The third phase formation of neodymium (III) and nitric acid in N,N-di-2-ethylhexyl-N',N'-di-octyl-3-oxapentane-1,5-diamide (DEHDODGA) was studied. The limiting organic concentration (LOC) and critical aqueous concentration (CAC) of nitric acid and neodymium (Ill) were determined as a function of various parameters such as aqueous phase acidity, extractant concentration, temperature and the nature of diluent. The influence of phase modifier, N,N-di-hexyloctanamide (DHOA) on the third phase formation behaviour was studied at different temperatures. The LOC of Nd (III) in a solution of DEHDODGA in n-dodecane (n-DD) increased with increasing temperature, concentrations of extractant and phase modifier, and decreased with increase of aqueous phase acidity and alkyl chain length of the diluent. The concentration of DHOA needed to prevent the third phase formation during minor actinide partitioning from high-level liquid waste was optimised. (C) 2011 Elsevier B.V. All rights reserved.