biostudies-literatureVelasco CANational Institute of Environmental Health SciencesNIEHS NIH HHSDivision of Chemical, Bioengineering, Environmental, and Transport SystemsDirectorate for Education and Human Resources16246-16256https://www.ebi.ac.uk/biostudies/studies/S-EPMC8680647biostudies-literatureUnknown55(23)We investigated interfacial reactions of U(VI) in the presence of Suwannee River natural organic matter (NOM) at acidic and neutral pH. Laboratory batch experiments show that the adsorption and precipitation of U(VI) in the presence of NOM occur at pH 2 and pH 4, while the aqueous complexation of U by dissolved organic matter is favored at pH 7, preventing its precipitation. Spectroscopic analyses indicate that U(VI) is mainly adsorbed to the particulate organic matter at pH 4. However, U(VI)-bearing ultrafine to nanocrystalline solids were identified at pH 4 by electron microscopy. This study shows the promotion of U(VI) precipitation by NOM at low pH which may be relevant to the formation of mineralized deposits, radioactive waste repositories, wetlands, and other U- and organic-rich envEnvironmental science & technologyFrom Adsorption to Precipitation of U(VI): What is the Role of pH and Natural Organic Matter?PMC868064719144901652619P42 ES025589R01 ES027145R01ES0271451 P42 ES025589Gonzalez-Estrella JMeza MIThomson BMForbes TZVelasco CAAli ASCerrato JMBrearley AJLezama Pacheco JSCabaniss SEfalseFrom Adsorption to Precipitation of U(VI): What is the Role of pH and Natural Organic Matter?We investigated interfacial reactions of U(VI) in the presence of Suwannee River natural organic matter (NOM) at acidic and neutral pH. Laboratory batch experiments show that the adsorption and precipitation of U(VI) in the presence of NOM occur at pH 2 and pH 4, while the aqueous complexation of U by dissolved organic matter is favored at pH 7, preventing its precipitation. Spectroscopic analyses indicate that U(VI) is mainly adsorbed to the particulate organic matter at pH 4. However, U(VI)-bearing ultrafine to nanocrystalline solids were identified at pH 4 by electron microscopy. This study shows the promotion of U(VI) precipitation by NOM at low pH which may be relevant to the formation of mineralized deposits, radioactive waste repositories, wetlands, and other U- and organic-rich env2021-01-01T00:00:00Z2021 Dec2026-05-09T06:16:26.149Z2022-02-11T14:04:10.56ZS-EPMC86806473479704610.1021/acs.est.1c05429