Converting industrial and agricultural waste streams into carbon-storing oxalate minerals

Carbon mineralization is a promising method for long-term carbon storage. One way to sustainably mineralize carbon is by utilizing Ca and Mg bearing industrial waste products to form carbonate minerals. However, solid oxalates could potentially store twice the amount of carbon as carbonates. Here we provide a proof of concept for the combined utilization of both industrial and agricultural waste products to form carbon-storing oxalate minerals. We tested the reaction between plant-based oxalic acid, extracted from Rumex and rhubarb leaves, with two calcium-bearing industrial waste products - gypsum and coal fly ash. We demonstrate that the method successfully converts 55 % - 79 % of the oxalate in the extracts into stable calcium oxalate phases. The carbon storage potential of this method was calculated to be ∼9 g of CO₂ per kg of Rumex leaves and 6 g per kg of rhubarb leaves. While the carbon storage potential is currently low relative to global removal requirements, this method could potentially be upscaled with technological enhancements, including genetic modification and crop manipulation.