RU2740063C1 - Method of processing spent sulphuric acid etching solutions - Google Patents

Abstract

FIELD: metallurgy; machine building.

SUBSTANCE: invention relates to recycling waste sulphate etching solutions of metallurgical and machine building. In the method, calcium chloride sludge is added to the reactor with spent sulphuric acid solution, and after achieving pH equal to 5.0–5.5, limestone waste dust is supplied to the reactor to pH equal to 7.0–8.0, after the reactions are completed, the obtained suspension is transferred into a vacuum crystallizer to form crystalline hydrates of calcium sulphate and calcium chloride. After that, obtained mixture is fed into centrifuge for separation of said crystalline hydrates, and then into combined drier of boiling layer, in which crystalline hydrates are milled to size of 10–15 mcM and simultaneously dried for 15–20 minutes at temperature of 110–340 °C to produce a binder containing gypsum with an admixture of crystalline calcium chloride and iron oxide pigment. In the reactor with the spent sulphuric acid solution, calcium chloride slurry and limestone waste dust are fed at the following ratio of components, wt. %: used sulphuric acid solution of metal etching 67–70, slurry of calcium chloride 20–22, limestone waste dust 10–11.

EFFECT: invention provides simplification of technological scheme of processing spent sulphuric acid etching solutions, as well as implementation of said processing without use of scarce products.

1 cl, 1 dwg, 2 tbl, 2 ex

Description

The invention relates to the disposal of waste sulfuric acid pickling solutions of metallurgical and machine-building industries and can be used in water treatment processes using the resulting coagulants.

A known method of disposal of spent pickling solutions containing sulfates and chlorides of iron (II), which are utilized by oxidation of iron (II) cations using an oxidizing agent and the targeted use of processed solutions (RF patent for invention No. 2428522, IPC C23G 1/36, dated 09/10/2010 ). Sodium hypochlorite concentrate containing sodium hypochlorite and sodium hydroxide is used as an oxidizing agent. The resulting suspension is treated with a minimum amount of mineral acid until the precipitate dissolves, and the processed solutions are used as coagulants in water purification processes.

The disadvantages of this method are the content in the coagulants difficult to remove during the purification of sodium compounds, as well as the use of a deficient oxidizing agent, hypochlorite.

A known method of obtaining magnesium sulfate, including the interaction of magnesium-containing raw materials - fine dust of magnesite with spent sulfuric acid, crystallization of the target product and drying it (RF Patent for invention No. 2078041, IPC C01F 5/40, 1997). An etching sulfuric acid solution is used as a spent sulfuric acid, and the initial reagents are fed to the interaction in a mass ratio of magnesite: sulfate ions in the etching solution (1.05-1.2): 1, followed by hydrothermal treatment of the resulting suspension at a temperature of 60-80 ° C within 1.5-2.0 hours.

However, this method also has the following disadvantages:

1. low yield of obtained magnesium sulfate and pigment;

2. high energy consumption for solution evaporation;

3. The quality of magnesium sulfate and iron oxide pigments does not meet the requirements for the production of some kinds of materials.

The closest in technical essence and the achieved effect of the proposed is a method for processing a sulfuric acid pickling solution of sulfuric acid with fine magnesium-containing raw materials (RF patent for invention No. 2634017, Method for producing magnesium sulfate and iron oxide pigments from industrial waste, IPC C01F 5/40, dated 12.10.2017 ). As a magnesium-containing raw material, dolomite dust is used, which is formed when dolomite is calcined at a temperature of 600-750 ° C. The ratio of sulfate ions - dolomite dust in the pickling solution is 1: 1.1. Hydrothermal treatment of the resulting suspension is carried out by blowing the solution with air, the oxygen of which oxidizes iron Fe ⁺² to Fe ⁺³ . The precipitate is separated on a filter press and washed from water-soluble compounds. Heat treatment of the precipitate is carried out into an iron oxide pigment. Drying and grinding of the iron oxide pigment is carried out simultaneously in a combined spray dryer. The filtrate separated by the filter press and the washing water containing magnesium sulfate are fed to the reactor. The content of sulfate ions in the solution is increased to 35-40% by adding concentrated sulfuric acid, and neutralization is carried out with dolomite dust at a temperature of 80-100 ° C to a pH equal to 7.0-7.5. Crystallization of magnesium sulfate is carried out in a crystallizer.

The disadvantages of this method are the complex technological scheme of waste processing, the use of concentrated sulfuric acid, high consumption of scarce dolomite dust.

A technical problem at present is the complexity of the development of a waste-free effective method for processing spent sulfuric acid solution of metal pickling to obtain a binder suitable for the manufacture of high quality building materials for external use.

The technical result of the proposed solution is to simplify the process flow diagram and eliminate the use of scarce materials.

The set technical result is achieved by the fact that in the method of processing spent sulfuric acid solutions of metal etching, including feeding a sulfuric acid solution into the reactor and introducing an alkaline reagent into it, obtaining a suspension from this mixture, separating the precipitate and obtaining marketable products from it, according to the proposed solution, into the reactor together with the sulfuric acid solution, calcium chloride slurry and limestone dust-entrainment are fed with the following ratio of components, wt. %:

Spent sulfuric acid solution etching metals 67-70 calcium chloride sludge 20-22 dust-carryover of limestone 10-11

At the same time, calcium chloride sludge is first added to the reactor with a sulfuric acid solution, and after reaching a pH of 5.0-5.5, dust-entrainment of limestone is fed into the reactor to a pH of 7.0-8.0, after the end of the reactions, the suspension is transferred into a vacuum crystallizer, where crystalline hydrates of calcium sulfate and crystalline hydrates of calcium chloride are formed, and after crystallization, the resulting mixture is fed into a centrifuge and the indicated crystalline hydrates are separated on it, after which they are fed to a combined fluidized bed dryer, where crystalline hydrates are ground to a size of 10- 15 microns and simultaneous drying for 15-20 minutes at a temperature of 110-340 ° C, while receiving a binder containing gypsum with an admixture of crystalline calcium chloride and iron oxide pigment.

Spent sulfuric acid solution of metal etching containing masses. %: 4-5 H ₂ SO ₄ and 18-20 Fe ₂ SO ₄ . is processed by the Zlatoust Metallurgical Plant by neutralization with lime milk to form a gypsum-containing suspension, separating excess moisture from it to obtain a low-quality gypsum-containing sludge.

Calcium chloride sludge containing, mass. %: CaCl ₂ 82-83 and impurities of aluminum oxide, obtained by neutralizing metal etching solutions with milk of lime of OJSC MMK. The sludge is partially used as an additive to the concrete mix.

Dust-entrainment of limestone containing, masses. %: CaO-74.2; SiO ₂ -1.8; MgO 2.8; CaCO ₃ -21.2. Fly dust is generated by the Zlatoust Metallurgical Plant and is partially used to neutralize wastewater.

The choice of the above wastes to achieve the set technical result is explained not only by their high activity, but they, being part of the products formed, including gypsum, significantly increase the strength of the products, which is confirmed by the data below.

Natural gypsum has a low compressive strength of 2-16 MPa and it increases during heat treatment in an autoclave in saturated steam at a pressure of 0.15-0.3 MPa. Instead of an autoclave, it is possible to use some salts (calcium chloride, lime) as a thermal medium of aqueous solutions. The addition of lime (CaO) also activates the chemical interaction of gypsum with water, increasing the strength of products obtained on its basis in compression by 10-20 MPa (Volzhensky A.V., Burov Yu.S., Kolokolnikov BC, Mineral binders. M. : Stroyizdat, 1979, p. 358).

In this regard, in industrial conditions to increase the strength of natural gypsum, it is processed in steamers (steam boilers) at a temperature of 140-190 ° C and a pressure of 1.3 atm. within 1.0-1.5 hours, while receiving 15% of gypsum of the first grade with a strength of 55 MPa and 25% of the second grade with a strength of 40 MPa (Encyclopedia (short chemical). M .: "Soviet encyclopedia", 1964, T. 3, p. 66). When lime (CaO) is added to calcium sulfate, the temperature rises to 140 ° C and dispersion, the quality of gypsum and the strength of the products increase, which is explained by the formation of a more durable gypsum-containing structure formed by the reactions below (1 and 2):

The proposed method for processing spent sulfuric acid solution of metal etching is carried out in the following three stages.

At the first stage, the solution is reacted with calcium chloride slurry in a sulfuric acid reactor at pH 5.0-5.5 and a temperature of 80-90 ° C according to reaction (3) with the formation of a suspension containing calcium sulfate and hydrochloric acid.

After the end of the reaction in the same reactor, the suspension is neutralized with calcium oxide of limestone dust to a pH of 7.0-8.0, while the temperature in the suspension rises to 90-100 ° C and reactions (4 and 5) proceed with the formation of sulfate and calcium chloride and iron hydroxide.

After the end of the reactions, the suspension is transferred to the second stage in a vacuum crystallizer-mash, in which at a temperature below 60 ° C, according to reaction (6), crystalline calcium sulfate-gypsum hydrate is formed, and at a temperature below 30.2 ° C - crystalline calcium chloride hydrate according to reaction ( 7).

The characteristics and conditions of their formation are given in table. 1 (Brief chemical encyclopedia. -M. Soviet encyclopedia, 1964, T. 3, p. 1028).

The chemical composition of the crystalline hydrates released upon cooling the solution under the conditions of their formation.

After the end of crystallization, the mixture is fed into a centrifuge, in which these crystalline hydrates are separated from it and fed to the third stage in a combined fluidized bed dryer, in which the crystalline hydrates are ground to a particle size of 15-19 microns and at the same time the mixture is dried for 15-20 min. at a temperature of 110-340 ° C. In this case, according to reactions (10), a binder is obtained containing gypsum with an admixture of crystalline hydrate of calcium chloride and iron oxide pigment, the color of which depends on the processing temperature: yellow at 110 ° C, black at 200 ° C and red at 340 ° C.

The binder obtained in the dryer, containing gypsum with an admixture of the above crystalline hydrates and pigments, has a strength of 65-75 MPa and is suitable for the manufacture of building materials for outdoor use, for example, facing boards or panels.

Reducing the content of sulfuric acid solution from etching metals in the reactor is less than 67 wt. % will reduce the amount of gypsum in the binder, and an increase in its amount over 70 wt. % will increase the consumption of imported calcium chloride sludge.

When the content of calcium chloride sludge is less than 20 wt. %, all sulfuric acid in the solution will not be bound and the pH will be below 5.0, and an increase in its content is more than 22 wt % will increase the consumption of calcium chloride sludge, which is not economical due to its delivery from other enterprises.

With a decrease in the content of dust-entrainment of limestone less than 10 wt. % the solution will not be completely neutralized and the pH in it will be below 7.0, and an increase in its content is more than 11 wt. % will raise the pH of the suspension above 8.0, which will reduce the quality of the binder.

Grinding crystalline hydrates in a fluidized bed dryer to a size of less than 10 microns significantly increases the grinding time, and grinding them to a size of more than 15 microns worsens the hiding power of pigments.

A decrease in the drying temperature less than 110 ° C increases the drying time and energy consumption, while an increase in the drying temperature above 340 ° C leads to an overconsumption of energy and a decrease in the quality of the pigment ("burnout").

The proposed method for processing a spent metal etching solution is illustrated by a technological scheme.

The indicated diagram indicates:

1 - capacity of the spent sulfuric acid solution of metal etching;

2 - bunker of calcium chloride sludge:

3- limestone dust-carryover hopper;

4 - reactor;

5 - intermediate tank;

6 - slurry pump;

7 - vacuum crystallizer;

8 - centrifuge;

9 - container for mixing gypsum;

10 - fluidized bed dryer;

11 - binders hopper.

A method for processing a spent metal pickling solution is carried out as follows.

The spent sulphate solution is fed into the reactor 4 from the tank 1 and the calculated amount of calcium chloride sludge is fed into it from the hopper 2 to a pH equal to 5.0-5.5. In this case, reaction (3) proceeds in the reactor and the temperature rises to 80-90 ° C. After the end of the reaction, the same reactor is fed from the hopper 3 dust-entrainment of limestone to a pH of 7.0-8.0. At the same time, the temperature in the reactor rises to 90-100 ° C and reactions (4 and 5) proceed with the formation of calcium sulfate and chloride and iron hydroxide. After the end of the reaction, the suspension is poured into an intermediate tank 5 and from it by a slurry pump 6 a crystallizer 7 is fed into a vacuum, in which a crystalline hydrate of calcium sulfate-gypsum is formed at a temperature below 60 ° C, and at a temperature below 30.2 ° C - a crystalline hydrate of calcium chloride. After the end of the crystallization process, the suspension is transferred to the centrifuge 8, which separates the excess water (filtrate). The filtrate is accumulated in a container 9 and is used for mixing gypsum in the manufacture of building products, and the mixture of crystalline hydrates is transferred to a combined fluidized bed dryer 10, in which it is crushed to particles of 10-15 microns and simultaneously dried at a temperature of 110-340 ° C for 15-20 minutes. This results in a binder containing gypsum with an admixture of calcium chloride crystalline hydrate and pigment.

In the dryer, one of three colors of iron oxide pigments (yellow, black or red) is formed simultaneously. The binder obtained under these conditions is collected in a container 11. The binder has a strength of 65-75 MPa and is suitable for the manufacture of outdoor building materials, for example, facing boards or panels.

The high efficiency of the proposed method is confirmed by the data below of the two binder samples produced.

Experience number 1. 1 L (1260 g) of spent sulfate solution of metal etching containing 5% sulfuric acid and 20% ferrous sulfate was poured into the laboratory reactor, and while the stirrer was operating, 411 g of calcium chloride slurry was gradually added to the reactor, avoiding strong foaming of the suspension. At the same time, the temperature in the solution increased to 90 ° C and reaction (3) proceeded with the formation of 122.4 g of calcium sulfate and 63.9 g of hydrochloric acid.

After the end of the reaction, 207 g of limestone carryover was added (also slowly) to the reactor to a pH of 7.0-8.0. At the same time, the temperature in the reactor increased to 110 ° C and the reactions proceeded (3 and 5). Then the suspension was immersed in a vacuum crystallizer, in which the temperature was maintained below 30 ° C. After cooling on a press filter, the precipitate was separated from the suspension, transferred to a platinum beaker and placed in a laboratory fluidized bed dryer and heat treated at 110 ° C for 15 minutes. After cooling, the resulting binder was analyzed and weighed. A yellow binder weighing 1654 g was obtained, containing 636 g of gypsum, 811 g of crystalline hydrates of calcium chloride, 207 g of iron oxide and 224 g of filtrate. The binder has a strength of 75 MPa.

Experience number 2. In the laboratory reactor was poured 1 liter (1210 g) of a spent sulfuric acid solution of metal etching containing 3% sulfuric acid and 18% ferrous sulfate, and while the stirrer was operating, 345 g of calcium chloride slurry was added to the reactor, preventing strong foaming of the suspension. At the same time, the temperature in the reactor increased to 80 ° C and reaction (3) proceeded with the formation of 102.6 g of calcium sulfate and 53.6 g of hydrochloric acid.

After the end of the reaction, 174 g of limestone fly-away were added to the reactor (also slowly) to a pH of 7.0-8.0. In this case, the temperature in the reactor increased to 100 ° C and the reactions proceeded (3 and 5). Then the suspension was placed in a vacuum crystallizer, in which the temperature was maintained below 30 ° C. After cooling on a press filter, the precipitate was separated from the suspension, transferred to a platinum beaker and placed in a laboratory fluidized bed dryer. Heat treatment was carried out at a temperature of 100 ° C for 10 minutes. After cooling, the resulting binder was analyzed and weighed. Received a yellow binder weighing 1384 g, containing 534 g of gypsum, 681 g of crystalline hydrates of calcium chloride and 169 g of iron oxide and 345 g of filtrate. The binder has a strength of 65 MPa.

The balance results of the experiments carried out are shown in the table.

The proposed method will find application in the disposal of waste sulfuric acid pickling solutions of metallurgical and machine-building industries and can be used in water treatment processes using the resulting coagulants.

Claims (3)

A method for processing a spent sulfuric acid solution for etching metals, including feeding a spent sulfuric acid solution into a reactor and adding an alkaline reagent to it, obtaining a suspension from said mixture, separating a precipitate and obtaining a product from it, characterized in that chloride slurry is fed into the reactor together with the spent sulfuric acid solution calcium and dust-entrainment of limestone with the following ratio of components, wt. %: spent sulfuric acid solution etching metals 67-70 calcium chloride sludge 20-22 dust-carryover of limestone 10-11, at the same time, calcium chloride sludge is first added to the reactor with the spent sulfuric acid solution, and after reaching a pH of 5.0-5.5, limestone entrainment dust is fed into the reactor to a pH of 7.0-8.0, after the end of the reactions, the suspension transferred to a vacuum crystallizer, in which crystalline hydrates of calcium sulfate and calcium chloride are formed, and after crystallization, the resulting mixture is fed into a centrifuge and the indicated crystalline hydrates are separated on it, after which they are fed to a combined fluidized bed dryer, in which crystalline hydrates are ground to a size of 10- 15 microns and simultaneous drying for 15-20 minutes at a temperature of 110-340 ° C, at which the product is obtained in the form of a binder containing gypsum with an admixture of calcium chloride crystalline hydrate and iron oxide pigment.

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