Does the release of toxic metals due to subsurface CO2 storage in basalts pose an environmental hazard?

[Geoengineering News]

https://www.sciencedirect.com/science/article/pii/S1750583625002245

Authors: Deirdre E. Clark, Iwona M. Galeczka, Sigurður R. Gíslason, Sandra Ó. Snæbjörnsdóttir, Ingvi Gunnarsson, Eric H. Oelkers 

02 December 2025

https://doi.org/10.1016/j.ijggc.2025.104526

Highlights

•The concentrations of most trace and toxic elements in CarbFix1 and CarbFix2 waters were low.

•These concentrations were substantially lower than that estimated from stoichiometric basalt dissolution.

•Low concentrations of trace and toxic elements are consistent with secondary mineral precipitation of carbonates and sulfides.

•Results suggest negligible risk of substantial water contamination from dissolved CO2 and H2S injection into basalts.

Abstract

Carbon dioxide storage through the carbonation of subsurface basaltic rocks is currently being explored to limit carbon emissions to the atmosphere. Basaltic rocks, however, contain trace and toxic metals that could potentially be mobilized by the carbonation process. This study reports the degree to which selected trace and toxic metals were mobilized during CarbFix1 and CarbFix2 projects. CarbFix1 injected 175 tons of CO2-charged water followed by 73 tons of CO2/H2S-charged water into basalts at 35 °C, whereas CarbFix2 continuously injected CO2/H2S-charged water into basalts at >250 °C. In most cases dissolved concentrations of Ba, Sr, Mo, Cu, Cr, Ni, Cd, and Pb in monitoring well fluids remained low. Although these fluids are not intended for human consumption, the aqueous trace element concentrations were generally below the WHO, EU, and Iceland drinking water standards, except for Fe and Mn in CarbFix1. Aluminum and As concentrations exceeded these standards during CarbFix2, but were elevated before injection. The low concentrations of most trace and toxic metals are consistent with their removal by secondary processes, particularly co-precipitation into carbonate and sulfide minerals formed during gas-water-basalt interaction. Solid precipitates recovered from CarbFix1 show strong enrichment of transition metals in calcite, consistent with natural and engineered analogues. As the two CarbFix injections bound the lower and upper temperature ranges of likely mineral carbon storage efforts, these results suggest limited risk of water contamination due to toxic and trace element release from subsurface basalts due to the injection of dissolved CO2 and H2S.

Source: ScienceDirect 

[Michael Hayes]

After reading this highly informative paper, I began to wonder about creating a non-corrosive and non-conductive well cassing that can be tipped with 2 downwell DC energized electrodes at the CO2/H2S injector nozzels. This would create an in situ reactor that could be used in a number of ways for a number of results. I'll stay with CDR.

The CO2/H2S mix can be rather explosive, or possibly be used as a feedstock/fuel in an interesting electrolysis-based H gas production method and C storage method. So, I asked AI what it thought, and it pointed out that CDR can be enhances by reducing downwell cavity wall porosity and permeability. Importantly, generating H for the market might pay for the CO/H2S supply:

Pumping hydrogen sulfide (

H2SH sub 2 S

H2S

) and carbon dioxide (

CO2CO sub 2

CO2

) into a well with energized electrodes would likely lead to complex electrochemical reactions, primarily corrosion of the well infrastructure and the potential conversion of the gases into other products, such as elemental sulfur, carbon monoxide, and possibly hydrogen, depending on the specific conditions (e.g., presence of water/brine, catalysts, temperature, and pressure)

. 

Potential Outcomes and Reactions 

• Corrosion: Both
  H2SH sub 2 S

  H2S
  and
  CO2CO sub 2

  CO2
  form acids when mixed with water present in the well or the surrounding formation (carbonic acid and hydrosulfuric acid). The presence of these acids, combined with the application of direct current (DC), would significantly accelerate the corrosion of the metal well casing and electrodes through electrochemical processes. Iron sulfide scales, which form in
  H2SH sub 2 S

  H2S
  environments, could also impact the electrochemical reactions and the integrity of the well.

• Electrochemical Conversion: The energized electrodes could facilitate the conversion of the gases in an aqueous (water) solution. This process is similar to technologies being researched for waste treatment or resource recovery:
  • H2SH sub 2 S

    H2S
    conversion: At the anode (positive electrode),
    H2SH sub 2 S

    H2S
    could be oxidized to form elemental sulfur (
    SS

    S
    ) and possibly sulfates or sulfites.
  • CO2CO sub 2

    CO2
    conversion: At the cathode (negative electrode),
    CO2CO sub 2

    CO2
    could be reduced to form carbon monoxide (
    COCO

    CO
    ), formic acid, methane, or other products, depending on the conditions and electrode materials (catalysts).
  • Hydrogen Production: If water is present, the electrical current might also lead to the electrolysis of water, producing hydrogen gas (
    H2H sub 2

    H2
    ) at the cathode and oxygen gas (
    O2O sub 2

    O2
    ) at the anode.
• Mineral Precipitation: The injected acid gases charged fluids can react with the surrounding carbonate or basaltic rock formations, leading to the dissolution of existing minerals and the precipitation of new secondary minerals like iron sulfides, carbonates (e.g., siderite, calcite), and sulfates (e.g., anhydrite). This could alter the porosity and permeability of the reservoir rock and help sequester the carbon and sulfur in stable solid forms.
• Safety and Operational Risks:
  H2SH sub 2 S

  H2S
  is a highly toxic and flammable gas. Introducing a high-voltage electrical source into a wellbore containing flammable gases poses a significant explosion and safety hazard. The complex and unpredictable nature of downhole electrochemical reactions under high pressure and temperature conditions, combined with the corrosive environment, makes this a risky and potentially unstable operation. 

Summary 

The proposed scenario would involve a mix of intended electrochemical conversions and unintended, highly destructive corrosion processes. The primary challenge would be managing the severe corrosion of the well materials and ensuring the safety of such an operation, which is why existing research focuses on controlled electrochemical reactors in surface facilities, not directly within an un-modified wellbore. 

MH] The AI chat can likely be easily replicated.

Best regards 

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