Characteristics of Fe and Mn bearing precipitates generated by Fe(II) and Mn(II) co-oxidation with O2, MnO4 and HOCl in the presence of groundwater ions

Arslan Ahmad*, Albert van der Wal, Prosun Bhattacharya, Case M. van Genuchten

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

4 Citations (Scopus)

Abstract

In this work, we combined macroscopic measurements of precipitate aggregation and chemical composition (Mn/Fe solids ratio) with Fe and Mn K-edge X-ray absorption spectroscopy to investigate the solids formed by co-oxidation of Fe(II) and Mn(II) with O2, MnO4, and HOCl in the presence of groundwater ions. In the absence of the strongly sorbing oxyanions, phosphate (P) and silicate (Si), and calcium (Ca), O2 and HOCl produced suspensions that aggregated rapidly, whereas co-oxidation of Fe(II) and Mn(II) by MnO4 generated colloidally stable suspensions. The aggregation of all suspensions decreased in P and Si solutions, but Ca counteracted these oxyanion effects. The speciation of oxidized Fe and Mn in the absence of P and Si also depended on the oxidant, with O2 producing Mn(III)-incorporated lepidocrocite (Mn/Fe = 0.01–0.02 mol/mol), HOCl producing Mn(III)-incorporated hydrous ferric oxide (HFO) (Mn/Fe = 0.08 mol/mol), and MnO4 producing poorly-ordered MnO2 and HFO (Mn/Fe > 0.5 mol/mol). In general, the presence of P and Si decreased the crystallinity of the Fe(III) phase and increased the Mn/Fe solids ratio, which was found by Mn K-edge XAS analysis to be due to an increase in surface-bound Mn(II). By contrast, Ca decreased the Mn/Fe solids ratio and decreased the fraction of Mn(II) associated with the solids, suggesting that Ca and Mn(II) compete for sorption sites. Based on these results, we discuss strategies to optimize the design (i.e. filter bed operation and chemical dosing) of water treatment plants that aim to remove Fe(II) and Mn(II) by co-oxidation.

Original languageEnglish
Pages (from-to)505-516
Number of pages12
JournalWater Research
Volume161
DOIs
Publication statusPublished - 15 Sep 2019

Keywords

  • Drinking water
  • Filtration
  • Groundwater treatment
  • Iron and manganese oxidation and precipitation
  • Mn and Fe removal
  • X-ray absorption spectroscopy

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