Simultaneous Reduction of Arsenic(V) and Uranium(VI) by Mackinawite: Role of Uranyl Arsenate Precipitate Formation

Abstract

Uranium (U) and arsenic (As) often occur together naturally and, as a result, can be co-contaminants at sites of uranium mining and processing, yet few studies have examined the simultaneous redox dynamics of U and As. This study examines the influence of arsenate (As(V)) on the reduction of uranyl (U(VI)) by the redox-active mineral mackinawite (FeS). As(V) was added to systems containing 47 or 470 μM U(VI) at concentrations ranging from 0 to 640 μM. In the absence of As(V), U was completely removed from solution and fully reduced to nano-uraninite (nano-UO2). While the addition of As(V) did not reduce U uptake, at As(V) concentrations above 320 μM, the reduction of U(VI) was limited due to the formation of a trögerite-like uranyl arsenate precipitate. The presence of U also significantly inhibited As(V) reduction. While less U(VI) reduction to nano-UO2 may take place in systems with high As(V) concentrations, formation of trögerite-like mineral phases may be an acceptable reclamation end point due to their high stability under oxic conditions.

RETRACTED: Effects of Bacillus subtilis on the reduction of U(VI) by nano-Fe0

“…However, tetravalent uranium U(IV) is often immobilised a s s o l i d U ( I V ) ( s u c h a s u r a n i n i t e ( U O 2 )), which inhibits uranium transport in contaminated soils and groundwater (Langmuir, 1978). Therefore, the reduction of mobile U(VI) to U (IV) O 2(s) by reducing agents has been extensively investigated for the remediation and prediction of U(VI) in groundwater and soils (Bernier-Latmani et al, 2010;Riba et al, 2008;Troyer et al, 2014;Veeramani et al, 2011). Recent studies have revealed that reduced U species include the U(IV) uraninite (UO 2 ) and non-uraninite species (monomeric U(IV)) species lacking the 3.85 Å U U associations in the corresponding EXAFS spectrum (Bernier-Latmani et al, 2010;Fletcher et al, 2010;Boyanov et al, 2011;Alessi et al, 2014).…”

Fe(II) Redox Chemistry in the Environment

“…However, different reduction mechanisms have been reported even for the same chemical probe. Some researchers have suggested that the reduction of U­(VI) might result from either Fe­(II) or S­(-II), while others have proposed the reduction is due to S­(-II) instead of Fe­(II). ,, Additionally, the reduction of Cr­(VI) by FeS occurs primarily at the FeS surface, while aqueous Fe­(II) and S­(-II) released from the partial dissolution of FeS can contribute to the reactivity by either surface or solution reaction . Further research is needed to examine the relative contribtuion of these potential reductants.…”

Elevated Concentrations of U and Co-occurring Metals in Abandoned Mine Wastes in a Northeastern Arizona Native American Community

“…Examples of these are U(VI) adsorbed to ferrihydrite, As(V) or As(III) adsorbed to goethite, and the mineral trogerite (UO 2 HAsO 4 •4H 2 O). 50 Limited studies have focused on understanding the chemical interaction and mechanisms controlling the potential release of metal mixtures of U, As, and co-occurring elements from mine wastes into water sources. 50,53 The main objective of this study was to assess the presence and chemical interaction of U and other co-occurring metals in soils in the Claim 28 abandoned mine waste site and in adjacent and nearby springs in Blue Gap/Tachee Chapter of the Navajo Nation in northeastern Arizona.…”