Lithium,rubidium and cesium ion removal using potassium iron(III) hexacyanoferrate(II) supported on polymethylmethacrylate

Potassium iron(III) hexacyanoferrate(II) supported on poly methyl methacrylate, has been developed and investigated for the removal of lithium, rubidium and cesium ions. The material is capable of sorbing maximum quantities of these ions from 5.0, 2.5 and 4.5 M HNO₃ solutions respectively. Sorption studies, conducted individually for each metal ion, under optimized conditions, demonstrated that it was predominantly physisorption in the case of lithium ion while shifting to chemisorption with increasing ionic size. Distribution coefficient (K _d) values followed the order Cs⁺ > Rb⁺ > Li⁺ at low concentrations of metal ions. Following these findings Cs⁺ can preferably be removed from 1.5 to 5 M HNO₃ nuclear waste solutions.     

Titrimetric determination of tin with potassium hexacyanoferrate(III) in the presence of redox indicators

A titrimetric determination of tin^II in strong hydrochloric acid solution with standard potassium hexacyanoferrate(III) solution using 3,3'-dimethylnaphthidine or o-dianisidine as indicator is described.     

Determination of antimony(III) with potassium hexacyanoferrate(III)

The determination of antimony(III) with potassium hexacyanoferrate(III) in 5M hydrochloric acid medium and in the presence of 40% v/v acetic acid is described. Ferroin is used as the indicator. Antimony has been determined in tartar emetic, solder and pig lead. Arsenic(III) does not interfere.     

Cyanide-bridged iron(II,III) cube with multistepped redox behavior

A building unit of Prussian blue was isolated as a cyanide-bridged iron cube of [Fe(II)4Fe(III)4(CN)12(tp)8] x 12 DMF x 2 Et2O x 4 H2O [tp(-) = hydrotris(pyrazolyl)borate]. A cyclic voltammogram showed quasi-reversible four-stepped redox waves, which correspond to [Fe(III)4Fe(II)4]/[Fe(III)5Fe(II)3](+), [Fe(III)5Fe(II)3](+)/[Fe(III)6Fe(II)2](2+), [Fe(III)6Fe(II)2](2+)/[Fe(III)7Fe(II)1](3+), and [Fe(III)7Fe(II)1](3+)/[Fe(III)8](4+) processes. Controlled potential absorption spectral measurements revealed two intervalence charge-transfer bands at 816 and 1000 nm, which were assigned to charge transfers from Fe(II) ions to adjacent and remote Fe(III) ions, respectively, in the cube.     

Nile blue and brilliant cresyl blue as redox indicators in iron(II) titrations

Nile Blue and Brilliant Cresyl Blue, two compounds related to diaminophenoxazine, have been studied as indicators in titrations of iron(II) with cerium(IV)(in hydrochloric, sulphuric and perchloric acid media), dichromate, vanadate and permanganate. They are particularly suited for titrations in a fairly concentrated sulphuric acid medium and for titrations with dilute solutions. A probable indicator mechanism is suggested.     

Potassium iron(III)hexacyanoferrate(II) supported on polymethylmethacrylate ion-exchanger for removal of strontium(II)

Potassium iron(III)hexacyanoferrate(II) supported on poly metylmethacrylate has been synthesized and investigated for the strontium(II) removal from HNO₃ and HCl solutions. The ion exchange material characterized by different techniques and found to be stable in 1.0–4.0 M HNO₃ solutions, has been used to elaborate different parameters related to ion exchange and sorption processes involved. The data collected suggested its use to undertake removal of Sr(II) from more acidic active waste solutions. Thus the material synthesized had been adjudged to present better chances of application for Sr(II) removal as compared to other such materials.     

Thermal decomposition of potassium cobalt hexacyanoferrate(II)

Potassium cobalt hexacyanoferrate(II), K₂CoFe(CN)₆ · 1.4H₂O, loses its water when heated up to 170°C, and the anhydrous compound begins to decompose above 230°C. The cyanide groups are evaporated off in the temperature range 230–350°C, and the solid products thus formed are K₂CO₃, Fe₂O₃, Co₃O₄ and CoFe₂O₄. In the range 550–900°C, the cobalt-containing compounds become CoO, and K₂CO₃ probably partly decomposes to K₂O, so that the product mixture at 900°C is K₂CO₃/K₂O, Fe₂O₃ and CoO. Above this temperature, K₂CO₃ decomposes to K₂O.     

Thermal decomposition of potassium hexacyanoferrate(II) trihydrate

Potassium hexacyanoferrate(II) trihydrate, K₄Fe(CN)₆·3H₂O, was heated under controlled conditions of mass and rate in a derivatograph in the presence of oxygen. The heating was stopped at different temperatures and Mössbauer spectra and X-ray diffractograms were taken on the quenched material at room temperature. The reaction pathway was studied in this way and the advantages and drawbacks of each of the techniques are described. At different stages of the thermal process we were able to show the presence of K₄Fe(CN)₆,-Fe₂O₃, Fe₃O₄, Fe₃C, Fe, FeO, KFeO₂,-FeOOH, KOCN, K₂CO₃ and KCN.

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Zusammenfassung Kaliumhexacyanoferrat(II)trihydrat, K₄[Fe(CN)₆.3H₂O wurde unter kontrollierten Bedingungen in einem Derivatographen in Gegenwart von Sauerstoff erhitzt. Das Aufheizen wurde bei verschiedenen Temperaturen gestoppt und Mössbauer-Spektren, sowie Röntgendiffraktogramme aufgenommen. Der Reaktionsweg wurde auf diese Weise untersucht und die Vor- und Nachteile jeder der Techniken beschrieben. Bei den verschiedenen Stufen des thermischen Vorganges konnten K₄[Fe(CN)₆],-Fe₂O₃, Fe₃O₄, Fe₃C, Fe, FeO, KFeO₂,-FeOOH, KOCN, K₂CO₃ und KCN nachgewiesen werden.

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Resumé Le ferrocyanure de potassium trihydraté, K₄Fe(CN)₆·3H₂O, a été chauffé en présence d'oxygÊne dans un Derivatograph, dans des conditions bien déterminées de masse et de vitesse de chauffage. Le chauffage a été interrompu à diverses températures et les spectres Mössbauer ainsi que les diffractogrammes de rayons X ont été enregistrés aprÊs trempe du matériau à la température ambiante. On a étudié de cette faÇon le déroulement de la réaction; on décrit les avantages et les inconvénients de chacune de ces techniques. On a pu déceler la présence de K₄Fe(CN)₆,-Fe₂O₃, Fe₃O₄ Fe₃C, Fe, FeO, KFeO₂,-FeOOH, KOCN, K₂CO₃ et KCN aux différentes étapes du traitement thermique.

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- (II)- -₄F/)₆. 3₃- . . . K₄Fe(CN)₆, -Fe₂O₃, Fe₃O₄, Fe₃C, Fe, FeO, KFeO₂,-FeOOH, KOCN, K₂CO₃ KCN.

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This research was performed with financial support from the Conselho Nacional de Desenvolvimento Científico e TecnolÔgico (CNPq) and Financiadora de Estudos e Projetos (FINEP). We are grateful to Profs. A. Bristoti, J. Danon, P. J. Aymonino, E. Baran and M. A. Blessa for valuable suggestions and criticisms, and Miss E. A. Veit for performing the thermal measurements at the Pontificia Universidade Católica, Porto Alegre. This work was submitted in partial fulfilment of the conditions for the degree of Livre Docente by one of us (J. I. K.).     

Catalytic effect of copper on the hexacyanoferrate(III)-cyanide redox reaction-I The uncatalysed and catalysed reactions

A kinetic study of the hexacyanoferrate(III)-cyanide redox reaction has been made in connection with development of a new catalytic method for copper. The reaction kinetics change with time from first- to second-order dependence with respect to hexacyanoferrate(III). The reaction is nearly inverse first-order with respect to hexacyanoferrate(II) and first-order with respect to cyanide. The reaction shows a strong positive primary salt effect, but a very small increase in the reaction rate with temperature is found. A parallel reaction proceeds with a first-order dependence with respect to hydroxide. A tentative mechanism is proposed for the first reaction, involving the formation of cyanogen radicals. The second reaction corresponds to the well-known decomposition of hexacyanoferrate(III) in alkaline medium. The catalysed reaction exhibits similar kinetics with respect to hexacyanoferrate(II) and (III) but is zero-order with respect to cyanide and hydroxide and first-order with respect to catalyst. The proposed mechanism involves two consecutive interactions of the hexacyanoferrate(III) with copper(I) and with copper(II) cyanide complexes respectively, followed by a 2-electron oxidation of a co-ordinatively bridging cyanide group.     

Solvent effects on the redox potentials of tetraethylammonium hexacyanomanganate(III) and hexacyanoferrate(III)

Tetraethylammonium hexacyanomanganate(III) was studied in formamide, N-methylformamide, methanol, propylenecarbonate, N,N-dimethylthioformamide, N-methylthiopyrrolidinone(2), butyrolactone, acetonitrile, dimethylsulfoxide, N,N-dimethylformamide, N-methylpyrrolidinone(2), nitromethane and tetramethylenesulfone employing polarographic and voltammetric techniques. Reversible or nearly reversible behaviour for the reaction Mn(CN)₆^3?/Mn(CN)₆^2? was observed in most solvents on the stationary platinum electrode. The reaction Mn(CN)₆^3?/Mn(CN)₆^4? was studied on both the dropping mercury electrode and the stationary platinum electrode. Besides the reaction Mn(CN)₆^3?/Mn(CN)₆^4? several anodic waves due to successive reactions of mercury with the cyano-ligand of the complex occurred at the dropping mercury electrode. No redox reaction for (et₄N)₃Mn(CN)₆ was found in nitromethane. The polarographic behaviour of tetraethylammonium hexacyanoferrate(III) was studied in formamide, N-methylformamide, N-methylpyrrolidinone(2) and butyrolactone. The variation of E_1/2 and 1/2 (E_pa+E_pc) values versus bisphenylchromium(I)/bisbiphenylchromium(0) as reference redox system of the processes Mn(CN)₆^3?/Mn(CN)₆^2?, Mn(CN)₆^3?/Mn(CN)₆^4? and Fe(CN)₆^3?/Fe(CN)₆^4? with the nature of the solvent is discussed within the donor-acceptor concept. Correlations between the E_1/2 and 1/2(E_pa+E_pc) values and the acceptor properties of the solvent have been observed. The preparation of tetraethyl- and tetrabutylammonium hexacyanomanganate(III) is described.     

Oxidimetric determination of indigo with iron(III) and hexacyanoferrate(III)

The use of iron(III) in sulphuric acid medium and of potassium hexacyanoferrate(III) in hydrochloric acid medium has been investigated for the oxidimetric determination of indigo and indigo sulphonic acid. Conditions have been established for the assay of the dye with iron(III) sulphate at 100 degrees and with potassium hexacyanoferrate(III) at room temperature.     

Titrimetric determination of sodium dithionite with potassium hexacyanoferrate(III) as reagent and methylene blue as indicator

Summary A rapid titration procedure is recommended for the estimation of Na₂S₂O₄ in commercial sodium dithionite (sodium hydrosulphite, sodium hyposulphite) and in aqueous solutions of this compound, using potassium hexacyanoferrate(III) as reagent and methylene blue as indicator.With the procedure described there is no interference of decomposition products of dithionite (sulphate, sulphide, sulphite, trithionate, thiosulphate), additives (sodium chloride, phosphates, soda, EDTA, urea), methanol, ethanol, acetone or groundwood.For a commercial sodium hydrosulphite containing 91% of Na₂S₂O₄ the standard deviation is 0,3% absolute (degrees of freedom 9).

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Zusammenfassung Na₂S₂O₄ wird in technischem Natriumdithionit und dessen Lösungen mit Kaliumhexacyanoferrat(III) unter Verwendung von Methylenblau als Indicator titriert. Zersetzungsprodukte des Dithionits (Sulfat, Trithionat, Sulfit, Thiosulfat, Sulfid), Zusätze (Kochsalz, Soda, Phosphate, ÄDTA, Harnstoff), Methanol, Äthanol, Aceton oder Holzschliff stören nicht. In einem technischen Natriumdithionit mit 91% Na₂S₂O₄ betrug die Standardabweichung 0,3% absolut (9 Freiheitsgrade).

     

Solvent effects on the redox properties of tris-(1,10-phenanthroline)iron(II/III) complexes

The redox properties of the system Fe(tmphen)₃(II/III) (tmphen=3,4,7,8-tetramethyl-1,10-phenanthroline) have been studied in the solvents nitromethane, acetonitrile, propanediol-1,2-carbonate, dimethylformamide, dimethylacetamide, dimethylsulfoxide and of the systems Fe(phen)₃(II/III) (phen=1,10-phenanthroline) and Fe(niphen)₃(II/III) (niphen=5-nitro-1,10-phenanthroline) in the solvents nitromethane, acetonitrile, propanediol-1,2-carbonate and acetone. The redox potentials of Fe(tmphen)₃(II/III) are nearly independent of the solvent suggesting that the system might be used as a reference redox couple similar to the systems ferrocene/ferricinium or bisbiphenylchromium(0/I). In contrast the redox potentials of Fe(niphen)₃(II/III) show a significant decrease with increasing donor number of the solvent which can be explained by nucleophilic attack of solvent molecules at the iron. It is shown that such a mechanism is consistent with the known solvent and salt effects on the kinetics of dissociation of ferroin and ferriin type complexes.     

Thermal decomposition of hydrotalcitewith hexacyanoferrate(II) and hexacyanoferrate(III) anions in the interlayer

The thermal decompositions of hydrotalcites with hexacyanoferrate(II) and hexacyanoferrate(III) in the interlayer have been studied using thermogravimetry combined with mass spectrometry. X-ray diffraction shows the hydrotalcites have a d(003) spacing of 11.1 and 10.9 Å which compares with a d-spacing of 7.9 and 7.98 Å for the hydrotalcite with carbonate or sulphate in the interlayer. XRD was also used to determine the products of the thermal decomposition. For the hydrotalcite decomposition the products were MgO, Fe₂O₃ and a spinel MgAl₂O₄. Dehydration and dehydroxylation take place in three steps each and the loss of cyanide ions in two steps.     

Catalytic effect of copper on the hexacyanoferrate(III)-cyanide redox reaction

The oxidation of cyanide with hexacyanoferrate(III) is a thermodynamically possible but kinetically slow reaction, which is catalysed by copper(II). The catalysed reaction has a second-order dependence on hexacyanoferrate(III) concentration, and the pseudo second-order rate constant increases linearly with the copper concentration, at least in the range from 10(-7) to 10(-3)M.     

Solvent effects upon reactions between ions: hexacyanoferrate(II)-peroxodisulphate and sulphite-hexacyanoferate(III)

Summary Different approaches to the interpretation of solvent effects on reactions between ionic reactants are analysed, taking as a basis the kinetic data corresponding to the sulphite-hexacyanoferrate(III) and peroxodisulphate-hexacyanoferrate(III) oxidations. It is concluded that the approach based on the use of solvent parameters is the more promising, although knowledge of the transfer chemical potentials of the reactants may also be useful in the interpretation of kinetic behaviour.