Feldspar dissolution in acidic and organic solutions: Compositional and pH dependence of dissolution rate
- Univ. of Delaware, Lewes, DE (United States)
The steady-state dissolution rates of plagioclase feldspars into inorganic acid solutions in a flow-through reactor increased with Al content of the mineral from 1.4 {circ} 10{sup {minus}11} mol Si/m{sup 2}/s for albite to 5.6 {circ} 10{sup -9} mol Si/m{sup 2}/s for bytownite. A similar trend was observed for minerals dissolved in neutral solutions although the rates were lower. The results of these experiments are used to develop a simple empirical equation to describe the dissolution of tectosilicates (quartz + feldspars): R{sub H} = k{sub H}a{sup nH}{sub H+} where R{sub H} is the dissolution rate of tectosilicates in acid solution, a{sub H+} is the activity of H{sup +} ion, and k{sub H} and n{sub H} are dependent on the aluminum fraction in the tectosilicate framework [Al/Al + Si] : log k{sub H} = -11.24 + 25.98 * [Al/Al + Si]{sup 2} and n{sub H} = -0.052 + 4.23 * [Al/Al + Si]{sup 2}. This model, with its strong dependence on Al fraction, suggests that tectosilicate dissolution in acid solution results primarily from attack at Al sites at the mineral surface. In acidic oxalate solutions the steady-state dissolution rates were, in some cases, up to a factor of 10 higher than dissolution rates in inorganic solutions at the same pH and appeared to have a similar dependence on pH and mineral composition, at least away from the extremes in aluminum fraction (quartz and bytownite). The strong dependence of dissolution rate in acidic organic solutions on aluminum fraction indicates that both protons and ligands attack the mineral surface at the same, presumably Al, sites. 45 refs., 5 figs., 2 tabs.
- OSTI ID:
- 476821
- Journal Information:
- Geochimica et Cosmochimica Acta, Vol. 60, Issue 16; Other Information: PBD: Aug 1996
- Country of Publication:
- United States
- Language:
- English
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