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Nanoscale zero-valent iron for metal/metalloid removal from model hydraulic fracturing wastewater. | LitMetric

AI Article Synopsis

  • Nanoscale zero-valent iron (nZVI) was evaluated for its effectiveness in removing heavy metals (Cu(II), Zn(II), Cr(VI), and As(V)) from saline wastewaters, particularly focusing on changes over time from Day-1 to Day-90 samples.
  • Increasing the ionic strength of the wastewater impacted the removal rates differently, with Cu(II) removal increasing significantly, while Zn(II) removal decreased and the removal of Cr(VI) fluctuated, with As(V) remaining relatively stable.
  • The study found that modifying nZVI with alginate and polyvinyl alcohol enhanced its performance, reduced iron dissolution, and demonstrated the importance of solution chemistry on contaminant removal mechanisms.

Article Abstract

Nanoscale zero-valent iron (nZVI) was tested for the removal of Cu(II), Zn(II), Cr(VI), and As(V) in model saline wastewaters from hydraulic fracturing. Increasing ionic strength (I) from 0.35 to 4.10 M (Day-1 to Day-90 wastewaters) increased Cu(II) removal (25.4-80.0%), inhibited Zn(II) removal (58.7-42.9%), slightly increased and then reduced Cr(VI) removal (65.7-44.1%), and almost unaffected As(V) removal (66.7-75.1%) by 8-h reaction with nZVI at 1-2 g L. The removal kinetics conformed to pseudo-second-order model, and increasing I decreased the surface area-normalized rate coefficient (k) of Cu(II) and Cr(VI), probably because agglomeration of nZVI in saline wastewaters restricted diffusion of metal(loid)s to active surface sites. Increasing I induced severe Fe dissolution from 0.37 to 0.77% in DIW to 4.87-13.0% in Day-90 wastewater; and Fe dissolution showed a significant positive correlation with Cu(II) removal. With surface stabilization by alginate and polyvinyl alcohol, the performance of entrapped nZVI in Day-90 wastewater was improved for Zn(II) and Cr(VI), and Fe dissolution was restrained (3.20-7.36%). The X-ray spectroscopic analysis and chemical speciation modelling demonstrated that the difference in removal trends from Day-1 to Day-90 wastewaters was attributed to: (i) distinctive removal mechanisms of Cu(II) and Cr(VI) (adsorption, (co-)precipitation, and reduction), compared to Zn(II) (adsorption) and As(V) (bidentate inner-sphere complexation); and (ii) changes in solution speciation (e.g., from Zn to ZnCl and ZnCl; from CrO to CaCrO complex). Bare nZVI was susceptible to variations in wastewater chemistry while entrapped nZVI was more stable and environmentally benign, which could be used to remove metals/metalloids before subsequent treatment for reuse/disposal.

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Source
http://dx.doi.org/10.1016/j.chemosphere.2017.02.119DOI Listing

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