Role of reactor type on Cr(VI) removal by zero-valent iron in the presence of pyrite: Batch versus sequential batch reactors

J Environ Manage. 2022 Oct 15:320:115854. doi: 10.1016/j.jenvman.2022.115854. Epub 2022 Aug 9.

Abstract

This study was conducted to understand the role of application sequence of pyrite and zero-valent iron (Fe0) (simultaneous vs. sequential) on chromium (VI) removal by Fe0. In batch experiments, pyrite and Fe0 were homogeneously mixed in batch reactors maintained at a constant total solids loading of 2 g L-1. In sequential batch experiments, however, the first reactor containing variable doses of pyrite was operated for 20 min, and the liquid fraction from the first reactor was then subsequently loaded into the second reactor containing a fixed Fe0 dose of 1.2 g L-1. The batch reactors achieved much higher Cr(VI) removal efficiency than sequential batch reactors under similar operating conditions due to discrepancies in Fe redox cycling activities between these two systems. In batch reactors, the Fe0 particles deposited on pyrite surface due to electrostatic attraction between negatively charged pyrite and positively charged Fe0, thus, rendering the overall solids surface charge neutral at optimum pyrite and Fe0 doses. As a result, the whole system behaved like a composite material, with pyrite functioning as a support material for Fe0. This stimulated Fe redox cycling more effectively to generate new Fe(II) sites on Fe0 for enhanced Cr(VI) removal relative to Fe0 only system. In sequential batch reactors, however, the Fe redox cycling activity was limited, but significantly increased with increasing pyrite dose in the first reactor. Overall, our results indicate that the stimulatory effect of pyrite on Cr(VI) removal by Fe0 may be much higher if the reactors are operated in batch mode.

Keywords: Batch reactor; Chromium; Pyrite; Sequential batch reactor; Zero-valent iron.

MeSH terms

  • Chromium* / analysis
  • Iron
  • Sulfides
  • Water Pollutants, Chemical* / analysis

Substances

  • Sulfides
  • Water Pollutants, Chemical
  • Chromium
  • pyrite
  • chromium hexavalent ion
  • Iron