Abstract
Manganese (Mn) oxide is a ubiquitous metal oxide in sub-environments. The adsorption of Cd(II) on Mn oxide as function of adsorption time, pH, ionic strength, temperature, and initial Cd(II) concentration was investigated by batch techniques. The adsorption kinetics showed that the adsorption of Cd(II) on Mn oxide can be satisfactorily simulated by pseudo-second-order kinetic model with high correlation coefficients (R2 > 0.999). The adsorption of Cd(II) on Mn oxide significantly decreased with increasing ionic strength at pH < 5.0, whereas Cd(II) adsorption was independent of ionic strength at pH > 6.0, which indicated that outer-sphere and inner-sphere surface complexation dominated the adsorption of Cd(II) on Mn oxide at pH < 5.0 and pH > 6.0, respectively. The maximum adsorption capacity of Mn oxide for Cd(II) calculated from Langmuir model was 104.17 mg/g at pH 6.0 and 298 K. The thermodynamic parameters showed that the adsorption of Cd(II) on Mn oxide was an endothermic and spontaneous process. According to the results of surface complexation modeling, the adsorption of Cd(II) on Mn oxide can be satisfactorily simulated by ion exchange sites (X2Cd) at low pH and inner-sphere surface complexation sites (SOCd+ and (SO)2CdOH− species) at high pH conditions. The finding presented herein plays an important role in understanding the fate and transport of heavy metals at the water–mineral interface.
Highlights
The contamination of heavy metals is of great concern to humans due to their toxicity, bioaccumulation, and non-biodegradation [1]
It has been reported that adsorption of Cd(II) by Mn oxide may be attributed to formation of inner-sphere surface complexes due to their insensitivity to Ca2+ and Mg2+ [46]. These results proved that Mn oxides are a potential preferable absorbent for heavy metals removal
The batch adsorption experiments indicated that Mn oxide could achieve a fast and efficient adsorption of Cd(II) from aqueous solutions
Summary
The contamination of heavy metals is of great concern to humans due to their toxicity, bioaccumulation, and non-biodegradation [1]. Other heavy metals from water and wastewater has been recently investigated by using various methods such as adsorption, chemical precipitation, electrodialysis, ion exchange, membrane separation, and redox [4,5]. Among these methods, adsorption is considered as an effective technique due to its properties of operation, low cost, and high efficiency over a wide concentration range of pollutant [6]. Great attention has been paid to research on different types of low-cost natural and modified minerals for the removal of Cd(II) from aqueous solutions
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