The Effect Of Surface Properties Of Rock-forming Minerals On Nucleation And Growth Of Calcium Carbonates

The increase of atmospheric carbon dioxide concentration caused by the extensive use of fossil fuels has evoked global climate anomalies and a series of environmental problems.In face of gradually urgent need for carbon emission reduction,it has been stated that China will aim to hit peak emissions before 2030 and to achieve carbon neutrality by 2060,which calls for the development of carbon capture and carbon sequestration(CCS)technologies.Among the existing methods,in-situ geological storage is the most potential for emission reduction by injecting carbon dioxide into geological reservoirs.The stability of the storage method above is influenced by the reaction of carbon dioxide with calcium in geological fluids,which is controlled by the heterogeneous nucleation and growth of calcium carbonate.In this study,three common rock-forming minerals—mica,feldspar and pyrite—are selected as nucleation substrates,and an ammonia diffusion system and a stable system are respectively applied to conduct experiments of heterogeneous nucleation of calcium carbonate.Through scanning electron microscopy(SEM),electron backscattered diffraction(EBSD)and other techniques,the process of heterogeneous nucleation and growth of calcium carbonate and its controlling factors have been systematically studied.According to the experimental results,in the ammonia diffusion system,ammonia will induce the nucleation of vaterite,the ripening process of calcium carbonate will decrease the nucleation density and meanwhile complicate the structure of the metastable phase.In the stable system,the nucleation density of different substrate surfaces is positively correlated with the surface charge of substrate.Calcite on the surface of mica and feldspar substrates appears to grow in(104)orientation.The effective interfacial energy of biotite,muscovite and fluorophlogopite are 13.9-29.5 mJ·m-2,14.1?30.0 mJ·m-2,13.3?28.3 mJ·m-2 respectively.This study has extended the theory that the electrochemical properties of the interface control the nucleation process and put forward a model of how the substrate and solution properties control the nucleation pathway and density:(?)?i=j,Kj=IAP N=min{Np(q),Jnt}-Nri(IAP)-NagThe model of nucleation pathway follows to the theory of stepwise phase transition(SPT),which is divided into n steps and consists of n energy barriers.When i=1,it represents the reaction of the substrate interface.In the equations,?Gc is the total energy barrier of the nucleation pathway,?Gci is the energy barrier of stepwise reaction,?cl-i is the interfacial energy between the phase and the solution,controlled by the properties of the ion I in the solution,?sl is the interfacial energy between the substrate and the solution,controlled by the ion I in the solution and the surface charge of the substrate q.Ksp-i is the control factor of the post-generation phase,Ki is the control factor of the pre-reaction phase(for example,when the pre-reaction phase is the solution,the post-generation phase is calcite,Ki=Kj=IAP,Ksp-i=Ksp-calctie),Iind is other inducing factors of ions in the solution.N is the nucleation density,Np is the number of nucleation sites,which is positively correlated with the surface charge q of the substrate,Jn is the nucleation rate,Nri is the number of nucleation due to the ripening,and Nag is the number of nucleation due to the aggregation.This model is of certain theoretical instructive significance to geological storage.