Evaluation of Adsorption of Cadmium onto Ferrihydrite-Humic Acid Coprecipitation

Cadmium in contaminated water attract public attention for its toxicity, bioavailability and removal difficulty. Two-line Ferrihydrite (Fh) coprecipitated with humic acid (HA) is expected to provide an environment friendly and highly efficient adsorption process for aqueous cadmium removal. C-Fe coprecipitates were prepared and examined by X-ray Diffraction (XRD), Scanning electron microscope (SEM) and Fourier transform infrared spectra (FTIR), and the product was determined as 2L ferrihydrite with poor crystallinity. The influence of adsorbent dosage, relative ionic strength, pH, adsorption time and initial concentration on adsorption mechanism was investigated. The experimental results showed the removal rate of Cd(II) was up to -99.76% from aqueous solutions. The adsorption isotherms followed the Langmuir isotherm model better than the Freundlich isotherm model. The adsorption kinetic data could be described well by Lagergren second-order kinetic equation, which assumes chemical adsorption. The amount of Cd adsorbed is a function of pH, alkaline environment can reinforce adsorption due to dissociation of phenolic groups to inhibit H bond generation which can contribute to aggregation.