Understanding arsenic-ulexite interactions in evaporite environments: Evidence from XRPD, micro-XRF, micro-FT-IR, and...

Area of Science:

• Geochemistry
• Mineralogy
• Environmental Science

Background:

• Borate deposits form from arsenic (As)-rich waters.
• The association between arsenic species and evaporite borates is understudied.
• Focus on Puna region borate deposits in the Central Andes of Argentina.

Purpose of the Study:

• Characterize the association between borate minerals and high As concentrations in brines and thermal waters.
• Determine the speciation of As and boron in borate deposits.
• Investigate the interaction mechanisms between arsenic species and borate minerals.

Main Methods:

• Sample collection from Olaroz salt flat and thermal springs.
• Analysis using ICP-MS, ICP-OES, synchrotron-based micro-XRF, XRPD, Rietveld analysis, micro-FT-IR, and XPS.
• Determination of bulk and surface chemical compositions, mineral identification, and solid speciation.

Main Results:

• Under oxidizing conditions, As(V) interacts with ulexite via charge neutralization, cationic bridges, and surface complexation.
• In organic-rich environments, As(V) is reduced to As(III), forming complexes with organic matter.
• Coexistence of As(III) and As(V) in specific layers indicates potential remediation pathways.

Conclusions:

• Arsenic speciation in borate deposits is influenced by redox conditions and organic matter presence.
• Organic matter plays a key role in arsenic transformation and sequestration.
• Targeting organic matter offers potential remediation strategies for toxic As(III) in similar geological settings.