Influence of Phosphate and Silica on U(VI) Precipitation from Acidic and Neutralized Wastewaters

详细信息    查看全文

• 作者：Masakazu Kanematsu ; Nicolas Perdrial ; Wooyong Um ; Jon Chorover ; Peggy A. O鈥橠ay
• 刊名：Environmental Science & Technology
• 出版年：2014
• 出版时间：June 3, 2014
• 年：2014
• 卷：48
• 期：11
• 页码：6097-6106
• 全文大小：562K
• 年卷期：v.48,no.11(June 3, 2014)
• ISSN：1520-5851

文摘

Uranium speciation and physical鈥揷hemical characteristics were studied in solids precipitated from synthetic acidic to circumneutral wastewaters in the presence and absence of dissolved silica and phosphate to examine thermodynamic and kinetic controls on phase formation. Composition of synthetic wastewater was based on disposal sites 216-U-8 and 216-U-12 Cribs at the Hanford site (WA, USA). In the absence of dissolved silica or phosphate, crystalline or amorphous uranyl oxide hydrates, either compreignacite or meta-schoepite, precipitated at pH 5 or 7 after 30 d of reaction, in agreement with thermodynamic calculations. In the presence of 1 mM dissolved silica representative of groundwater concentrations, amorphous phases dominated by compreignacite precipitated rapidly at pH 5 or 7 as a metastable phase and formation of poorly crystalline boltwoodite, the thermodynamically stable uranyl silicate phase, was slow. In the presence of phosphate (3 mM), meta-ankoleite initially precipitated as the primary phase at pH 3, 5, or 7 regardless of the presence of 1 mM dissolved silica. Analysis of precipitates by U L_III-edge extended X-ray absorption fine structure (EXAFS) indicated that 鈥渁utunite-type鈥?sheets of meta-ankoleite transformed to 鈥減hosphuranylite-type鈥?sheets after 30 d of reaction, probably due to Ca substitution in the structure. Low solubility of uranyl phosphate phases limits dissolved U(VI) concentrations but differences in particle size, crystallinity, and precipitate composition vary with pH and base cation concentration, which will influence the thermodynamic and kinetic stability of these phases.