Coupled alkali-feldspar dissolution and secondary mineral precipitation in batch systems: 1. New experiments at 200° C and 300 bars

Journal Article · Thu Jan 01 04:00:00 EST 2009 · Chemical Geology

DOI:https://doi.org/10.1016/j.chemgeo.2008.09.014· OSTI ID:1014883

Fu, Qi ^[1]; Lu, Peng ^[2]; Konishi, Hiromi ^[2]; Dilmore, Robert ^[3]; Xu, Huifang ^[4]; Seyfried, W.E. ^[1]; Zhu, Chen ^[2]

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1. Univ. of Minnesota, Minneapolis, MN (United States)
2. Indiana Univ., Bloomington, IN (United States)
3. National Energy Technology Lab. (NETL), Pittsburgh, PA, (United States)
4. Univ. of Wisconsin, Madison, WI (United States)

Batch reactor experiments were conducted to assess perthitic alkali-feldspar dissolution and secondary mineral formation in an initially acidic fluid (pH=3.1) at 200º C and 300 bars. Temporal evolution of fluid chemistry was monitored by major element analysis of in situ fluid samples. Solid reaction products were retrieved from two identical experiments terminated after 5 and 78 days. Scanning electron microscopy revealed dissolution features and significant secondary mineral coverage on feldspar surfaces. Boehmite and kaolinite were identified as secondary minerals by X-ray diffraction and transmission electron microscopy. X-ray photoelectron spectroscopy analysis of alkali-feldspar surfaces before and after reaction showed a trend of increasing Al/Si ratios and decreasing K/Al ratios with reaction progress, consistent with the formation of boehmite and kaolinite. Saturation indices of feldspars and secondary minerals suggest that albite dissolution occurred throughout the experiments, while K-fieldspar exceeded saturation after 216 h of reaction. Reactions proceeded slowly and full equilibrium was not achieved, the relatively high temperature of the experiments notwithstanding. Thus, time series observations indicate continuous supersaturation with respect to boehmite and kaolinite, although the extent of this decreased with reaction progress as the driving force for albite dissolution decreased. The first experimental evidence of metastable co-existence of boehmite, kaolinite and alkali feldspar in the feldspar hydrolysis system is consistent with theoretical models of mineral dissolution/precipitation kinetics where the ratio of the secondary mineral precipitation rate constant to the rate constant of feldspar dissolution is well below unity. This has important implications for modeling the time-dependent evolution of feldspar dissolution and secondary mineral formation in natural systems.

• Research Organization: National Energy Technology Laboratory (NETL), Pittsburgh, PA, Morgantown, WV, and Albany, OR (United States)
• Sponsoring Organization: USDOE Assistant Secretary for Fossil Energy (FE)
• OSTI ID: 1014883
• Report Number(s): NETL-TPR--1684
• Journal Information: Chemical Geology, Journal Name: Chemical Geology Journal Issue: 3-4 Vol. 258; ISSN 0009-2541
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
58 GEOSCIENCES
DISSOLUTION
FELDSPAR
KINETICS
MASS TRANSFER
PRECIPITATION
SECONDARY MINERALS