Interactions of calcium and fulvic acid at the goethite-water interface

Humic substance charge determination by titration with a flexible cationic polyelectrolyte

“…For both FA samples the pH IEP values range from 5.0 to 4.8, and the calculated charge adjustment is about 0.15 mmol g À1 . This is about half that of the HA samples and it corresponds with the weak salt dependency of the FA charge density (Weng et al, 2005). The difference between FA and HA is related to the much smaller number of functional groups per FA molecule than per HA particle.…”

“…The charge density of HS depends on the pH and at the pH conditions in most natural waters HS are negatively charged (Milne et al, 1995;Ritchie and Perdue, 2003). The charge density of humic particles is a dominant factor for the interactions of HS with: (1) heavy metal ions (Milne et al, 2003;Koopal et al, 2005;Merdy et al, 2006), (2) oppositely charged polyelectrolytes (Bolto et al, 1999;Kam and Gregory, 2001;Hankins et al, 2006), (3) proteins (Tan et al, 2008(Tan et al, , 2009), (4) cationic surfactants Yee et al, 2006;Ishiguro et al, 2007) and (5) mineral surfaces Filius et al, 2000;Saito et al, 2004;Weng et al, 2005). Therefore, for a good understanding of these interactions reliable information on charge characteristics of HS is of vital importance.…”

Cu2+ and Ca2+adsorption to goethite in the presence of fulvic acids

“…Both goethite and FA material used in this work are the same as those used in the study on Ca (Weng et al, 2005). The goethite material was prepared based on the procedure described by Hiemstra et al(1989a).…”

“…In a previous investigation, we have studied the interactions between calcium ion (Ca 2+ ) and fulvic acids (FA) in a ternary system using goethite (a-FeOOH) (Ca-FA-goethite) (Weng et al, 2005). With the help of model calculations, we concluded that the mutual effects on the adsorption of FA and Ca 2+ to the surface of goethite are mainly due to electrostatic interactions.…”

“…Adsorption of Cu 2+ and FA in the Cu-FA-goethite system is measured and the data are compared to those using Ca 2+ . Better understanding of the dominant mechanisms of the interactions between metal ions and NOM at the surface of oxides is obtained by comparing results of the application of the linear additivity assumption and results of application of the more advanced LCD (Ligand and Charge Distribution) model (Filius et al, 2001(Filius et al, , 2003Weng et al, 2005Weng et al, , 2006Weng et al, , 2007.…”