Adsorption characteristics of Cu(II) on humus-kaolin complexes

The sorption of Cu(II) was investigated on synthetic humus-kaolin complexes. Two groups of humic fractions were compared to investigate the effect of molar mass on the Cu(II) adsorption capacity. Another approach was to compare the capacities of humic acid (HA) and fulvic acid (FA) to adsorb Cu(II). The adsorption capacity of fulvic acid on kaolin is smaller than that of humic acid. The adsorption behavior of fulvic acid on kaolin can be described by a Langmuir-type isotherm. However, the adsorption isotherm of humic acid on kaolin exhibits non-Langmuir behavior. The results showed the affinity of Cu(II) on humic acid was greater than by fulvic acid. However, the affinity of Cu(II) adsorption by humic acid with large molar mass was equal to that by humic acid with small molar mass. A modified model incorporating a proton competition coefficient can differentiate the competitive effect from Cu(II) adsorption. A constant (Km) independent of pH was derived from this model. HA-Kaolin complex has a greater Cu(II) affinity constant that FA-Kaolin complex according to models with either a single-site or a continuous distribution.