Combating Global Warming: Modeling Enhanced Rock Weathering
of Wollastonite Using Density Functional Theory
Brian Luan
Abstract
Negative emissions technologies target the removal of carbon dioxide (CO2) from
the atmosphere as a way of combating global warming. Enhanced rock weathering (ERW)
is a vital negative emissions technology that applied globally could remove gigatons of
CO2 per year from the atmosphere. In ERW, silicate minerals exposed to the atmosphere
trap CO2 via mineral carbonation as thermodynamically stable carbonates. To obtain an
atomic scale understanding of the weathering process and to design more reactive silicates
for enhanced rock weathering, CO2 adsorption on low Miller index wollastonite (CaSiO3)
surfaces was modeled using density functional theory. Atomic scale structure of (100),
(010), and (001) surfaces of wollastonite was predicted and the thermodynamics of their
interaction with CO2 was modeled. Based on surface energy calculations, (001) and (010)
surfaces of wollastonite exhibit similar stabilities, while (100) surface is found to be least
stable. Depending on the surface structure and chemistry, different CO2 adsorption
geometries are possible. A common trend emerges, wherein CO2 adsorbs molecularly and
demonstrates proclivity to bond with surface layer calcium and oxygen binding sites.
Mechanisms for electronic charge transfer between the adsorbate and the substrate were
studied to shed light on the fundamental aspects of these interactions. The most favorable
bent CO2 geometry was bridged between calcium atoms, revealing that the enhancement
of the likelihood of this geometry and binding site could pave the way to designing reactive
silicates for efficient CO2 sequestration via ERW.