In nature, mineral weathering is a carbon removal process that exists in the natural biogeochemical cycle and already removes approximately 3% of our anthropogenic emissions annually. Through the chemical breakdown of rocks with rainwater, CO2 is converted to dissolved bicarbonate, which eventually drains away through rivers to the oceans where it is remains stable on the order of tens to hundreds of thousands of years with limited risk of reversal.Enhanced weathering artificially accelerates the natural mineral weathering process by finely grinding silicate and carbonate materials, such as basalt, olivine, or concrete, thereby increasing their surface area and reactivity. The resulting ground minerals are spread to land where the weathering reaction takes place when it rains. The minerals also serve as a soil amendment replacing lime in agriculture. Enhanced weathering in coastal areas, where minerals are spread on beaches and the bicarbonates directly enter the ocean carbon cycle, is also being proposed.When used on land, silicate rocks are applied to agricultural soils, where they can serve as a liming agent replacement, supply micronutrients to soil, and can also increase crop yields. Enhanced weathering applications have significant co-benefits: the application of powdered silicate materials doesn’t require any practice change by farmers, it can be adopted alongside regenerative agriculture practices, and has a much lower environmental footprint than agricultural lime.
Potential and scalability:
The process of rock weathering and precipitation into dissolved organic carbon is well characterized and studied but challenges remain to accurately measure this carbon removal process in situ at field sites. The quantification and mechanisms of the weathering process and the fate of the resulting carbonates are the subject of extensive research efforts. Current quantification methods can establish that enhanced weathering leads to carbon removal (CDR) and ongoing trials are decreasing the uncertainty of these estimates following a clear scientific roadmap. The basic premise is to track the release or accumulation of weathering products in soils or waters, or direct CO2 gas fluxes. Weathering rates can vary from months to years depending on the specific local conditions such as soil pH, temperature, local precipitation patterns or farming practices. Enhanced weathering applications that rely on silicate rocks are currently mostly using mine tailings, existing by-products of the mining industry. As projects scale up, there emerges a potential sustainability challenge around the reliance of these projects on mining activities, which can have significant environmental impacts themselves. The proximity of mines to the enhanced weathering sites is also critical due to high transportation costs of heavy and bulky rock materials. A local source of input materials is required to make projects economically viable.
Several enhanced weathering companies in 5 continents are already successfully deploying pilots on land, with plans to expand their operations in the near term. Methodologies for accounting for the CDR contributions are being proposed, and soon, third-party certified carbon removal credits will be able to be generated from enhanced weathering projects.