Abstract
The apparent stability constant, β, for the complexation of Sr(II) with humic acid (HA) was determined by a dialysis method in the pH range horn 4 to 10 at the ionic strength of 0.1mol/dm3 (NaClO4) at 298K under N2 atmosphere. It was found that log β increased with pH from 2.5 at pH 4.0 to 4.1 at pH 10.0. The log β tended to level off at higher pHs, indicating that saturation was being reached. Further, the apparent ligand to metal ratio was found to be 1.15±0.10. Dissociation of carboxylic and phenolic groups of HA with pH is probably the main factor that gives rise to the changes in stability constants.