The Effect Of Surface Properties Of Mica On Nucleation And Growth Of Calcium Carbonates

The most concerning issue about geological sequestration of CO2 is the risk of leakage from fracture,which can be reduced by inducing the nucleation of carbonate on rock-forming.Field experiment in Iceland showed that certain surface properties of rock-forming minerals accelerate the nucleation of carbonates.Therefore,the effect of surface properties of rock-forming minerals on nucleation of carbonates(heterogeneous nucleation)becomes a new issue.Previous studies thought that surface charge,pHpzc and the degree of matching in structures might play an important role in deciding the heterogeneous nucleation of carbonate.These hypotheses need to be further tested and improved.In this study,different kinds of mica(muscovite,biotite,fluorophlogopite and hydrobiotite)are chosen to explore the effect of surface properties(such as crystal structure,interfacial energy,surface charge and pHpzc)on the nucleation and growth of calcium carbonate(such as induction time,polymorph,orientation,grain size,shape of crystals and nucleation density)using SEM,EBSD and pH monitoring methods.We found that nucleation rate of calcium carbonates can be improved.Sequestrating CO2 in locations that rich in mica might decrease the possibility of leakage.What's more the substrate and reaction system can affect the nucleation of calcium carbonates in the ways that follow:1?The effect of substrates:(1)The surface charge can affect the nucleation density.The higher the surface charge density is,the higher nucleation density will be.When saturability of solution is 3.396,nucleation density of calcium carbonates is the highest(232 grains/mm2)on the biotite with the highest surface charge density.On the contrary,nucleation density of calcium carbonates on fluorophlogopite is the lowest(50 grains/mm2).(2)Crystal structure affect the orientation of calcite.The lower the mismatch between mica and some certain surface of calcite is,the higher proportion of calcite which grows in this growth orientation will be.The mismatch between muscovite and(001)surface of calcite is low,so the proportion of calcite which grows in this growth orientation is the highest(15%).On the contrary,the mismatch between fluorophlogopite and(001)surface of calcite is high,so the proportion of calcite which grows in this growth orientation is the lowest(3%).2.The effect of reaction system:(1)The net interfacial energy of system affect carbonate polymorphs.The lower net interfacial energy of system is,the more carbonate polymorphs will grow.The net interfacial energy of system is the lowest(28.3 mJ/mol)when the substrate is fluorophlogopite.As a result,three kinds of carbonate polymorphs all appear.When the substrate is muscovite and biotite,net interfacial energy is high(30.0 mJ/mol and 29.5 mJ/mol respectively)and the polymorph is mainly calcite.(2)The reaction system can affect the grain size of calcium carbonates.The lower the induction time is,the larger the grain size will be.When the saturability of solution is 3.396,the grain size of calcium carbonates which grows on muscovite is small(4-6 ?m)because of long induction time.On the contrary,the grain size of calcium carbonates which grows on hydrobiotite is large(14-16 ?m).(3)The ration of Mg/Ca affect the morphology of calcite.When Mg occupying the location of Ca,the lattice imperfection grows.It makes calcite look coarse on the marco level.Meanwhile,Mg tends to be absorbed onto the site of K and S.That makes the growth velocity of K and S site slower than the site of F.As a result,the morphology of calcite looks sunken.