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

Yuqing Sun, Cheng Lei, Eakalak Khan, Season S. Chen, Daniel C.W. Tsang, Yong Sik Ok, Daohui Lin, Yujie Feng, Xiang dong Li

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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−1. The removal kinetics conformed to pseudo-second-order model, and increasing I decreased the surface area-normalized rate coefficient (ksa) 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 Zn2+ to ZnCl3 and ZnCl4 2−; from CrO4 2− to CaCrO4 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.

Original languageEnglish
Pages (from-to)315-323
Number of pages9
JournalChemosphere
Volume176
DOIs
Publication statusPublished - 2017 Jan 1
Externally publishedYes

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Keywords

  • Alginate entrapment
  • Hydraulic fracturing
  • Metals/metalloids
  • Nanoscale zero-valent iron
  • Salinity
  • Wastewater treatment

ASJC Scopus subject areas

  • Environmental Chemistry
  • Chemistry(all)

Cite this

Sun, Y., Lei, C., Khan, E., Chen, S. S., Tsang, D. C. W., Ok, Y. S., Lin, D., Feng, Y., & Li, X. D. (2017). Nanoscale zero-valent iron for metal/metalloid removal from model hydraulic fracturing wastewater. Chemosphere, 176, 315-323. https://doi.org/10.1016/j.chemosphere.2017.02.119