Influencing factors of binding of humic acid and cadmium ion in the water environment

Under different chemical conditions, the influencing factors of the binding action of humic acid (HA) with cadmium ion (Cd²⁺) were studied by measuring the free Cd²⁺ concentrations and their binding ratios. The results showed that pH, ionic strength, total added Cd²⁺ concentrations and reaction temperature could affect the binding of the humic acid and Cd²⁺. When pH was from 4.5 to 6.5, the binding ratios increased and the free Cd²⁺ concentrations reduced with the pH increasing. The increasing of the ionic strength inhibited their complexation reactions. The bound Cd²⁺ concentrations and the free Cd²⁺ concentrations increased when the total Cd²⁺ concentrations increased, while the binding ratios decreased. The binding ratios of the humic acid and Cd²⁺ increased gradually with the concentration of humic acid increasing. The free Cd²⁺ concentrations decreased with increasing the reaction temperature from 20°C to 50°C, while the binding raions increased gradually.