Interaction of Microelements at Coprecipitation with Humic Acids

Through the example of the sorption-coprecipitation data for microelements simulating the corrosion, activation, and fission products, the nature of the isotherms of sorption of cations (M) by natural humic acids (HAs) was discussed. The dependence of the microelement distribution coefficient (K-d) on the ratio of the mass to volume of the HA solution in the 10-990 mg/L concentration range was associated with the occurrence of two parallel processes in the sorption system: competitive sorption of the M and Ca(II) ions by the HA precipitate and the formation of nonsorbable (K-d < 10 mL/g) complex of the M ion with high-molecular-weight organic compounds remaining in solution after HA precipitation. Optical spectroscopic data for the HA solutions and solutions above the solid HA precipitate revealed the presence of high-molecular-weight organic compounds in solution, as indicated by a maximum at 220 +/- 20 nm and a shoulder at 264 +/- 30 nm, characteristic for fulvic acids (FAs). A probable scheme of the interaction of the sorbate cations with the precipitate of HAs and their accompanying fulvic acid molecules was proposed. For the first time, removal of tritium (THO) from aqueous solutions by HA precipitates via isotope exchange reaction was reported.