The effect of calcium and magnesium on carbonate mineral precipitation during reactive transport in a model subsurface pore structure

Carbonate mineral precipitation in the subsurface at the interface of two advecting fluids can result in physical and chemical changes in the pore network. This can affect the effectiveness of various applications including carbon sequestration and in situ remediation. In this work we evaluate the precipitation kinetics of carbonates in a microfluidic pore network when carbonate in water is mixed transverse to flow with a synthetic brine containing an equimolar concentration of calcium (Ca, 10 mM) and concentrations of magnesium (Mg) ranging from 2 to 40 mM. Mineral precipitation was monitored using reflected brightfield microscopy and mineral polymorphs were determined using Raman spectroscopy. Although Mg was present, only calcium carbonate (CaCO3) polymorphs were observed. The presence of Mg affected both the rate of precipitation and the prevalence of different CaCO3 morphologies. The rate of precipitation with 40mM Mg was about half of the rate as when no Mg was present. The calcium carbonate polymorph aragonite increased from <5% of the precipitated crystal area to >20% as the Mg concentration increased from 0 mM to 40 mM. Energy dispersive spectroscopy (EDS) results showed Mg2+ incorporated into the crystal lattice of the CaCO3 polymorph calcite at 8 to 14 mole% when Mg concentration in solution was highest. The incorporation of Mg2+ into the crystals was likely responsible for the reduction in precipitation rate at high solution concentrations of Mg. Significant pore blockage occurred along the mixing zone, indicating that carbonate precipitation may be of concern along the CO2 or contaminant plume margins and affect the efficiency of CO2 injection or contaminant remediation.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Environ Engr in Civil Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2012

Author dc:creator

• Boyd, Victoria

Contributors dc:contributor

• Werth, Charles J.

• Carbonate mineral precipitation
• Reactive transport
• Micromodel

Statement dc:rights

• Copyright 2012 Victoria Boyd

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/34312

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/34312