for other synthetic becquerelites, but is drastically different from a value reported for a natural sample.

  • the Solubility Product of crystalline ferric selenite hexahydrate and the complexation constant of feseo 3
    Journal of Solution Chemistry, 1995
    Co-Authors: Andrew R Felmy, Dean A Moore
    Abstract:

    The aqueous Solubility of Fe2(SeO3)3·6H2O(c) was studied in deionized water adjusted to a range in pH values from 0.77 to 5.1 and in Na2SeO3 solutions ranging in concentrations from 0.0002 to 0.02 mol-dm−3. The studies were conducted from both the undersaturation and oversaturation directions, with equilibration periods ranging from 7 to 1725 days. Stoichiometric dissolution of the solid was observed in solutions with pH values up to nearly 4. In general, concentrations of both Se and Fe decreased as pH increased from 1 to 4. Analyses of the equilibrated suspensions confirmed the equilibrium solid to be Fe2(SeO3)3·6H2O(c) and the aqueous Se to be selenite. Pitzer's ion-interaction model was used with selected ion pairs to interpret the Solubility data. The logarithm of the Solubility Product of ferric selenite $$Fe_2 (SeO_3 )_3 .6H_2 O(c) \begin{array}{*{20}c} \to \\ \leftarrow \\ \end{array} 2Fe^{3 + } + 3SeO_3^{2 - } + 6H_2 O$$ was found to be −41.58±0.11. This value is less than any reported in the literature for a ferric selenite by more than 10 orders of magnitude. The Solubility data and calculations show an extremely strong interaction between aqueous Fe3+ and SeO32−; interpretation of these data requires the inclusion of FeSeO3+ i.e. $$Fe^{3 + } + SeO_3^{2 - } \begin{array}{*{20}c} \to \\ \leftarrow \\ \end{array} FeSeO_3^ + , log K = 11.15 \pm 0.11$$

Hirotake Moriyama - One of the best experts on this subject based on the ideXlab platform.

  • determination of uranium iv hydrolysis constants and Solubility Product of uo2 xh2o
    Radiochimica Acta, 2003
    Co-Authors: Kenso Fujiwara, Hajimu Yamana, Toshiyuki Fujii, Hirotake Moriyama
    Abstract:

    The hydrolysis constants of tetravalent uranium were determined by a solvent extraction method using thenoyltrifluoroacetone(TTA) and 2 3 3 U. The distribution ratio of U(IV) was measured as a function of the pH c value in the aqueous phase at I=0.1, 0.5 and 1.0, and was analyzed to obtain the hydrolysis constants (β m ) of U(OH) m (4-m)+ at the standard state (I=0). By taking the specific ion interaction theory (SIT) for ionic strength corrections, the hydrolysis constants at I = 0 were determined to be β 1 ° = 13.71 ′ 0.31, β 2 ° = 26.12 ′ 0.21 and β 3 ° = 36.85 ′ 0.36, together with the ion interaction coefficients of UOH 3 + , U(OH) 2 2+ and U(OH) 3 +. The Solubility Product (K s p ) for the reaction of UO 2 .xH 2 O = U 4 + + 4OH + (x-2)H 2 O was also calculated to be log K s p ° = -53.93 ′ 0.20 by considering the hydrolysis constants.

  • Solubility Product of Pu(VI) hydrous oxide
    Radiochimica Acta, 2003
    Co-Authors: Kenso Fujiwara, Hajimu Yamana, Toshiyuki Fujii, Hirotake Moriyama
    Abstract:

    The Solubility of Pu(Vl) hydrous oxide was measured in the pH c range from 4 to 5.5 at 25′1°C in a NaClO 4 solution containing O 3 gas. The experiment was carried out by oversaturation and undersaturation methods at ionicstrength I=0.1, 0.5 and 1.0. The concentration of Pu(VI) was measured by α-spectrometry and UV/visible spectrophotometry, and the equilibrium constant of the reaction, PuO 2 (OH) 2 = PuO 2 2+ +2OH - , was obtained. From the obtained results, the Solubility Products (K s P ) of Pu hydrous oxide at I=0.1, 0.5 and 1.0 were determined. The experimental values were extrapolated to the standard state (I=0) by using the specific interaction theory (SIT), and the Solubility Product of Pu hydrous oxide was determined to be log K s P ° =-22.88′0.39. The ion interaction coefficient e (PuO 2 2+, ClO 4 -) was also evaluated to be 0.30′0.09.

  • Solubility Product of uranium iv hydrous oxide
    Journal of Nuclear Science and Technology, 2002
    Co-Authors: Kenso Fujiwara, Hajimu Yamana, Toshiyuki Fujii, Hirotake Moriyama
    Abstract:

    The Solubility of UO2.xH2O was measured in the pH range around 3 in NaCl solutions of I=0.1, 0.5, 1.0 and 2.0 M at 25 °C containing NH2OH and zinc powder. The concentration of U(IV) solution species was measured by UV/Visible spectrophotometry and the formation of UO2.xH2O was confirmed by X-ray diffraction. The Solubility Product (Ksp) of the reaction, UO2.xH2O = U4+ + 40H- + (x-2)H2O, was calculated taking into account the coexistence of U(IV) hydrolysis species, of which the hydrolysis constants β1 and β2 were determined by a TTA solvent extraction method and, β3 and β4 were estimated by a semi-empirical equation, Ionic strength corrections by specific interaction theory were made to obtain the standard state values.

  • Solubility Product of plutonium hydrous oxide and its ionic strength dependence
    Radiochimica Acta, 2002
    Co-Authors: Kenso Fujiwara, Hajimu Yamana, Toshiyuki Fujii, Hirotake Moriyama
    Abstract:

    The Solubility of PuO 2 .xH 2 O was measured at 25°C in a NaClO 4 solution containing Na 2 S 2 O 4 as a reductant. The experiment was carried out by an over-saturation method at I = 1.0 and by an undersaturation method at I =0.5, 1.0 and 2.0. The concentration of Pu 3 + was measured by α-spectrometry and UV/Visible spectrophotometry, and the equilibrium constant of the reaction, PuO 2 .xH 2 O + e - = Pu 3 + + 40H - + (x - 2)H 2 O, was obtained. From the obtained results, the Solubility Product (K s p ) of PuO 2 .xH 2 O, for PuO 2 .xH 2 O = Pu 4 + + 4OH - + (x - 2)H 2 O at I = 0.5, 1.0 and 2.0 was determined. By using the specific interaction theory (SIT), the Solubility Product of PuO 2 .xH 2 O at the standard state (I = 0) was determined to be log K o s p = -57.97 ′ 0.24, and the ion interaction coefficient e (Pu 4 + , ClO 4 -) was also evaluated to be 0.99′0.20.

Paul H Anderson - One of the best experts on this subject based on the ideXlab platform.

  • a novel kinetic method to measure apparent Solubility Product of bulk human enamel
    Frontiers in Physiology, 2017
    Co-Authors: Linda Hassanali, F S L Wong, R J M Lynch, Paul H Anderson
    Abstract:

    Introduction Tooth enamel mineral loss is influenced by its Solubility Product value, which is fundamental to the understanding of de- and remineralisation resulting from a carious or erosive challenge. Published pKsp values for human enamel and hydroxyapatite range from 110-126 suggesting a heterogeneous nature of enamel Solubility. However, this range of values may also result from the variety of methods used, e.g. some authors reporting values for suspensions of enamel powder and others for bulk enamel. The aim of this study was to develop a method to measure the Solubility of bulk human enamel under controlled in vitro conditions simulating demineralisation behaviour of enamel within the oral environment using scanning microradiography (SMR). SMR was used to monitor real-time changes in enamel demineralisation rates at increasing calcium concentrations in a caries simulating demineralisation solution until the concentration at which thermodynamic equilibrium between enamel and solution was achieved. Method: 2 mm thick caries free erupted human enamel slabs with the natural buccal surfaces exposed were placed in SMR cells exposed to circulating caries-simulating 2.0 L 0.1 M pH=4.0 acetic acid, at 25oC. SMR was used to continuously measure in real-time the decrease in mineral mass during the demineralisation at 5 different points from on each slab. Demineralisation rates were calculated from a linear regression curve of projected mineral mass against demineralisation time. Changes in the demineralisation rates were monitored following a series of successive increases in calcium (and phosphate at hydroxyapatite stoichiometric ratios of Ca:P 1.67) were added to the demineralising solution, until demineralisation ceased. The pH was maintained constant throughout. Results: Demineralisation halted when the calcium concentration was ~30mM. At higher calcium concentrations, mineral deposition (remineralisation) occurred. By comparison with results from speciation software calculations for the calcium phosphate ternary system, this result suggests that the bulk Solubility Product of enamel (pKspBEnamel) under the conditions used is 121. Discussion: The pKspBEnamel under these conditions was lower than many previous reported values, and much closer to those previously reported for HAp. However, this is a bulk value, and does not reflect that enamel is a heterogeneous material, nor the influence of ionic