Monazite as a nuclear waste form for encapsulating actinides: a mineralogical study of natural

monazite from Steenkampskraal

Supervisor: M. KnoperCo-supervisor: D. Harlov

GABRIELLE FICQ 201300823

Introduction to Steenkampskraal SteenkampskraalRegional geologyAlterationHistory and mining background

Introduction to nuclear wasteWhy use thorium and not uranium?Why use monazite?

Purpose of the research projectData analysis

Petrographic analysisScanning Electron Microscope analysisElectron Microprobe Analysis

ConclusionImprovementsReferences

CONTENT

STEENKAMPSKRAAL

• Western Cape Province, South Africa

• Formed during the amalgamation of the Kaapvaal craton and the

Namaqua-Natal Belt (Bachmann et al., 2015)

• Namaqualand Metamorphic Complex (Andreoli et al., 1994)

• Mesoproterozoic (1600 – 1000 Ma) (McCarthy and Rubidge, 2005)

• Monazite ore is hosted within a metamorphic rock of amphibolite to

granulite facies (Spear and Pyle, 2002)

• Largest monazite deposit in terms of the REE, Th and U concentration (Read and Williams, 2001; Read et al., 2002)

STEENKAMPSKRAAL

Adapted from Andreoli et al. (1994)

REGIONAL GEOLOGY

• Southern part of the Bushmanland sub-province (Andreoli et al., 1994)

• Dominated by granite gneisses, granites and charnockite gneisses (Andreoli et al., 1994; Andreoli et al., 2006)

• Best exposed along the Roodewal Suite (Andreoli et al., 1994)

• Radioactive terrains such as Steenkampskraal are underlain by granulite-facies rocks (Andreoli et al., 2006)

ALTERATION

Three alteration theories:

•1st - Intrusive granulite-facies (Andreoli et al., 1994) • High temperature granulite-facies region

•2nd - Greenschist-facies metamorphism (Read et al., 2002)

•3rd - Hydrothermal alteration during metamorphism (Wall. 2014)

HISTORY AND MINING BACKGROUND

• According to Steenkampskraal Thorium Limited (2016)• Deposit discovered in the 1940’s• Mined for the high thorium concentration• Ore was processed for the full range of REE• Mining took place from1952 – 1963• Late 1960’s the mine closed due to mining of uranium

• Monazite ore is starting to make a comeback • Higher demand for REE (Basson et al., 2016)

• Better understanding of Th (Basson et al., 2016)

Concerns regarding the encapsulation of Th as nuclear waste has started to take place

WHY THORIUM AND NOT URANIUM?

According to Staff (2015)

•Safer radioactive element

•Produces a cleaner fuel source

•Produces a lower amount of nuclear waste

•Affordable fuel source

•Minimal water usage needed

•Environment and human health will improve

So why use phosphates to encapsulate actinides?

WHY USE MONAZITE?

• Durable phosphate mineral (Ewing and Wang, 2002)

• High chemical stability (Montel et al., 2006)

• High resistivity to radioactive damage (Montel et al., 2006)

• Immobilization of actinides (Ewing and Wang, 2002)

• Strong chemical structure, minimum damage through alpha decay (Harrison et al., 2002)

• Resistant to strong alkaline and acidic solutions (Read and Williams,

2001)

PURPOSE OF THE STUDY

Determine the capability of monazite for the encapsulation of actinides without mobilisation

during alteration

PETROGRAPHIC ANALYSIS

STK 108

• Granoblastic texture

• Monazite and apatite surrounded by

chalcopyrite

• Brown alteration

• Quartz vein

• Hydrothermal alteration

STK 091 FW

• Interlocking texture

• Granoblastic texture

• Triple point grain boundaries

• Internal zonation

• Brown alteration

NAM 1675 A

• Altered samples

• Granoblastic texture

• Associated with magnetite

and rutile

SCANNING ELECTRON

MICROSCOPE ANALYSIS

STK 79 HW• Monazite associated with magnetite and rutile• Figure B

• Monazite vein associated with lime (CaO) • Thermal input through metamorphism (Betts, 1990)

STK 108 C 93.21 and STK 082 HW

• Monazite associated with magnetite and rutile• Grid pattern

ELECTRON MICROPROBE

ANALYSIS

  STK 108 STK 091 FW NAM 1675 A NAM 1675 C

  Cry 5 Cry 6 Cry 1 C1 Cry 2 C1 Cry 1 C1 Cry 2 C1 Cry 1 C1 Cry 2 C1

Analysis Molar weight percentage

P2O5 28.80 29.30 29.10 28.80 28.70 28.90 28.00 24.10

SiO2 1.00 0.80 0.90 1.10 1.00 1.00 0.70 7.40

ThO2 8.30 8.40 8.90 8.80 8.50 8.30 3.40 7.30

U2O3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Y2O3 2.30 2.20 2.20 2.10 2.30 2.30 0.40 0.50

La2O3 12.40 12.30 12.30 12.20 12.60 12.60 15.20 12.40

Ce2O3 27.10 27.10 26.80 27.00 26.60 27.10 32.50 26.40

Pr2O3 2.90 3.00 2.90 3.10 2.80 2.80 3.50 2.90

Nd2O3 11.00 11.10 10.70 11.00 10.80 10.60 12.30 10.90

SmO 1.80 1.80 1.70 1.90 1.70 1.80 1.60 1.80

EuO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Gd2O3 0.60 0.60 0.60 0.60 0.60 0.60 0.00 0.00

Dy2O3 0.50 0.50 0.60 0.50 0.70 0.60 0.00 0.00

Al2O3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 4.60

FeO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.60

CaO 1.10 1.30 1.30 1.10 1.20 1.10 0.20 1.20

PbO 0.00 0.00 0.00 0.00 0.00 0.50 0.00 0.00

Total 97.80 98.40 98.00 98.20 97.50 98.20 97.80 101.10

Adapted from Andreoli et al. (1994)

CAN MONAZITE BE USED FOR THE

ENCAPSULATION OF ACTINIDES?

CONCLUSION

Monazite cannot be used for the encapsulation of actinides

No uranium was detected

All samples are slightly altered

Hydrothermal alteration

Thermal alteration

Due to the alteration of the monazite, the thorium and

uranium concentration became depleted

IMPROVEMENTS

• Fresh samples must be analysed

• Compare definite altered and unaltered monazite samples

• Determine the alteration type and how the alteration took

place

• Improve the study to use all phosphates as a possible

method for the encapsulate of actinides

REFERENCES

Andreoli, M., Smith, C., Watkeys, M., Moore, J., Ashwal, L. and Hart, R. (1994). The geology of the Steenkampskraal monazite deposit, South Africa; implications for REE-Th-Cu

mineralization in charnockite-granulite terranes. Economic geology, 89(5):994-1016.Andreoli, M.A.G., Hart, R.J., Ashwal, L.D. and Coetzee, H. (2006). Correlations between U, Th

content and metamorphic grade in the western Namaqualand belt, South Africa, with implications for radioactive heating of the crust. Journal of Petrology, 47(6):1095-1118.

Bachmann, K,. Schulz, B., Bailie, R. and Gutzmer, J. (2015). Monazite geochronology and geothermobarometry in polymetamorphic host rocks of volcanic-hosted massive sulphide mineralizations in the mesoproterozoic Areachap terrane, South Africa. Journal of African Earth Sciences, 111:258-272.

Basson, I.J., Muntings, J.A., Jellicoe, B.C. and Anthoniesen, C.J. (2016). Structural interpretation of the Steenkampskraal monazite deposit, Western Cape, South Africa. Journals of African

Earth Science. 121: 301-315. Betts, J. (1990). Fine minerals: Lime mineral database. Accessed from:

http://webmineral.com/data/Lime.shtml#.V5d8zfl97IV Accessed on: 26/07/2016 Ewing, R.C. and Wang, L. (2002). Phosphates and nuclear waste forms. Reviews in Mineralogy and

Geochemistry, 48(1): 673-699.Harrison, T.M., Catlos, E.J. and Montel, J.M. (2002). U-Th-Pb dating of phosphate minerals. Reviews

in Mineralogy and Geochemistry, 48(1): 523-559.

REFERENCES

McCarthy, T. and Rubidge, B. (2005). The story of earth and life. A southern African perspective on a 4.6- billion year journey. Struik Nature. Cape Town.

Montel, J.M., Glorieux, B., Seydoux-Guillaume, A.M. and Wirth, R. (2006). Synthesis and sintering of a monazite-brabantite solid solution ceramic for nuclear waste storage. Journal of Physics and Chemistry of Solids. 67: 2489-2500.

Read, D. and Williams, C.T. (2001). Degradation of phosphatic waste forms incorporating long-lived radioactive isotopes. Mineralogical Magazine. 65 (5): 589-601

Read, D., Andreoli. M.A.G., Knoper, M., Williams, C.T. and Jarvis, N. (2002). The degradation of monazite: Implications for the mobility of rare-earth and actinide elements during low- temperature alteration. Eur. J. Mineral. 14: 487-497.

Spear, F.S. & Pyle, J.M. (2002). Apatite, monazite and xenotime in metamorphic rocks. Reviews in Mineralogy and Geochemistry, 48(1):293-335.

Staff, W. (2015). Thorium could avert the energy crisis. Environmental Management. Steenkampskraal Thorium Limited. (2016). Thorium refinery plant: Thorium refinery project ThRP.

Accessed from: http://www.thorium100.com/Thorium%20Refinery%20Plant.php Accessed on: 11/08/2016 and Historical and future operations for Steenkampskraal Monazite mine. Accessed from: http://www.thorium100.com/SMM.php Accessed on: 11/08/2016.

Wall, F. (2014). Critical metals handbook. First Edition. John Wiley & Sons. United Kingdom p312-339