Geophysical monitoring and reactive transport modeling of ureolytically-driven calcium carbonate precipitation

Geochemical Transactions

Research Article

Yoshiko Fujita¹  Joanna Taylor²  Robert Smith²  Susan S Hubbard³  Yuxin Wu³  Jonathan B Ajo-Franklin³  Nicolas Spycher³  Kenneth H Williams³  Guoxiang Zhang⁴ 

[1] Biological Systems Department, Idaho National Laboratory, P.O. Box 1625, 83415, Idaho Falls, ID, USA;Center for Advanced Energy Studies, University of Idaho, 1776 Science Center Drive, 83402, Idaho Falls, ID, USA;Earth Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, 94720, Berkeley, CA, USA;Royal Dutch Shell International Exploration and Production Company, 200 N. Dairy Ashford Rd, 77079, Houston, TX, USA;

关键词: Total Dissolve Solid;    Calcium Carbonate;    Pore Fluid;    Calcium Carbonate Precipitation;    Fluid Conductivity;   

DOI  :  10.1186/1467-4866-12-7

 received in 2011-04-30, accepted in 2011-09-23,  发布年份 2011

来源: Springer

【 摘 要 】

Ureolytically-driven calcium carbonate precipitation is the basis for a promising in-situ remediation method for sequestration of divalent radionuclide and trace metal ions. It has also been proposed for use in geotechnical engineering for soil strengthening applications. Monitoring the occurrence, spatial distribution, and temporal evolution of calcium carbonate precipitation in the subsurface is critical for evaluating the performance of this technology and for developing the predictive models needed for engineering application. In this study, we conducted laboratory column experiments using natural sediment and groundwater to evaluate the utility of geophysical (complex resistivity and seismic) sensing methods, dynamic synchrotron x-ray computed tomography (micro-CT), and reactive transport modeling for tracking ureolytically-driven calcium carbonate precipitation processes under site relevant conditions. Reactive transport modeling with TOUGHREACT successfully simulated the changes of the major chemical components during urea hydrolysis. Even at the relatively low level of urea hydrolysis observed in the experiments, the simulations predicted an enhanced calcium carbonate precipitation rate that was 3-4 times greater than the baseline level. Reactive transport modeling results, geophysical monitoring data and micro-CT imaging correlated well with reaction processes validated by geochemical data. In particular, increases in ionic strength of the pore fluid during urea hydrolysis predicted by geochemical modeling were successfully captured by electrical conductivity measurements and confirmed by geochemical data. The low level of urea hydrolysis and calcium carbonate precipitation suggested by the model and geochemical data was corroborated by minor changes in seismic P-wave velocity measurements and micro-CT imaging; the latter provided direct evidence of sparsely distributed calcium carbonate precipitation. Ion exchange processes promoted through NH4+ production during urea hydrolysis were incorporated in the model and captured critical changes in the major metal species. The electrical phase increases were potentially due to ion exchange processes that modified charge structure at mineral/water interfaces. Our study revealed the potential of geophysical monitoring for geochemical changes during urea hydrolysis and the advantages of combining multiple approaches to understand complex biogeochemical processes in the subsurface.

【 授权许可】

CC BY   
© Wu et al; licensee Chemistry Central Ltd. 2011. This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.