Comparative Effects of Organic and Inorganic Ligands on Uranium Release from Uranophane Mineral

Zarina Salkenova^a, Bhupendra Kumar Singh^a,c, Wooyong Uma^a,b,c*

^aDivision of Advanced Nuclear Engineering (DANE), Pohang University of Science and Technology (POSTECH), 77 Cheongam-ro, Nam-Gu, Pohang, Gyeongbuk, 790-784, Republic of Korea
^bDivision of Environmental Sciences and Engineering (DESE), Pohang University of Science 4and Technology (POSTECH), 77 Chongam-ro, Nam-Gu, Pohang 790-784, Republic of Korea
^cNuclear Environmental Technology Institute (NETI), Pohang University of Science and Technology (POSTECH), Pohang, Gyeongbuk 790-784, Republic of Korea

Received 2025-02-03 ; Revised 2025-02-25 ; Approved 2025-03-13

Abstract

Uranium (U), an essential source for nuclear energy production, poses serious environmental and radiological threat due to its high mobility and long half-life. Uranophane [Ca(UO₂)₂SiO₃(OH)₂·5H₂O], a secondary U silicate mineral, is known as a solubility-limiting phase in U mining deposits and nuclear waste repositories (controlling U immobilization). However, research on uranophane dissolution, particularly under the influence of organic and inorganic ligands, remains lacking. This study investigates uranophane synthesis and its dissolution at pH 8 through batch experiments using organic ligands (citric acid (CA) and humic acid (HA) at 50–150 ppm) and inorganic ligands (carbonate, nitrate, chloride, and silicate at 10⁻⁴ M to 10⁻⁶ M). Obtained results suggested that CA and carbonate significantly enhanced U release, reaching 27.6 ppm. Mixed systems containing both organic (50–150 ppm CA) and inorganic (10⁻⁴ M carbonate) ligands revealed increased U release, however were less effective than single-ligand systems due to competitive interactions with carbonate dominating U speciation. Visual MINTEQ modeling was used to identify uranyl complex species in the solutions. Dissolution rate and kinetic modeling were determined to predict U release trends. These findings emphasize the role of various ligand types in nature and their impact on U mobility, aiding remediation strategies for contaminated environments.

Key Words : Uranium, Uranyl silicate minerals, Uranophane, Inorganic ligands, Organic ligands, Dissolution