Geological carbon sequestration: Modeling mafic rock carbonation using point-source flue gases: Fid-Bau Portal

Geological carbon sequestration: Modeling mafic rock carbonation using point-source flue gases

Sturmer, Daniel M. / Tempel, Regina N. / Soltanian, Mohamad Reza

Highlights • Reacting CO2 with mafic rocks generates mafic carbonates. • Addition of SO2 results in formation of sulfide and sulfate minerals. • Sulfur competes with carbon for cations, generally decreasing carbon sequestration. • Pyrite presence may limit how products of ex-situ carbonation can be used. • Addition of NO2 increases fO2, inhibiting pyrite formation.

Abstract Basaltic rocks are being considered as a key host for carbon dioxide (CO2) storage. This is a function of their global distribution and relative reactivity, resulting in CO2 mineralization. However, the reactivity of mafic minerals allows for reaction and sequestration of other gases associated with point source emissions. Though many mechanisms exist to separate CO2 from flue gas, these can be costly system additions for existing point source emitters. In this study, we model the effect of adding minor amounts of SO2 to CO2 during ex-situ mineral carbonation of basalt samples from Nevada, USA. We compare reaction path geochemical models at temperatures between 0° and 200 °C and at three different SO2 concentrations. Results from these models are compared to published data evaluating the interaction of these samples with CO2 only. The models have carbon trapped in four minerals (magnesite, siderite, dolomite, and dawsonite). Sulfur is sequestered as one sulfide (pyrite) and up to four sulfates (alunite, anhydrite, gypsum, and thenardite). With added SO2, between 43–161 grams of carbon are trapped per kg rock reacted. These models show -25 % to +18 % change in carbon sequestration, though decreases are more prevalent with increasing SO2. One major issue with adding SO2 as a reactant is pyrite precipitation, which may result in acid rock drainage from the reaction product. However, adding NO2 as a reactant inhibits pyrite formation by increasing oxygen fugacity. Ultimately, these methods can be used as an initial, inexpensive screening tool when evaluating between potential mafic rock carbonation projects.