Arsenic in natural carbonates: The role of the biogeochemical conditions in its solid speciation

BIA, G.; GARCÍA, M.G.; RUEDA, E. SOTO; MORS, R.A.; MLEWSKI, E.C.; GOMEZ, F.J.; BORGNINO, L.

CHEMICAL GEOLOGY

ELSEVIER SCIENCE BV

Año: 2021 vol. 583

0009-2541

The interaction of geogenic arsenic (As) with carbonate minerals depends on the biological and geochemicalconditions of the environment. This study sheds light on how different environmental conditions influence thecarbonate mineral formation and the interaction with As. Three different samples were analyzed: carbonatesassociated with thermal springs, oncolites and a soil carbonate sample. Synchrotron-based XAS was used toevaluate the As solid speciation while micro-focused XPS analysis was performed to determine the surfacespeciation of Fe and S. Chemical and mineralogical characterization were performed using conventionaltechniques.The results revealed that the calcium carbonates minerals are a consequence of the environmental chemicalcomposition (Sr2+, Mg2+ and arsenate), although physical factors (i.e., temperature) and the influence of microorganismscould not be ruled out. These conditions, identified in thermal springs samples and oncolites,determine the precipitation of aragonite, calcite and Sr/Mg-rich calcite and the inclusion of As(V)/(III) withincrystal lattice. As(III) could be a product of the arsenate reduction by microbial activities. Conversely, in the soilcarbonate sample, As(V) is adsorbed onto calcite. In addition, the As(1-) species was determined in one samplefrom Laguna Negra; this species likely corresponds to an As-bearing sulfide compound (i.e., arsenian pyrite).