Kinetics of copper complexation with dissolved organic matter using stopped‐flow fluorescence technique

Abstract

This study provided direct observations on reaction kinetics of Cu and dissolved organic matter (DOM). Stopped‐flow method and fluorescence technique were used to measure Cu(II)‐DOM complexation over time. Suwannee River reference fulvic acid and water soluble soil organic matter were used as model DOM. Experimental conditions of pH 6, 5 × 10‐5 M Cu(II), and 5 mg C/L of DOM were used and the results were to simulate the relevant natural conditions. Both organic ligands reacted fairly rapidly with Cu(II). Reaction half‐life of DOM was in the millisecond range. Two types of metal binding sites of organic ligands were identified. Fulvic acid yield forward rate constants: 1 x 106 M‐1 s‐1 and 5.15 × 103 M‐1 s‐1, based on second‐order reaction rate model. Water soluble soil organic matter gave forward rate constants: 1.34 × 105 M‐1 s‐1 and 2.2 × 103 M‐1 s‐1. From comparison of kinetic natures, the fast‐reacting ligands were comparable to nitrilotriacetic acid (NTA) and slow‐reacting ligands were more like salcy...