Stability of Fe- and Mn-(oxyhydr)oxides in Common Soil Dispersion Solutions

Manh, Phung N.; Ali Khan, Moonis; Jeon, Byong-Hun; Kim, Jae Gon; Lee, Giehyeon

Stability of Fe- and Mn-(oxyhydr)oxides in Common Soil Dispersion Solutions

2011

Manh, Phung N. | Ali Khan, Moonis | Jeon, Byong-Hun | Kim, Jae Gon | Lee, Giehyeon

Soil dispersion is a prerequisite process for the separation of metal oxides from bulk soil when magnetic separation is employed to enhance the efficiency for soil treatment. This study examined the stability of goethite, hematite, birnessite, and manganite in common dispersion solutions. The stability of pH in the oxide suspension decreased in the order carbonate (50Â mM Na2CO3) > pyrophosphate (50Â mM Na4P2O7) > simple alkaline (1Â mM NaOH) solutions regardless of the oxides. Dissolution of the four oxides was negligible in the carbonate and the simple alkaline solutions. In the pyrophosphate solutions, however, the oxides were subject to ligand-promoted dissolution by pyrophosphate ion. The extent of dissolution was highest for goethite followed by manganite, hematite, and birnessite. Dissolved Fe and Mn concentrations reached 68.3 and 4.1Â μM for goethite and manganite suspensions, respectively, in 21Â days with 5Â mM pyrophosphate. Higher pyrophosphate concentrations (up to 150Â mM) did not substantially affect the extent of ligand-promoted dissolution due to the limited surface sites of the oxides. The results of this study suggest that the carbonate solution would be more desirable than the simple alkaline or the pyrophosphate solution for soil dispersion in the presence of common Fe or Mn oxides.

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