Influence of a CO2 long term exposure on the mobilisation and speciation of metals in soils

• The response of soil chemical parameters as a result of CO2 exposure was studied.
• Geochemical modelling was carried out to elucidate the metal speciation in soils.
• CO2-soil incubation induces the acidification of soils via CO2 hydrolysis.
• CO2-soil incubation increases the concentration of Al, Cr, Fe, Ni, and Pb.
• Al3+, Fe2+, Cr3+, Ni2+, and PbHCO3 predominate in the pore water of soils.

This study investigates the potential risks associated with high levels and long term exposure of carbon dioxide (CO2) on the mobility and speciation of exchangeable metals in soils. CO2 incubation batch experiments at high pressure and temperature coupled with geochemical modelling were carried out to elucidate the behaviour and mobilisation of metals and the response of soil chemical parameters as a result of long term CO2 exposure. A t-Student analysis was performed to ascertain whether differences in the mean concentration of exchangeable metals in soils before and after CO2-incubations are attributable to increase of metal molibilisation because of the long term CO2 exposure. The t-Student revealed the CO2 long term incubation was statistically significant (p < 0.05) for the exchangeable concentration of Ni, Zn, and Pb. The CO2-soil incubation induces the acidification of the pore water of soils via CO2 hydrolysis and as a consequence, it increases the exchangeable concentration of Ni, Zn, and Pb in the soils. As, Al, Cr, Cu, and Fe show a different mobilisation pattern depending on the moisture content in soils. Al3+, Fe2+, Cr3+, and Cu2+ as free cations, As as HAsO2, Pb2+and PbHCO3−, Zn2+ and ZnHCO3−, are predicted to be the predominant aqueous complexes in the pore water of the incubated soils.

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