Factors affecting the precipitation of chromium(III) in jarosite-type compounds
Autor: | J. E. Dutrizac, T. T. Chen |
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Rok vydání: | 2005 |
Předmět: |
Materials science
Precipitation (chemistry) Potassium Inorganic chemistry Metals and Alloys chemistry.chemical_element Recrystallization (metallurgy) engineering.material Condensed Matter Physics Microstructure Amorphous phase Amorphous solid Chromium chemistry Mechanics of Materials Jarosite Materials Chemistry engineering |
Zdroj: | Metallurgical and Materials Transactions B. 36:33-42 |
ISSN: | 1543-1916 1073-5615 |
DOI: | 10.1007/s11663-005-0003-6 |
Popis: | Jarosite precipitation is a useful means of stabilizing toxic species, and accordingly, the factors affecting the precipitation of chromium(III) in jarosite-type compounds was systematically investigated in a series of laboratory experiments. Although end-member Cr(III) analogues of jarosite-type compounds could not be precipitated at temperatures 200 °C, the Cr(III) analogue of potassium jarosite (KCr3(SO4)2(OH)6) is readily precipitated. The Cr(III) analogue has the R\(\bar 3\)m structure characteristic of jarosite-type compounds, with a=7.23±0.02A and c=17.02±0.02 A. The well-crystallized material typically contains (wt pct): ∼7K, ∼25Cr, and ∼41SO4. The composition suggests the partial substitution of hydronium ion for potassium and some chromium vacancies in the structure. The formation of the Cr(III) analogue is promoted by increasing temperatures, retention times, and Cr(III) concentrations. Increasing acid concentrations reduce the amount of product formed but suppress the undesirable precipitation of amorphous phases. Although increasing K2SO4 concentrations result in a greater mass of precipitate, the products formed from concentrated K2SO4 solutions are contaminated with an amorphous phase. In fact, the overall results suggest that an amorphous phase precipitates initially and that the Cr(III) analogue of potassium jarosite forms by the recrystallization, or the dissolution-reprecipitation, of the amorphous phase. |
Databáze: | OpenAIRE |
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