δ238U of Coal Reference Materials Determined by MC-ICP-MS

Uranium (U) associated with coal can be an important source of U and result in environmental pollution during coal combustion. In this study, we developed a method for measurement of U isotope ratios in coals using multiple-collector inductively coupled plasma-mass spectrometry. The ²³³U-²³⁶U double-spike was utilised to calibrate the instrumental isotopic fractionation. High-pressure bomb and dry ashing were adopted to digest the coal samples. The δ²³⁸U_CRM-145 values obtained from the two different digestion procedures were in good agreement. The δ²³⁸U_CRM-145 of seven coal and one fly ash reference materials are reported. Furthermore, the results of fly ash, bottom ash and feed coal samples reveal that the combustion processes lead to relatively small U isotopic fractionation between the samples within the same coal-fired power plant, indicating that U isotope data can be used as a tracer for heavy metal pollution resulting from coal combustion. The U isotope measurement method of coal established in this study provides technical support to understand the behaviour of U during coal formation and combustion.