ERW involves crushing basalt to a fine-grained powder (to make it more soluble) and then spreading the powder on land, most commonly cropland. CO₂ is removed from the atmosphere through chemical weathering reactions that occur when rainwater infiltrates the soil and dissolves (weathers) the rock powder. ERW aims to mimic — in accelerated fashion — the chemical weathering cycle of rock that occurs in nature.

The weathering reactions - ERW is essentially a series of acid-base neutralization reactions. Simplistically speaking, carbonic acid (H₂CO₃) in rainwater dissolves alkaline rock powder in soil, resulting in a chemically neutral solution in soil water of bicarbonate (HCO₃^-), a base, and calcium (Ca²⁺) and magnesium (Mg²⁺) ions which are acidic.

The soil water migrates downward in the subsurface carrying the bicarbonate and calcium and magnesium ions to groundwater which eventually migrates to rivers and then to the ocean (see diagram below; Ca²⁺ and Mg²⁺ are not shown, but follow the same path as bicarbonate).

Dissolved in ocean water, the bicarbonate (HCO₃^-), magnesium (Mg²⁺), and calcium (Ca²⁺) remain chemically stable over the long term due to their counterbalancing charges. The bicarbonate (HCO₃^-) contains the C and the O₂ that were originally in CO₂ in the atmosphere.

Deployment status - Currently, ERW is being performed on croplands in trials and in the first large-scale commercial operations. The sale of carbon credits in the voluntary market drive commercial operations. A supply chain is developing to support the emerging commercial ERW industry, including project developers and measurement and verification service providers. Crushed basalt or similar rock has been spread on croplands in the following ERW projects.

Environmental impacts - Potential adverse impacts of ERW include: impacts to plants and wildlife from loading agricultural soils with trace metals in rock powder, and loading groundwater, stream waters, and the ocean with bicarbonate that is produced when rock powder is dissolved.

Carbon negative status - ERW requires a significant amount of energy to mine, grind, and transport rock for rock powder. The energy for an ERW project must come from a low or no carbon source in order to be carbon negative (i.e., remove more carbon dioxide than the project produces). A cradle-to-grave life-cycle assessment of a project is necessary for verifying the project will be carbon negative.

Cost per ton of CO₂ removed - ERW costs include: mining, grinding, transporting, spreading rock powder, and MRV. Energy cost of grinding, alone, was estimated in 2024 to range between $0.95 to $5.81 (USD) per ton of rock. The total cost of removing and storing one ton of CO₂ using ERW in 2020 was estimated to be between approximately $40 to $375 (USD) per ton of CO₂ removed. This cost has been projected to drop to roughly the $40 to $175 range by the year 2050 due to gains in economy of scale and technology advances.

Measurement, reporting, and verification (MRV) - A common method of performing MRV is to measure the increase in bicarbonate (HCO₃^-), Mg²⁺, or Ca²⁺ after applying rock powder to soil. The increase is measured in soil particles, soil water, groundwater, or surface water draining from land areas where rock powder has been applied. MRV methods need refinement to enable ERW projects to sell carbon credits, a potential long-term funding source of a self-sustaining ERW industry.

Rock powder application rates and resulting CO₂ uptake - The results of only a few field-scale ERW projects have been published. A recent project in the U.S. reported spreading basalt powder on cropland at the rate of 50 tons per hectare per year over four years, resulting in an estimated cumulative carbon removal rate of about 10.5 tons of CO2 removed from the atmosphere per hectare. This equates to a CO₂ removal rate of 0.05 ton of CO₂ per ton of basalt applied to the soil.

Side benefits of ERW - Applying basaltic rock powder to cropland as a soil amendment has been reported in a field study to have increased crop yields. The study concluded ERW also added micronutrients to soil (e.g., zinc, copper, managanese, boron, and iron) and has the potential to increase the pH of acidic soils. Another recent field study reported increased uptake of calcium and phosphorus in crops.

CO₂ storage durability - ERW converts CO₂ to bicarbonate (HCO₃^-) which eventually ends up being stored in ocean water (see explanation above). Storage of bicarbonate in ocean water via ERW is considered to be virtually permanent (10,000 or more years).

Long-term global CDR potential - One study estimated ERW applied globally to 7.4 million square kilometers of cropland (1,000 sites) over a 74-year period has the potential to remove a cumulative total of 64 gigatons of CO2 from the atmosphere. This compares to the 1,000 gigatons needing removal within the next century in order to cap global warming at 1.5^oC above pre-industrial times (circa 1850) — using all types of CDR (estimate by the IPCC in 2018).