Dolerite Fines Used as a Calcium Source for Microbially Induced Calcite Precipitation Reduce the Environmental Carbon Cost in Sandy Soil

Abstract

Microbial-Induced Calcite Precipitation (MICP) stimulates soil microbiota to induce a cementation of the soil matrix. Urea, calcium and simple carbon nutrients are supplied to produce carbonates via urea hydrolysis and induce the precipitation of the mineral calcite. Calcium chloride (CaCl₂) is typically used as a source for calcium, but basic silicate rocks and other materials have been investigated as alternatives. Weathering of calcium-rich silicate rocks (e.g., basalt and dolerite) releases calcium, magnesium and iron; this process is associated with sequestration of atmospheric CO₂ and formation of pedogenic carbonates. We investigated atmospheric carbon fluxes of a MICP treated sandy soil using CaCl₂ and dolerite fines applied on the soil surface as sources for calcium. Soil-atmosphere carbon fluxes were monitored over 2 months and determined with an infrared gas analyser connected to a soil chamber. Soil inorganic carbon content and isotopic composition were determined with isotope-ratio mass spectrometry. In addition, soil-atmosphere CO₂ fluxes during chemical weathering of dolerite fines were investigated in incubation experiments with gas chromatography. Larger CO₂ emissions resulted from the application of dolerite fines (116 g CO₂-C m^-2) compared to CaCl₂ (79 g CO₂-C m^-2) but larger inorganic carbon precipitation also occurred (172.8 and 76.9 g C m^-2, respectively). Normalising to the emitted carbon to precipitated carbon, the environmental carbon cost was reduced with dolerite fines (0.67) compared to the traditional MICP treatment (1.01). The carbon isotopic signature indicated pedogenic carbonates (δ¹³C_av = -8.2 ± 5.0‰) formed when dolerite was applied and carbon originating from urea (δ¹³C_av = -46.4 ± 1.0‰) precipitated when CaCl₂ was used. Dolerite fines had a large but short-lived (<2 d) carbon sequestration potential, and results indicated peak CO₂ emissions during MICP could be balanced optimising the application of dolerite fines.

Keywords: CO2 emissions; CO2 sequestration; MICP; basaltic quarry fines; calcite; calcium-rich silicate rock; pedogenic carbonates; weathering.

FIGURE 1

Time series of soil-atmosphere CO₂ fluxes of sandy soil columns treated with the traditional MICP treatment (MICP) and using dolerite fines applied on the soil surface as source for calcium (dolerite and MICP). CO₂ fluxes and cumulative CO₂ emission link to left and right vertical axes, relatively. Divisions on bottom horizontal axis represent 1 d. The application of dolerite is indicated with a vertical arrow and ‘solution drainage’ are pointed as examples. The end of the experiment phases are indicated with dropping vertical dashed lines.

FIGURE 2

Average CO₂ fluxes during 24 h reaction time of soil column treated with traditional (MICP), and for soil column containing dolerite fines added to the MICP treatment (dolerite and MICP). The first and second treatments were excluded from the computed average for both treatments for comparison purposes and to remove the initial near-zero CO₂ fluxes not observed in posterior treatments in the soil column containing dolerite fines. Dark and light grey shaded areas indicate ± two standard deviations for MICP and dolerite and MICP, respectively.

FIGURE 3

ICP-OES analysis (n = 1) of common (above) and trace (below) weathered elements dissolved in soil leachate samples obtained after first (t₁) and last (t₈) cementation treatments and a month after finalising the treatment (rewetting) for columns treated with traditional MICP and soil column containing dolerite fines treated with MICP (Dolerite). Analysis carried out by James Hutton Ltd., Aberdeen, United Kingdom.

FIGURE 4

Soil total inorganic carbon during the MICP treatment phase for soil column treated with traditional MICP solution (MICP) and soil column containing dolerite fines (dolerite and MICP) determined by EA-IRMS (n = 2; SD < 0.002, SD smaller than markers). Regression line and equation fit of traditional MICP treatment data.

FIGURE 5

Stable isotopic signature of precipitated carbonates (δ¹⁸O ‰ and δ¹³C ‰, VPDB) (n = 2; SD < 1.9, SD smaller than markers) in soil column treated with traditional MICP (MICP) and soil column containing dolerite fines treated with MICP (dolerite and MICP). Numeric labels indicate the treatment number and “r” label stands for “re-wetting.” Data from concrete (Macleod et al., 1991; Krishnamurthy et al., 2003), steel slag (Renforth et al., 2009), brownfield sites (Washbourne et al., 2015; Jorat et al., 2020), Permian carbonate rock (Harwood and Coleman, 1981), and pedogenic soil carbonates (Salomons et al., 1978) included for comparison.

FIGURE 6

Evolution of CO₂-C normalised to the mass of solids in vial headspace during chemical weathering of dolerite fines in distilled water at fixed liquid-to-solid ratios (L/S = 0, 0.6, 1.0, 1.5, 2.5, 5, 10, and 15) over 60 min, analysed with gas chromatography (n = 3; SD indicated with error bars). Lines correspond to the fitting model described by Eq. (1). Data corresponds to experiment day 1.