Abstract
The sorption of Cd2+ from natural seawater, artificial seawater, distilled water and NaCl solution of the same ionic strength as the seawater onto zeolite modified by iron(III) oxide (Fe(III)-zeolite) was investigated. The sorption was found to be time, concentration and pH dependent. The sorption capacity at the initial pH = 7 decreased in the following order: distilled water > NaCl solution > artificial seawater > natural seawater. The isotherm study showed that Langmuir isotherm model could be adequately applied for the sorption in distilled water, indicating the homogeneous monolayer coverage at Fe(III)-zeolite surface, while the Freundlich isotherm model showed a better fit than the Langmuir model of the sorption data in saline waters, indicating multilayer heterogeneous coverage at the sorbent surface. The values of Freundlich parameter n suggested that the sorption was a favorable process and bonds between Cd2+ and Fe(III)-zeolite surface were stronger in NaCl solution than in natural and artificial seawater. Kinetics analyzes showed that the mechanism of Cd2+ sorption from natural seawater differed from the sorption mechanism out of distilled water, NaCl solution and artificial seawater. The intra-particle diffusion kinetic model indicated that both boundary layer diffusion and intra-particle diffusion influenced the rate of sorption.
Highlights
The sorption of Cd2+ from natural seawater, artificial seawater, distilled water and NaCl solution of the same ionic strength as the seawater onto zeolite modified by iron(III) oxide (Fe(III)-zeolite) was investigated
The sorbent capacity at initial pH 7 decreased in the following order: distilled water > NaCl solution > artificial seawater > natural seawater
The Freundlich isotherm model provides the best fit to the sorption equilibrium data obtained from saline waters, which indicates heterogeneity of the sorbent surface and the multilayer adsorption
Summary
The sorption of Cd2+ from natural seawater, artificial seawater, distilled water and NaCl solution of the same ionic strength as the seawater onto zeolite modified by iron(III) oxide (Fe(III)-zeolite) was investigated. The sorption capacity at the initial pH 7 decreased in the following order: distilled water > NaCl solution > artificial seawater > natural seawater. The values of Freundlich parameter n suggested that the sorption was a favorable process and bonds between Cd2+ and Fe(III)-zeolite surface were stronger in NaCl solution than in natural and artificial seawater. Kinetics analysis showed that the mechanism of Cd2+ sorption from natural seawater differed from the sorption mechanism out of distilled water, NaCl solution and artificial seawater. There are various technologies for the removal of cadmium and other heavy metals from water systems: chemical precipitation, ion exchange, sorption, membrane processing, electrochemical treatment, etc. Much higher capacity of the iron(III)-modified zeolite for Pb2+, Cd2+ and Zn2+ in comparison to parent zeolite was explained [14] by: higher specific sorption resulting from the new functional groups on the surface; ion exchange due to the presence of exchangeable ions; the hydroxide precipitation caused by the higher point of zero charge
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