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TcO2 oxidative dissolution by birnessite under anaerobic conditions: a solid–solid redox reaction impacting the environmental mobility of Tc-99
Environmental Science: Processes & Impacts ( IF 5.5 ) Pub Date : 2021-4-16 , DOI: 10.1039/d1em00011j
Jordan Stanberry 1 , Ilana Szlamkowicz 1 , Lauren R Purdy 1 , Vasileios Anagnostopoulos 1
Affiliation  

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). Effectiveness of the reductive immobilization of Tc-99 depends on the susceptibility of TcO2 to oxidation to TcO4 in situ, as it is subject to dissolution by oxidizing agents, such as oxygen. Manganese minerals can be a liability for the long-term in situ immobilization of Tc-99, even in suboxic and anoxic systems due to their strong oxidizing capacity. This study presents for the first time the oxidative dissolution of TcO2 to pertechnetate by birnessite under anaerobic conditions. Oxidative dissolution of TcO2 was studied as a function of pH and birnessite:TcO2 ratios and in the presence of Ca2+ and Mn2+. As low as 5 mg of birnessite dissolved ∼65% of the original TcO2 in the suspensions and subsequently released TcO4 in the aqueous phase at both pH 6.5 and 8 in the absence of oxygen. On the other hand, the ability of birnessite to sequester calcium and manganese on its surface at pH 6.5 through sorption was shown to inhibit the oxidative capacity of birnessite. Maximum TcO4 release in the aqueous phase by Ca- and Mn-loaded birnessite was ∼50% less compared to pure birnessite, indicating that divalent cations sorb on active centers responsible for birnessite's oxidative capacity and potentially passivate the mineral. In summary, birnessite exerts strong geochemical controls over the mobility of Tc-99 in anoxic systems by oxidatively mobilizing the otherwise insoluble Tc(IV) to Tc(VII) and their presence in natural systems needs to be taken into account when long-term remediation strategies are being designed.

中文翻译:

水钠锰矿在厌氧条件下的TcO2氧化溶解:固-固氧化还原反应影响Tc-99的环境迁移

为TC-99污染的环境中的除害补救努力历来集中在可溶性高锝酸盐(TC(还原VII)O 4 - ),以不溶性的,并且流动性较小,锝(IV)氧化物(TCO 2)。的Tc-99的还原性固定的有效性取决于TCO的易感性2氧化到TCO 4 - 原位,因为它是受由溶解氧化剂,如氧。锰矿产可能是长期的原地责任由于其强大的氧化能力,即使在低氧和缺氧系统中也能固定Tc-99。这项研究首次提出了水钠锰矿在厌氧条件下TcO 2的氧化溶解为高net酸盐。研究了在Ca 2+和Mn 2+存在下,TcO 2的氧化溶解度与pH和水钠锰矿:TcO 2的比例的关系。低至5毫克水钠锰矿的溶解原TCO的〜65%2中的悬浮液,并且随后释放TCO 4 -在无氧条件下,在pH 6.5和8的水相中溶解。另一方面,表明水钠锰矿通过吸附将pH 6.5的钙和锰螯合在其表面上的能力抑制了水钠锰矿的氧化能力。最大TCO 4 -释放在水相中通过Ca-和锰加载的水钠锰矿是〜50%相比少纯水钠锰矿,表明二价阳离子吸着上负责水钠锰矿的氧化能力活性中心和潜在钝化矿物。总之,水钠锰矿通过氧化将原本不溶的Tc(IV)氧化为Tc(VII),对缺氧系统中Tc-99的迁移性具有强大的地球化学控制作用)以及在设计长期补救策略时需要考虑它们在自然系统中的存在。
更新日期:2021-04-22
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