Kinetics of americium(III) extraction and back extraction with BTP

2,6-Di(5,6-dipropyl-1,2,4-triazin-3-yl) pyridine (BTP) extracts trivalent actinides from nitric acid with high separation factors over the lanthanides. The kinetics of americium(III) extraction and back extraction of this extraction system was studied in a constant-interface stirred cell. The americium( III) extraction rate was found to be independent of the stirring speed. This means that the rate of mass transfer is limited by a slow chemical complexation reaction (chemical regime). The americium( III) extraction rate was found to increase linearly with BTP concentration. Nitric acid concentration had a strong influence on the rate of the americium( III) extraction, due to its influence on the free extractant concentration. The addition of ammonium nitrate did not affect the rate of americium( III) extraction. By investigating the influence of the interfacial area on the americium( III) extraction rate, the interface was identified as the site of the chemical reaction. The americium( III) back extraction rate increased linearly with the stirring speed, indicating that the back extraction is limited by diffusion. The extraction and the back extraction rates could be calculated by a simple model based on equilibrium data for the co-extraction of americium( III) and nitric acid.