Effects of Copper, Lead, and Cadmium on the Sorption of 2,4,6-Trichlorophenol Onto and Desorption from Wheat Ash and Two Commercial Humic Acids

The effects of copper (Cu2+), lead (Pb2+), and cadmium (Cd2+) on the sorption of 2,4,6-trichlorophenol (TCP) to and desorption from wheat ash and two commercial humic acids were studied. Copper and Pb2+ diminished the sorption of TCP onto all adsorbents, and made desorption of TCP less hysteretic from ash and German humic acids (GeHA), but more hysteretic from Tianjin humic acids (TJHA). Cadmium had little effect on TCP sorption and desorption. Fourier-transform infra red (FTIR) and X-ray absorption spectroscopy (XAS) in conjunction with fluorescence quenching studies provided insights into the mechanisms of TCP sorption and desorption as affected by Cu2+ and Pb2+, indicating that complexation of Cu2+ and Pb2+ was likely via carboxylic, hydroxylic and phenolic groups of ash, TJHA and GeHA, and that theses same functional groups also reacted with TCP during sorption. In contrast, Cd, a “soft acid”, had no effect on the adsorption of TCP. Hydration shells of dense water around adsorbed Cu2+ and Pb2+ ions may also compete with TCP for available surface area. Fluorescence quenching of pyrene verified that for TJHA, Cu2+ and Pb2+ promoted the formation of supramolecular associations with interior hydrophobic regions separated from aqueous surroundings by exterior hydrophilic layers.