Sulfamate, ferrous

Historically, ferrous sulfamate, Fe(NH2S02)2, was added to the HNO scmbbing solution in sufficient excess to ensure the destmction of nitrite ions and the resulting reduction of the Pu to the less extractable Pu . However, the sulfate ion is undesirable because sulfate complexes with the plutonium to compHcate the subsequent plutonium purification step, adds to corrosion problems, and as SO2 is an off-gas pollutant during any subsequent high temperature waste solidification operations. The associated ferric ion contributes significantly to the solidified waste volume. 

Hydroxjiamine is used as a substitute for the ferrous sulfamate (26). These systems are called salt-free flow sheets. The main purpose is to ease the problems associated with the processing and storage of the Hquid waste streams (27). Another approach is to use an electropulse column to electrolyticaHy produce to reduce Pu to Pu on a continuous basis (28,29). The half reactions for the flow sheets are... 

Conceptual Flowsheet for the Extraction of Actinides from HLLW. Figure 5 shows a conceptual flowsheet for the extraction of all the actinides (U, Np, Pu, Am, and Cm) from HLLW using 0.4 M 0< >D[IB]CMP0 in DEB. The CMPO compound was selected for this process because of the high D m values attainable with a small concentration of extractant and because of the absence of macro-concentrations of uranyl ion. Distribution ratios relevant to the flowsheet are shown in previous tables, IV, V, VI, and VII and figures 1 and 2. One of the key features of the flowsheet is that plutonium is extracted from the feed solution and stripped from the organic phase without the addition of any nitric acid or use of ferrous sulfamate. However, oxalic acid is added to complex Zr and Mo (see Table IV). The presence of oxalic acid reduces any Np(VI) to Np(IV) (15). The presence of ferrous ion, which is... 

NO. However, ferrous sulfamate adds some undesirable inorganic salts to the aqueous high-level waste. 

The Purex process, ie, plutonium uranium reduction extraction, employs an organic phase consisting of 30 wt % TBP dissolved in a kerosene-type diluent. Purification and separation of U and Pu is achieved because of the extractability of U02+2 and Pu(IV) nitrates by TBP and the relative inextractability of Pu(III) and most fission product nitrates. Plutonium nitrate and U02(N03)2 are extracted into the organic phase by the formation of compounds, eg, Pu(N03)4 -2TBP. The plutonium is reduced to Pu(III) by treatment with ferrous sulfamate, hydrazine, or hydroxylamine and is transferred to the aqueous phase U remains in the organic phase. Further purification is achieved by oxidation of Pu(III) to Pu(IV) and re-extraction with TBP. The plutonium is transferred to an aqueous product. Plutonium recovery from the Purex process is ca 99.9 wt % (128). Decontamination factors are 106 — 10s (97,126,129). A flow sheet of the Purex process is shown in Figure 7. 

Ferrous sulfamate [SULFAMIC ACID AND SULFAMATES] (Vol 23) use m chemical reprocessing of nuclear fuel [NUCLEARREACTORS - CHEMICALREPROCESSING] (Vol 17)... 

As a consequence, whereas NaN02 was employed for feed adjustment of the reprocessing solution in the earlier plants, N204 is being used increasingly for this purpose today. Similarly, in the partitioning cycle, U(IV) has replaced ferrous sulfamate. The... 

Tljie U-Pu separation is bas d on the much lower extractability of Pu3 ions by TBP than of Pu ions and the relative ease of oxidation and reduction of+plutonium in solutions. The original Pur x process utilized Fe2 to achieve the reduction of Pu1 to Pu. Since nitrite ions, whjch are generally present in nitric acid solutions, reoxidize Pu3 and thus affect the net reduction rate, a "holding reductant" is added to scavenge nitrite ions. Sulfamate ion, NH2S03 is an effective holding reductant and this led to the selection of ferrous sulfamate, Fe(NH2S03)2as the... 

In the Purex process, plutonium and uranium are coextracted into an organic phase and partitioned by reducing plutonium(IV) to the aqueous-favoring plutonium(III). This has been achieved chemically by use of a suitable reductant such as ferrous sulfamate ( 1) or uranium(IV). (2, 3, 4, 5) The use of ferrous sulfamate results in accelerated corrosion of the stainless steel, due to the presence of ferric ions and sulfuric acid, and in an increase in the volume of wastes. The use of natural uranium(IV) can cause dilution of the 235U in slightly enriched uranium, thus lowering the value of the recovered uranium. 

In the sixties hydrazine stabilized U(IV) solutions, electrochemically produced, successfully substituted the traditional corrosive and salt generating ferrous sulfamate C5) reducing agent for the U/Pu separation (e.g. Eurochemic in Mol, Karlsruhe Reprocessing Plant WAK). 

Therefore, many alternatives for the ferrous sulfamate reduction method have been studied(1,2,3) besides, the use of U(IY) as the reductant has actually found some practical application. Since U(IY) is being prepared by means of electrolytic reduction of U(VI)t it is natural to go a step further, namely, to introduce electrolytic reduction to the process stream itself. In such an in-sltu electrolytic process, not only P(IY) would be expected to be directly reduciable to Pu(III), but any U(IY) formed would also be expected to serve as the reductant for Pu(IV). 

The feed solution (3AF) was treated with ferrous sulfamate (FeSA) to reduce Pu to Pu(III) and FeSA was also added with the scrub stream (3AS) to reduce any Pu(IV) formed in the scrub section. The concentration of FeSA in both solutions was 0.05 mol/L and both were stabilized with 0.05 mol/L sulfamic acid. 

Successful partitioning of Pu(III) from Th was achieved when ferrous sulfamate was used as the Pu-holding reductant. 

Plutonium in this feed solution is removed by an anion exchange column process. The anion exchange resin is Dowex 1-X4, 50 to 80 mesh nitrate form, obtained from Bio-Rad Laboratories. Ferrous sulfamate is added to the solution to eliminate hexavalent plutonium, and the feed is passed through the column. The ion column effluent (ICE) contains the americium and impurities. Residual americium and impurities are washed from the column with 7M HNO3 anc t 1e was s combined with the ICE this is the feed to the bidentate process. A typical composition in g/1 is Am, 0.15 Pu, 8.2 x 10 3, Al,... 

Ferrous sulfamate has been the reductant for plutonium during partitioning of uranium and plutonium in the Purex process at SRP since startup. In recent years, a desire to reduce waste volumes has led to studies of alternative reductants or combinations of FeSA with other reductants. The FeSA in the Pu strip solution produces Fe(OH) 3 and Na2S0i in neutralized waste these compounds account for a large percentage of the solid material in Purex low activity waste. In an effort to reduce these wastes, we investigated HAN as a substitute for part or all of the FeSA in the Purex first cycle. 

Figure 6. Aqueous Pu with mixtures of ferrous sulfamate and hydroxylamine...

Solvent from contactor I containing uranyl nitrate and Pu(N03)4 is fed to the center of contactor II. This is refluxed at one end by clean solvent and at the other by a dilute nitric acid solution of a reducing agent strong enough to reduce plutonium to the trivalent form, but not so strong as to reduce uranium from the hexavalent form. Ferrous sulfamate is frequently used. In contactor II plutonium is transferred to the aqueous phase, while uranium remains in the solvent. Solvent from contactor II is fed to one end of contactor III, which is stripped at... 

In the partition contactor, plutonium was converted to inextractable, trivalent Pu (N03)3 by a reductant solution of ferrous sulfamate containing aluminum nitrate to keep uranium in the hexone phase. Plutonium was thus separated from uranium and transferred back to the aqueous phase along with the aluminum nitrate. Impure plutonium nitrate was purified by additional cycles of solvent extraction, not shown. 

Purex plant. Reprocessing was first done by the bismuth phosphate process, operational in 1944. Ferrous sulfamate. 

Also processed 93% at reduced rate and lower v/o TBP. U(1V), tetravalent uranium FeSAm, ferrous sulfamate. 

Reduction with ferrous ion was the reaction used in the first Purex flow sheets, at Hanford and Savannah River. The specific reductant used was ferrous sulfamate Fe(S03NHj)j, a compound selected because it stabilized ferrous ion against oxidation in a nitric acid-nitrous acid system. The process was satisfactory in all respects except its addition of extraneous, nonvolatile components to the wastes. 

In the IB column remaining traces of plutonium are stripped from the solvent by a strippant IBX, stream 10, containing hydrazine as holding reductant. A decontamination factor of 200 for removal of plutonium from uranium is anticipated for the IB columns. The big advantage of this partitioning system is that it adds no nonvolatile materials such as ferrous sulfamate to the system. 

In the scrubbing section of the HA column, fission products were scrubbed from the organic phase leaving the extraction section by the HAS scrub stream. It contained 0.01 Af H3PO4 to complex protactinium and zirconium-niobium and reduce their extraction. It also contained 0.01 Af ferrous sulfamate to reduce plutonium and chromium corrosion product to inextractable species. 

The second part of Table 10.22 gives equations for the concentration ratio of tetravalent to pentavalent neptunium calculated for the three reductants listed there. In the older Purex plants the ferrous sulfamate used to reduce plutonium to inextractable Pu reduced neptunium partly to inextractable Np(V) and partly to extractable Np(IV). The reductants now preferred, tetravalent uranium (possibly made electrolytically) or hydroxylamine, are sufficiently strong, in sufficient time, to make neptunium almost completely tetravalent, but the reactions are much slower than reduction of tetravalent plutonium, because of slow deoxidation of the NpOj radical. Kinetics of these reductions are also discussed in Sec. 7.5. 

Hanfoid [D3]. Nitrite concentration in feed to the HA column of a standard Purex plant was adjusted to route most of the neptunium in inadiated natural uranium into the extract from the HS scrubbing column. Sufficient ferrous sulfamate was used in the partitioning column to reduce neptunium to Np(IV), which followed uranium. This neptunium was separated from uranium by fractional extraction with TBP in the second uranium cycle. The dilute neptunium product was recycled to HA column feed, to build up its concentration. Periodically, irradiated uranium feed was replaced by unirradiated uranium, which flushed plutonium and fission products from the system. The impure neptunium remaining was concentrated and purified by solvent extraction and ion exchange. 

The extraction of 237Np involves similar principles of adjustment of oxidation state and solvent extraction Pu is reduced by ferrous sulfamate plus hydrazine to 11 nextractable Pu111, while Nplv remains in the solvent from which it is differentially stripped by water to separate it from U. 

This principle of oxidizing and reducing plutonium at various stages of the purification scheme has been retained in all subsequent processes. No other element has the same set of redox and chemical properties as plutonium, though some elemoits behave as Pu (o. g-the lanthanides), some like Pu (e,g. zirconium) and some like PuO (e.g. uranium). Numerous redox agents have been used, e.g. K2Cr20y (to PuC " ), NaN02 (to Pu " "), hydrazine, ferrous sulfamate, and U (to Pu "), cf. 16.3. 

---