Effects of humics on calcium and copper adsorption to goethite

摘要

Humic substances adsorb strongly to metal (hydr) oxide minerals, which influences cation and anion adsorption to both particles. Compared to the adsorption to pure goethite, the presence of fulvic acids (FA) enhanced the adsorption of Ca significantly. In comparison to the simple linear sum of Ca bound to FA and goethite, the interactions between goethite and FA led to a reduced adsorption of Ca at low pH and an enhanced adsorption at high pH. For copper, depending on the loading and pH, the presence of FA can decrease or increase Cu adsorption in compassion with Cu bound to pure goethite. Under the experimental conditions studied, the amount of Cu adsorbed to the FA-goethite complex is close to that predicted with the linear additivity model. Preliminary model calculations indicate that FA effects on Ca adsorption to goethite is mainly due to electrostatic interactions, whereas for Cu, cation bridging maybe an important mechanism.