Understanding Competitive Adsorption of NTMP and Silica on Ferric Hydroxide

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

Ferric hydroxide adsorbents are commonly used to remove phosphonate antiscalants from membrane concentrate solutions. This research investigated competitive adsorption of nitrilotris(methylenephosphonic acid) (NTMP) and silica on ferric hydroxide. Equilibrium adsorption isotherms were measured and column breakthrough and regeneration experiments were performed for an NTMP adsorbate in simulated membrane concentrate solutions with and without dissolved orthosilicic acid. Quantum chemistry simulations using density functional theory (DFT) were used to evaluate the thermodynamic favorability of possible adsorption mechanisms for NTMP and silica. Column breakthrough experiments showed that 86 mg/L of dissolved silica decreased adsorption of NTMP by 36% after 3,685 bed volumes. DFT modeling indicated that NTMP and silica adsorption on ferric hydroxide may occur through both mono- and bidentate complex formation. NTMP adsorption through a bidentate binuclear complex was 12 kcal/mol more energetically favorable than monodentate complexation. Dimerization reactions between adsorbed silica and dissolved silica greatly increased silica adsorption for dissolved silica concentrations greater than 60 mg/L. DFT modeling and experimental results also indicated that dissolved NTMP may react with adsorbed silica through condensation reactions. Although adsorbed silica decreased the total uptake of NTMP, it increased the efficiency of regeneration by 0.10 M NaOH solutions. This is consistent with adsorbed silica decreasing formation of bidentate binuclear NTMP complexes.

Original languageEnglish (US)
Pages (from-to)401-409
Number of pages9
JournalEnvironmental Engineering Science
Volume34
Issue number6
DOIs
StatePublished - Jun 1 2017

Fingerprint

Silicon Dioxide
hydroxide
silica
Silica
adsorption
Adsorption
Density functional theory
ferric hydroxide
regeneration
membrane
Membranes
Quantum chemistry
Organophosphonates
Condensation reactions
Dimerization
Acids
acid
Adsorbates
Complexation
Adsorption isotherms

Keywords

  • density functional theory
  • ferric hydroxide
  • nitrilotris(methylenephosphonic acid)
  • silica
  • surface complexation

ASJC Scopus subject areas

  • Environmental Chemistry
  • Waste Management and Disposal
  • Pollution

Cite this

Understanding Competitive Adsorption of NTMP and Silica on Ferric Hydroxide. / Chen, Yingying; Baygents, James C; Farrell, James.

In: Environmental Engineering Science, Vol. 34, No. 6, 01.06.2017, p. 401-409.

Research output: Contribution to journalArticle

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