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Title: Dedolomitization in Na-Ca-Cl brines from 100/sup 0/ to 200/sup 0/C at 300 bars

Abstract

Dedolomitization experiments were run at 300 bars for 7 to 8 weeks at 100/sup 0/, 150/sup 0/, and 200/sup 0/C in chloride brines containing 2 m (molal) Na, 0.5 m Ca, and 0.02 m Sr. The ordered dolomite dissolved and low-Mg calcite back precipitated as a replacement and/or rim cement of equant spar calcite crystals 10 to 50 ..mu..m in diameter. Between 100/sup 0/ and 200/sup 0/C the mode of calcite formation changed from direct precipitation into void space produced by dissolving dolomite to pseudomorphic replacement of dolomite. The dedolomitization textures formed in these experiments are similar to those found in the rock record. Solution compositions were monitored as a function of experimental time and imply that calcite-dolomite equilibrium was approached at 100/sup 0/C and reached at 150/sup 0/ and 200/sup 0/C. The final aqueous molality ratios of Ca:Mg were 14.2, 23.5, and 35.4, respectively, at 100/sup 0/, 150/sup 0/, and 200/sup 0/C. The respective activity ratios, computed using Pitzer's model, were 14.3, 23.6, and 37.0, representing estimated constants for the dissolution of dolomite. The estimated standard state enthalpy of reaction is 3.6 kcal between 150/sup 0/ and 200/sup 0/C. The empirical Sr distribution coefficient for the precipitated calcite wasmore » determined from micro-probe analyses of the calcite and solution data. The average coefficient values increased with increasing temperature, being 0.027, 0.048, and 0.063, respectively, at 100/sup 0/, 150/sup 0/, and 200/sup 0/C.« less

Authors:
; ;
Publication Date:
Research Org.:
Univ. of New Orleans, LA (USA)
OSTI Identifier:
7188784
Resource Type:
Journal Article
Journal Name:
Geochim. Cosmochim. Acta; (United States)
Additional Journal Information:
Journal Volume: 51:4
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; BRINES; CHEMICAL COMPOSITION; GEOCHEMISTRY; DOLOMITE; ACTIVATION ENERGY; DISSOLUTION; ENTHALPY; CALCITE; CALCIUM COMPOUNDS; CHLORIDES; CRYSTALLIZATION; EQUILIBRIUM; MINERALIZATION; PRECIPITATION; SODIUM COMPOUNDS; STRONTIUM COMPOUNDS; TEMPERATURE EFFECTS; THERMODYNAMICS; ALKALI METAL COMPOUNDS; ALKALINE EARTH METAL COMPOUNDS; CALCIUM CARBONATES; CARBON COMPOUNDS; CARBONATE MINERALS; CARBONATES; CHEMISTRY; CHLORINE COMPOUNDS; ENERGY; HALIDES; HALOGEN COMPOUNDS; MAGNESIUM CARBONATES; MAGNESIUM COMPOUNDS; MINERALS; OXYGEN COMPOUNDS; PHASE TRANSFORMATIONS; PHYSICAL PROPERTIES; SEPARATION PROCESSES; THERMODYNAMIC PROPERTIES; 580400* - Geochemistry- (-1989)

Citation Formats

Stoessell, R.K., Klimentidis, R.E., and Prezbindowski, D.R. Dedolomitization in Na-Ca-Cl brines from 100/sup 0/ to 200/sup 0/C at 300 bars. United States: N. p., 1987. Web. doi:10.1016/0016-7037(87)90098-6.
Stoessell, R.K., Klimentidis, R.E., & Prezbindowski, D.R. Dedolomitization in Na-Ca-Cl brines from 100/sup 0/ to 200/sup 0/C at 300 bars. United States. doi:10.1016/0016-7037(87)90098-6.
Stoessell, R.K., Klimentidis, R.E., and Prezbindowski, D.R. Wed . "Dedolomitization in Na-Ca-Cl brines from 100/sup 0/ to 200/sup 0/C at 300 bars". United States. doi:10.1016/0016-7037(87)90098-6.
@article{osti_7188784,
title = {Dedolomitization in Na-Ca-Cl brines from 100/sup 0/ to 200/sup 0/C at 300 bars},
author = {Stoessell, R.K. and Klimentidis, R.E. and Prezbindowski, D.R.},
abstractNote = {Dedolomitization experiments were run at 300 bars for 7 to 8 weeks at 100/sup 0/, 150/sup 0/, and 200/sup 0/C in chloride brines containing 2 m (molal) Na, 0.5 m Ca, and 0.02 m Sr. The ordered dolomite dissolved and low-Mg calcite back precipitated as a replacement and/or rim cement of equant spar calcite crystals 10 to 50 ..mu..m in diameter. Between 100/sup 0/ and 200/sup 0/C the mode of calcite formation changed from direct precipitation into void space produced by dissolving dolomite to pseudomorphic replacement of dolomite. The dedolomitization textures formed in these experiments are similar to those found in the rock record. Solution compositions were monitored as a function of experimental time and imply that calcite-dolomite equilibrium was approached at 100/sup 0/C and reached at 150/sup 0/ and 200/sup 0/C. The final aqueous molality ratios of Ca:Mg were 14.2, 23.5, and 35.4, respectively, at 100/sup 0/, 150/sup 0/, and 200/sup 0/C. The respective activity ratios, computed using Pitzer's model, were 14.3, 23.6, and 37.0, representing estimated constants for the dissolution of dolomite. The estimated standard state enthalpy of reaction is 3.6 kcal between 150/sup 0/ and 200/sup 0/C. The empirical Sr distribution coefficient for the precipitated calcite was determined from micro-probe analyses of the calcite and solution data. The average coefficient values increased with increasing temperature, being 0.027, 0.048, and 0.063, respectively, at 100/sup 0/, 150/sup 0/, and 200/sup 0/C.},
doi = {10.1016/0016-7037(87)90098-6},
journal = {Geochim. Cosmochim. Acta; (United States)},
number = ,
volume = 51:4,
place = {United States},
year = {1987},
month = {4}
}