Radiolysis of di-2-ethylhexyl hydrogen phosphate and its toluene solutions

Abstract

The products of radiolytic decomposition of a 25% solution of di-2-ethylhexyl hydrogen phosphate in toluene and of the separate solution components in the dose range 0.10–5.00 MGy were studied by viscometry, pH-metry, and electronic spectrophotometry. The γ-ray radiolysis of this solution occurs via decomposition of the ester molecules by the free radical mechanism to form mono-2-ethylhexyl dihydrogen phosphate C8H17OP(O)(OH)2 (via cleavage of the C-O bond), orthophosphoric acid, and polymeric products. The kinetic scheme of the process is presented. Irradiation with doses of up to 0.80 MGy leads to the HDEHP dealkylation with the formation of C8H17OP(O)(OH)2 with the radiation-chemical yield G = 0.1 molecule/100 eV. At higher doses (2.50–5.00 MGy), orthophosphoric acid is formed with a yield G = 0.01 molecule/100 eV. In the dose range 0.80–5.00 MGy, the radiolytic decomposition of di-2-ethylhexyl hydrogen phosphate yields polymeric products, which is associated with insufficient radiation resistance of toluene and with the loss of its protective properties at high absorbed doses. The limiting absorbed dose at which the extractant is efficiently protected by toluene was estimated at 0.8 MGy. Aromatic additives (biphenyl, naphthalene, anthracene, etc.) are suggested for enhancing the extracting solvent performance. These additives are capable of scavenging charges of both signs; in addition, they exhibit higher radiation resistance compared to toluene. In their presence, it is possible to suppress the formation of both acidic esters and polymeric products in the extracting solvent.