Concentrations of Pt and Pd in a hydrous silicate glass

The platinum group elements (PGE: platinum, palladium, ruthenium, rhodium, iridium, and osmium) are vital in today’s economy for their catalytic properties, high melting points, and corrosion resistance. While crustal concentrations of Pt are ~0.5 ppb and basaltic concentrations can reach 10 ppb, economic deposits of PGE in sulfide seams <1m thick (called PGE reefs) can have Pt concentrations up to 10 ppm. How these PGE-rich layers form in layered mafic intrusions remains debated. Commonly proposed ideas to explain reef formation involve sulfide settling and sulfide concentration by secondary fluids. I have performed experiments in a rapid quench cold seal system measuring solubilities of PGE source phases in H2O-Na2Si2O5 liquids at 1 kbar with variable f(O2) and temperatures of 550 °C to 760 °C. This system allows us to probe liquids ranging from hydrothermal fluids to anhydrous silicate melts. Gold capsules were loaded in layers having 10 mg of hydrous sodium disilicate ~10 mg of 50:50 quartz:albite and ~0.5 mg of Pt or Pd (as PtO2, PtCl2, PdO, PdCl2). I analyzed major elements using SEM-EDS and PGEs by LA-ICP-MS. I collected XANES and EXAFS on glasses at the Advanced Photon Source (APS) at Argonne National Laboratory to determine valence and nearest neighbor bonding. While Ni-NiO experiments yielded heterogeneous Pt and Pd distributions with concentrations in the 10s of ppm in glass, XANES indicated dominantly zero valent Pt and Pd. Under more oxidized f(O2) conditions buffered using double capsules with hematite-magnetite, Ru-RuO2, or MnO-MnO2 present, Pt and Pd concentrations increased to 100s of ppm with the most oxidizing experiments showing that Pt and Pd existed as Pt+2, Pt+4, and Pd+2 complexes forming within the hydrous silicate melt. Based on our experiments and the assumption that LMIs are buffered near QFM, we conclude that silicate melt temperatures greater than 1250 °C are required for Pt and Pd to exist in valences above the metal state.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Geology

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2024

Author dc:creator

• Huffaker, Jacob

Contributors dc:contributor

• Lundstrom, Craig

• Pge
• Petrology
• Layered Mafic Intrusions

Statement dc:rights

• Copyright 2024 Jacob Huffaker

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/125643

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F125643