CaCO₃ Precipitation, Transport and Sensing in Porous Media with In Situ Generation of Reactants

Abstract

Ureolytically driven calcite precipitation is a promising approach for inducing subsurface mineral precipitation, but engineered application requires the ability to control and predict precipitate distribution. To study the coupling between reactant transport and precipitate distribution, columns with defined zones of immobilized urease were used to examine the distribution of calcium carbonate precipitation along the flow path, at two different initial flow rates. As expected, with slower flow precipitate was concentrated toward the upstream end of the enzyme zone and with higher flow the solid was more uniformly distributed over the enzyme zone. Under constant hydraulic head conditions the flow rate decreased as precipitates decreased porosity and permeability. The hydrolysis/precipitation zone was expected to become compressed in the upstream direction. However, apparent reductions in the urea hydrolysis rate and changes in the distribution of enzyme activity, possibly due to CaCO3 precipitate hindering urea transport to the enzyme, or enzyme mobilization, mitigated reaction zone compression. Co-injected strontium was expected to be sequestered by coprecipitation with CaCO3, but the results suggested that coprecipitation was not an effective sequestration mechanism in this system. In addition, spectral induced polarization (SIP) was used to monitor the spatial and temporal evolution of the reaction zone.

Impact of multicomponent ionic transport on pH fronts propagation in saturated porous media

“…The correct quantification of pH distribution is of utmost importance in various areas of subsurface research including the study of groundwater acidification [e.g., Moss and Edmunds ., ; de Caritat , ; Hansen and Postma , ; Donovan et al ., ; Kjøller et al ., ; Fest et al ., , ; Franken et al ., ], sorption‐desorption, and surface complexation of trace metals onto mineral surfaces [e.g., Davis and Kent , ; Zachara et al ., ; Kent et al ., ; Davis et al ., ; Prigiobbe and Bryant , ], ion exchange [e.g., Griffioen , ; Appelo , ], redox‐controlled reaction fronts [e.g., Engesgaard and Kipp , ], as well as mineral equilibria and reactive transport [e.g., Maher et al ., ; Li et al ., , 2014; Molins et al ., ; Redden et al ., ; Haberer et al ., ]. In particular, groundwater acidification, mainly caused by acid rain precipitation, has been identified as a serious problem especially in aquifers with sediments containing low pH buffering capacity [ Edmunds and Kinniburgh , ; Hansen and Postma , ; Kjøller et al ., ; Franken et al ., ].…”

Calcium carbonate precipitation in compacted bentonite using electromigration reaction method and its application to estimate the ion activity coefficient in the porewater

“…The reaction of these two ions can generate CaCO3 precipitates, which may affect the transport of radionuclides by porosity clogging [5,7,8] and/or incorporation of radionuclides in the precipitates [9,10]. Although CaCO3 precipitation has been studied extensively in bulk solution [11,12] and in porous media [13][14][15][16], little is known about its behavior in compacted bentonite.…”

Estimation of a biofilm-specific reaction rate: kinetics of bacterial urea hydrolysis in a biofilm

“…Ureolysis in planktonic cultures has been investigated thoroughly and there have been a number of studies to quantify volume-averaged ureolysis rates in porous media containing microorganisms 6–9 and immobilised enzyme. 10,11 The most applicable studies concentrate on the rate of precipitation in these systems leaving the micro-scale reactive transport characteristics of ureolysis in biofilms largely undiscussed.…”