Harnessing naturally occurring sodium carbonate and bicarbonate for gigatonne-scale carbon dioxide removal

Ocean alkalinity enhancement is a promising carbon dioxide removal (CDR) approach, but scaling up to gigatonnes (Gt) of CO 2 per year will require safe, sustainable, and abundant alkaline feedstocks. Here, we propose the use of a relatively unexplored resource for OAE, namely naturally occurring sodium (bi)carbonates. We identified and mapped 109 such deposits globally, although quantitative resource information is available for only 16. Quantified deposits collectively contain >200 Gt of sodium (bi)carbonate-rich minerals and brines, dominated by trona (Na 2 CO 3 ·NaHCO 3 ·2H 2 O) and nahcolite (NaHCO 3 ) mainly concentrated in the USA, China, Turkey, and Africa. We then assessed three OAE pathways using trona as a feedstock, i.e., 1) Mining, crushing, and ocean dispersal of trona (gross CDR capacity 0.16 tCO 2 t −1 ); 2) Calcining trona (with carbon capture and storage) to produce soda ash (Na 2 CO 3 ) (0.31 tCO 2 t −1 ) prior to dispersal; and 3) Purification of soda ash via dissolution, crystallisation, and drying prior to dispersal. Using Green River, Wyoming, USA (∼116 Gt of bedded trona) as a case study, life cycle assessment informed on the net-negativity of each pathway. Provided that mining and transportation have largely decarbonised, all pathways are net-negative (carbon penalties in the range 29–41%), with pathway 2 achieving the highest net CDR capacity. Solution mining and reserves nearer the coastline can optimise net-negativity. Overall, naturally occurring sodium (bi)carbonate resources emerge as a promising future feedstock for soluble, safe, and scalable OAE. • >200 Gt sodium (bi)carbonate minerals/brines could be used for OAE. • Trona is most abundant, but has a modest CO 2 uptake (0.16 tCO 2 t −1 ). • Thermal upgrading to soda ash nearly doubles uptake (0.31 tCO 2 t −1 ). • Green River trona alone could enable ∼24 Gt of gross CO 2 removal.