The stability and solubility of UO2(OH)2 has been studied as a function of the humic acid concentration in 0.1M NaClO4, in the pH range from 4 to 7 under normal atmospheric conditions. The solid phase under investigation has been prepared by
alkaline precipitation and characterized by TGA, ATR-FTIR, XRD, SEM and solubility measurements. According to the experimental
data UO2(OH)2 is stable and remains the solubility limiting solid phase even in the presence of increased humic acid concentration in the
solution. However, humic acid affects texture and particle size of the solid phase. Increasing humic acid concentration results
in decreasing crystallite size of the UO2(OH)2 solid phase. Based on the solubility data, the logKsp(UO2(OH)2) has been evaluated to be −22.0±0.3 and the stability constant for the UO2(OH)HA(I) species has been estimated to be logβ1101 = 15.3±0.5.