Electrochemical acceleration of chemical weathering as an energetically feasible approach to mitigating anthropogenic climate change

We describe an approach to CO₂ capture and storage from the atmosphere that involves enhancing the solubility of CO₂ in the ocean by a process equivalent to the natural silicate weathering reaction. HCl is electrochemically removed from the ocean and neutralized through reaction with silicate rocks. The increase in ocean alkalinity resulting from the removal of HCl causes atmospheric CO₂ to dissolve into the ocean where it will be stored primarily as HCO₃^- without further acidifying the ocean. On timescales of hundreds of years or longer, some of the additional alkalinity will likely lead to precipitation or enhanced preservation of CaCO₃, resulting in the permanent storage of the associated carbon, and the return of an equal amount of carbon to the atmosphere. Whereas the natural silicate weathering process is effected primarily by carbonic acid, the engineered process accelerates the weathering kinetics to industrial rates by replacing this weak acid with HCl. In the thermodynamic limit - and with the appropriate silicate rocks-the overall reaction is spontaneous. A range of efficiency scenarios indicates that the process should require 100-400 kJ of work per mol of CO₂ captured and stored for relevant timescales. The process can be powered from stranded energy sources too remote to be useful for the direct needs of population centers. It may also be useful on a regional scale for protection of coral reefs from further ocean acidification. Application of this technology may involve neutralizing the alkaline solution that is coproduced with HCl with CO₂ from a point source or from the atmosphere prior to being returned to the ocean.