China Nonferrous Metallurgy

Low-radioactivity alumina is highly demanded in high-end applications. However, the emerging synthetic route using 4 N high-purity aluminum (with extremely low radionuclide content) as feedstock leads to a remarkable increase in production cost. In this work, low-α alumina was prepared from ordinary industrial aluminum hydroxide via a combined process: hydrothermal synthesis of boehmite, acid leaching for removal of radioactive elements, and high-temperature calcination. The process was optimized, and the products were systematically characterized. The maximum specific surface area and pore volume of boehmite were achieved at a hydrothermal temperature of 200℃ for 2 h. Grinding pretreatment destroyed the agglomerate structure of aluminum hydroxide, exposing the encapsulated radioactive elements, which facilitated the efficient removal of Th, U and other impurities in the subsequent hydrothermal process. Acid neutralization converted the entrapped U and Th in the boehmite precursor into soluble ions. After acid leaching with 10% HCl for 2 h and calcination at 1 250℃ for 2 h, the contents of Th and U in the product were both below 10 ppb(10^-9), the Na₂O content was only 0.006%, and the α-phase conversion ratio exceeded 90%. Using industrial aluminum hydroxide as raw material, high-performance low- α alumina satisfying high-end application requirements was obtained via the grinding-hydrothermal-acid washing-calcination process. This strategy breaks the dependence on high-purity feedstocks for low-α alumina production, and significantly reduces the manufacturing cost.