Effect of iron oxide removal on heavy metal sorption by acid subsoils

Herschel Adams Elliott, M. R. Liberati, C. P. Huang

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Abstract

The adsorption of Cd, Cu, Pb, and Zn from 0.025 M NaClO4 solutions by two ferruginous subsoils, Christiana silty clay loam and Dothan sandy clay, was investigated. Under acidic conditions, selective dissolution and removal of the Fe oxide soil component by dithionite-citrate-bicarbonate (DCB) generally increased heavy metal adsorption by the soils. This effect was attributed to increased electrostatic attraction of cations to the DCB-washed soils as evidenced by substantial reduction in the zero point of charge (ZPC) for the Dothan soil following DCB extraction. Alternately, the DCB extraction stripped Fe and Al species bound to structural exchange sites or eliminated coatings which reduce cation accessibility to such sites. Addition of low levels (10-6 M) of ferric iron suppressed heavy metal adsorption capacity of the DCB-extracted Christiana soil to values comparable to the unmodified whole soil system. While hydrous oxide surfaces represent highly reactive sites for cation binding, Fe oxides can modify both the pH-dependent and structural exchange sites in a manner which hinders heavy metal adsorption. Thus, a soil's Fe-oxide content is unlikely to be a reliable guide to heavy metal adsorption capacity.

Original languageEnglish (US)
Pages (from-to)379-389
Number of pages11
JournalWater, Air, & Soil Pollution
Volume27
Issue number3-4
DOIs
Publication statusPublished - Feb 1 1986

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All Science Journal Classification (ASJC) codes

  • Environmental Engineering
  • Environmental Chemistry
  • Ecological Modeling
  • Water Science and Technology
  • Pollution

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