RE2: Basic Processes and Parameterization
Lead: Yoshiko Fujita (INL)
Participants: James Heriksen (INL), Tsigabu Gebrehiwet (U of Idaho), Robert Smith (U of Idaho), George Redden (INL), Karen Wright (INL)
The role of Research Element 2 (RE2) is to provide descriptions of the basic processes that are coupled with flow in the RE1 experiments, for the conditions expected to be encountered in the experiments and representative of engineered systems. The primary basic processes of interest for the current experimental campaigns are calcium carbonate precipitation/dissolution and urea hydrolysis. Examples of RE2 research activities are provided below.
Effects of carbonate to calcium ion ratio on calcite precipitation kinetics and Sr partitioning
Steep gradients in reactant concentration can be created by the addition of reagent solutions to porous media to induce mineral precipitation. These gradients can result in spatially and temporally varying ratios of the soluble components. Constant composition experiments at a constant saturation state (Ω=12.8) but varying ratios of a(CO32-)/a(Ca2+) have been conducted to examine effects on precipitation rate and Sr partitioning.
Figure The setup of the constant composition reaction used for ion ration experiments and the resulted plot for measured precipitation rate vs. log of carbonate to calcium ratio.
Selection of urea hydrolysis rate expression and parameterization
A commercially available jackbean urease (Sigma U4002; Urease from Canavalia ensiformis (Jack bean), Type IX) was selected for use in the in situ reactant generation campaign. Specific activity and KM were determined for the urease preparation, and provided to the modeling team (RE3) for use in the following rate expression, modified from Fidaleo and Lavecchia (2003):
where [E]o is the total enzyme concentration, kref is a reference rate constant, Ea is the activation energy, Tref is the temperature at which kref is measured, KM is the Midhaelis constant, KP is a product inhibition constant, and KES,1 and KES,2 are dissociation costants for the enzyme-substrate complex.