Separation of Thorium from Zirconium Carbide Waste by Liquid–Liquid Extraction Using Tri‑n‑octylamine Solvent after Selective Acid Leaching

• Published in: Industrial & engineering chemistry research 2020-11, Vol.59 (47), p.20866-20876
• Main Authors: Baghalian Nejad, Reza, Amini, Mohammad K, Ghaziaskar, Hassan S
• Format: Article
• Language: English
• Subjects: Separations
• ISSN: 0888-5885; 1520-5045
• DOI: 10.1021/acs.iecr.0c04486

Separation of thorium from zirconium carbide waste is reported. The waste typically contains zirconium, yttrium, uranium, and thorium, along with other impurities including rare earth elements (REEs), iron, calcium, aluminum, hafnium, and titanium. The first step in the separation was selective leaching of zirconium, uranium, and most other impurities with HNO3–HF, leaving thorium and REEs as insoluble fluorides. The effective parameters such as HNO3 and HF concentrations, temperature, and time were optimized for achieving the maximum leaching of zirconium and the minimum leaching of thorium, using central composite design and a multiple response optimization algorithm. Thorium and REEs were leached from the residual solid with H2SO4, followed by their precipitation with ammonia, dissolution of the precipitate in HNO3, and extraction of thorium with tri-n-octylamine–kerosene. The factors affecting the extraction of thorium were optimized with respect to HNO3, TOA, diluent, V org/V aq, and extraction time. Using the above sample preparation and extraction methods, thorium could be extracted with an efficiency of 95.6%.