TcO₂ oxidative dissolution by birnessite under anaerobic conditions: a solid–solid redox reaction impacting the environmental mobility of Tc-99

Abstract

Remediation efforts for the abatement of Tc-99 contamination in the environment have traditionally focused on the reduction of soluble pertechnetate (Tc(VII)O4−) to insoluble, and less mobile, technetium (IV) oxide (TcO2)....

Transformations and Speciation of Iodine in the Environment as a Result of Oxidation by Manganese Minerals

“…The synthesis and characterization of γ-MnOOH and acid δ-MnO 2 were completed following previously reported procedures. , The α-Mn 2 O 3 (99%, Strem Chemicals) and β-MnO 2 (98%, Alfa Aesar) were commercially purchased.…”

“…X-ray Diffraction (XRD, Empyrean, PANalytical) and InfraRed Spectroscopy (IR, Jasco 6600 MIR and FIR equipped with diamond ATR) were used for the characterization of γ-MnOOH and acid δ-MnO 2 after synthesis. The analysis parameters and the γ-MnOOH characteristic peaks have been described elsewhere in detail. , These XRD spectra were combined with those from the purchased manganese oxide minerals, as seen in Figure S1, with the reference peaks listed for comparison in Table Supporting Information. ,− …”

“…The analysis parameters and the γ-MnOOH characteristic peaks have been described elsewhere in detail. 3,32 These XRD spectra were combined with those from the purchased manganese oxide minerals, as seen in Figure S1, with the reference peaks listed for comparison in Table Supporting Information. 11,34−36 ■ RESULTS AND DISCUSSION Oxidation of I − by Manganese Minerals.…”

“…Additionally, the high oxidative capacity of manganese oxides is attributed to the high redox potentials of the two redox couples: Mn(IV)/Mn(II) and Mn(III)/Mn(II). 3 The high valence redox couple has a standard reduction potential of approximately 1.2 V, rivaling that of O 2 , allowing it to oxidize almost any reduced metal and metalloid species in the environment. 1,4−6 Other contributions to the high sorption and redox capacities of manganese oxide minerals are poor crystallinity, high specific surface area, and highly reactive vacancy sites.…”

“…The oxidation states of manganese oxides range from +II to +IV, with there being mixed valence state minerals (i.e., birnessite, a Mn­(III/IV) oxide). Additionally, the high oxidative capacity of manganese oxides is attributed to the high redox potentials of the two redox couples: Mn­(IV)/Mn­(II) and Mn­(III)/Mn­(II) . The high valence redox couple has a standard reduction potential of approximately 1.2 V, rivaling that of O 2 , allowing it to oxidize almost any reduced metal and metalloid species in the environment. ,− Other contributions to the high sorption and redox capacities of manganese oxide minerals are poor crystallinity, high specific surface area, and highly reactive vacancy sites. , These traits allow manganese oxides to exert geochemical regulation on the fate and transport of contaminants through combined redox sorption processes, either by enhancing natural attenuation or through remobilization of contaminants.…”