SU1724585A1 - Method of ferric hydroxide preparation - Google Patents

Abstract

This invention relates to a process for producing pigments. The purpose of the invention is to increase the yield of ocher yellow crystalline iron (III) monohydroxide. This goal is achieved by oxidizing metallic iron with oxygen in a 1-10% aqueous solution of ammonium chloride, filtering, washing to a negative reaction to chloride ions in the washing water and drying the product. The proposed method allows to increase the yield of iron (III) hydroxide, which has a pure ocher-yellow color. The method is less material- and energy-intensive. 1 tab.

Description

The invention relates to methods for producing iron hydroxides and can be used in pigment technology.

Methods are known for producing yellow crystalline metahydroxides of iron oxide Fe203 H20 or FeO (OH), for example, by oxidizing the solution of an iron (II) salt in air in the presence of metallic iron with constant addition of ammonia. In this process, iron (II) is oxidized to iron (III), which is then precipitated with ammonia as a hydrate:

2FeS04 + NaO + O - 2FeiOH) S04;

Fe (OH) S04 + 2MN3 + 2N20 - - FeO (OH) + MH4) 2S04.

The disadvantage of this method is the large material and energy intensity of the process. The method requires the use of reagents FeS04, INN. This forms a reaction by-product (MS) 2504, the utilization of which (evaporation of the solution, recrystallization) requires labor and energy. In addition, the original FeS04 salt must be obtained by dissolving metallic iron in sulfuric acid, which requires additional costs for acid and the availability of expensive acid-resistant equipment. The use of an ammonia solution in this method causes great inconvenience from a safety point of view: ammonia causes irritation of the upper respiratory tract and mucous membranes of the eyes, therefore, a powerful exhaust ventilation is required to carry out this process.

A known method for producing yellow crystalline iron (III) metahydroxide by oxidation of metallic iron with aromatic nitro compounds, most often nitrobenzene in an aqueous medium at VI

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the absence of hydrochloric acid or, more precisely, ferric chloride (II) chloride and electrolytes — salts of aluminum, chromium, tin, cerium, and some other metals. The method allows to obtain yellow metahydroxide directly from metallic iron, using iron waste (chips, scrap).

The disadvantages of the method include the use as a oxidant of a toxic substance - nitrobenzene, which with prolonged inhalation of even small amounts leads to serious consequences. In addition, for carrying out the method it is necessary to use additional reagents HCI, AYUZI etc., the utilization of which is difficult.

A known method for producing iron oxide pigment by treating metallic iron with oxygen in air in a solution of an iron (II) salt while maintaining the pH of the solution is 3-6.

The disadvantage of this method is that the oxidation product of metallic iron in a solution of an iron salt is not pure iron (III) metahydroxide. It inevitably contains, for example, basic iron (III) salts, which are the product of the oxidation and hydrolysis of iron (II) salts:

2FeSCM + H20 + 0-2Fe (OH) S04.

Polymeric basic iron salts precipitate due to contamination with metahydroxide. Their content is greater, the smaller the amount of iron in the reactor and the higher the pH of the solution. Typically, the content of base salts in the pigment is 1.0-4.0 wt.% At pH 3.5-4.0 and should increase at pH 6. In addition, seed particles of iron oxide are additionally introduced into the reactor, and metallic iron is introduced in the form of a military ilmenite, therefore the pigment contains impurities of a certain amount of titanium dioxide. Thus, a pigment consisting of a number of different compounds, but not pure iron (III) metahydroxide, is obtained by this method.

The closest in technical essence to the present invention is a method for producing iron (III) hydroxide, which involves oxidizing metallic iron with oxygen in an aqueous solution containing chloride at 40 ° C, filtering, washing to a negative reaction to chloride ions in the wash water and drying product. Sodium chloride NaCl is used as chloride.

The method makes it possible to obtain iron (III) hydroxide directly from metallic iron using iron waste (chips, scrap metal) and inexpensive reagents: air, water, and sodium chloride, while sodium chloride is not consumed during the oxidation process and can be used again after filtration. iron (III) hydroxide precipitate.

The disadvantage of this method is that during the oxidation of metallic iron (by air) in an aqueous solution of sodium chloride, the yield of iron (III) metahydroxide is insignificant. The mechanism for the oxidation of metallic iron can be represented as follows:

2Fe-4e - + 2Fe2 +;

02 + 4e + 2H20-40H;

2Fe2 + + (OH) 2;

2Fe (OH) 2 + 02 + 2H20-2Fe (OH) 3.

Neutral environment, which is created by solutions of NaCI, contributes to the development of the amphoteric properties of iron (III) hydroxide, as a result of which Fe (OH) a, reacting with iron hydroxide (II), gives the addition products Fe (OH) 2 -Fe (OH ) 3, i.e. FeO-Pv20z-pN20, which are then either dehydrated to form the black FeO compound Pb20z, or oxidized further to brown Pb20z pN20. The content of these compounds varies and depends on the rate of oxygen supply and the concentration of sodium chloride. The color of the oxidation products varies from sepia to dark ocher, and the water content varies from 0.63 to 1.56 mol of H2O based on 1 mol of Fe20s. The derivatogram of a sample obtained by oxidation of metallic iron with atmospheric oxygen (natural convection) in 1% NaCI solution has three endothermic effects: at 373 K (loss of adsorption water), 553 K and 620 K, and a diffuse exothermic effect, indicating the presence of a mixture hydroxides.

The purpose of the invention is to increase the yield of the ocher-yellow crystalline iron (III) metahydroxide.

The goal is achieved by the fact that in a known method, including oxidation of metallic iron with oxygen in an aqueous solution containing chloride, filtration, washing to a negative reaction to chloride ions in the washing water and drying the product, ammonium chloride with a concentration of 1-10 is used as the chloride wt.%

The NH4CI aqueous solution contains an excess of H ions, which suppress the appearance of iron (III) hydroxide with acidic properties, and therefore the formation of Fe (OH) 2 -Pe (OH) 3 addition products, i.e. sustainable black FeO-Fe203, which

contaminates iron (III) hydroxide. In addition, in an aqueous solution of ammonium chloride, oxidation of metallic iron is possible with the formation of unstable ammonia compounds, which shifts the oxidation potential in a negative direction and facilitates the oxidation of metallic iron to a triple ion.

The oxidation of metallic iron is preferably carried out at room temperature. Heating even to 50-60 ° С causes a decrease in the yield of yellow meta-hydroxide of iron (III) FeO (OH) or Fe203H20, i.e. darkening of the product, and when the solution is heated to 98-100 ° C, the formation of a dark brown hydroxide of composition Fe203 (1.13-1.37) NaO.

Increasing the concentration of the aqueous solution from 1 to 10 wt.% Leads to an increase in the oxidation rate of metallic iron, and its further increase to 15 wt.% Leads to a decrease in the rate of the process, complicates the washing of chloride ions. With regard to the oxidation rate of metallic iron, an optimum concentration of ammonium aqueous solution of 5–10 wt.% Should be considered optimal. This increases the dispersion (specific surface area) of iron (III) hydroxide.

The sequence of the method is as follows. Iron waste (chips, scrap) is poured with an aqueous solution of ammonium chloride with a concentration of 1-10 wt.% And gradually at room temperature oxygen (or air) is passed through the solution, and natural convection of oxygen from the air is also possible. The resulting precipitate of an ocher-yellow crystalline iron (III) metahydroxide is filtered, washed with water until the reaction with the chloride ions is negative and air-dried to obtain portions of FeO (OH), i.e. Р20з-Н20,

Ammonium chloride used in the process is widely used in technological processes: during the melting process, it serves as an electrolyte in Leclanche cells and in dry cells, and also finds various applications in the chemical industry and in laboratories. It is also used in medicine.

Iron plates measuring 102 x х55 mm, cut from scrap roofing iron, cleaned of rust, pour 220 cm3 of an aqueous solution of ammonium chloride with a concentration of 1; 5; 10 and 15 wt.%. Through solutions, oxygen is passed at a bulk velocity of 0.04 l / min or is kept in air for the purpose of natural

convection of air oxygen for 10 days. The temperature of the ammonium chloride solution was in most experiments at room temperature 18–22 ° C, in some experiments it was heated to 53–57 ° C and 98–100 ° C. After accumulation of sediment, it is separated from the mother liquor by filtration, washed with distilled water until a negative reaction to chloride ions

using Hell (Moz) and air dried.

The obtained precipitates, after keeping to constant weight in a desiccator over an anhidron, are analyzed for the water content by calcination up to 750 ° C;

their dispersity was measured by specific surface area; a derivatographic analysis was made for individual samples. The results are presented in the table.

Iron hydroxide; obtained in aqueous solutions of ammonium chloride concentration of 1-10 wt.%, has an ocher-yellow color and corresponds to the formula Rv20z-H20, i.e. ReO (OH).

Thermograms of the samples have an endothermic effect corresponding to 300-360 ° C, which is typical for goethite, i.e. metahydroxide a-form. The oxidation temperature should be at room temperature (18-22 ° C), since at higher temperatures (5357 and 98-100 ° C) precipitation darkens and an increase in the amount of hydration water in them occurs. Moreover, the oxidation rate of metallic iron increases by more than 1.5 times when the concentration of ammonium chloride solution is 5-10 wt.% As compared to the oxidation rate when the concentration of the NH4GI solution is 1 wt.%, I.e. dispersion increases. With further increase in the concentration of chloride solution

ammonium up to 15 wt.%, the oxidation rate decreases and, in addition, it is difficult to wash the precipitate from the chloride ions.

The technical advantages of the proposed method are that

The proposed method increases the yield of iron (III) metahydroxide, which has a pure ocher-yellow color, in comparison with the known, when a mixture of various hydroxides of Pe203 (0.67-1, 45) H20 is obtained.

In comparison with the known, the proposed method is less material-intensive, energy-consuming and virtually waste-free, since it allows to obtain an ocher-yellow crystalline monohydrate directly from iron waste (shavings, cuttings) and scrap metal using oxygen and without toxic substances.

Claims (1)

Claims method for producing iron (III) hydroxide, comprising oxidizing metallic iron with oxygen in an aqueous solution containing chloride, filtering, flushing to a negative reaction to chloride ions in wash water and drying the product, characterized in that, in order to increase the yield of ocher-yellow crystalline iron (III) metahydroxide, ammonium chloride with a concentration of 1-10 wt.% is used as chloride.