LAUSR

The solubility of amorphous zirconium hydroxide [Zr(OH)4(am)] was investigated in carbonate solutions containing various concentrations of sodium nitrate. The observed dependences of Zr(IV) solubility on the hydrogen ion concentration (pHc) and carbonate concentration suggested the formation of $$ {\text{Zr}}({{\text{CO}}}_{3} )_{4}^{4 - } $$Zr(CO3)44-, $$ {\text{Zr}}({{\text{CO}}}_{3} )_{5}^{6 - } $$Zr(CO3)56-, and $$ {\text{Zr(OH)}}_{ 2} ( {{\text{CO}}}_{3} )_{2}^{2 - } $$Zr(OH)2(CO3)22- as the dominant species in the neutral to weakly alkaline pH regions. The solubility of Zr(IV) at certain pHc values and carbonate concentrations was observed to increase slightly with increasing ionic strength, while the solid phase was determined to be Zr(OH)4(am) at all ionic strengths by using thermal analysis. By applying the specific ion interaction theory, the solubility data at different pHcs, carbonate concentrations, and ionic strengths were analyzed to determine the formation constants of the Zr(IV) carbonate complexes and their ion interaction coefficients. The obtained values explain well the solubility data, which are discussed in comparison with those of analogous tetravalent actinide carbonates.