Cadmium adsorption by a humic acid

Abstract

Even though there have been a number of studies on interaction between heavy metals and humic substances, however, investigations on the interaction between humic acid and cadmium have been few in calcareous conditions, if any. In this study, humic acid was extracted from commercial humic fertilizer. Adsorption of cadmium by humic acid was determined as a function of pH and different concentrations of background electrolyte. In all levels of pH (5, 7 and 8.6), cadmium adsorption by humic acid declined tremendously by increasing of concentration of background electrolyte. Cadmium adsorption by humic acid increased significantly from pH 5 to 8.6 in low, intermediate, high electrolyte concentrations. Adsorption was greatest at high pH and low electrolyte concentration. The data fit well the Langmuir model at all pH and electrolyte concentration values. Maximum sorption capacity (B L ) from Langmuir equations indicated that data in pH = 8.6 had the greatest Cd sorption capacity in all electrolyte concentrations (I) (I = 6, 12, 25 mmol/L). It can be explained by increasing solubility of humic acid in high pHs.