Dissolution of Nickel Ferrite in Aqueous Solutions Containing Oxalic Acid and Ferrous Salts

The dissolution of nickel ferrite in oxalic acid and in ferrous oxalate–oxalic acid aqueous solution was studied. Nickel ferrite was synthesized by thermal decomposition of a mixed tartrate; the particles were shown to be coated with a thin ferric oxide layer. Dissolution takes place in two stages,...

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Bibliographic Details
Published in:Journal of colloid and interface science 2000-05, Vol.225 (2), p.403-410
Main Authors: Figueroa, Carlos A., Sileo, Elsa E., Morando, Pedro J., Blesa, Miguel A.
Format: Article
Language:English
Subjects:
Chemistry
DISSOLUTION
Exact sciences and technology
FERRITE
ferrous oxalate
General and physical chemistry
GENERAL STUDIES OF NUCLEAR REACTORS
HEAT TRANSFER
MATERIALS SCIENCE
mixed oxides
NICKEL COMPOUNDS
nickel ferrite
NUCLEAR POWER PLANTS
OXALIC ACID
Solution properties
Solutions
surface complexation
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Summary:The dissolution of nickel ferrite in oxalic acid and in ferrous oxalate–oxalic acid aqueous solution was studied. Nickel ferrite was synthesized by thermal decomposition of a mixed tartrate; the particles were shown to be coated with a thin ferric oxide layer. Dissolution takes place in two stages, the first one corresponding to the dissolution of the ferric oxide outer layer and the second one being the dissolution of Ni1.06Fe1.96O4. The kinetics of dissolution during this first stage is typical of ferric oxides: in oxalic acid, both a ligand-assisted and a redox mechanism operates, whereas in the presence of ferrous ions, redox catalysis leads to a faster dissolution. The rate dependence on both oxalic acid and on ferrous ion is described by the Langmuir–Hinshelwood equation; the best fitting corresponds to K1ads=25.6 mol−1 dm−3 and k1max=9.17×10−7 mol m−2 s−1 and K2ads=37.1×103 mol−1 dm−3 and k2max=62.3×10−7 mol m−2 s−1, respectively. In the second stage, Langmuir–Hinshelwood kinetics also describes the dissolution of iron and nickel from nickel ferrite, with K1ads=20.8 mol−1 dm3 and K2ads=1.16×105 mol−1 dm3. For iron, k1max=1.02×10−7 mol of Fe m−2 s−1 and k2max=2.38×10−7 mol of Fe m−2 s−1; for nickel, the rate constants k1max and k2max are 2.4 and 1.79 times smaller, respectively. The factor 1.79 agrees nicely with the stoichiometric ratio, whereas the factor 2.4 implies the accumulation of some nickel in the residual particles. The rate of nickel dissolution in oxalic acid is higher than that in bunsenite by a factor of 8, whereas hematite is more reactive by a factor of 9 (in the absence of Fe(II)) and 27 (in the presence of Fe (II)). It may be concluded that oxalic acid operates to dissolve iron, and the ensuing disruption of the solid framework accelerates the release of nickel.
ISSN:0021-9797
1095-7103
DOI:10.1006/jcis.2000.6734