10 20 30 40 50 60 70 80 90 100-3.00

-2.00

Aqueous NiSorbed Ni

% Ni Sorbed

δ60/

58 N

iSRM

986

(‰)

Nickel Isotope Fractionation via Adsorption onto Ferromanganese OxyhydroxidesWells, Ryan M., Wasylenki, L.E., Department of Geological Sciences, Indiana University, Bloomington, Indiana, USA

References and AcknowledgementsLev Spivak-Birndorf and Haleigh HowePeacock and Sherman (2007)Cameron and Vance (2013) Mineralogical Magazine 77, 811

Introduction• Ni isotopes could give us insight into the evolution of marine life over

much of Earth’s history• To be able to interpret Ni isotope signatures correctly in the rock record,

it is important to be able to understand and quantify every major process that fractionates Ni isotopes

• Elected to study Fe-Mn oxyhydroxides for the following reasons:• They adsorb/desorb Ni during rock weathering• They are a major Ni repository in ocean

• These processes may fractionate Ni isotopes

Birnessite Formula: K0.5(Mn3+,Mn4+)2O4 1.5H∙ 2O

Solution containing: Dissolved Ni andNi sorbed to birnessite

Filter

Sorbed Ni& birnessite

Dissolved Ni

Methods• Mix our ferromanganese mineral (birnessite) with dissolved Ni in solution

• Separate sorbed Ni from dissolved Ni• Measure δ60/58 Ni for dissolved and sorbed samples on Nu MC-ICP-MS

Results Discussion• The three experiments produced three different

fractionation effects:• Low Ionic Strength Exp: Equilibrium effect

• High Ionic Exp. (24 hr): Effect TBD• High Ionic Exp. (27 d): Rayleigh effect• Increased adsorption over time (in high ionic exp.)

suggests that Ni may be getting incorporated into the birnessite mineral structure.• Figure to right shows adsorption of Ni to birnessite

(a) and incorporation of Ni into birnessite mineral structure (b)

20 40 60 80 100-1.60

-1.20

-0.80

-0.40

0.00

0.40

0.80

Aqueous Ni Sorbed Ni

% Ni Sorbed

δ60/

58 N

iSRM

986

(‰)

Starting Composition = -0.08‰

Δ≈ 1.4 ‰

Starting Composition = -0.08‰

Δ≈ 3.0 ‰ Δ≈ 4.0 ‰

20 30 40 50 60 70 80 90 100-1.80

-1.60

-1.40

-1.20

-1.00

-0.80

-0.60

-0.40

-0.20

0.00

Aqueous NiSorbed Ni

% Ni Sorbed

δ60/

58 N

iSRM

986

(‰)

Starting Composition = -0.08‰

Δ≈ 2.0 ‰

Δ≈ 3.6 ‰

Low Ionic Strength Exp. (48 hr)

High Ionic Strength Exp. (27 days)

High Ionic Strength Exp. (48 hrs)

2 Experiment Types:

Low Ionic Strength High Ionic Strength

Solution Composition

• Milli-Q water• Ni (aq) • Birnessite• KOH and HNO3 (to control pH)

• Synthetic sea water • Ni (aq) • Birnessite• KOH and HNO3 (to control pH)

pH 8.3 7.5

Mixing Time 48 hrs 48 hrs and 27 days

Ni Concentration

600 ppb to 4.5 ppm 400 ppb to 5 ppm

Amount of birnessite

.6 mg 1.5 mg

20 30 40 50 60 70 80 90 100-3.00

-2.00

-1.00

0.00

1.00

2.00

3.00

High Ionic Aqueous Ni (48 hr)

High Ionic Sorbed Ni (48 hr)

High Ionic Aqueous Ni (27 d)

High Ionic Sorbed Ni (27 d)

Low Ionic Aqueous Ni (48 hr)

Low Ionic Sorbed Ni (48 hr)

% Ni Sorbed

δ60/5

8 Ni SR

M98

6 (‰

)

Overlay of all 3 experiments

Conclusions• Sorption of Ni onto birnessite produces a significant isotope fractionation

effect• Light Ni adsorbs/incorporates into birnessite structure• Heavy Ni remains in solution

• Low Ionic Strength Δ60/58 Ni ≈ 1.4 ‰• High Ionic Strength Δ60/58 Ni ≈ 2.0 - 4.0‰

Starting Composition = -0.08‰