ORCID

0000-0002-6308-0226

Keywords

iodine, selenium, oxidation, sorption, incorporation, concentration

Abstract

The environmental chemistry and mobility of iodine and selenium contaminants were investigated through redox interactions with manganese oxides and incorporation into carbonate minerals. The study examined iodide (I-) and selenite (SeO32-) oxidation under varying pH conditions using manganese oxide minerals, which are geochemical regulators. Using tandem ion chromatography-inductively coupled plasma-mass spectrometry (IC-ICP-MS), the oxidation and speciation of iodine and selenium were quantified under environmentally relevant conditions. The results demonstrate that oxidation of I- and SeO32- by manganese oxides are highly concentration dependent. Acid birnessite, a common manganese oxide, exhibited significant reactivity toward I-, oxidizing up to 28% within five hours under acidic conditions, while only limited oxidation to iodate (IO3-) occurred. Selenium primarily underwent adsorption rather than oxidation at realistic concentrations, with oxidation only observed under artificially elevated conditions.

Mineral incorporation is a significant geochemical pathway for the sequestration of contaminants. Incorporation experiments assessed the sequestration of contaminants into calcium carbonate (CaCO3) and manganese carbonate (MnCO3) using co-precipitation. IO3- displayed strong adsorption onto CaCO3 but incorporated effectively into MnCO3. Selenite exhibited high incorporation efficiency in both carbonate minerals, whereas selenate (SeO42-) showed limited incorporation due to its larger molecular size and tetrahedral geometry. Chromate (CrO42-) was effectively removed by both carbonate minerals, with a shift from incorporation to surface sorption at lower concentrations. Uranyl (UO22+) demonstrated substantial incorporation, particularly in MnCO3, while pertechnetate (TcO4-) exhibited minimal interaction with either mineral. Competitive ion studies revealed MnCO3 maintained high contaminant removal efficiency even in mixed systems, whereas CaCO3 exhibited reduced incorporation under competition.

These findings underscore the complexity and the different geochemical pathways that anionic contaminants can follow in the environment, by participating in redox, adsorption, and precipitation processes. Future research should focus on long-term stability, competitive effects with additional contaminants, and environmental conditions that may influence contaminant sequestration and potential remobilization.

Completion Date

2025

Semester

Spring

Committee Chair

Anagnostopoulos, Vasileios

Degree

Doctor of Philosophy (Ph.D.)

College

College of Sciences

Department

Chemistry

Identifier

DP0029402

Document Type

Dissertation/Thesis

Campus Location

Orlando (Main) Campus

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