Journal of Safety and Environment

The present paper has investigated the removal of heavy metals Pb 2+, Cd 2+ and Cu 2+ from the aqueous solutions by adsorption onto insoluble humic acid (IHA) at different pH and temperatures. As is known, insoluble humic acid (IHA) has an excellent adsorptive ability, which can be prepared by heating the highly soluble HA at 330 ℃ and the treated with 2 mol/L CaCl2 solution. The insoluble humic acid are characterized by such means as thermo-gravimetry and differential thermal analysis (TG-DTA) as well as scanning electron micrograph (SEM). While investigating the effect of temperature, pH and time on the adsorption behaviors of heavy metals, it has found that the adsorption capacity increases with the increase of the temperature and pH. At the same time, the paper has also analyzed the adsorption experimental data by using three different isotherm models: Langmuir, Frendlich and Linear isotherm. As the result, it has obtained the optimal correlation for Frendlich isotherm equations. In addition, the paper has calculated the thermodynamic quantities ΔH in accordance with the Clausius-Claperyon,s theory. The ΔH values for Pb 2+,Cd 2+ and Cu 2+ prove to be -75.37 J/mol, -117.92 J/mol and -110.76 J/mol, respectively, which are smaller than the lower limit of the chenmisorption (42.0 kJ/mol ). It means that the type of adsorption of Pb 2+,Cd 2+ and Cu 2+ onto IHA is physisorption, rather than by chemical bonding. And finally, the adsorption equilibrium gained within 12 hours, and a high and stable removal of heavy metals on insoluble humic acid has been obtained almost under the neutral conditions. The above results suggests that IHA is a potentially efficient absorbent to purify water from the heavy metal contaminants.