Pure zircon process for removing radionuclides from zircon concentrates

Abstract

The presence of U and Th as impurities in zircon makes it radioactive. Provided the U and Th levels are below 500 ppm, or 70 Bq g^-1 activity, the limits that allow transportation of the material as a non-radioactive substance, it is acceptable as a commercial product. However, some zircon sands contain radioactivity levels well above this limit. A new process (the pure zircon process) is described for the removal of radioactivity from zircon. Tests to identify the best flux addition, calcination temperature and time, and leaching conditions indicated that by grinding a zircon sample containing 1059 ppm U + Th to a particle size of about 15–20 μm, calcining it with 15 wt-% calcium borate (colemanite) at 1200°C for 4 h and leaching the calcine with up to 1M HCl at 80°C for 30 min gave a product with <500 ppm U + Th. While the grade of Zr of the final product was slightly increased, the levels of major impurities, Al, Fe, Ti and P were decreased. Operating costs for the pure zircon process using the optimum conditions were estimated to be A$243/t leach product.