Determination of 237Np in marine sediment and seawater

Procedures for determination of neptunium in marine sediment and seawater samples are described. Iron hydroxide Fe(OH)2-Fe(OH)3 is used for preliminary pre-concentration of neptunium. Secondly, neptunium Np4+ and Pu3+ are separated by tri-isooctylamine-(TIOA) extraction in 8-10M HCl by redox with SO32--Fe3+. Neptunium Np4+ and uranium U6+ are separated by back extraction the Np4+ with 2M HCl. Finally, the neptunium is purified from the uranium and thorium by anion exchange in 8M HNO3 and 12M HCl. The stripping of 6M HC1 + NH2OH·HCl further separates the neptunium Np3+ and uranium. Reduction by SO32--Fe3+ appeared to be an efficient way to obtain Np4+. The decontamination factors of the procedure are 4.0·104 for 232Th, 5.6·104 for uranium and 1.6·104 for plutonium.