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Title: Effect of solution saturation state and temperature on diopside dissolution

Abstract

Steady-state dissolution rates of diopside are measured as a function of solution saturation state using a titanium flow-through reactor at pH 7.5 and temperature ranging from 125 to 175 C. Diopside dissolved stoichiometrically under all experimental conditions and rates were not dependent on sample history. At each temperature, rates continuously decreased by two orders of magnitude as equilibrium was approached and did not exhibit a dissolution plateau of constant rates at high degrees of undersaturation. The variation of diopside dissolution rates with solution saturation can be described equally well with a ion exchange model based on transition state theory or pit nucleation model based on crystal growth/dissolution theory from 125 to 175 C. At 175 C, both models over predict dissolution rates by two orders of magnitude indicating that a secondary phase precipitated in the experiments. The ion exchange model assumes the formation of a Si-rich, Mg-deficient precursor complex. Lack of dependence of rates on steady-state aqueous calcium concentration supports the formation of such a complex, which is formed by exchange of protons for magnesium ions at the surface.

Authors:
;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
940871
Report Number(s):
UCRL-JRNL-229477
TRN: US0807232
DOE Contract Number:  
W-7405-ENG-48
Resource Type:
Journal Article
Resource Relation:
Journal Name: Geochemical Transactions, vol. 8, N/A, March 26, 2007, pp. 1-14; Journal Volume: 8
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; CALCIUM; DIOPSIDE; DISSOLUTION; ION EXCHANGE; MAGNESIUM IONS; NUCLEATION; PRECURSOR; PROTONS; SATURATION; TITANIUM

Citation Formats

Dixit, S, and Carroll, S A. Effect of solution saturation state and temperature on diopside dissolution. United States: N. p., 2007. Web. doi:10.1186/1467-4866-8-3.
Dixit, S, & Carroll, S A. Effect of solution saturation state and temperature on diopside dissolution. United States. doi:10.1186/1467-4866-8-3.
Dixit, S, and Carroll, S A. Fri . "Effect of solution saturation state and temperature on diopside dissolution". United States. doi:10.1186/1467-4866-8-3. https://www.osti.gov/servlets/purl/940871.
@article{osti_940871,
title = {Effect of solution saturation state and temperature on diopside dissolution},
author = {Dixit, S and Carroll, S A},
abstractNote = {Steady-state dissolution rates of diopside are measured as a function of solution saturation state using a titanium flow-through reactor at pH 7.5 and temperature ranging from 125 to 175 C. Diopside dissolved stoichiometrically under all experimental conditions and rates were not dependent on sample history. At each temperature, rates continuously decreased by two orders of magnitude as equilibrium was approached and did not exhibit a dissolution plateau of constant rates at high degrees of undersaturation. The variation of diopside dissolution rates with solution saturation can be described equally well with a ion exchange model based on transition state theory or pit nucleation model based on crystal growth/dissolution theory from 125 to 175 C. At 175 C, both models over predict dissolution rates by two orders of magnitude indicating that a secondary phase precipitated in the experiments. The ion exchange model assumes the formation of a Si-rich, Mg-deficient precursor complex. Lack of dependence of rates on steady-state aqueous calcium concentration supports the formation of such a complex, which is formed by exchange of protons for magnesium ions at the surface.},
doi = {10.1186/1467-4866-8-3},
journal = {Geochemical Transactions, vol. 8, N/A, March 26, 2007, pp. 1-14},
number = ,
volume = 8,
place = {United States},
year = {Fri Mar 23 00:00:00 EDT 2007},
month = {Fri Mar 23 00:00:00 EDT 2007}
}