Solubility of Siderite (FeCO3) in NaCl Solutions期刊界 All Journals 搜尽天下杂志传播学术成果专业期刊搜索期刊信息化学术搜索

Solubility of Siderite (FeCO3) in NaCl Solutions

Authors:

Carlos A. R. Silva Xuewu Liu F. J. Millero

Affiliation:

(1) Departamento de Oceanografia e Limnologia, Centro de Biociências, Universidade Federal do Rio Grande do Norte, CP 1202, 59075-970, Brasil;(2) Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Causeway, Miami, Florida, 33149-1098

Abstract:

The solubility of siderite (FeCO₃) at 25°C under constant CO₂ partial pressure [p(CO₂)] was determined in NaCl solutions as a function of ionic strength. The dissolution of FeCO₃(s) for the reaction

$begin{gathered}{FeCO}_{3} ({s}) + 2{text{H}}^+ = {Fe}^{2 + } + {CO}_{2} ({g}) + {H}_{2}{O} hfill K{so}^{*} = [{Fe}^{2 + } ];p{CO}_{2} /[{H}^{ + } ]^2 hfill end{gathered}$

has been determined as a function of pH = – log[H⁺]. From these values we have determined the equilibrium constant for the stoichiometric solubility to FeCO₃(s) in NaCl

$K_{so}^{*} = [{Fe}^{2 + }];left[{CO}_{3}^{2} - right]$

These values have been fitted to the equation

$log [K_{sp}^{*}] = - 10.9 + 2.518;I^{0.5} - 0.657;I$

with a standard error of s = 0.15. The extrapolated value of log(K^o_sp) – 10.9 in water is in good agreement with data in the literature (– 10.8 to – 11.2) determined in solutions of different composition and ionic strength.The measured values of the activity coefficient, gamma

_T(Fe²⁺)

_T(CO₃^2–), have been used to estimate the stability constant for the formation of the FeCO₃ ion pair, K*(FeCO₃). The values of K*(FeCO₃) have been fitted to the equation (s = 0.09)

$log [K^* ({FeCO}_{3})] = 6.3 - 2.3135;I^{0.5} + 0.7091;I$

The value of log[K^o(FeCO₃)] in water found in this study (6.3 ± 0.2) is slightly higher than the value found from extrapolations in 1.0 m NaClO₄ solutions (5.9 ± 0.2). These differences are related to the model used to determine the activity coefficients of the Fe(II) and carbonate species in the two solutions.

Keywords:

Siderite solubility activity coefficients sodium chloride Pitzer equations

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