Probing Trace-elements in Bitumen by Neutron Activation Analysis

Abstract

Trace elements and their concentrations play an important role in both chemical and physical properties of bitumen. Instrumental Neutron Activation Analysis (INAA) has been applied to determine the concentration of trace elements in bitumen. This method requires irradiation of the material with neutrons that transform the elements into radioactive isotopes. By analyzing the activity of the individual nuclides, the concentration of each detectable trace element can be determined with high precision. In this work, we perform trace elemental analyses of 13 distinct bitumens, including 2 modified and 3 bitumens from the material library of Strategic Highway Research Program (SHRP. Three elements, vanadium, nickel and cobalt are found to be present in all bitumens. Vanadium and nickel are found to be the most abundant among all the elements detected. Next to vanadium and nickel, significant concentrations of iron are found in 11 bitumens. The total number of trace elements identified varied from 17 to 28 for the bitumens studied. For modified bitumens, the concentration of trace elements is used as a parameter to measure the extent of modification. The sum of most abundant trace elements (vanadium and nickel) correlates well with the sulphur and asphaltene contents of the same bitumen. Moreover, the concentration of the latter metals are known to be an indicator for the aging characteristics of bitumen. Thus, INAA provides the content of trace elements in bitumen, where the concentrations vary (ppm to ppb) depending on the crude origin of the material. Thus, INAA can be used to trace back the crude origin of the material, which may have applications in the field of asphalt recycling (RAP and RAS).