Eion, an American climate tech startup founded in 2021, specializes in silicate mineral amendment for carbon farming and verification of the amount of carbon dioxide (CO₂) removed through enhanced rock weathering (ERW). By working with partners in agriculture, Eion provides economic opportunity and environmental benefits for farmers. By 2026, Eion aims to deliver 500,000 tons of carbon removal every year.
Challenges: carbon emissions and carbon mineralization
Carbon emissions
Since the early 1900s, carbon dioxide (CO₂) levels in the atmosphere have increased by 50% due to human activities. When fossil fuels (such as coal, oil, and natural gas) are burned for energy production, transportation, and industrial processes, CO₂ is released into the atmosphere. This excess CO₂ acts as a greenhouse gas, trapping heat and causing the air and ocean temperatures to rise. CO₂ emissions play a crucial role in driving climate change.
This warming effect has caused the global average temperature to rise by about 1.1 ºC since the pre-industrial period. This has led to rising in the frequency and intensity of extreme weather events, melting of polar ice caps and glaciers and rising sea levels, shifts in species ranges and increased risk of species extinction, agriculture and food security, and ocean acidification.
To mitigate these impacts, the Paris Agreement aims to limit global warming to well below 2 ºC above pre-industrial levels. The Intergovernmental Panel on Climate Change (IPCC) estimates that a “carbon budget” of about 500 GtCO₂, which corresponds to about ten years at current emission rates, provides a 66% chance of limiting global warming to 1.5 ºC.
Carbon mineralization
When exposed to CO₂ and water, certain rocks, like olivine or basalt, undergo a process called carbon mineralization that sequesters carbon permanently. Rainwater that falls upon these rocks is mildly acidic because CO₂ from the air has dissolved in it and formed carbonic acid (H₂CO₃):
CO₂ + H₂O ⇆ H₂CO₃
The carbonic acid dissociates into a large amount of bicarbonate (HCO₃⁻) and a small amount of carbonate (CO₃²⁻) according to the following chemical reactions:
H₂CO₃ ⇆ H⁺ + HCO₃⁻
HCO₃⁻ ⇆ H⁺ + CO₃²⁻
When olivine or basalt rocks are slowly leached in mildly acidic rainwater, magnesium (Mg²⁺) and calcium (Ca²⁺) cations are released to combine with carbonate (CO₃²⁻), forming solid precipitates of magnesium carbonate (MgCO₃) and calcium carbonate (CaCO₃) via the following reactions:
CO₃²⁻ + Mg²⁺ ⇆ MgCO₃↓
CO₃²⁻ + Ca²⁺ ⇆ CaCO₃↓
The precipitation reactions shift the equilibrium of the above chemical reactions towards the right, causing more atmospheric CO₂ to be converted into bicarbonate (HCO₃⁻) and carbonate (CO₃²⁻) and thereby achieving carbon sequestration. Finally, the mineral carbonation is drained into the oceans.
One ton of basalts or olivine can remove 0.3 and 0.8 tons of CO₂ through weathering, respectively, indicating a substantial overall theoretical potential. However, carbon mineralization occurs naturally over centuries or millennia.
Enhanced rock weathering technologies aim to accelerate the natural carbon mineralization process and make it more efficient for carbon capture, storage, and utilization, which can be scaled up to mitigate climate change impacts.
Enhanced rock weathering can cost as little as $8/tCO₂e. This low cost attracts buyers and promotes the industry’s acceptance of enhanced weathering in comparison to advanced techniques such as Direct Air Capture (DAC), which cost >$500/tCO₂e.
However, unlike DAC, it is difficult to verify the amount of CO₂ removed by enhanced rock weathering. The low-cost enhanced rock weathering solutions have been scrutinized closely for "gaming" the rules or failing to deliver anticipated benefits. Therefore, there is a need for a method to measure the carbon removed by enhanced weathering process.
Eion Technology
Eion has developed a method to measure the amount of CO₂ removed by enhanced rock weathering. Eion has introduced immobile trace elements (ITEs) into silicate mineral amendment. The trace elements are strongly bound to mineral and biological surfaces, preventing them from easily leaching from the soil and being removed by plants. During weathering, magnesium in silicate minerals is dissolved in soil solution, reacts with carbonate ions, and forms solid magnesium carbonate that is drained away as described above. Consequently, a measure of cumulative cation flux and carbon removal can be calculated by comparing the ratio of the lost magnesium to immobile trace elements, after accounting for the initial soil’s background concentrations of immobile trace elements.
Eion’s mineral amendment
Eion’s mineral amendment comprises an agglomerated silicate mineral and immobile trace elements.
- Agglomerated silicate mineral
The average particle size of the agglomerated silicate mineral is between 0.5 mm and 3 mm. It comprises silicate mineral fine particles, a binder (3-5%wt), a slow-release acidifier (1-5%wt), zinc (1-5%wt), a nutrient, and a biologically-derived ingredient.
Silicate mineral are forsterite (Mg₂SiO₄) or blast furnace slag. Fine particles of solicit minerals have an average particle size between 80 and 100 microns.
Common binder such as lignosulfate improves performance characteristics during transport and application and reduces the amount of water and energy required to dissolve the pellet once it is in the field.
The slow-release acidifier is gibbsite (Al(OH)₃) or gypsum (CaSO₄∙2H₂O). They keep the soil acidic and thus maintain high rates of weathering, counteracting the tendency of forsterite weathering to increase alkalinity, which slows rates of weathering.
Zinc slows the mobility of phosphate in the subsoil via precipitation reactions with phosphates. This allows plants more time to access the phosphate application, thereby reducing the frequency of fertilization.
- Immobile trace elements
Immobile trace elements include rare earth elements, rare metals, and transition metals. The immobile trace elements are enriched in abundance compared to their abundance in naturally found silicate minerals.
Rare earth elements include scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).
Rare metals include beryllium (Be), cesium (Cs), gallium (Ga), germanium (Ge), hafnium (Hf), niobium (Nb), rubidium (Rb), tantalum (Ta), and zirconium (Zr).
Transition metals include nickel (Ni), chromium (Cr), and zinc (Zn).
How Eion measures removed CO₂ by mineral weathering
The process of verification of removed carbon by mineral rock weathering includes the following steps:
- First, local crop advisors and soil specialists determine the amount of silicate mineral amendment to be applied per acre in order to remove carbon and increase crop yields.
- Then, Eion’s team collects samples of the to-be-applied mineral amendment, places them in a secure vessel, and seals them with another secondary bag to achieve airtight containment. The samples are labeled as Mineral Amendment. Prior to applying mineral amendment, Eion’s team collects soil samples from cultivated zones (0 to 30 cm deep) that the farmer and their agronomists have already collected, places them in a secure vessel, and seals them with another secondary bag to ensure airtight containment. The samples are labeled as Soil A.
- Once the crops are harvested, Eion’s team returns to collect samples in the same control zone as soil A, and store them under similar conditions. The samples are labeled as Soil B.
- In the lab, using an inductively coupled plasma mass spectrometer (ICP-MS) or a low-cost portable x-ray fluorescence spectroscopy (XRF), Eion’s team determines the elemental composition of Mineral Amendment, Soil A, and Soil B.
- Eion’s team directly calculates cumulative cation flux and carbon removal by comparing the ratio of the lost magnesium to immobile trace elements, after accounting for background concentrations of immobile trace elements in the initial soil. (Patent US11644454B2 includes details of calculation)
Typically, six to nine months after applying a mineral amendment, Eion can demonstrate that 40% to 70% of the mineral has dissolved to capture atmospheric CO₂ that will be permanently stored in the ocean.