Abstract
One of the most promising strategies for the safe and permanent disposal of anthropogenic CO2 is its conversion into carbonate minerals via the carbonation of calcium and magnesium silicates. However, the mechanism of such a reaction is not well constrained, and its slow kinetics is a handicap for the implementation of silicate mineral carbonation as an effective method for CO2 capture and storage (CCS). Here, we studied the different steps of wollastonite (CaSiO3) carbonation (silicate dissolution → carbonate precipitation) as a model CCS system for the screening of natural and biomimetic catalysts for this reaction. Tested catalysts included carbonic anhydrase (CA), a natural enzyme that catalyzes the reversible hydration of CO2(aq), and biomimetic metal-organic frameworks (MOFs). Our results show that dissolution is the rate-limiting step for wollastonite carbonation. The overall reaction progresses anisotropically along different [hkl] directions via a pseudomorphic interface-coupled dissolution–precipitation mechanism, leading to partial passivation via secondary surface precipitation of amorphous silica and calcite, which in both cases is anisotropic (i.e., (hkl)-specific). CA accelerates the final carbonate precipitation step but hinders the overall carbonation of wollastonite. Remarkably, one of the tested Zr-based MOFs accelerates the dissolution of the silicate. The use of MOFs for enhanced silicate dissolution alone or in combination with other natural or biomimetic catalysts for accelerated carbonation could represent a potentially effective strategy for enhanced mineral CCS.
Highlights
The alarming increase in the concentration of atmospheric CO2 from pre-industrial levels of~280 ppmv to current levels of ~400 ppmv and the effects this greenhouse gas can have on the Earth system [1], have prompted extensive research aiming at reducing anthropogenic CO2 emissions and its capture and storage [2,3]
Regarding the effect of carbonic anhydrase (CA), our results show that its main role during carbonation of wollastonite is the acceleration of calcium carbonate precipitation
The present study reports two types of experimental studies aimed at observing the possible catalytic effect of CA and Zr-based metal-organic frameworks (MOFs) toward the reaction of replacement of a silicate mineral into a carbonate
Summary
The alarming increase in the concentration of atmospheric CO2 from pre-industrial levels of~280 ppmv to current levels of ~400 ppmv and the effects this greenhouse gas can have on the Earth system [1], have prompted extensive research aiming at reducing anthropogenic CO2 emissions and its capture and storage [2,3]. Carbonation of primary silicates is a natural weathering process [10] that has regulated Earth’s atmospheric CO2 concentration and climate over geologic time-scales [11,12,13,14,15] Such a natural process is the basis of several current ex situ and in situ technologies for carbon capture and storage (CCS) [4,6,16,17]. Among the many ex situ methods proposed so far, involving either solid–gas or liquid–gas carbonation reactions, the most promising ones are those based on aqueous mineral carbonation [6,18] This is the case, for instance, of the acid-promoted dissolution of primary silicates in a reactor followed by the injection of CO2 in the resulting Ca- and/or Mg-rich solution, whose pH is increased to favor carbonate precipitation [17]. In situ carbonation involves the direct deep injection of CO2 (e.g., dissolved in water as a brine) into mafic and ultramafic silicate rock formations [2,4,24]
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