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Investigating mineral dissolution kinetics by Flow-Through Time-Resolved Analysis (FT-TRA) De Baere, Bart


This thesis evaluates the applicability of flow-through time-resolved analysis (FT-TRA) to address problems ranging from determining mineral dissolution kinetics and dissolution regimes, to unraveling the elemental composition of multiple mineral phases in microfossils, to predicting drainage chemistry from mine waste. FT-TRA consists of a gradient pump, which continuously passes eluent of fixed or varying composition through a small flow-through reactor containing a small amount of solid sample. The effluent composition is then analyzed online using an inductively coupled plasma mass spectrometer in time-resolved mode, or is collected in a fraction collector for subsequent offline analysis, depending on the goal of the experiment. It is found that FT-TRA is well suited to study mineral dissolution kinetics. Using forsterite as a case study, it is shown that FT-TRA can be used to rapidly determine mineral dissolution rate parameters. The high temporal resolution data generated by FT-TRA documents in detail, and in real-time the gradual formation of surface leached layers as well as sporadic and abrupt exfoliation events occurring during dissolution. A range in eluent residence times in the reactor can be applied by controlling the eluent flow with the gradient pump, allowing for the empirical determination of the dissolution regime (surface- or transport-controlled), which must be established prior to interpreting mineral dissolution rates measured during the experiment. When combining FT-TRA data with pore scale modeling, dissolution rate constants can still be determined, even when the dissolution experiment is conducted under transport-controlled conditions. The added value of this continuous eluent flow system for assessing the leaching behavior of mine waste is also evaluated. The ability to carry out experiments in a relatively short time period provides a new means to elucidate the mechanism and conditions resulting in the release of toxic metals from mine waste during weathering. Finally, using insight gained from studying mineral dissolution kinetics, the premise on which FT-TRA was used to distinguish the elemental ratios of different biogenic mineral phases in microfossils for paleoceanographic reconstruction is re-evaluated.

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