zircon solubility in alkaline aqueous fluids at upper ... · solubility diagram for the system zro...

Ayers J.C.1, Zhang L.1,2, Luo Y.1,3, Peters T.1

1. Dept. of Earth & Environmental Sciences, Vanderbilt University

2. Division of Geological and Planetary Sciences, California Institute of Technology

3. Department of Earth Sciences, The University of New Brunswick, Canada

ZIRCON SOLUBILITY IN ALKALINE AQUEOUS FLUIDS AT UPPER

CRUSTAL CONDITIONS

Zircon Solubility Diagram

Solubility diagram for the system ZrO2-SiO2-H2O at 200°C and 1m NaOH calc. using LLNL.dat of GWB (Bethke, 1996) and the stability constants of Adair et al. (1997).

log Si concentration (molality)

-4 -3 -2 -1 0 1 2

log

Zr c

once

ntra

tion

(mol

ality

)

-14

-12

-10

-8

-6

-4

BaddeleyiteZircon

Zr(OH)5-

Qua

rtz s

atur

atio

na

b

In alkaline solution: ZrSiO4(xt) + 2H2O + OH- = SiO2(aq) + Zr(OH)5-

We measured the solubilitiesof the assemblages“a” and “b.”

pH Dependence of Solubility of Zircon + Baddeleyite

The solubility of the assemblage baddeleyite + zircon at 200°C as a function of pH, calculated using LLNL.dat of GWB (Bethke, 1996) and stability constants of Adair et al. (1997).

Zircon Solubility In Quartz-saturated Fluid

0 2 4 6 8 10 12 14–22

–20

–18

–16

–14

–12

–10

–8

pH

log

a Zr

(OH

) 2++

Zr(OH)2++

Zr(OH)+++

Zr(OH)3+

Zr(OH)4(aq)

Zr(OH)5-

Zircon

25°C

ayersj Thu Apr 24 2003

25°C and 1 bar pressure,thermodynamic data from Adair et al. (1997)

Presenter

Presentation Notes

# Act2 script, saved Thu Apr 24 2003 by ayersj data = "C:\Program Files\Gwb\Gtdata\GMEAP_Classproject_thermo_v2.dat" verify swap Quartz for SiO2(aq) diagram Zr(OH)2++ on Zr(OH)2++ vs pH x-axis from 0 to 14 increment 1 y-axis from -22 to -8 increment 1

Zircon Solubility In Quartz-saturated Fluid

0 2 4 6 8 10 12 14–30

–28

–26

–24

–22

–20

–18

–16

–14

–12

–10

–8

–6

–4

–2

0

pH

log

a Zr

(OH

) 2++

Zr(OH)2++

Zr(OH)3+ Zr(OH)4(aq)ZrOH+++

Zircon

25°C

berrios Mon Apr 28 2003

Diag

ram

Zr(O

H)2++

, T =

25

°C ,

P =

1.0

13 b

ars,

a [H

2O]

= 1

, a [Q

uartz

] =

1

25°C and 1 bar pressure, default LLNL thermodynamic data from Naumov et al. (1974)

Presenter

Presentation Notes

# Act2 script, saved Wed Apr 23 2003 by berrios data = \\Geo1\Anonymous\GMEAP\GMEAP_Classproject_thermo_v3.dat verify swap Quartz for SiO2(aq) diagram Zr(OH)2++ on Zr(OH)2++ vs pH x-axis from 0 to 14 increment 1 y-axis from -10 to 0 increment 1 *Note that solubility does not increase at high pH (no U-shaped curve)

Methods

Quench Zr and Si leached from outercapsule; leachate analyzed by ICP-MS.

Presenter

Presentation Notes

Fluid compositions 1m or 0.1m, 0m NaOH. One inner capsule contains natural crystals of Z (250-500 μm) or Z+Q; a second contains fO2 buffer (Ni + NiO + H2O, or Hematite for HM). Outer capsule contains fluid + trace elements (100 ppm).

Zir-003 (Z + B) Run Product Zircons

Zir-001 (Z + Q) Run Product Zircon

Zircon grains250-500microns indiameter.

SM BE SM CL

RP BE RP CL

Presenter

Presentation Notes

a) BSE image of zircon starting material grain. b) CL image of same starting material grain as (a). c) BSE image of zircon grains from experiment Zir-012. d) CL image of same zircon grains as (c).

Baddeleyite Crystals on Surface of Run Product Zircon Grain

Presenter

Presentation Notes

SEM image of bladed baddeleyite crystals on the surface of a run product zircon grain from experiment Zir-001.

Baddeleyite Crystals Filling a Pore Within a Run Product Zircon Grain

Presenter

Presentation Notes

a) BSE image of bladed baddeleyite crystals filling a pore within a run product zircon grain from experiment Zir-002. b) Close-up of baddeleyite crystals in a pore in zircon from experiment Zir-002.

Zircon Unstable in 1m NaOH at 450°C?

Vlasovite (Na2ZrSi4O11)

Zircon

Presenter

Presentation Notes

BSE image of run products from experiment Zir-10 run at 450C showing a vlasovite rim on a zircon grain.

Summary Of Zircon Experiments At 0.2 GPaSample SMa T (°C) NaOH

(m) pH t (days) RP SEM RP XRD moles Zr/kg H2O

moles Si/kg H2Oc

Zir-001 Z 600 1 10.4 25 Z+B 3.62(0.03)×10-5 1.7×10-2

Zir-002 Z 600 1 10.4 31 Z+B Z 2.66(0.09)×10-5 3.2×10-2

Zir-003 Z+Q 600 1 10.4 25 Z+Q 1.30(0.03)×10-5 2.7×10-2

Zir-004 Z+Q 450 1 10.0 31 Z+Q+V Z+Q+V 3.32(0.03)×10-5 9.1×10-2

Zir-005 Z 450 1 10.0 31 Z+B+V Z+B+V 1.46(0.003)×10-4 2.4×10-2

Zir-006 Z 450 1 10.0 35 Z+B+V 2.0(0.3)×10-6 2.6×10-2

Zir-007 Z 450 1 10.0 21 Z+B+V 4.0(2.4)×10-5 7.0×10-1

Zir-008 Z 450 1 10.0 14 Z+B+V 8.2(2.9)×10-7 8.9×10-3

Zir-009 Z 450 1 10.0 21 1.4(0.3)×10-6 8.1×10-3

Zir-010 Z 450 1 10.0 25 Z+B+V 2.5(0.4)×10-6 1.2×10-2

Zir-011 Z 750 1 10.9 25 Z+B 1.7(0.3)×10-6 5.0×10-3

Zir-012 Z 600 0.1 9.7 25 Z+B Z 2.1(0.3)×10-6 1.2×10-2

Zir-013 Z 450 0.1 9.3 33 Z+B Z 1.8(0.8)×10-6 1.2×10-2

Zir-014 Z 750 0.1 10.4 25 Z+B 1.2(0.3)×10-6 1.2×10-2

Zir-015 Z 600 0.1 9.7 28 Z+B 1.2(0.3)×10-6 1.3×10-2

Zir-016 Z 600 0 5.5 25 Z+B Z 4.5(2.3)×10-7 3.7×10-3

Zir-017 Z 750 0 5.9 21 Z 4.4(3.3)×10-7 6.4×10-3

Zir-018 Z+Q 450 1 10.0 21 Z+Q+V 1.1(0.3)×10-6 4.3×10-3

Zir-019 Z 600 1 10.4 21 Z 3.6(0.3)×10-6 1.1×10-2

Zir-020 Z 600 0.1 9.7 21 Z 2.3(0.3)×10-6 9.4×10-3

Zir-021 Z 600 1 10.4 21 5.3(0.6)×10-6 1.2×10-2

Time Dependence of Z+B Solubilityin 1m NaOH at 600°C

Duration (days)

20 22 24 26 28 30 32

Zr c

once

ntra

tion

(mol

ality

)

1e-9

1e-8

1e-7

1e-6

1e-5

1e-4

1e-3

MDL

PB

IDL

Presenter

Presentation Notes

Summary of measured solubilities of Z+B in 1m NaOH at 600C as a function of run duration with 2σ error bars. IDL = instrument detection limit, MDL = method detection limit, and PB = procedural blank.

pH Dependence of Zircon Solubility

pH5 6 7 8 9 10 11 12

Zr c

once

ntra

tion

(mol

ality

)

1e-8

1e-7

1e-6

1e-5

1e-4

600°C 750°C

Presenter

Presentation Notes

Solubility of the assemblage zircon + baddeleyite at 0.2 GPa as a function of pH, plotted with 1σ error bars.

Zircon Solubility at 1.0 GPa and 1000°C(Single Crystal Weight Loss in Piston Cylinder)

y = 0.35x + 0.27R2 = 0.990

y = 0.50x + 0.39R2 = 0.995

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0 0.5 1 1.5 2 2.5 3m Na

m Z

rSiO

4

Zircon in NaF

Zircon in NaOH

DC

DC

Solubility Equation Derivation

• Performed MLR with dependent variable ln (Zr) and independent variables 1/T, [OH-], and ln (Si); the terms ΔS/R, ln γZr(OH)5-(aq), and ln γSiO2(aq) are lumped together as the intercept b:

ln (Zr) = -ΔH/R(1/T) + ln [OH-] – ln (Si) + bThe term ln (Si) has a (-) coefficient, implying that as (Si) ↑ (Zr) should ↓.

• We made measurements at 3 different values of 1/T and [OH-], but the coefficients for these parameters were not statistically different from zero at the 95% level (P > 0.05). The term ln (Si) accounted for 85% of the observed variation in ln (Zr):

ln (Zr) = 2.9* ln (Si) + 0.25• The positive coefficient for ln (Si) gives the zircon solubility curve a (+)

slope, implying that Zr complexes with Si.

• In alkaline solution: ZrSiO4(xt) + 2H2O + OH- = SiO2(aq) + Zr(OH)5-

ln K = ln [Zr(OH)5-(aq)] + ln [SiO2(aq)] – ln [OH-] = -ΔG/RT

ln [Zr(OH)5-(aq)] = -ΔH/RT + ΔS/R + ln [OH-] – ln [SiO2(aq)]

- ln γSiO2(aq) – ln γZr(OH)5-(aq)

Presenter

Presentation Notes

ΔG, ΔH, ΔS and ΔV are the free energy, enthalpy, entropy and volume change of the dissolution reaction and lnγZr(OH5-fl is the activity coefficient of Zr(OH)5- in the fluid. We did not vary P, so we ignored the ΔV(P-1)/RT term.

Evidence of Zr-Si Complexing

y=2.9x+0.25r=0.85

ln Si concentration (molality)-6.0 -5.5 -5.0 -4.5 -4.0 -3.5 -3.0

ln Z

r con

cent

ratio

n (m

olal

ity)

-20

-18

-16

-14

-12

-10

-8

-6

Presenter

Presentation Notes

The aqueous solubility of zircon expressed as natural log of the molal concentration of zirconium in the fluid as a function of natural log of the molal concentration of silica at 600°C with 1σ error bars. The best-fit Deming regression equation shown with 95% confidence limits is ln (Zr) = 0.25 + 2.9*ln(Si). Test for slope = 0: F= 2553.848P= <0.0001

Revised Zircon Solubility Diagram

ln Si concentration (molality)-8 -6 -4 -2 0

ln Z

r con

cent

ratio

n (m

olal

ity)

-14

-12

-10

-8

-6

-4

Baddeleyite

Zirc

on

Zr(OH)5- Qua

rtz

0.2 GPa, 600°C

Evidence for Al-Si Complexing

from Manning (2007)

Conclusions

• Zircon dissolved incongruently to form baddeleyite at all temperatures, + vlasovite at 450°C.

• In quartz-saturated fluids zircon dissolved congruently at 600 and 750°C, while vlasovite formed at 450°C.

• Zircon solubility increases with increasing molality of NaOH (pH), possibly due to formation of Zr(OH)5

- at low silica activities.

• Zircon solubility is enhanced by aqueous complexing of Zr with Si according to:

ln (Zr) = 0.25 + 2.9 * ln (Si)

References

Adair, J. H., Krarup, H. G., Venigalla, S., and Tsukada, T., 1997, A review of the aqueous chemistry of the zirconium-water system to 200C: Materials Research Society Symposium Proceedings, v. 432, p. 101-112.

Bethke, C., 1996, Geochemical Reaction Modeling: Concepts and Applications: New York, NY, Oxford University Press, Inc., 397 p.

Manning, C. E., 2007, Solubility of corundum + kyanite in H2O at 700°C and 10 kbar: evidence for Al-Si complexing at high pressure and temperature: Geofluids, v. 7, p. 258-269.

Naumov G. B. et al.. (1974) Handhook of Thermodynamic Data. U.S. Dept. Comm. Natl. Techn. Info. Serv., Reproduction No. Pb. 226 722, 328 pp.

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zircon solubility in alkaline aqueous fluids at upper ... · solubility diagram for the system zro...

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