EFFECT OF PH ON STABILITY-CONSTANTS OF SR(II)-HUMATE COMPLEXES

The apparent stability constant, beta for the complexation of Sr(II) w ith humic acid (HA) was determined by a dialysis method in the pH rang e from 4 to 10 at the ionic strength of 0.1 mol/dm(3) (NaClO4) at 298 K under N-2 atmosphere. It was found that log beta increased with pH f rom 2.5 at pH 4.0 to 4.1 at pH 10.0. The log beta tended to level off at higher pHs, indicating that saturation; was being readied. Further, the apparent ligand to metal ratio was found to be 1.15+/-0.10. Disso ciation of carboxylic and phenolic groups of Hh with pH is probably th e main factor that gives rise to the changes in stability constants.