CS273653B1 - Method of iron (iii) sulphate production - Google Patents

Abstract

The production of titanium dioxide from ilmenite by a sulphate process produces several types of ferrous sulphate with various levels of contamination. This is resolved by an inexpensive and operationally simple method of processing these waste ferrous sulphates into an ferric sulphate solution, usable for purifying water or processing minerals. These waste iron sulphates can be suitably combined in order to use the free sulphuric acid contained in them for the occurrence of ferric sulphate.

Description

The invention relates to the production of ferric sulfate.

The development of industry and energy entails the need to purify large volumes of water both entering the production process and from the production process falling off and discharged into public streams. The same problems are connected with the growth of urban agglomerations, for which it is necessary to prepare drinking water and waste water treatment.

Recently, the quality of wastewater treatment, both industrial and urban, has been of particular importance, especially in terms of environmental protection.

Various technological processes are used for water purification. One commonly used technology is water clarification using ferric salts. The low pH of ferric salt hydrolysis and the high coagulation capacity of ferric hydroxide for impurities put ferric salts in an important place among the chemicals used for water purification.

Water purification is not the only area where ferric salts are used. Another consumer of ferric salts is mineral processing where they are used in leaching poor polymetallic ores. In this application, the ferric salts are used as an oxidizing agent and as a source of the acid component.

A number of technological processes have been proposed for the production of ferric salts. Because it is a relatively inexpensive chemical, individual manufacturers generally start from waste materials for which they have no sales or for which processing into ferric salts is more economical. An important role is also played by the extent of the machinery of the plants, connected with the investment costs.

The proposed methods for producing ferric salts can be divided into two basic groups.

The first group includes processes involving the dissolution of iron oxide in acids, the second group includes technologies based on the oxidation of ferrous salts.

According to the first method, iron oxide, which derives from the so-called Ruthner pickling process, is dissolved in hydrochloric acid (Chemische Technik / Leipzig / 1985, 37, No. 1) or in sulfuric acid. Waste dilute acids are commonly used in this technology and their concentration or use in other areas of manufacture is not economically advantageous.

The actual technological process is easy to operate and implement on a simple device.

According to a second method, ferrous salts are oxidized using various oxidizing agents to the ferric salt.

For example, in air oxygen oxidation, ferrous sulphate is oxidized at higher temperature to basic ferric sulphate and converted to ferric sulphate by reaction with sulfuric acid (German Patent 3326506/1983). A difficult operation in this production is to conduct the oxidation reaction so as to oxidize the divalent iron to a high degree and at the same time prevent the formation of sulfur oxides.

In chlorine oxidation, chlorine gas is contacted with a ferrous salt solution in absorbent devices of various types (NSR Pat. 2147999 (1971); NSR Pat. 2710969 (1977)). The most technologically important device is the absorption of chlorine gas in ferrous salt solution. If the absorption efficiency is less than 100%, it is necessary to trap chlorine residues in alkaline solutions to form another by-product, for example sodium hypochlorite. Handling large quantities of chlorine requires special precautions.

The oxidation of the ferrous salt can be carried out electrolytically by separating the catholyte and the anolyte by an ion exchange membrane. The electrolytic oxidation of the ferrous salt can be combined with the production of hydrogen gas or with another reduction reaction on the cathode, for example with the reduction of titanium solutions. The size of the most important device, the electrolyzer, depends on the current density achieved. Electrolytic production of ferric salts while reducing the titanium solution is particularly important for reducing the production of green vitriol in the production of titanium dioxide from ilmenite by the sulfate process.

CS 273653 Bl

Oxidation of the ferrous salts can also be carried out with chemical oxidizing agents such as ozone, hydrogen peroxide (U.S. Patent No. 195208 (1978)), nitric acid and oxygenated chlorine compounds. Ozone and hydrogen peroxide are relatively expensive oxidizers for the production of ferric salts. Oxidation with cheap nitric acid requires an after-treatment device for nitrogen oxide. Among the oxygen-containing chlorine compounds, hypochlorites and chlorates are suitable for the oxidation of ferrous salts, and the use of hypochlorites is of little benefit in terms of the purity of the ferrous salt, since it provides a product heavily contaminated with ballast chlorides. The use of hypochlorites and chlorates to oxidize ferrous chloride in the presence of hydrochloric acid is suggested in Japanese patent 82 067 027 (1980) and European patent 110848 (1983).

The process for producing ferric sulphate according to the invention consists in oxidizing various types of iron sulphate which fall off in solid form and in solution in the production of titanium dioxide or by pickling iron with sodium chlorate solution. In the production of titanium dioxide in a sulphate process from iron-containing titanium raw materials, two types of ferrous sulfate in solid form and a solution of ferrous sulfate in dilute sulfuric acid are eliminated. When ironing the titanium dioxide sulphate solution, ferrous sulphate heptahydrate (green vitriol) falls off in relatively little contaminated state. The main impurities of this product are magnesium sulphate and titanium dioxide sulphate.

The so-called cleavage acid, which is about 20% sulfuric acid with dissolved ferrous sulphate, is removed from the hydrolysis of the titanium dioxide sulphate solution. In addition to ferrous sulphate, fission acid contains magnesium sulphate, manganese sulphate, aluminum sulphate, titanium dioxide sulphate and many others.

Under vacuum crystallization, little contaminated ferrous sulfate precipitates heptahydrate. When concentrated to approximately 50% sulfuric acid, ferrous sulphate monohydrate, which is heavily contaminated with sulfuric acid, titanium sulphate, magnesium sulphate, manganese sulphate and a number of other sulphates, is separated from the cleavage acid.

During the heaping of ferrous sulphate heptahydrate and monohydrate in the open air, other types of solid iron sulphates, which differ from those originally deposited by different degrees of iron oxidation and the acid component content, arise due to weather conditions and atmospheric oxygen. As another product in the heaping process, a solution of iron sulphates is formed by leaching the heaps with rain water. Direct use has not yet been found for some of these by-products of titanium dioxide production. These are mainly heaping partially oxidized green vitriol, heap extracts and heavily contaminated ferrous sulphate monohydrate. The so-called cleavable acid is only usable after costly concentration and ironing, and green vitriol, when present in large quantities, has a limited sales potential.

In the process for producing the ferric salts of the present invention, various types of iron sulphate are oxidized with sodium chlorate either individually or in a mixture so as to obtain a product with the desired properties at the lowest production cost. For example, the equivalent of sulfuric acid required to form ferric sulfate from ferrous sulfate can be supplied in two forms. In the production of ferric sulphate for the preparation of drinking water, pure (contact) sulfuric acid may be used and freshly produced or scalded little green dicotta may be used. In the production of ferric sulphate intended for wastewater treatment or leaching of ores, it is possible to use more polluted ferrous sulphate and sulfuric acid can be supplied together with ferrous sulphate monohydrate or so-called fission acid. Furthermore, in order to reduce production costs (saving of sodium chlorates), oxidized batches of green vitriol heaps can be used to produce ferric sulphate. A further reduction in production is achieved by using sodium chlorate solution directly from the electrolysis instead of the crystalline salt, whereby the technological stage of crystallization is eliminated.

The ferrous sulfate oxidation reaction itself is conducted so that a small amount of iron (II) is left in the product, thereby guaranteeing a quantitative reduction of the chlorates to the chloride and the possible chromate present to the chromite salt. Because of the quantitative course of the reaction, the ratio of acid to iron salt is chosen to be higher than stoichiometric.

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Example 1

K 1,54 kg of green vitriol with composition: Fe ²⁺ - 17,61%; Fe ³⁺ - 0.27%; Ti = 0.20%;

300 ml of water and 70 ml of concentrated sulfuric acid (92%) were added.

The suspension was poured in with stirring over 10 min. 100 ml of an NaClO 2 solution from an electrolytic preparation having the following composition: NaClO ₃ - 452 g / l; NaCl - 119 g / L; Na 2 CrO 4 - 4.6 g / L. Upon completion of the addition of NaClO ₃ solution, an additional 76 mL of sulfuric acid was poured in and over 10 min. added with stirring an additional 100 ml of NaClO ₃ solution - a total of 146 ml of concentrated sulfuric acid and 200 ml of NaClO ₃ solution were added.

2+

Since the solution sample did not react to Fe (with K ₃ Fe (CN) g) after dilution with water, green vitriol was gradually added in small portions until the solution sample gave a weak reaction to Fe. Additionally 10 g of green vitriol.

3+

1.46 L of a dark brown ferric sulfate solution produced: Fe - 185.93 g per liter, Fe ²⁺ - 0.56 g / l; SO ² '- 483.38 g / l.

Example_2

K 1.51 kg of heaped green vitriol of the composition Fe ²⁺ - 13.05 8; Fe ³⁺ - 5.20%;

SO ^ ² - 28.58%, 300 ml water and 100 ml of concentrated sulfuric acid (92%).

80 ml of a 500 g / l NaClC solution> _{3 are} gradually added to the suspension with stirring over 10 minutes. Another 87 ml of concentrated sulfuric acid was added and 45 ml of NaCl ₁₀ solution were added over a period of 5 minutes - 187 ml of concentrated sulfuric acid and 125 ml of NaClO solution were added in total, while the solution temperature rose to 60 ° C. , Fe (CN), 20 g of iron vitriol. After homogenization of ^J 2 + 0, the solution gave a weak reaction to Fe. Allow the solution to sediment for 2 hours from insoluble matter.

3+

1.45 L of ferrous sulphate solution of Fe content - 179.21 g / l produced;

94 · 9+

Fe - 1.12 g / L; SO ₄ 2- - 507.52 g / L; Ca - 0.72 g / l.

Example_3

1.46 kg of green vitriol containing Fe - 17.6%, Fe ^J - 0.27%, Ti - 0.20 i,

2- 2+

SO. - 32,07% added to a mixture of 300 ml of fissile acid having a Fe-content of 50,68 g / l,

Fe ³⁺ - 0 g / L, Ti ⁴⁺ - 4.20 g / L, SO ² - - 364.95 g / L and 99 ml of concentrated H ₂ SO ₄ (92%) and mixed. 180 ml of a 500 g / l NaClO ₃ solution were added to the suspension with stirring over 26 minutes. After the addition of NaClO was complete, the solution gave a weak reaction

2+, per Fe (with K ₃ Fe (CN) g). Doreden solution with 100 ml of water to a total volume of 1.5 L.

Product composition: Fe ³⁺ - 181,80 g / l, Fe ²⁺ - 0,52 g / l, SO ² - 482,75 g / l.

Example 4

4 * 3

1.38 kg of ferrous sulphate monohydrate of Fe - 16.70%, Fe - 0.10%,

4+ 9— 94Ti - 1,62%, SO ^ - 48,38% and 0,24 kg of green vitriol containing Fe - 17,61%,

SO? - 32.07% mixed with 0.4 1 of water 85 ´C warm and at

Fe ³⁺ - 0.27%, Ti ⁴⁺ - 0.20%, an initial suspension temperature of 40 ° C, with stirring, was dosed with 500 g / l NaClO 3 solution. Dosing of NaCl ₁₀ solution was complete after 1.5 hours at total consumption

2+

179 ml, when the sample solution gave only a weak reaction to Fe (with K ₃ Fe (CN) g). The NaClO ₃ solution was brought under the stirring slurry. During dosing of the NaClO ₃ solution, the temperature spontaneously rose to 85 ° C.

Add ferric sulphate solution to 220 ml of water to a total volume of 1,5 l.

Product composition: Fe ³⁺ - 181.0 g / l, Fe ²⁺ - 1.7 g / l, Ti ⁴⁺ - 14.9 g / l, SO ² ”- 490.2 g / l. '

Claims (5)

SUBJECT OF THE INVENTION Process for the production of ferric sulphate, characterized in that a suspension of ferrous sulphate is oxidized with sodium hypochlorite in the presence of free sulfuric acid. 2. A process according to claim 1, wherein the ferrous sulphate used is a variety of ferrous sulphate, which falls off in solid form or in solution in the production of titanium dioxide and the pickling of iron with sulfuric acid. 3. The process of claim 1, wherein the free sulfuric acid is sulfuric acid accompanying the ferrous sulfate in solid form or in solution. 4. A process according to claim 1, wherein the ferrous sulphate having a low free sulfuric acid content is mixed with ferrous sulphate having a higher free sulfuric acid content in such a proportion that at least 1.5 moles of acid per mole of iron is obtained in the resulting mixture. sulfuric. 5. The process according to claim 1, wherein the sodium chlorate is a sodium chlorate solution produced by its electrolytic production.