Measuring mineral dissolution kinetics using on-line flow-through time resolved analysis (FT-TRA): an exploratory study with forsterite

Abstract

We explore the applicability of on-line flow-through time-resolved analysis (FT-TRA) to measure mineral dissolution rates, determine dissolution rate parameters, and monitor dissolution stoichiometry under both constant and transient eluent conditions. A custom-built automated flow-through system is used to subject mineral samples to controlled eluent flows of constant or varying composition, and the dissolution products are measured online with a quadrupole ICP-MS. Because forsterite dissolution has been extensively studied, this mineral provides an ideal benchmark to test the approach. FT-TRA has several advantages compared to the mixed-flow reactors conventionally used to measure mineral dissolution. The mineral dissolution regime (surface vs transport-controlled) can be readily established prior to conducting dissolution experiments, which is important if the goal of the experiment is to determine dissolution rate parameters. Because of the small volume (25 μL) of the flow-through reactor, the time to reach steady state concentration in the effluent is shorter and is limited by the intrinsic properties of the mineral, instead of the residence time of the effluent in the reactor. For minerals reaching steady-state dissolution rapidly, dissolution rate parameters (rate constant(s) and reaction order(s)) are established in a few hours, allowing for replications, statistical analysis of the results, and investigation of the underlying causes of variability. The experimental setup can be adapted for minerals that require longer periods of time to reach steady-state dissolution. In addition, FT-TRA lends itself particularly well for detailed monitoring of dissolution rates and dissolution stoichiometry under transient conditions. For forsterite dissolution under acidic conditions, preferential release of Mg when pH transits to lower values, and preferential release of Si when pH transits to higher values is clearly documented and can be interpreted as indicating changes in the mean depth of the Si-rich surface layer in response to changes in eluent acidity. Episodes of exfoliation of the Si-rich surface layer can also be identified, providing a means to study one of the potential rate limiting steps for CO 2 sequestration by carbonation of olivine. The results presented here indicate that FT-TRA with online ICP-MS analysis could be a useful and multifaceted addition to the toolbox available to study mineral dissolution.

Determination of mineral dissolution regimes using flow-through time-resolved analysis (FT-TRA) and numerical simulation

“…The multi-faceted applications and encouraging results obtained in this study and a companion paper (De Baere et al, 2015) warrants further development of FT-TRA for mineral dissolution kinetics studies (De Baere, 2015). proportionally with eluent residence time (Panel B, at relatively short eluent residence times).…”

“…Rimstidt et al, 2012). Although not directly relevant to the present study, the high temporal resolution afforded by FT-TRA also provides detailed information on the evolution of dissolution rates and stoichiometries when minerals are subjected to abrupt or transient dissolution episodes, documenting in particular the gradual formation of surface leached layers in unprecedented detail and identifying sporadic and abrupt exfoliation events (De Baere et al, 2015).…”

“…Combining FT-TRA with numerical simulations is facilitated by the low detection limits of ICP-MS, which allows dissolution of single crystals (and potentially single mineral cleavage surfaces) in small reaction cells of simple geometry. The small volume of the reaction cell also reduces the time needed to reach steady-state dissolution, which in conventional larger mixed flow reactors is primarily dictated by the residence time of the eluent in the reactor (De Baere et al, 2015). This characteristic of the experimental set up used in this study also facilitates efficient duplication of dissolution experiments and statistical analysis of the results to assess the underlying causes for the large variability observed in dissolution rates measured in laboratories (e.g.…”

Carbon Mineralization with North American PGM Mine Tailings—Characterization and Reactivity Analysis

“…To determine the labile calcium and magnesium cations present in the Stillwater tailings, a flow-through dissolution experiment was performed on Tail 2a using an apparatus shown in Figure 2 and described previously [29,30]. Prior to the experiment, 10% CO 2 (Praxair, balance N 2 ) was equilibrated with deionized water overnight to reach a pH of 4.41.…”

<b>Extractant efficiency in the solubilization of alternative sources of potassium

“…Rock sample preparation (crushing and milling) may affect the reactive site density and distribution (Baere, François, & Mayer, 2015), and the presence of ultrafine particles on the mineral surface may promote an initial intense element release, decreasing mineral dissolution over time (Sokolova, 2013).…”