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Representative structures showing the inner (adduct based) and outer (covalent bond breaking/making) mechanistic pathways. Atom colouring: C, grey; O, red; H, white; alkali metal, purple. Chemical transformation steps are indicated by numbered green circles and physical diffusion by orange circles. Inner mechanism: (1) CO 2 is absorbed into the melt and interacts with a water adduct alkali-carbonate cluster C H2O [H 2 OMnCO 3 ] to form an adduct cluster A [H 2 OMnCO 3 CO 2 ]. (2) Subsequently, water dissociates from A, releasing a CO 2 carrier species C CO2 [MnCO 3 CO 2 ], which is a CO 2 adduct alkali-carbonate cluster. (3) C CO2 diffuses through the melt. (4) Near the surface, [MnCO 3 CO 2 ] reacts with water to again form A [H 2 OMnCO 3 CO 2 ]. (5) A subsequently releases CO 2 and reforms C H2O [H 2 OMnCO 3 ]. (6) C H2O then diffuses due to the concentration gradient in H 2 O, starting the transport cycle again. The C CO2 , A and C H2O adducts can also undergo chemical reactions and, hence, exist in equilibria with other species; A [MnC 2 O 5 H 2 O], A [HCO 3 MnOHCO 2 ], C CO2 pyrocarbonate [MnC 2 O 5 ] and C H2O bicarbonate/hydroxide [HCO 3 MnOH]. The outer mechanism between species C CO2 , A, A and C H2O follow a similar cycle but now with transient pyrocarbonate and bicarbonate species diffusing through the melt.

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