Extraction of Pu(Ⅳ) in Nitric Acid Medium With Di(1-Methyl-Heptyl)Methyl Phosphonate

The extraction behavior of Pu(Ⅳ) in HNO₃ medium with di(1-methyl-heptyl) methyl phosphonate(DMHMP) was studied. The effects of DMHMP concentration, NO^-₃ concentration, HNO₃ concentration and temperature on Pu(Ⅳ) distribution ratio were investigated. The complex formation of Pu(Ⅳ) with DMHMP is Pu(NO₃)₄·2DMHMP and the extraction reaction equation is determined as follows:
Pu⁴⁺_(a)+2DMHMP_(o)+4NO^-_3(a)   Pu(NO₃)₄·2DMHMP_(o)
Pu(Ⅳ) is formed neutral molecules with NO^-₃, which then combine with DMHMP to form a neutral complex and enter the organic phase. Pu(Ⅳ) distribution ratio is proportional to the square of DMHMP concentration and the fourth power of NO^-₃ concentration. The extraction reaction is exothermic, and the enthalpy of the reaction is -34.46 kJ/mol.