The influence of calcium, sodium and bicarbonate on the uptake of uranium onto nanoscale zero-valent iron particles

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Vol. 277; pp. 252 - 259
• Main Authors: Crane, Richard A., Pullin, Huw, Scott, Thomas B.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.10.2015
• Subjects: Bicarbonate; Calcium; Mine water; Nanoscale zero-valent iron particles; Remediation; Uranium; Nanoscale zero-valent iron particles; Bicarbonate; Uranium; Remediation; Calcium; Mine water
• ISSN: 1385-8947; 1873-3212
• DOI: 10.1016/j.cej.2015.03.085

•We test the influence of Na, Ca and HCO3− on U removal onto nZVI.•Ca, Na and HCO3− did not significantly inhibit initial U removal onto nZVI.•Ca-bearing systems exhibited partial U desorption concurrent with nZVI oxidation.•Ca-absent systems exhibited no U desorption concurrent with nZVI oxidation.•Ca has a significant inhibitive influence on the long-term retention of U on nZVI. This work investigates the influence of calcium (Ca), sodium (Na) and bicarbonate (HCO3−) on the uptake of uranium (U) onto nanoscale zero-valent iron particles (nZVI). Solutions tested contained U at 1mg/L, NaHCO3 ranging from 0 to 100mg/L and CaCl2 or NaCl ranging from 625 to 719mg/L to normalise the ionic strength. Mine water containing a similar concentration of U (1.03mg/L) and HCO3− at 845mg/L was also tested as a natural analogue. All solutions were stored in sealed glass jars in the open laboratory with headspace comprising ambient air. Results demonstrate Ca, Na and HCO3− as having no significant inhibitive influence on the efficacy of nZVI for initial U removal from solution, with ⩾95.7% uptake recorded for all systems studied after 0.5h reaction. Similar U retention (>97.1%) was recorded throughout the entire 672h experiment for all solutions with Ca absent. In contrast, partial U desorption in the latter stages of the experiment was recorded for all solutions with Ca present, with 87.3%, 85.2% and 84.7% removal recorded after 672h for solutions containing 0, 10 and 100mg/L HCO3−, respectively, and 10.9% removal recorded for the mine water. Maximum U removal onto nZVI was recorded as directly proportional to HCO3− concentration for solutions with Ca absent, however, no trend was identified for the Ca-bearing solutions. Overall results demonstrate Ca as having a significant inhibitive influence on the long-term retention (e.g. >48h) of U on nZVI, which is independent of HCO3− concentration when also present at <100mg/L.