Tc O4 Research Articles

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

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.

Oxidative dissolution of Tc(IV)O2·nH2O colloids by sonolysis

Abstract Redox reactions of Tc in aqueous solutions by sonolysis were investigated. Aqueous pertechnetate (Tc(VII)O4 −) solutions and Tc(IV)O2· n H2O colloids solutions were sonicated (200 kHz, 200 W) in a glass cell with flat bottom under Ar or He atmosphere at 20 °C. No reduction of TcO4 − was observed in this study. However, we found that the TcO2· n H2O colloids dispersed in an aqueous solution were completely dissolved by ultrasonic irradiation within 30 min under Ar atmosphere, and TcO4 − was eventually produced. The production of TcO4 − was considerably suppressed in the presence of t-butyl alcohol (an effective scavenger of OH radicals), indicating that Tc(IV) was oxidized by OH radicals (produced by dissociation of water molecules) in hot cavitation bubbles created by ultrasound. The formation rate of TcO4 − under He atmosphere was smaller than that under Ar atmosphere. This can be attributed to a difference of the effective maximum temperature in the collapsing bubbles. Because thermal conductivity of He is much higher than Ar, thermal transport effectively occurs from the bubbles to the surrounding liquid. Thus, temperature of cavitation bubbles filled with He should be lower than those filled with Ar, resulting in the smaller OH formation rate.

Finger bougie method compared with pyloroplasty in the gastric replacement of the esophagus.

To elucidate the necessity of pyloroplasty for the gastric tube through the posterior mediastinum in esophageal surgery, gastric emptying and duodenogastric reflux (DGR) were evaluated in 16 cases undergoing an anterior pylorectomy (group P) and in 16 cases treated by the finger bougie method (group F). First, the obstruction and reflux symptoms were examined based on a patient questionnaire using a brief scoring system. The median value of the symptom score showed the patients in P to have more symptoms than those in F; however, the difference was not significant (8.0 vs 6.0). Secondly, the swallowed Tc O4- (85MBq) was counted using a gamma camera at three sites on the sternal bone in the upright position based on a gastric transit scintigram. Both the descending time of the RI peak and the clearance rates were similar between the two groups. Thirdly, intragastric 24-h pH monitoring was carried out. Antimony pH sensors were anchored 5 and 15cm below the esophagogastrostomy. We could not find any difference between the two groups in both the %time pH > 4 and %time pH > 7. These findings thus revealed no big difference between groups P and F. The finger bougie method to drain the vagotomized posterior mediastinal stomach was found to achieve results similar to conventional pyloroplasty, while it was also simpler and safer.