Abstract
Batch experiments were conducted to investigate the behavior and mechanisms for the adsorption of Cd(II) from aqueous solutions by tourmaline under acidic conditions. The results indicated that the adsorption of Cd(II) significantly depend on the adsorption time, temperature, and the initial concentration of the metal ion. Furthermore, tourmaline had a very good adsorption capacity for Cd(II) in acidic, neutral and alkaline aqueous solutions. This good adsorption capacity is attributed to the observation that tourmaline can automatically adjust the pH values of acidic (except pH 2.0 and 3.0), neutral or alkaline aqueous solutions to 6.4. Specifically, the removal capacity for Cd(II) was higher at strongly acidic pH values (in contrast to industrial wastewater pH values) compared to that obtained for other types of adsorbents. Furthermore, the results obtained in this study showed good fits to the Langmuir and Freundlich adsorption isotherms. However, the Langmuir model fit better than the Freundlich model. The maximum uptake of Cd(II) by tourmaline was 31.77, 33.11 and 40.16 mg/g at pH 4.0 at 15, 25 and 35°C, respectively. Therefore, tourmaline is an effective adsorbent for the removal of Cd(II) from acidic aqueous solutions. In addition, the kinetics for the Cd(II) adsorption by tourmaline closely followed the pseudo-second-order model. The thermodynamic parameters indicated that adsorption was feasible, spontaneous, and endothermic. Furthermore, the pH variation after adsorption, gZ-potential, metal ions desorbed and released, and FT-IR analysis indicated that the physisorption and chemisorption mechanisms of tourmaline for heavy metals. These mechanisms included water that was automatically polarized by tourmaline, the ion exchange process, and electropolar adsorption. Among the mechanisms, the automatic polarization of water caused by tourmaline is a unique adsorption mechanism for tourmaline.
Highlights
Batch experiments were conducted to investigate the behavior and mechanisms for the adsorption of Cd(II) from aqueous solutions by tourmaline under acidic conditions
This study demonstrated the effectiveness of tourmaline for removing metal ions from acidic, neutral and alkaline aqueous solutions
The kinetics data presented a good correlation with the pseudo-second-order model, which indicated that chemisorption was involved during the absorption of heavy metal by tourmaline
Summary
Batch experiments were conducted to investigate the behavior and mechanisms for the adsorption of Cd(II) from aqueous solutions by tourmaline under acidic conditions. The pH variation after adsorption, ζ-potential, metal ions desorbed and released, and FT-IR analysis indicated that the physisorption and chemisorption mechanisms of tourmaline for heavy metals These mechanisms included water that was automatically polarized by tourmaline, the ion exchange process, and electropolar adsorption. A number of methods, including adsorption, chemical precipitation, ion exchange, and membrane technologies have been developed and implemented for removing heavy metal ions from different types of wastewater. Different types of minerals, including zeolites [2], quartz [3], apatites [4], goethite [5], calcite [6], and dolomite [7] have been successfully utilized collectively and separately to remove heavy metal ions from aqueous solutions using adsorption techniques. This study can provide a novel adsorbent and theoretical basis for controlling heavy metal pollution in acidic wastewater
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