Adsorption of zinc on colloidal (hydr)oxides of Si, Al and Fe in the presence of a fulvic acid

Abstract The adsorption of Zn (total concentration 10 −6 M) to colloidal quartz, hydrargillite and goethite (50, 300 and 70 mg/l, respectively) was studied by a batch technique at a constant ionic strength (0.01 M) but with variation of pH (3–10) and fulvic acid (FA) concentration (0, 2 or 20 mg/l). The adsorption had similar pH-dependence in all systems in the absence of FA giving a pH 50 (pH of 50% adsorption) of 7.6 under these conditions. The presence of the FA reduced the overall adsorption to quartz (pH 50 of 7.9 at 2 mg FA/I and 9.3 at 20 mg/1) and shifted the adsorption curves downwards (pH 50 of 6.8) in the hydrargillite and goethite systems at 2 mg FA/l. At 20 mg FA/l, the adsorption in the two latter systems was increased at pH 6.5. The results reflect the affinity of the surfaces for FA as well as the formation of Zn–FA complexes (in solution and on solid surfaces).