The Self-Ignition Temperatures of Bitumen Mixtures Containing Transition Metal Nitrates

Abstract

Information is provided on the self-ignition temperature (SIT) of blown bitumen asphalt mixed with sodium nitrate and some chemicals that are added in the bituminization process to adjust pH and to immobilize the radioactive isotopes of Cs, Sr, and I. In each ignition temperature test, the prepared bitumen sample was heated at a constant rate of temperature increase, and the ignition point was measured. Among the tested chemicals added to the bitumen, Ni(NO₃)₂ shows a relatively large SIT decrease, and furthermore, the mixture of Ni(NO₃)₂ and AgNO₃ has been shown to greatly lower the SIT of blown bitumen. It is suggested that, in general, segregation of these nitrates should be avoided in bituminization, and care should be taken in handling Ag in a Purex reprocessing plant from the viewpoint of waste treatment. Furthermore, the oxidation effects of Fe(NO₃)₃ were tested by measuring torque of the bitumen sample. It was confirmed that the addition of Fe(NO₃)₃ to bitumen rapidly oxidizes the bitumen and increases the viscosity of the bitumen mixture.