Treatment of Cr(VI) in aqueous solution by Ni-Al and Co-Al layered double hydroxides: Equilibrium and kinetic studies

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Abstract

Ni-Al layered double hydroxide (Ni-Al LDH) and Co-Al LDH were prepared using a coprecipitation method. Ni-Al LDH and Co-Al LDH were found to remove Cr(VI) from aqueous solution through anion exchange of Cr2O72- with Cl- intercalated in the interlayer of the LDHs. Ni-Al LDH and Co-Al LDH were both found to be superior to Mg-Al LDH for removal of Cr(VI). This excellent behavior is attributed to the buffering effect of Ni-Al LDH and Co-Al LDH that results in a lower amount of OH- in solution and allows Cr2O72- to be more easily intercalated in the LDH interlayer. The Cr(VI) removal process was consistent with a Langmuir-type adsorption, indicating that the removal of Cr(VI) proceeded via chemical adsorption involving the anion exchange of Cr2O72- with intercalated Cl-. The maximum adsorption and equilibrium adsorption constant values were 2.0mmolg-1 and 2.4, respectively, for Ni-Al LDH, and 1.9mmolg-1 and 1.5, respectively, for Co-Al LDH. The kinetics of Cr(VI) removal by Ni-Al LDH and Co-Al LDH were consistent with a pseudo-second-order reaction, and the rate-determining step for Cr(VI) removal was found to be the anion exchange. The apparent rate constants at 10, 30, and 60°C for Ni-Al LDH were 2.2×10-3, 2.4×10-3, and 3.2×10-3gmmol-1min-1, respectively. The apparent rate constants at 10, 30, and 60°C for Co-Al LDH were 1.2×10-3, 1.6×10-3, and 1.9×10-3gmmol-1min-1, respectively. The Arrhenius plot of the rate constants yielded apparent activation energies of 6.1 and 6.6kJmol-1 for Ni-Al LDH and Co-Al LDH, respectively.

Original languageEnglish
Pages (from-to)e75-e80
JournalJournal of Water Process Engineering
Volume8
DOIs
Publication statusPublished - 2015 Dec 1

Keywords

  • Buffering action
  • Cr(VI)
  • Langmuir-type adsorption
  • Layered double hydroxide
  • Pseudo-second-order kinetics

ASJC Scopus subject areas

  • Biotechnology
  • Safety, Risk, Reliability and Quality
  • Waste Management and Disposal
  • Process Chemistry and Technology

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