CS225286B1 - The preparation of the hydrated magnetite - Google Patents

Description

BACKGROUND OF THE INVENTION The present invention relates to a process for the production of hydrated magnetite Fe ^O ^nH HO, especially for the preparation of so-called magnetic liquids, for sorption-separation purposes, particularly in a magnetic field or as a black pigment.

Recently, so-called magnetic fluids have been increasingly applied in wider technical practice. These are magnetic suspensions to colloids, dispersed in water and in some non-polar solvents, with a particle size of mostly 1 to 100 nm. The application of these mixtures proves to be very attractive in many fields of human activity. The solutions can operate on the basis of a magnetic or electromagnetic pulse, for example as an optical shutter at a rate of 0.01 second, liquids can be pulsed to a solid with a strength of 2 to 3 kg / cm and can liquefy again by abolishing the magnetic field; the use of this effect is therefore extremely interesting, for example, for rotary shaft seals with a minimum resistance, etc.

Another promising application of such ferromagnetic materials is their application as sorbent carriers for filtration and separation from colloidal to suspension media in the magnetic field. For technical practice, magnetite Fe? O? Is the most accessible material for these applications. Its fine suspension is prepared from a crude starting material by usually effective grinding in liquid medium in the presence of a surface

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225 286

225 286 active stabilizers. The basic component Fe základníO základní is prepared either by the conventional method of hydrogenation of ferric oxide

400 ° C ^Fe 2 ° 3 ^{+ H} 2 Τ '* Τι- * ^{2 Pe} 3 ° 4 * ^H 2 ° ² 3OO ² minutes or eg according to jap.pat. No. 8184,322 was prepared from Fe ^O ^ from an aqueous solution of green vitriol and an excess of ammonium sulfate in the presence of ammonia by oxidation with atmospheric oxygen for several hours. This is essentially a modified preparation process for the production of black pigment according to Martin of the 1960s, according to U.S. Patent 2,939,767.

The first method works dry at very high temperature and pressure and results in anhydrous magnetite. The second method uses higher amounts of auxiliary ammonium sulfate; however, the process does not guarantee a completely correct ratio of divalent and trivalent iron in the compound. The raw material and the ferromagnetic properties of the material are not essential either, as it is the production of a pigmentary raw material.

The process for the preparation of the hydrated magnetite according to the invention removes these drawbacks.

The present invention relates to a process for the preparation of hydrated magnetite Fe 2 O 4 · n H 2 O, wherein n = 0.5 to 8, characterized in that stoichiometric proportions of solutions of ferrous and trivalent iron salts, preferably chlorides or sulphates, are mixed. or an alkali metal hydroxide to a value of 5.5 to 8.0 and the resulting hydrated magnetite is separated and concentrated, e.g., in a magnetic field, wherein the input ferric compound is prepared by oxidation of ferrous chloride or sulfate, preferably by contact with nitrous exhalations.

The process according to the invention is generally carried out in such a way that the starting aqueous solution of ferric chloride or sulphate, usually at a concentration of 10 to 20% by weight, is divided into three equal volumes, the two parts being included as washing solution at the outlet of waste nitrous exhalation; after complete oxidation of the divalent iron cation to trivalent in this fraction, the solution is mixed with the remaining separate part, the pH of the mixture is then adjusted to 5.5 to 8.0 and at about 60 ° C the black precipitate or hydrated magnetite colloid is separated, preferably in a magnetic field.

The method of preparation of the hydrated magnetite according to the invention ensures an accurate ratio of Fe 2: Fe in the compound and thus optimum ferromagnetic properties of the preparation, eliminates the need for conventional auxiliary admixtures of salts to solutions, eliminates increased waste production and in homogeneous mixture with particles up to 1 nm; the sorption ability of the magnetite thus formed is also demonstrable.

The prepared hydrated magnetite Fe-O ^ .n HgO binds in a molecule of 0.5 to 8 moles of HgO, corresponding to approximately 60% by weight of the water content of the solid phase. Weight obtained

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The preparation is in the range of 2.60 to 5.00 g / cm. The structure of the preparation prior to mechanical treatment has the character of spherical particles having a size of 0.1 to 0.5 with a tendency to form agglomerates having a size of about 40 to 50 µm.

The method of preparation of the hydrated magnetite is further illustrated in the examples, which, however, do not fully cover the preparation possibilities and by variation, e.g.

Example 1

A solution of green vitriol containing 92.6 g of FeSO4.7HgO in 200 cm of water was included as a wash solution at the outlet of the nitrous gas exhalation.

II III

The solution after complete oxidation of the contained Fe to Fe was further mixed with half the volume of the initial non-oxidized ferrous sulfate solution, the mixed solution adjusted to pH 8.0 with ammonia gas, with a natural temperature rise to 60 ° C. Serum colloidal pigment - hydrated magnetite was smoothly separated from the water phase in the magnetic field by 0.1 T free flow.

The weight of the obtained preparation was 4.3 g / cm @ 2, the particle size of the precipitated preparation ranged from 0.1 to 0.5 .mu.m.

Example 2

500 cm @ 2 of a 22 wt. was included as II IIT wash solution for NO exhalation. After complete oxidation of Fe to Fe, the solution was mixed with half the volume of the starting ferrous chloride solution. The mixture was further adjusted to pH 5.5 with aqueous NaOH and the black hydrated magnetite precipitate was treated with a turbine disintegrator to form an aqueous mixture of colloidal character with a particle size of 1.

Claims (1)

to 5 nm. P fi E D I.I E T INVENTION Process for the preparation of hydrated magnetite Fe ^O ^nH HO, wherein n = 0.5 to 8, characterized in that the stoichiometric proportions of solutions of ferrous and trivalent iron salts, preferably chlorides or sulphates, are mixed, the pH of the mixture is adjusted with ammonia or alkaline hydroxide. to a value of 5.5 to 8.0 and the resulting hydrated magnetite is separated and concentrated e.g. in a magnetic field.