ELECTROLYTE-MODIFIED PARTITION OF Cu IN A TERNARY SYSTEM CONTAINING HUMIC ACID

The fate of metals in the soil environment is directly related to their interaction and partitioning behavior in terrestrial environments. The effect of background electrolyte on the partitioning of Cu under humic conditions in soil-solution system was investigated and it was observed that increasing background electrolyte pushes humic acid (HA) aggregation through stages of thermodynamic non-spontaneous phase to an equilibrium phase and finally to a spontaneous aggregation stage. At pH 4.7 HA adsorption other than aggregation influences Cu distribution. And at pH 10 both HA adsorption and aggregation are responsible. It was noted that, the effect of background electrolyte concentration on Cu distribution is as a result of its ability to induce ligand aggregation, reduce metal ? ligand complexation, and initiate competition of electrolyte cation (K+) with the Cu for sorption sites in the soil. Modeling studies revealed that, metal adsorption and HA aggregation factors account for the modified partition by the electrolyte, and this accounts for 90.5% of the variables which modify Cu partition at pH 4.7, and 99.79% at pH 10. Factor analysis revealed that at pH 4.7 increasing electrolyte concentration decreases metal distribution in the system by reducing metal adsorption and decreasing metal ligand complexation. At pH 10 Cu adsorption factors accounts for only 14.83% of the processes influenced by electrolyte concentration, and aggregation factor accounts for 84.95%. Increasing electrolyte concentration essentially transfers Cu to the solution phase and HA the solid phase of the system.