Mineral weathering is a geochemical process in which common rocks react with CO2 to form dissolved mineral bicarbonates. These bicarbonates wash into the ocean and over many thousands of years eventually precipitate as solid carbonate minerals. This process is the primary way that excess atmospheric CO2 is consumed and stored on geologic time scales, and explains why bicarbonate in seawater is the largest carbon reservoir on Earth's surface, holding the equivalent of 139,000 billion metric tonnes of CO2. For comparison, the atmosphere contains only about 3,100 billion metric tonnes of CO2. Each year some 1 billion metric tonnes of CO2, about 1/40 of human CO2 emissions, is consumed by this geochemistry.
Electro-geo-chemistry uses an electrochemical process to increase the rate of geochemical CO2 removal. This approach also produces energy in the form of hydrogen gas (H2). It uses saline water electrolysis in the presence of minerals to generate H2 while at the same time creating a highly reactive solution that acts like a chemical sponge, absorbing and converting CO2 into dissolved mineral bicarbonate. Adding this bicarbonate to the ocean not only provides long term carbon storage, but it also helps counteract ocean acidification. Thus, when powered by renewable electricity, this electro-geo-chemistry can be used to produce a non-fossil transportation fuel, H2, while simultaneously removing CO2 from the atmosphere and countering ocean acidification. The global abundances of the required materials and energy for this negative-emissions H2 process suggest that it can be done at very large scales.