Interactions of 2,2′-bipyridine herbicide intermediate with humic acid

Abstract

Abstract The binding of the neutral 2,2′-bipyridine (BP) molecule to solid humic acid (HA) was studied in the presence of CaCl2 background electrolyte (10-2 mol/l), at pH=6.1–6.3. To investigate the binding, two different methods were used: the well-established static adsorption equilibrium measurements and the technique of equilibrium dialysis (ED). The obtained isotherms were fitted by the Langmuir equation, yielding values for the total binding capacity (qT) and the Langmuir constant (K). The values obtained from the batch experiment were: qT=3.3×10-4 mol/gHA, K=4.1×102 l/mol and from the ED experiment were: qT=5.7×10-4 mol/gHA, K=2.8×102 l/mol. From the linear range of the isotherm, the value of the distribution coefficient KD was calculated as 3.3×102 l/kgHA (by both methods). This parameter was used to calculate the value of KOC: 6.6×102 l/kgOC, indicating that BP is a slightly mobile pollutant in the HA dominated soil.