SU1713892A1 - Method of preparing seed for direct crystallization of red iron oxide - Google Patents

Abstract

The invention relates to the technology of preparation of the embryo for the direct crystallization of ferric oxide of iron. Crystalline hematite nuclei are obtained by oxidative precipitation of iron sulfate with air at 10-38 ° C and simultaneously maintaining pH 8-9 with ammonia or sodium hydroxide, followed by thermal dehydration of lepidocrocite in ferric sulfate solution at 80-100 ° C for 0, 1-6 hours. Preferably, lepidocrocite is heat treated at normal pressure in air from 120 to 200 ° C for 4-6 hours before thermal dehydration. Moreover, heat treatment is carried out by heating a suspension of lepidocrocite in water or in a solution of ammonium sulfate, and / or sodium concentration of 0.1-1.6 mol of sulfate per 1 liter at a temperature of from 95 ° C to the boiling point of the reaction medium for 1-10 hours. The method ensures high phase purity of the crystals a Re203, as well as the homogeneity of germinal crystals. 3 hp f-ly.elS

Description

The invention relates to a method for preparing a germ for the direct crystallization of red iron oxide by oxidative precipitation of iron sulfate with air while neutralizing with ammonia or sodium hydroxide at 10-50 ° C and subsequent thermal dehydration of the lepidocrocite formed in crystalline hematite.

Red iron oxide is prepared by oxidatively precipitating a solution of iron sulfate with air while simultaneously neutralizing the reaction mixture with a base, such as alkali or ammonia. The process is carried out at 90-95 ° C and a pH of about 4 in the presence of nuclei for the crystallization of pigment particles.

One of the main factors that determine the optimal properties of the pigment produced is the physical and chemical properties of the germ crystals. As nuclei for crystallization of iron oxide, less stable iron oxyhydroxides are used (except for goethite, i.e., a-FeOOH), namely amorphous hydroxide (US Patent No. 2620261, Cl. 23200 published 19S2) or 3-Feooh (HGF Ns 2249274. Cl. 12p 49/06, published 1974). The crystallization process is carried out in two successive stages, with pigment crystals with predetermined particle sizes being precipitated again for the second precipitate obtained from the solution by wild crystallization (US Patent Mg 2716595. Cl, 23-200, published 1955)

Lepidocrocite (y-POOH) is also used to prepare germinal crystals of a-Fe2Bz (hematite) of high phase purity. However, under the conditions of production of red iron oxide, lepidocrocite undergoes simultaneous dehydration of hematite into iron sulfate solutions and conversion into a-FeOOH (goethite) which in the reaction mixture is generally undesirable, since it shifts the main reaction to another direction (J, Inorg, Nucl. Chem., 1967, 29, 1235). To achieve satisfactory results, t, e, when preparing a -Fe203 of high phase purity take it at the same time Hematite embryo preparation has a difficult hydrothermal treatment at elevated pressure (certificate of authorship of Czechoslovakia No. 178615.kl, C 01 G 49/02, 1977).

A systematic study showed that the behavior of lepidocrocite in heated solutions of ferrous sulfate depends largely on the conditions of the previous preparation of lepidocrocite by oxidatively precipitating solutions of ferrous sulfate with air during neutralization with ammonia.

The proposed method for preparation of germs for direct crystallization of red iron oxide, based on oxidative precipitation of iron sulfate with air while neutralizing with ammonia or sodium hydroxide at 10-50 ° C and subsequent thermal dehydration of the lepidocrocite formed into crystalline hematite, consists in the oxidation of sulfate solution. iron is carried out at a constant pH in the range of 8–9, and lepidocrocite obtained in this manner after it is subjected to transformation into a hematite germ by heating in a solution of iron sulfate at 8 p –100 ° C for 0.1–6 h. The lepidocrocite obtained before transformation into the embryo is subjected to heat treatment under normal pressure. This heat treatment can be carried out either by heating lepidocrocite in air at 120–200 ° C for 1–6 hours, or by heating

its suspensions in water or in a solution of ammonium sulfate and / or sodium with a concentration of 0.1–3 mol of sulfate per 1 liter, at a temperature from 95 ° C to the boiling point of the system during

MOCH,

The behavior of lerirocrocite prepared by oxidative precipitation of ferrous sulfate with simultaneous neutralization with ammonia at 0–50 ° C and a pH in the range of 6–10 (certificate of Czechoslovakia No. 195784. Cells, C 09 C 1/24, 1979) when heated in sulphate solutions iron depends on the stabilized pH. wherein oxidation is carried out. It should be noted that separate, at different pH values within the indicated limits, lepidocrocite samples prepared cannot be distinguished by ordinary physicochemical methods. Participation of lepidocrocite dehydration, t, e, conversion to a-ResOZ at

heating in iron sulphate solutions rises sharply from a lower value corresponding to the behavior at pH 6 of the prepared Lepids Crocite, to 100% dehydration observed during heating of Lepid Crocit prepared at pH 8.5, after which it decreases sharply.

Lepidocrocite preparations prepared by oxidative precipitation of iron sulfate with an air-ammonia system

PIRV 8.5 and a temperature of 10-35 ° C, are converted in solutions of ferrous sulfate at elevated temperatures exclusively to hematite, and only such preparations are convenient for preparing embryos for

crystallization of red iron oxide.

It has been established that the joint transformation of lepidocrocite into goethite and its dehydration 8 hematite in heated solutions of ferrous sulfate include, at least. four reactions:

y -FeOOH (scaly) - y-FeOOH (rod-shaped); (one)

y-FeOOH (rod-shaped) -FeOOH (needle-shaped); (2)

y-FeOOH (scaly) - a-Fe203 (microcrystalline); (3)

a-FeOOH (needle-like) - “-Fe203 (macrocrystalline); (four)

Reactions (1) and (3) act as competitive, but only reaction (3) leads to the desired product. In reaction (4), the hematite that arises does not impair phase purity, but it is inconvenient due to the considerably large size of its particles,

In addition, reaction (4) proceeds much slower than reaction (2), with the result that goethite accumulates in the mixture. The preparation of lepidocrocite with

A constant pH of 8.5 allows one to shift the course of its thermal transformation in favor of a given reaction. (3) whereby this transformation is carried out by heating the same solution in the sulfate solution to a temperature of 80-100 ° C for OJ-6 h.

In industry it is impossible to precisely maintain the desired parameters, especially pH, within fairly narrow limits. In order to achieve standard optimal results during the preparation of the nucleus for the crystallization of red iron, it may therefore be advisable to turn the oxidation of the prepared lepidocrocite into a further stage by changing the distribution of adsorbed (non-structural) water in the microcrystals of lepidocrocite, resulting in heating the lepidocrocite in a solution of ferrous sulfate. leads to the formation of microcrystalline hematite. Pretreatment is carried out either by heating lepidocrocite in air at 120–200 ° C for 1–6 h, by heating its aqueous suspension to 95100 ° C for 5–10 h or by heating its suspension in solutions of inorganic salts, for example in solutions of ammonium sulfate or sodium with a concentration of 0.1–3 mol per liter (for example, in the mother liquor remaining after preparation of lepidocrocite), at a temperature of from 95 ° C to the boiling point of the corresponding solution for 1–6 h.

The proposed preparation method ensures a high phase purity of a-Fe203 crystals, since it prevents the formation of other undesirable oxide compounds in the reaction mixture. In addition to this, it also guarantees the uniformity of the seed crystals, as regards the particle size.

Example 1. In a 1.5 liter vessel, the preparation was made by oxidizing 1 liter of iron sulphate solution (1 mol / l) of 88.5 g (1 mol) of y-hydroxy iron oxide (lepidocrocite), while maintaining the pH of the solution automatically during air inlet 8, 5 ± 0.05 by addition of ammonia solution. The temperature of the reaction mixture 19-38 ° C. After the ferrous ions disappear from the reaction mixture, the contents of the vessel are heated at 95-100 ° C for 6 hours. The solid phase is then filtered out of the reaction mixture and transferred to a reaction vessel containing 10 liters of ferrous sulfate solution (90 g Fe / l) and the mixture is heated at 90-95 ° C for 2 hours. With vigorous stirring, air is introduced at this temperature.

for 10 h, neutralize at the same time a mixture of 25% ammonia solution to maintain the pH in the range of 3.8-4.1. After completion of the reaction, a red iron oxide is obtained containing 99.5% a-iron oxide.

EXAMPLE 2 Lepidocrocite is prepared analogously to Example 1, with the only difference that the pH is maintained within 6.87, 5. 90 g of the solid phase is isolated and slowly dried from the mixture. After further heating at 170 ° C for 4 hours, the product is used as a nucleus for the direct crystallization of red iron oxide, the process is carried out as in Example 1. The oxidative precipitation of the solution of iron sulphate produces a red pigment containing, in addition to hematite, only 0.7. % impurity a-hydroxy iron oxide (goethite).

Example 3. Analogously to Example 1, 1 mol of lepidocrocite is prepared, and the pH is maintained within 8.5 ± 0.5. Lepidocrocite is isolated, washed and heated in water at 100 ° C for 10 hours. After cooling to 80 ° C, 1.5 mol of ferrous sulfate is dissolved in the reaction mixture and the mixture is heated at 80-95 ° C for 3 hours. After the mixture is transferred to a vessel with a capacity of 20 liters containing 15 liters. a solution of ferrous sulfate with a content of 88.5 g Fe / l. Turning the reaction mixture to red iron oxide wire is the same as Example 1. After isolation, a red pigment containing, apart from hematite, only 0.3% of other oxide iron compounds is obtained.

Example 4. Analogously to Example 1, y-hydroxy iron oxide is prepared, except that the pH of the reaction mixture is maintained in sections 7.0-7.6. The temperature of the reaction mixture rises from 20 to 35 ° C during the reaction. After filtration and washing, 86.3 g of pure lepidocrocite (y-RESO) are obtained. The product is introduced into a reaction vessel containing 10 liters of ferrosulphate solution (90 g Fe / l). The contents of the vessel were subjected to the same treatment as in Example 1. The X-ray analysis determined that the product formed contained, in addition to a-FeaOs (83%), also 17% or-FeOOH, Kotor significantly reduces the quality of the product.

EXAMPLE 5 Analogously to Example 1, 88.8 g of lepidocrocite is prepared, maintaining the pH of the reaction mixture in the range of 8-8.3 and the temperature in the range of 18-34 ° C. The dried product is heated in a dryer at 120130 ° C for 6 hours. By transformation in ferrosulfate solution (76 g / l) for 6 minutes at 100 ° C, 79 g of hematite with a specific surface area of 85 is obtained. This product is very convenient as a seed for the crystallization of red iron oxide. Example 6. Analogously to Example 1, 88.5 g of lepidocrocite is prepared, maintaining the pH of the reaction mixture at 8.8–9 and temperature at 10–30 ° C for 6 h, and then it is introduced into ferrosulphate solution (15.2 g / l) with a volume of 4 l, and the mixture is heated at 80 ° e for 6 h. During this operation, the product undergoes a complete transformation to a-ReaO3 with a specific surface of 100. The resulting oxide is used as a germ, and get hematite containing only 0, p% aFeOOH. . . Example 7. In a manner similar to Example 2, 88.5 g of lepidocrocite are prepared. After filtration, the product is introduced into 4 liters of a solution containing 792 g of sodium sulfate and 852 g of ammonium sulfate, and the mixture is heated at the boiling point for 1 hour. Due to this heat treatment, lepidocrocite changed during the transformation process, which was carried out as described in Example 5, into pure a-FeaOz. Example 8. The method described in Example 2 was used to prepare lepidocrocite, which, without pretreatment, was converted into a mixture of hematite and goethite in ferrosulfate solution. Therefore, it is heated at 95-100 ° C for 6 hours in a solution of sodium sulfate (14.2 g / l), and then subjected to transformation into a-ReaO3 as described in Example 5. Microcrystalline hematite with a specific surface of 60 is obtained, containing only 1% iron oxyhydroxides. Ph o rumula and 3 o rams 1. Method of preparing the embryo for direct crystallization of red iron oxide, including oxidative precipitation of iron sulfate by air at 10-38 ° C and simultaneously maintaining pH 8 with ammonia or sodium hydroxide -9 followed by thermal dehydration of lepidocrocite to produce crystalline hematite, characterized in that thermal dehydration is carried out in a solution of ferrous sulfate at 80-100 ° C for 0.1 to 6 hours. 2. Method pop. 1, wherein lepidocrocite is thermally treated at normal pressure prior to thermal dehydration. 3. Method according to paragraphs. 1 and 2, that is, so that heat treatment is carried out in air from 120 to 200 ° C for 4-6 hours. 4. Method according to claims. 1 and 2, that is, so that the heat treatment is carried out by heating a suspension of lepidocrocite in water or in a solution of ammonium and / or sodium sulfate with a concentration of 0.1-1.6 mol of sulfate per 1 liter at a temperature of from 95 ° C to the boiling point of the reaction medium for 1-10 hours.

Claims (4)

Claim 1. A method of preparing a nucleus for direct crystallization of red iron oxide, including the oxidative precipitation of iron sulfate by air at 10-38 ° C and while maintaining ammonia or sodium hydroxide pH 8-9 with subsequent thermal dehydration of lepidocrocite to obtain crystalline hematite, characterized in that thermal dehydration is carried out in a solution of iron sulfate at 80-100 ° C for 0.1-6 hours 2. The method of pop. 1, characterized in that the lepidocrocite before thermal dehydration is subjected to heat treatment at normal pressure. 3. The method according to PP. 1 and 2, characterized in that the heat treatment is carried out in air from 120 to 200 ° C for 4-6 hours 4. The method according to PP. 1 and 2, which stipulates that the heat treatment is carried out by heating a suspension of lepidocrocite in water or in a solution of ammonium and / or sodium sulfate with a concentration of 0.1-1.6 mol of sulfate per 1 liter at a temperature of 95 ° C to the boiling point the reaction medium for 1-10 hours