A thermodynamic model for the solubility of HfO2(am) in the aqueous K + – HCO3 − – CO3 2 − – OH − – H2O system

Abstract

Abstract Solubility of HfO2(am) was determined as a function of KHCO3 concentrations ranging from 0.001 mol·kg−1 to 0.1 mol·kg−1. The solubility of HfO2(am) increased dramatically with the increase in KHCO3 concentrations, indicating that Hf(IV) makes strong complexes with carbonate. Thermodynamic equilibrium constants for the formation of Hf-carbonate complexes were determined using both the Pitzer and SIT models. The dramatic increase in Hf concentrations with the increase in KHCO3 concentrations can best be described by the formation of Hf(OH−)2(CO3)2 2− and Hf(CO3)5 6−. The log10 K 0 values for the reactions [Hf4++2CO3 2−+2OH−⇌Hf(OH)2(CO3)2 2−] and [Hf4++5CO3 2−⇌Hf(CO3)5 6−], based on the SIT model, were determined to be 44.53±0.46 and 41.53±0.46, respectively, and based on the Pitzer model they were 44.56±0.48 and 40.20±0.48, respectively.