Produit de solubilité de la calcite et constantes de dissociation de CaHCO3+ et CaCO30 entre 5 et 75 °C

Abstract

Les valeurs du produit de solubilité de la calcite et des constantes de dissociation de CaHCO3+ et CaCO30, notées K3 et K4, ont été déterminées à différentes températures comprises entre 5 et 75 °C (la calcite est instable aux températures plus élevées) à partir des mesures [(Ca2+)T, pH] de solubilité de ce sel dans l'eau carboniquement pure. Les résultats obtenus ont permis d'établir les relations empiriques suivantes :pKs= 7,8156 + 0,03111 T + (1 502/T) - 5,518 log TpK3= 6,2447 + 0,00437 T + (864,479/T) - 0,363 log TpK4= 2,89636 + 0,00707 T + (102,87/T) - 0,44176 log Texpressions dans lesquelles T désigne la température absolue (K) et log le logarithme décimal.Des variations de pKS avec la température nous avons déduit, à 25 °C, les grandeurs thermodynamiques relatives à la dissolution de la calcite :∆H0 = -2510 cal. mol-1, ∆S0 = -47,2 cal. mol-1. K-1et ∆C∘p = -73,9 cal. mol-1. K-1The values of the solubility product of calcite and dissociation constants of CaHCO3+ and CaCO30, K3 and K4 respectively, were determined at several temperatures between 5 and 75 °C (calcite becomes unstable at higher temperatures) from measurements [(Ca2+)T, pH] of calcite solubility using carbonically pure water. The results obtained lead to the following empirical expressions for the dependence of equilibrium constants on the temperature :pKs= 7,8156 + 0,03111 T + (1 502/T) - 5,518 log TpK3= 6,2447 + 0,00437 T + (864,479/T) - 0,363 log TpK4= 2,89636 + 0,00707 T + (102,87/T) - 0,44176 log Twhere log T is the common logarithm of the absolute temperature T(K).Using this expression of pKS, the calculated thermodynamic properties of the calcite dissolution reaction at 25 °C are :∆H0 = -2510 cal. mol-1, ∆S0 = -47,2 cal. mol-1. K-1et ∆C∘p = -73,9 cal. mol-1. K-

Coupled phase and aqueous species equilibrium of the H2O–CO2–NaCl–CaCO3 system from 0 to 250°C, 1 to 1000bar with NaCl concentrations up to saturation of halite

“…The dissociation of CaHCO 3 þ and CaCO 3 0 was first noted by Greenwald (1941). Many researchers afterwards measured the two dissociation constants (K 4 and K 5 ) at various temperatures up to 363 K (Neuman et al, 1956;Nakayama, 1968;Martynov et al, 1971;Martynov et al, 1972;Jacobson and Langmuir, 1974;Reardon and Langmuir, 1974;Moore and Verine, 1981;Plummer and Busenberg, 1982;Dorange et al, 1990). Since the experimental data are not sufficient to fit K 4 and K 5 up to 523 K and 1000 bar, we need to find a method to develop a predictive model with good extrapolation for these two constants.…”

Protectiveness, morphology and composition of corrosion products formed on carbon steel in the presence of Cl−, Ca2+ and Mg2+ in high pressure CO2 environments

“…The solubility constants for FeCO3, CaCO3 (calcite) and MgCO3 reported in the literature have been determined by Benezeth et al [28] , Dorange et al [29] and Benezeth et al [30] , respectively:…”

Scale precipitation on HDPE pipe by degassing of CO2 dissolved in water

“…CaCO 3 precipitation depends mainly on the solubility product value (K s ) which depends on temperature. The K s value of calcite was determined at several temperatures between 5 and 75°C, using the empirical expression (Dorange et al 1990): pK s ¼ 7:8156 þ 0:031111:T þ 1502=T-5518:log (T) (…”