Cadmium (II) ion adsorption of an industrial liquid waste-derived ferric oxide loaded with chitosan: Parameters optimization, isotherms, kinetics and thermodynamics

In this work, ferric oxide prepared from an industrial liquid waste was loaded with chitosan, then the as-received ferric oxide loaded with chitosan (FOLWC) was utilized as a novel adsorbing material for the elimination of trace cadmium(II) ion from cadmium(II)-containing solution. First, the microstructure and phase composition of FOLWC was explored. Then, the effects of initial pH, contact time and adsorbent dosage on the cadmium(II) ion adsorption were investigated. An empirical quadratic polynomial equation which could predict the response value of cadmium(II) ion removal efficiency was obtained as follow: W=93.69+11.38A+2.90B+0.99C-1.36AB-1.51AC-0.15BC-7.70A2-2.35B2+1.76C2, where A, B and C represent the initial pH, adsorbent dosage and contact time, respectively. In addition, the optimization study of adsorption parameters was carried out using response surface methodology. The pH value of cadmium(II)-containing solution has a most significant effect on the cadmium(II) ion removal onto from FOLWC. The pH value, contact time and adsorbent dosage corresponding to the optimum conditions were obtained to be 6.77, 15.27 min and 1.71 g/L, respectively. The cadmium(II) ion removal efficiency was reached nearly 100 % on the optimum conditions. The adsorption kinetics result implies that a pseudo-second-order model can be consistent with the adsorption process. The cadmium (II) ion adsorption isotherm accords with Langmuir model. The studied maximum cadmium(II) ion adsorption capacity of 17.08 mg/g by FOLWC reached at 55 ℃. In addition, thermodynamic experimental data indicates that the whole removal process of cadmium(II) ion by FOLWC is not only endothermic but spontaneous as well. The principal adsorption mechanism is surface complexation, where the dominant surface groups including -OH, CO and N-H of FOLWC were replaced by the cadmium(II) ions. In summary, it shows that FOLWC can be taken as an efficient adsorbent for Cadmium ion removal from polluted water.