adsorption and transport of naturally occurring

ShaleXenvironmenT 2018 Dissemination Event,Doha, Qatar March 16-18, 2018 1

Adsorption and Transport of Naturally OccurringRadioactive Materials (NORMs) in Clays —Atomistic Computational Modeling Approach

Andrey G. Kalinichev, Brice Ngouana, Iuliia Androniuk

E-mail: [email protected]://www.imt-atlantique.fr/en/person/andrey-kalinichev

Laboratoire SUBATECH, IMT-Atlantique, Nantes, FRANCE

50 nm

ShaleXenvironmenT 2018 Dissemination Event,Doha, Qatar March 16-18, 2018

Backgroung and Introduction

Shale formations are characterized by a small porosity and low permeability* that traphydrocarbons in the rocks. Hydraulic fracturing increases the extremely low permeabilityof shale rocks to enable the economic production of shale gas and shale oil**.

* Ho TA, Striolo A. AIChE Journal, 61, 2993 (2015)** Yethiraj A, Striolo A. J. Phys. Chem. Lett., 4, 687 (2013)*** http://www.virtualmuseum.ca/edu/ViewLoitDa.do?method=preview&lang=EN&id=25977

What is the fate of NORMs in the environment ?

Atomistic computational modeling of fluid-rock interactions

Schematic representation of shale gas extraction***

Fracfluid:

- Water

- Proppant (sand)

- Chemicals

inFlowback fluid:

- Water

- Chemicals

- Gas/oil

- Naturally occurring radioactive materials(NORMs)

out

The are several environmental issues related to shale gas exploration/extraction,including NOMRs and their fate as they could be released in the process

2


Clay Pyrite Feldspar Quartz CarbonatesOrganicmatter

Bowland shale (UK) 30 3 5 50 15 3

Alum shale (Denmark)* 51 3.7 2.1 24.6 0.7 16.5

Dotternhausen shale (Germany)* 18 1.8 0 12.7 41.6 14.9

Wickensen shale (Germany)* 25.6 2.2 1.6 13.2 33.9 17

Harderode shale (Germany)* 28.4 2.4 2.1 16.3 39.6 10.5

Haddessen shale (Germany)* 32.6 2.5 4.5 13.8 27.5 10.8

Because of their adsorption and retention properties, they can play a crucial role in theconfinement of NORMs that could be released in the context of fracking

* Rybacki et al. J. Petrol. Sci. Eng., 135, 702 (2015)

Clay minerals are one of the primary components of most shales

3

Mineral Composition of Some European Shales


Clay minerals are layered aluminosilicates, with properties changing as a function oftheir atomic structure and composition

Clay fractions of shales predominately contain kaolinite, smectite, and illite

4

Basic Structure and Composition of Clay Minerals

Kaolinite -no layer charge

Si8Al8O20(OH)16

T

O

Montmorillonite (smectite) -moderate layer charge

(Si7.75Al0.25)Al3.5Mg0.5O20(OH)4Na0.75

T

O

T

Muscovite (illite) –high layer charge

(Si6Al2)Al4O20(OH)4K2


Time averaging over a dynamic trajectory of the simulated system

Periodic boundary conditions (PBC)

Principal Tool: Molecular Dynamics Simulations

http://isaacs.sourceforge.net/phys/pbc.html

Numerically solve Newtonian equation of motion for N interacting particles:

ri(t+t) = ri(t) + vi(t) t + ½ ai(t) t2 ; t ~ 1 fs = 10-15 s

ai = Fi/m = [ - U(r1,r2,... rN) / ri ] / m ; i=1, 2 ,…, N (N ~ 103 - 106 atoms)

U = SSUij = SS(Aij/rij12 - Bij/rij

6 + qiqj /e0rij) + S ½kb (rij - r0)2 + S ½kq (qij - q0)

2

Short-range repulsion v-d-Waals Coulombic bond stretching bond bending


MD Modeling of Clays and Clay-Related Materials

ClayFF - specialized semi-empirical fully flexible force field model

Allows for realistic modeling of exchange of momentum and energy among all atoms –solid substrate and aqueous solution

Based on accurate theoretical models of oxides, hydroxides, silicates, etc.

Combines well with other available force fields for organic-inorganic systems

Non-trivial problems

Poorly characterized structure and composition

Low symmetry, high degree of compositional disorder

Large unit cells, stacking disorder

Strong local electrostatic fields due to site substitutions

Need for special force-field parameterization for realisticmodeling

1 m

Cygan, Liang, Kalinichev (2004) J.Phys.Chem. B, 108, 1255-1266.

Special focus: real-life complexity of shale rock mineral components on the atomic scale


Partial Charges based on ClayFF Parameterization

Accurate determinations of partial charges are required to represent chargedistributions of interlayer and external surfaces where electrostatic forces controlsorption and transport processes

Atomic charges derived from DFT/GGA calculations for cluster and periodic models ofsimple oxides and hydroxide phases

Allow for charge delocalization among coordinating oxygens for substitutions

Mg

Al

Al

Si

T

T

O

Cygan, Liang, Kalinichev (2004)J.Phys.Chem. B, 108, 1255-1266.


MD Modeling of Clay-Solution Interfaces

~3nm

~7nm

~10nm

Claylayers

Aqueoussolution

Classical Newtonian dynamics

Ntot ~ 3,000 – 10,000 atoms; NH2O ~ 0-1,000 mol

ClayFF force field (Cygan et al., 2004)

a b c ~ 3 3 10 nm3

Periodic boundary conditions

NVT- or NPT-ensemble T=300K; P =1 bar

Dt = 0.5-1.0 fs; ttotal ~ 0.2 - 10 ns

Confined fuid structure:

Atomic density profiles ()

Atomic density surface distributions ( )

Ion adsorption sites

Interfacial H-bonding network

Confined fluid dynamics:

Diffusion coefficients (longer time scale)

Spectra of vibrational and rotational dynamics(shorter time scale)


Basal (001) surfaces and interlayers are extensivelystudied and their properties are reasonably well known

Clay edges have received much less attention yet

Clay Particle Edges: Special Adsorption Sites

S.V.Churakov, Geochim. Cosmochim. Acta, 71, 1130-1144 (2007)

X. Liu et al., Geochim. Cosmochim. Acta (2012, 2013, 2014, 2015)

S. Tazi et al., Geochim. Cosmochim. Acta, 94 1-11 (2012)

Aggregate of clay particles

Primary clay particle Inter-particle pore

Interlayer pore

Edgesurfaces

Basal (001) surface

ClayFF Parametrization for Clay Edges

New special ClayFF bending termsfor Mg-O-H, Al-O-H, and Si-O-H

UClayFF-MOH = UClayFF-orig + UM-O-H == UClayFF-orig + k (q -q0 )²

k and q0 have to minimize the differencesbetween DFT and ClayFF-MOH results

Pouvreau, Greathouse, Cygan, Kalinichev, J.Phys.Chem.C, 2017, 121, 14757-14771; J.Phys.Chem.C, 2018 (in preparation)

Ab initio (quantum) MD is a direct answer,but it is very expensive computationally

AIMD ~n×100 atoms; ~15×15×15 Å3; t ~ 10-50 ps


Interlayers and (001) Surfaces of Charged Clays

Muscovite

Layer charge-2.0 e

Montmorillonite

Layer charge-0.75 e

Fully octahedral Fully tetrahedral 1/3 tetrahedral

and 2/3 octahedral

T = 298 K T = 363 K

Diffusion coefficient × 10-10 m²/s

D2w (Sr2+) 1.53 5.45

D2w (Ba2+) 1.17 2.36

D3w (Sr2+) 1.79

D3w (Ba2+) 3.09

FF parameters for Ra2+ have been developed and are currently tested

B.F.Ngouana-Wakou, A.G.Kalinichev, A. G. (2014) Structural arrangements of substitutions in smectites:Molecular simulation of the swelling properties, interlayer structure, and dynamics of hydrated Cs-montmorilloniterevisited with new clay models. J.Phys.Chem.C, 118, 12758-12773.


Ion Mobility at Basal (001) Surfaces of Clays

Diffusion coefficient (×10-9 m²/s) from MD simulation

IonInterface

BulkKaolinite Montmorillonite Muscovite

Ba2+ 0.4 ± 0.2 0.39 ± 0.05 0.6 ± 0.2 0.5 ± 0.2

Na+ 0.5 ± 0.3 0.68 ± 0.03 0.115 ± 0.001 1.0 ± 0.4

Water 1.8 ± 0.3 1.9 ± 0.1 1.8 ± 0.1 2.8 ± 0.1

Diffusion coefficient (×10-9 m²/s) from MD simulation

IonInterface

BulkKaolinite Montmorillonite Muscovite

Sr2+ 0.26 ± 0.05 0.5 ± 0.2 0.3 ± 0.1 0.5 ± 0.1

Na+ 1.2 ± 0.5 0.92 ± 0.06 0.6 ± 0.1 1.0 ± 0.4

Water 2.2 ± 0.3 2.1 ± 0.1 1.7 ± 0.2 2.8 ± 0.1

Increasing layer charge


Montmorillonite (010) Edge Surfaces

1480 H2O

6 NaCl ( 0.1M)

4 SrCl2/BaCl2 ( 0.07M)

substitutions sites are accessibleto solution (surface 1)

Substitution sites are not accessibleto solution (surface 2)

Montmorillonite: 96 × ([Si7.75Al0.25](Al3.5Mg0.5)O20(OH)4.5(H2O)10Na0.75)

45 Å × 41 Å × 81 Å

Simplifiedfluid composition

12


Atomic Density Profiles: Montmorillonite

Cation exchange between interfacial Ba2+ and interlayer Na+ ions is quite strong

75% of Ba2+ ions initially in the interfacial region enter the interlayers

13

Substitutions sites areaccessible to solution(surface 1)

Substitution sites arenot accessible to solution(surface 2)


Surface 1 Surface 2

The 25% of Ba2+ ions remaining in the interfacial region are in a outer sphere coordination

Most of the Na+ ions leaving the interlayer region accumulate near surface 1, preventingSr2+/Ba2+ ions to closely approach that surface

Two Na+ peaks on surface 1: the 1st around 2.0 Å and the 2nd around 3.0 Å

Two types of inner sphere adsorption configurations

14

Atomic Density Profiles: Montmorillonite


TOT

Si

Al

Ooh

Na+

Mg

Owa

t

Na+ ions in the 1st peak are located within the range of x coordinates correspondingto the edge surface atoms in the octahedral layer

Na+ ions in the 2nd peak are located within the range of x coordinates correspondingto the edge surface atoms in the tetrahedral layer

Surface 1

1st peak

Surface 2

2nd peak

15

Atomic Density Surface Maps: Montmorillonite


Na+ ions in the first peakoccupy octahedralvacancies

Na+

1st peak

Na+

Surface 1

Na+

Surface 2

owat oh obts ob

distance (Å)

2.3 2.3 2.3 2.5 - 3.0

Coordination number

2.5 1.8 0.6 0.8

owat oh obos

distance (Å)

2.3 2.3 2.3

Coordination number

3.0 1.5 1.0

On surface 1, they avoidthe Mg/Al substitutions butseat near the Al/Sisubstitutions (CN ≈ 6)

On surface 2, Na+ ions aremostly found near theinternal Mg/Alsubstitutions (CN ≈ 6)

16

Ion Coordination to Surface Atoms: Montmorillonite


2nd peakSurface 1 Surface 2

Na+

owat oh

distance (Å)

2.3 2.3

Coordination number

3.8 1.8 Na+ ions in the 2nd peakare found close to theSi-O-H groups (CN ≈ 6)

owat oh

distance (Å)

2.3 2.3

Coordination number

4.0 1.6

17



substitutions sites are accessibleto solution (surface 1)

Substitution sites are not accessibleto solution (surface 2)

Muscovite: 96 × ([Si6Al2][Al4]O19.5(OH)5(H2O)0.5K2)

29 Å × 41 Å × 103 Å

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Muscovite (010) Edge Surfaces

1480 H2O

6 NaCl ( 0.1M)

4 SrCl2/BaCl2 ( 0.07M)

Simplifiedfluid composition


Surface 1 Surface 2Ba2+

Most of the K+ ions leaving the interlayer region accumulate near surface 1

This prevents Na+ and Ba2+ to closely approach that surface

The smaller concentration of K+ ions on surface 2 allows Na+ and Ba2+ to comecloser, but Ba2+ is still in OS coordination

19

Atomic Density Profiles: Muscovite


Sr2+

All K+ ions leaving the interlayer region accumulate near surface 1, this prevents Na+

and Sr2+ to closely approach that surface

Hence Na+ and Sr2+ are found near surface 2, in both IS (peak around 2.5 Å) andOS (peak around 3.5 Å) coordination

Surface 1 Surface 2

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Atomic Density Profiles: Muscovite


Surface 1 Surface 2

Two types of adsorption sites are observed for Sr2+ on surface 2

Similar adsorption sites for Na+ and K+

Si

Al

Ooh

Na+

Owa

t

Sr2+

T

O

T

1st peak

2nd peak

K+

21

Atomic Density Surface Maps: Muscovite


1st peakSurface 2

Sr2+

owat oh ob

distance (Å)

2.5 2.5 2.6

Coordination number

4.1 3.0 0.9

Sr2+ and K+ ions in the firstpeak occupy octahedralvacancies, with a little shifttowards the tetrahedrallayer where they bind to aSi-O-H group

owat oh obts ob

distance (Å)

2.7 2.7 2.7 3.0

Coordination number

2.1 3.2 0.6 0.6

K+

Effects of ionic size, andhydration energy ?

CN (K+) ≈ 6.5

CN (Na+) ≈ 5.5

CN (Sr2+) ≈ 7.9

22


Surface 1


Kaolinite: 64 × (Si8Al8O19.5(OH)17(H2O)

28 Å × 41 Å × 108 Å

23

1480 H2O

6 NaCl ( 0.1M)

4 SrCl2/BaCl2 ( 0.07M)Simplifiedfluid composition

Kaolinite (010) Edge Surfaces


The first Ba2+/Sr2+ peak is in the range 5-6 Åfrom the surface (around 2.5 Å for muscovitewhen there is no screening effects of K+ ions)

Inner-sphere complexation is observed for Na+

(1st peak around 3 Å)

Similar types of adsorption sites as presented for montmorillonite and muscovite

H (edge OH

O (edge OH)

Na+

x (Å)

y (Å)

24

Atomic Density Profiles: Kaolinite


Next Step: Site-Specific Adsorption Free Energy Profilesand Cation Exchange Equilibria

1a (opposite)1b (nearby)1c (single)

1a (opposite)1b (nearby)1c (single)

K+surf + Cs+

aq K+aq + Cs+

surf

K+

Cs+

constzTkzW )(ln)(PMF B

Potential of Mean Force:

z - distance from the surface

inner-sphere

outer-sphere

N. Loganathan, A.G.Kalinichev (2017)J. Phys. Chem. C, 121, 7829–7836

2c

1b1c

2b1a

2a


Significant cation exchange between interfacial Sr2+/Ba2+ and interlayer Na+ ions in the(010) montmorillonite system

Effect of substitution location :

On surface 1 (substitutions accessible to solution), the adsorbed ions sit near the Al/Sitetrahedral substitutions but avoid the Mg/Al octahedral substitutions (present inmontmorillonite)

The Na+ and K+ ions dissociating from the interlayers of montmorillonite and muscoviteaccumulate on surface 1 pushing then the other ions to surface 2 (substitutions not accessibleto solution)

On surface 2 (substitutions not accessible to solution), Na+ ions are mostly found near theinternal Mg/Al substitutions in montmorillonite

Two types of inner sphere complexation with the (010) edges of kaolinite, montmorilloniteand muscovite:

The cation (Na+/K+/Sr2+/Ba2+) occupy an octahedral vacancy, interacting with 2 Al-O-H groupsor 2 Al-O-H groups and 1 Si-OH group

The cation (Na+/K+/Sr2+/Ba2+) sit in the tetrahedral layer, interacting with 1 Al-O-H group and 1Si-O-H group

Site-specific adsorption free energy profiles are now being calculated for the identifiedsites to quantitatively evaluate their adsorption strength and cation exchange capabilities

26

Conclusions and Outlook


Supercomputing resources allocation under DARI (projects n° x2015096921,t2016096921, and A0020906921 on the OCCIGEN cluster of CINES

CCIPL computer resources allocation on Waves cluster

Acknowledgments

N.Loganathan, M.Pouvreau

– Subatech, IMT Atlantique, Nantes

R.T.Cygan, J.A.Greathouse– Sandia National Labs, Albuquerque, USA

This project has receivedfunding from the EuropeanUnion's Horizon 2020research and innovationprogram under grantagreement No. 640979

adsorption and transport of naturally occurring

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