Strontium and calcium complexation by humic acid

The binding of strontium by humic acid was studied in systems designed to m odel soil leaching conditions. Ultrafiltration experiments were conducted f or a wide range of CaCl and NaCl concentrations and for the pH range 4 to 7 . It was found that the recovery of humic acid slowly decreased with increa sing pH. This occurred because at neutral and basic solutions the increasin g degree of ionization of the carboxylate groups leads to the full repulsio n state of the humic acid and to increasing of the strontium binding (stron tium recovery similar to 60% at pH 7) with this natural polyelectrolyte. Th e strontium complexation in the presence of calcium was studied in differen t series of metal concentrations at pH 5 and the ionic strength 0.1M NaCl. The results were explained on the base of the metal ion charge neutralizati on model of humic complexation (CNM). Loading capacity (cca 40%) and comple xation constants and Sr (3.51+/-0.27) and Ca (3.10+/-0.29) with Aldrich hum ic acid were found.