The paper discusses a newly-designed fluoride-nitric acid pattern for plumbomicrolite concentrate (PMC) processing, focusing on distribution of radionuclides in individual process stages. It is shown that under optimal conditions of PMC decomposition the bulk of radionuclides (mostly thorium) remains in the undigested residue. The method involves purifying of solution from radionuclides and lead before solvent extraction aimed at isolating the high-purity tantalum compounds. Radiological investigation of tantalum pentoxide samples has been carried out.