Analysis of uranium in the insoluble residues after decomposition of soil samples by various techniques

•Various most often used dissolution techniques for soil samples were investigated.•Conventional wet ashing, microwave dissolution and alkaline fusion were tested.•The residues obtained after dissolution were tested for uranium content.•Instrumental neutron activation analysis was used for uranium determination.•The results showed that the tested dissolution techniques must be improved.

A comparison of different dissolution techniques for determination of uranium in soil samples was made. Conventional wet dissolution with mixtures of HNO3, HClO4 and HF acids, microwave dissolution using HNO3 and HF, and alkaline fusion with Na2CO3 and Na2O2 were evaluated. For testing the effectiveness of the dissolution procedures, two reference materials and six soil samples from the surroundings of a former uranium mine were investigated. It was observed that the content of uranium in the residues determined by INAA represents a significant contribution to its total concentration in the sample, especially in the case of microwave dissolution.