Competitive adsorption of Cd (II) and Pb (II) ions from aqueous solution onto Iranian hematite (Sangan mine): optimum condition and adsorption isotherm study

In the present study, Iranian hematite (from Sangan area, in the east of Iran) was characterized by XRD, XRF, and FTIR spectroscopies. Then, the efficiency of Iranian hematite for the removal of Pb (II) and Cd (II) ions from aqueous solution was investigated by the optimum condition (contact time, metal concentrations, pH of solutions and the amount of hematite) and equilibrium isotherm models. The Freundlich isotherm indicated a very good fit with the experimental data of Pb (II) and Cd (II) adsorption in an individual solution. In the binary solution, the obtained adsorption isotherm data showed fittings for Langmuir model (homogeneous adsorption mechanism) with the maximum adsorption capacity of 17.86 and 1.887 mg/g for Pb (II) and Cd (II), respectively. These results have been confirmed by three-parameter isotherm studies. The chemical absorption and particle diffusion are predominated for Pb (II) and Cd (II) adsorption in the binary solution, respectively. The competitive adsorption characteristics of Pb (II) and Cd (II) ions were approved by the extended Freundlich and extended Langmuir isotherm models, respectively. The antagonistic competitive effect was observed for the maximum adsorption capacity of Pb (II) and Cd (II) in the binary solution. Industrial wastewater contains many heavy metals, thus the use of natural adsorbents, such as raw hematite for simultaneous removal of Pb (II) and Cd (II) is an important issue.