Leaching Process of Uranium in Waste Residue by Chloride Roasting

• Published in: Yuanzineng kexue jishu Vol. 57; no. 4; pp. 828 - 836
• Main Author: FAN Shiyao;ZHANG Cong;LEI Zhiwu;HU Eming;WANG Hongqiang;HAO Xuanzhang;HU Fang;WANG Qingliang
• Format: Journal Article
• Language: English
• Published: Editorial Board of Atomic Energy Science and Technology 01-04-2023
• Subjects: chlorination roasting; slag; uranium
• ISSN: 1000-6931

For a uranium purification enterprise in the south of China, the waste residue (uranium grade 12000%), which is a mixture of rubble from the extraction in the purification system and other wastewater passing through the plate and frame after resting, has a complex composition, with the presence of diatomaceous earth as a filter aid in addition to the impurities such as acidic solids and organic matter produced in the uranium leaching process. The conventional natural treatment method has a poor leaching effect and a low uranium recovery rate with nitric acid heating. To this end, low-temperature chlorination roasting nitric acid leaching study was conducted, in which sodium chloride was added to the specimen for roasting pretreatment. Then the roasted model was leached using nitric acid. The effects of roasting temperature, sodium chloride addition, roasting time, sample size and other influencing factors on the leaching behavior of uranium were investigated. The experimental results show that the uranium leaching rate reaches 95.97% under the conditions of 20% NaCl addition, 200 ℃ roasting temperature, 2 hour roasting time, 7.4 mol/L nitric acid concentration, 80 ℃ leaching temperature and 2 hour leaching time, which is 19.52% higher than that of the conventional acid leaching process. The results show that the waste slag’s specific surface area and porosity increase significantly after pretreatment with sodium chloride roasting, which promots the dissociation of uranium and increased the contact area between uranium and acid, thus leading to a significant increase in the uranium leaching rate. And the chlorination roasting can have an activating effect on the metal components in the specimen. It can play a role in screening some oxides, such as silica, iron oxide, etc. Combined with the specimen’s physical and chemical composition analysis, it is due to the formation process of the illustration mixed with iron-containing flocculants, binders, and other substances to form uranium wrapping. At the same time, the chlorine and hydrogen chloride gas generated by sodium chloride roasting can be part of the iron components chlorinated into ferric chloride, and with the iron oxide in the process of confinement due to chemical gas phase migration reaction to generate chloride, which not only to uranium wrapping structure. This not only causes damage to the uranium wrapper structure, which allows more exposure of the uranium component but also has a catalytic effect on the uranium leaching process, which leads to a significant increase in the leaching rate of uranium. At the same time, because solid sodium chloride is used, the roasting conditions are relatively mild, and therefore the generation of contaminating gases is within the control range.