Special campaigns for recovering neptunium from Purex solutions have been run at Oak Ridge [F4], Hanford [D3], Savannah River [P7], Windscale [Nl], and Marcoule [С6]. None of these sought complete recovery. A brief description will be given of the first three.

Oak Ridge [F4]. The solution obtained by dissolving irradiated, natural uranium in nitric acid was treated with 0.01 M NaN02 to convert most of the neptunium to extractable Np(VI) in 2 M HN03. In the first Purex cycle, 90 percent of the neptunium was extracted with the uranium and plutonium. Ferrous sulfamate used in the partitioning step reduced most of the neptunium to Np(V) and Np(IV), which followed Pu(III) into the aqueous phase, but some Np(IV) remained with the uranium. When the aqueous phase containing Pu(III) and most of the neptunium was reoxidized with HNO3 and NaN02 and extracted with TBP in the second cycle, from one-half to two-thirds of the neptunium was recovered with the plutonium, from which the neptunium was separated by anion exchange. The process produced 99.9 percent pure neptunium, but the recovery was incomplete and very sensitive to nitrite and nitric acid concentrations.

Hanford [D3]. Nitrite concentration in feed to the HA column of a standard Purex plant was adjusted to route most of the neptunium in irradiated 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.

Savannah River [Р7]. At the Savannah River Purex plant, neptunium in irradiated natural uranium was recovered by the alternative method of forcing most of it into the aqueous waste stream HAW from the first extraction cycle and then recovering it from waste directly by anion exchange. Neptunium in the first extraction step was converted mostly to the inextractable pentavalent state by adding sufficient nitrite to the next-to-the-last mixer-settler stage of the HA section to make the solvent 0.007 M in HNOj.