Coupled alkali feldspar dissolution and secondary mineral precipitation in batch systems: 5. Results of K-feldspar hydrolysis experiments

Abstract

This paper explores how dissolution and precipitation reactions are coupled in batch reactor experimental systems at elevated temperatures. This is the fifth paper in our series of “Coupled Alkali Feldspar Dissolution and Secondary Mineral Precipitation in Batch Systems.” In the previous four papers we presented batch experiments of alkali-feldspar hydrolysis and explored the coupling of dissolution and precipitation reactions (Fu et al. in Chem Geol 91:955–964, 2009; Zhu and Lu in Geochim Cosmochim Acta 73:3171–3200, 2009; Zhu et al.in Geochim Cosmochim Acta 74:3963–3983, 2010; Lu et al. in Appl Geochem 30:75–90, 2013). Here, we present the results of additional K-rich feldspar hydrolysis experiments at 150 °C. Our solution chemistry measurements have constrained feldspar dissolution rates, and our high resolution transmission electron microscopy work has identified boehmite precipitation. Reaction path modeling of K-feldspar dissolution and boehmite precipitation simulated the coupled reactions, but only with forced changes of boehmite rate law in the middle of experimental duration. The results which are reported in this article lend further support to our hypothesis that slow secondary mineral precipitation explains part of the well-known apparent discrepancy between lab measured and field estimated feldspar dissolution rates (Zhu et al. in Water–rock interaction, 2004).