Aging effects on chemical transformation and metal(loid) removal by entrapped nanoscale zero-valent iron for hydraulic fracturing wastewater treatment

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

Research output: Contribution to journalArticle

33 Citations (Scopus)

Abstract

In this study, alginate and polyvinyl alcohol (PVA)-alginate entrapped nanoscale zero-valent iron (nZVI) was tested for structural evolution, chemical transformation, and metals/metalloids removal (Cu(II), Cr(VI), Zn(II), and As(V)) after 1–2 month passivation in model saline wastewaters from hydraulic fracturing. X-ray diffraction analysis confirmed successful prevention of Fe0 corrosion by polymeric entrapment. Increasing ionic strength (I) from 0 to 4.10 M (deionized water to Day-90 fracturing wastewater (FWW)) with prolonged aging time induced chemical instability of alginate due to dissociation of carboxyl groups and competition for hydrogen bonding with nZVI, which caused high Na (7.17%) and total organic carbon (24.6%) dissolution from PVA-alginate entrapped nZVI after 2-month immersion in Day-90 FWW. Compared to freshly-made beads, 2-month aging of PVA-alginate entrapped nZVI in Day-90 FWW promoted Cu(II) and Cr(VI) uptake in terms of the highest removal efficiency (84.2% and 70.8%), pseudo-second-order surface area-normalized rate coefficient ksa (2.09 × 10− 1 L m− 2 h− 1 and 1.84 × 10− 1 L m− 2 h− 1), and Fe dissolution after 8-h reaction (13.9% and 8.45%). However, the same conditions inhibited Zn(II) and As(V) sequestration in terms of the lowest removal efficiency (31.2% and 39.8%) by PVA-alginate nZVI and ksa (4.74 × 10− 2 L m− 2 h− 1 and 6.15 × 10− 2 L m− 2 h− 1) by alginate nZVI. The X-ray spectroscopic analysis and chemical speciation modelling demonstrated that the difference in metals/metalloids removal by entrapped nZVI after aging was attributed to distinctive removal mechanisms: (i) enhanced Cu(II) and Cr(VI) removal by nZVI reduction with accelerated electron transfer after pronounced dissolution of non-conductive polymeric immobilization matrix; (ii) suppressed Zn(II) and As(V) removal by nZVI adsorption due to restrained mass transfer after blockage of surface-active micropores. Entrapped nZVI was chemically fragile and should be properly stored and regularly replaced for good performance.

Original languageEnglish
Pages (from-to)498-507
Number of pages10
JournalScience of the Total Environment
Volume615
DOIs
Publication statusPublished - 2018 Feb 15

Keywords

  • Aging effect
  • Alginate entrapment
  • Chemical speciation
  • Hydraulic fracturing
  • Metal/metalloid removal
  • Nanoscale zero-valent iron

ASJC Scopus subject areas

  • Environmental Engineering
  • Environmental Chemistry
  • Waste Management and Disposal
  • Pollution

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