G. W. Thompson, L. T. Ockerman, J. M. Schreyer: "Preparation and Purification of Potassium Ferrate. VI" in J. Am. Chem. Soc. 1951, 73(3), S. 1379–1381. doi:10.1021/ja01147a536
Fe + KNO3 ==(annealing)==> K2FeO4 + N2 + O2 (not 100% quantitative; impurity ...Fe3O4...and other oxids)
after cooling, leaching with ice water and filtration. The filtrate (solution!) contains the ferrat, but the solution isn`t stable! So immediatly adding BaCl2 to precipitate the BaFeO4. Washing the solid with water (cold) and ethanol (pure!) and drying in vacuum.
Hope I could help!
A more recent, reliable synthesis of K2FeO4 and BaFeO4 has been described by R.J. Audette and J.W. Quail, Inorganic Chemistry 11, 1904-1908 (1972)
DOI: 10.1021/ic50114a034
The authors used hypochorite as the oxidizing agent and the hydroxide ion as the precipitating medium:
Fe2O3 + 3ClO- + 4OH- => 2[FeO4]2- + 3Cl- + 2H2O
The barium salt was prepared using potassium ferrate as starting material.
The method cited by Ralph Huebner has been improved upon by C. Li
X. Z. Li and N. Graham in "A study of the Preparation and Reactivity of Potassium Ferrate", Chemosphere 61, 537-543 (2005)
This method yields potassium ferrate of higher purity.
A preprint of this paper can be downloaded at the following URL:
http://repository.lib.polyu.edu.hk/jspui/bitstream/10397/2438/1/53.pdf
The potassium ferrate preparation part of the preprint is:
165 ml of 37% HCl was slowly reacted with 26.7 g of KMnO4 to produce chlorine. The chlorine was subsequently added to pre-chilled KOH solution (60 g of KOH in 100 ml of water) with stirring for over 2 h. A quantity of 90 g of KOH was then added into this solution and the resulting suspension was cooled. The precipitate of KCl was removed from the suspension by filtration using a GF/C filter paper, leaving a concentrated and strongly alkaline solution of potassium hypochlorite.
This yellow solution of KClO was then stirred rapidly while 37.5 g of pulverized Fe(NO3)3.9H2O was added slowly for over 1 h under cooling conditions (< 5 °C). In these conditions, the Fe(III) ion was readily oxidized to Fe(VI) and the solution became dark purple in colour. A quantity of 30 g of KOH was then added in small portions to the Fe(VI) solution and the mixture was stirred for 20 min. The resulting solution was allowed to stand for a further 40 min. The resulting dark purple slurry was filtered with a glass filter (P-0), after which the filtrate was discarded, and the precipitate was washed six times with a 25 ml quantity every time of cold 1 M aqueous KOH solution. The filtrate from the washings was collected and added to a flask containing 300 ml of a chilled saturated KOH solution. The solution was mixed, allowed to stand for 10 min, and then filtered initially with a glass filter (P-3), followed by double filtering with GF/A filter papers (Whatman Φ70mm). The precipitate was flushed with n-hexane (four times × 25 ml), n-pentane (four times × 25 ml), methanol (four times × 10 ml), and diethyl ether (two times × 10 ml). The final product, solid
potassium ferrate (black in color), was collected and stored in a vacuum desiccator prior to further use.
As you see, this prearation method does not require expensive chemicals or equipment!
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