Ultra-low-radioactive titanium is the main perspective material for cryostat fabrication in dark matter search experiments. The pathways of the uranium and thorium contamination of Ti sponges produced by the Kroll process were analyzed. The general role of Mg in Ti sponge contamination by U and Th was established. It was found that when transformed to MgCl2 in the Kroll process, Mg was purified from U and Th, and further MgCl2 reduction and sublimation makes it possible to produce low-radioactive Ti sponges.
Keywords: Kroll process; inductively coupled plasma mass spectrometry; magnesium; pure substance; vacuum sublimation.