Geochemical Negative Emission Technologies

Weathering of alkaline rocks is a geochemical process which is fundamental to the Earth's natural carbon cycle. It is responsible for removing CO₂ from the atmosphere over geological time periods by transforming it into bicarbonate ions or solid carbonate minerals. Geochemical negative emission technologies (geochemical NETs) seek to harness and accelerate this process. The alkaline materials involved in geochemical NETs (e.g., basic or ultrabasic rocks or alkaline wastes/by-products from some industrial activities) are generally abundant, and, whilst the kinetics of the reaction are relatively slow, it is thermodynamically favourable. Furthermore, storage of CO₂ as solid carbonate minerals or dissolved bicarbonate is permanent in human relevant timescales. The challenge is implementing technically feasible processes or technologies that sufficiently accelerate rock weathering in a way that is environmentally responsible and socially acceptable. In this chapter, we broadly define the concept and evolution of geochemical negative emission technologies, and the associated environmental benefits and risks.