Uranium and Thorium in zircon sands processed in Northeastern Brazil

Zircon the main mineral of zirconium is a silicate mineral product (ZrSiO4) obtained from beach sand deposits, along with other minerals such as kyanite, ilmenite, and rutile. All zircons contain some radioactive impurities due to the presence of uranium, thorium and their respective decay products in the crystalline structure of zircon, as well as potassium-40. Uranium and thorium substitute Zr4+ in the mineral through an internal process called isomorphous replacement of zirconium. For this study, samples were collected both from a mineral sand processing plant located in the coastal region of Northeastern brazil and from the beach sands used in the process. The aim of this study was to assess the 238U, 232Th and 40K contents in the beach sands and in the mineral products extracted from the sands in that facility, with special emphasis on zircon. Measurements were performed through gamma spectrometry, by using a high-purity germanium detector (HPGe) coupled to a multichannel analyzer. Activity concentration for 238U and 232Th in zircon sands ranged from 5462±143 to 19286±46 Bq kg-1 and from 1016±7 to 7162±38 Bq kg-1, respectively. For 40K, on the other hand, activity concentration values ranged from 81±14 to 681±26 Bq Kg-1. The results of the measurements carried out for raw sand samples showed activity concentrations between 2.7±0.6 and 7.9±0.9 Bq kg-1 and 6.5±0.4 and 9.4±0.6 Bq kg-1 for 238U and 23Th respectively, and from 48.8±3.1 to 76.1±2.4 Bq kg-1 for 40K. Activity concentrations of 238U and 232Th in kyanite, ilmenite and rutile samples were also determined. (author)