Transformations of 2-line ferrihydrite and its effect on cadmium adsorption

In this study, 2LFh was synthesized, and the effects of 2LFh synthesis in the laboratory as well as its synthetic products' mineral crystal phase changes during high temperature aging process caused by Ca²⁺, Mg²⁺, and Cl^- were also studied. In addition, the Cd²⁺ adsorption effects of the products above with different pH values and different Cd²⁺ concentrations were studied in this experiment. The results showed that the existence of Ca²⁺ had no significant effect on the synthesis and aging of 2LFh. However, in the presence of Mg²⁺ and Cl^-, the akaganeite could be found in the synthetic material, and with the increase of the ion concentration, the crystallinity of the formed akaganeite was higher. And akaganeite had a significant inhibitory effect on the aging of 2LFh, causing the Cd²⁺adsorption effect of 2LFh after aging was better than that of pure 2LFh. The adsorption and removal rates of Cd²⁺ in Fh2 series and Fh2-200 series were increased with the increase of initial concentration. With the increase of pH, the adsorption capacity and removal rate were increased, and the removal rate reached nearly 100% when pH value is ranging from 10 to 11. The isothermal adsorption experiment showed that the isothermal adsorption process of Cd²⁺ in Fh2 series and Fh2-200 series was in accordance with the Freundlich model. The affinity coefficient (Kf) of the Freundlich model of Fh2-200 series arranged in descending order is Fh2-200-Mgs> Fh2-200-Cas> Fh2-200s, showing that the Cd²⁺ adsorption capacity of Fh2-200 was relatively weak, while that of Fh2-200-Ca series and Fh2-200-Mg series was relatively strong, which was confirmed by the experimental results.