Adsorption of Co2+and Zn2+Ions on Hydrous Fe(III), Sn(IV), and Fe(III)/Sn(IV) Oxides: II. Thermal Behavior of Loaded Oxides, Isotopic Exchange Equilibria, and Percentage Adsorption–pH Curves
✍ Scribed by Nasr Z. Misak; Hussein F. Ghoneimy; Tyser N. Morcos
- Publisher
- Elsevier Science
- Year
- 1996
- Tongue
- English
- Weight
- 220 KB
- Volume
- 184
- Category
- Article
- ISSN
- 0021-9797
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✦ Synopsis
Thermal analysis has shown that contrary to the case of Zn 2/ , phous whereas HSO gave very diffuse peaks characteristic considerable amounts of water enter in HFO (hydrous ferric oxof a SnO 2 mineral (cassiterite), indicating microcrystallinity. ide), HSO (hydrous stannic oxide), and HMO (hydrous mixed All the solids have the structure of oxides with surface OH oxide) when Co 2/ is adsorbed. A large amount of Co 2/ and Zn 2/ groups and water molecules and with water molecules in the in all the oxides cannot participate in isotopic exchange, seemingly interstices. The mixed oxide seems to have a surface strucbecause of being trapped inside the micropores, a fact hindering ture different from that of the component oxides, which was oxide capacity determination by isotopic dilution. The % adsorpsupported by the evaluation of the intrinsic acidity constants, tion-pH curves for tracer and 10 03 M transition metal chloride pH of the point of zero charge (pH PZC ), and apparent capacsolutions show a general preference to Zn 2/ over Co 2/ by all the oxides, in agreement with thermal analysis data. Large shifts of ity. The pH PZC was found (1, 2) to be equal to 6.8, 4.4, and these curves to the left occur with tracer experiments on many 6.2 for HFO, HSO, and HMO, respectively. The apparent samples on adding 0.1 M NaCl, probably due to Cl 0 adsorption capacity (1, 2) pointed to a stronger adsorption of Zn 2/ than accompanied by a change in the adsorption mechanism. Conclu-Co 2/ , in agreement with a stronger interaction with surface sions from log K d -pH plots may be erroneous, probably due to OH or H 2 O after removal of protons (3,4). Equilibria meachanges in the activity coefficients of surface species even at suffisurements of adsorption of the transition metal and Cl 0 ions ciently low surface coverages. More adsorption of Co 2/ and Zn 2/ in solutions containing both ions and of Cl 0 ions in solutions generally occurs on the oxide of lower pH PZC (higher acidity).
containing no transition metal ions have shown (1, 2) that