Chemistry of inorganic compounds – Oxygen or compound thereof – Metal containing
Patent
1992-05-06
1994-02-08
Hruskoci, Peter A.
Chemistry of inorganic compounds
Oxygen or compound thereof
Metal containing
210716, 210721, 210758, 25218625, 25218633, 423596, 423599, 423600, C01G 4902
Patent
active
052846423
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to new alkali or alkaline earth metal ferrates.
The invention is also concerned with their process of preparation and their industrial applications.
It is known that the ferrates of the formula M FeO.sub.4, in which M is an atom of Ca or Ba, or two atoms of Na or K, are powerful oxidizers.
When they are introduced into water, they liberate oxygen according to the following reaction: O.sub.2
However, these ferrates are not stable, so that they cannot be stored for long periods. This instability is incompatible with industrial use of these ferrates as oxidizers.
The object of the present invention is to provide stable ferrates, which is to say industrially usable particularly as oxidizers.
According to the invention, these ferrates are characterized in that they have the formula: is an atom whose cation has the electronic structure of a rare gas, said ferrates being isomorphs of ferrates of the formula M FeO.sub.4, in which M is as defined above.
Thus the ferrates according to the invention are distinguished from ferrates of the formula M FeO.sub.4 by the fact that certain Fe atoms have been replaced by atoms of X.
The formula M(Fe, X)O.sub.4 can be established by classical chemical analysis.
It has been established by X-ray diffraction that the ferrates M(Fe, X)O.sub.4 have a crystalline structure identical to that of M FeO.sub.4 ferrates. Only the dimension of the crystal lattice varies slightly because of the presence of the X atoms, particularly when the dimension of this latter is different from that of the atoms of Fe that they partially replace.
The stability of the ferrates according to the invention can be explained by the fact that the cation of the atom X has the electronic structure of a rare gas.
Thus the X atom can be selected from among the following: Al, Si, P, S, Cl, Mo, Mn, Cr and the mixture of these atoms.
The corresponding cations, namely:
Al.sup.3+, Si.sup.4+, P.sup.5+, S.sup.6+, Cl.sup.7+, Cr.sup.6+, Mo.sup.6+ and Mn.sup.7+ have the electronic structure of a rare gas.
According to a preferred embodiment of the invention, the ratio Fe/(X+Fe) (number of atoms of Fe over that of the (X+Fe) atoms) is between 0.5 and 0.9.
When the ferrates according to the invention fulfill this supplemental condition, they have both a high stability and an excellent oxidizing power.
According to another aspect of the invention, the process of preparation of the ferrates according to the invention is characterized in that there is caused to react the compound M OH and an oxidizer, with a chemical compound in which the atoms of Fe are combined with the X atoms.
The compound M OH can be NaOH, K OH, Ca(OH).sub.2 or Ba(OH).sub.2.
Thus, the compound M OH and an oxidizer can be reacted with iron sulphate, iron silicate, iron phosphate, iron chromate, iron molybdate, iron tungstate, iron manganate, iron perchlorate or iron aluminate.
By way of example, to prepare the ferrate of the formula: state into a solution of soda or potash, agitation is conducted and the product obtained is dried and an oxidizer is added thereto.
To this end, at least the stoichiometric quantity of iron sulphate is caused to react with the soda or potash.
According to another embodiment of the process according to the invention, there is caused to react with the soda or potash a mixture of iron sulphate and Ca hypochlorite.
The compound of the formula
M.sub.2 (Fe, S)O.sub.4 is the preferred ferrate according to the invention, because it can be obtained from iron sulphate FeSO.sub.4. 7 H.sub.2 O which is an inexpensive chemical product. It is particularly a residue of the industrial production of titanium.
There will now be developed the theoretical aspects which are fundamental to the present invention.
It is well known that the best known iron salts are those in which the metallic element has degrees of oxidation II and III, namely Fe(II) which has a mildly reducing nature, and Fe(III) which has a mild oxidizing nature.
The degrees of oxidation higher than III are on the other hand much less known, whether the
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Evrard Jean-Luc
Evrard Omer J.
Gerardin Rene A.
Schmitt Nathalie
Centre International de l'Eau de Nancy (NAN.C.I.E.)
Evrard Omer
Hruskoci Peter A.
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