Understanding the Lab‐Field Discrepancy in Mineral Dissolution From Flasks to Enhanced Rock Weathering

Abstract For decades it has been observed that rates of silicate mineral reactions appear slower in field settings than when measured in the laboratory. Since the 1980s, researchers have proposed explanations for the discrepancy. Over that time, researchers have also advanced the state of laboratory and field rate measurements as well as models of mineral‐water reaction kinetics at different temporal and spatial scales. Developments in reactive transport modeling are constantly whittling away at the discrepancy as models are improved, coupled to hydrologic models, and driven by climate data. The lab‐field discrepancy has great relevance today because of the proposal that weathering of silicates (especially basalts) could be accelerated to remove CO 2 from the atmosphere and sequester it either as aqueous alkalinity or as carbonate mineral precipitate. Such “enhanced rock weathering” relies on mining and grinding silicate rock for dispersal on farmland to enable weathering by carbonic acid. In general, field rates become increasingly slower than lab rates at larger spatial and temporal scales because of factors related to surface area, hydrology, heterogeneities, biota, and system‐level effects. This implies surface area is not always an appropriate scaling factor. The measurements of enhanced rates of basalt weathering on croplands published so far are relatively consistent with previously published lab and field rates of basalt weathering because the durations of weathering are small. But the rates of CO 2 consumption from the atmosphere are very slow, and will decrease with time, necessitating huge acreages of basalt spreading to reach gigatons of CO 2 sequestration.