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

BORDA, L.; BIA, G.; BORGNINO, L.; CHIARAMONTE, N.; GARCÍA, M.G.

JOURNAL OF HAZARDOUS MATERIALS.

ELSEVIER SCIENCE BV

Año: 2024 vol. 473

0304-3894

World-class borate deposits often form from As-rich waters, this study addresses the understudied association ofarsenic (As) species with evaporite borates, focusing on the Puna region’s borate deposits (Central Andes ofArgentina). The research aims to characterize the association between borate minerals and high As concentrationsin brines and thermal waters. To achieve this, five borate samples were collected from the Olaroz salt flatnucleus and thermal springs, alongside associated water samples. Comprehensive analytical techniques,including ICP-MS, ICP-OES, synchrotron-based micro-XRF, XRPD, Rietveld analysis, micro-FT-IR, and XPS, wereemployed to determine bulk and surface chemical compositions, mineral identification, and solid speciation of Asand boron. The study reveals that under oxidizing conditions and in absence of organic matter, aqueous arsenicspecies interact with ulexite through a stepwise process involving charge neutralization, cationic bridge formation,and surface complex formation with polyborate and As(V) oxyanions. However, in environments associatedwith microbial mats or organic-rich sediments, the dissolved As(V) is reduced to As(III), which formscomplexes with functional groups of organic matter. The coexistence of As(III) and As(V) in specific layerssuggests potential remediation strategies targeting organic matter for the removal of the more toxic As(III) insimilar geological settings.