A common concern in the approval of nanotechnology for water treatment is whether there are advantages of these nanomaterials over conventional water treatment reagents. In this work, nanoscale zero-valent iron (nZVI) is compared with lime (Ca(OH) 2 ), the most widely used heavy metal precipitant, for Pb(II) and Zn(II) removal, in laboratory and field experiments. Water chemistry, treatment efficiencies and reaction products of the two reagents are compared and the study shows that the moderate solution pH of nZVI and its seed effect play vital roles in producing high-quality effluents. The results are then verified in a field continuous-flow experiment using tons of lime and kilos of nZVI. The results show that sub-ppm levels (∼0.1 mg/L) of Pb(II) and Zn(II) could not be achieved via lime precipitation alone, due to the solubility limits of metal hydroxides and their re-dissolution caused by the strong alkalinity of lime. In comparison, stable and lower levels of Pb(II) and Zn(II) were easily attained using nZVI, due to its multifunctional properties and good tolerance for influent fluctuation enabled by its inherent pH-stabilizing nature. SEM characterizations, particle size analyses and quiescent settling experiments show the ability of nZVI to generate large and consolidated solids that are amenable to gravitational separation. The study shows several key advantages of nZVI over lime technology in Pb(II) and Zn(II) removal. As lime is widely used for heavy metal removal, this work provides an effective advanced treatment process to supplement lime-based treatment methods.
Sharafat Ali,Izaz Ali Shah,Aziz Ahmad,Javed Nawab,Haiou Huang
In this study, pristine multi-walled carbon nanotubes (MWCNTs) were functionalized by using Ar/O 2 plasma treatment technique, which enhanced adsorptive membrane filtration of zinc ions from water and wastewater. The XPS analysis showed that plasma treatment largely increased the surface oxygen groups content of MWCNTs from 2.78% to 6.79%. This change increased the surface negative charged, dispersion and adsorption properties of MWCNTs without causing any damages to the integrity of the nanotube pattern. Pressure-driven filtration of plasma-treated MWCNT (P-CNT) dispersion formed a stable layer inside the lumen of a hollow fiber membrane. The contact angle analysis demonstrated that after incorporation of P-CNT into the HF membrane increased membrane hydrophilicity. The P-CNT membrane effectively removed almost 100% of zinc from synthetic waters and approximately 80% of zinc from a wastewater effluent by surface complexation reaction. A follow-up regeneration study demonstrated that the adsorptive removal of zinc by the CNT membrane was reversible under selected conditions, thus making it possible to repeatedly use the membrane for long-term zinc filtration. This study suggests that HF membranes modified with P-CNTs possess superb adsorption properties for metal ions , allowing the operation of CNT membranes for water treatment .
A facile strategy was designed to prepare magnetically layered chalcogenide Fe3O4/KMS-1 (FK) composite adsorbents combining the advantages of rapid magnetic separation and satisfactory adsorption performance under vigorous stirring in ethanol solution at room temperature. The dispersion degree of Fe3O4 in ethanol was superior to that in water, which gave a better result with the preparation in ethanol. Characterization by SEM-EDS, XRD, magnetic test, N2 physical-adsorption and TG-DTG demonstrated formation of FK and its adsorption performance. The results showed that the Fe3O4 microspheres could be well distributed over the surface of KMS-1 by electrostatic attraction in ethanol and the obtained FK could be easily separated from water after adsorption using a magnet. The pH slightly affected the adsorption capacity in the range of 3 to 6. Both KMS-1 and Fe3O4 retained their own original adsorption capacity in FK and FK0.3 was the best composite adsorbent when the mass ratio of Fe3O4 and KMS-1 was 0.3. As the amount of loaded Fe3O4 was decreased, the adsorption capacity of the composite adsorbents increased. The kinetic data of FK0.3 fit well with pseudo-second-order models. The co-existing ions had a slight effect on the removal of Zn(II) by FK0.3. The interlayer spacing of KMS-1 in FK increased from 0.851 nm to 1.123 nm after adsorption. The FK composite adsorbents can be considered as an excellent recoverable adsorbent in the treatment of wastewater.
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