HU184279B - Process for utilizing pickling solutions produced with etching iron as side product - Google Patents

Abstract

The present invention relates to the complex utilization of marinating solutions for iron etching. During the processing, magnesium nitrate and calcium nitrate are added to the neutralized clay - high purity gypsum is separated, and after neutralization, iron hydroxide gel and finally a complex salt mixture containing calcium, magnesium, ammonium nitrate is formed. The latter product can be used as a fertilizer in agriculture. -1-

Description

The present invention relates to a process for the utilization of pickling solutions obtained by etching steels, characterized in that after neutralization, a mixture of Ca (NO ₃ ) ₂ and Mg (NO ₃ ) ₂ solutions is used to make gypsum in the first step and, after treatment with nitric acid, The ferric hydroxide formed by the introduction of gas or ammonium hydroxide is isolated by filtration and the filtrate, which is a solution containing ammonium magnesium nitrate, gives a salt mixture by evaporation.

The surface of semi-finished products obtained from the processing of iron and other metals must be free of any contamination before further processing. Complete cleaning of surfaces is most often done with acids, and during this process not only the oxide, rag, etc., adhering to the surface is removed. is removed, but the acid also attacks the surface of the semifinished product. Acids used in etching, mixtures thereof, and possibly added electrolytes and other substances are referred to as stains.

Iron etching is used for wire sheet rolling, galvanizing and tin plating, enamelling, tinplate making, etc. Sulfuric acid, sometimes hydrochloric or nitric acid, or mixtures thereof, is usually used for etching iron surfaces. Sulfuric acid curing takes place at high temperatures below 80 ° C. The sulfuric acid content of the pickle is initially 10 to 20% by weight, which decreases to 2 to 7% during pickling. If the acid content decreases, they are then replenished, "sharpening" the marinade. As a result, the dissolved iron content of the marinade is increasing; in the past, the limit was thought to be 2-300 g / l, and more recently 5 - 600 g / l are allowed to save acid.

Domestic problems in the utilization of pickle solutions are significant. It is not desirable to drain the used pickle solutions into streams or channels with lower discharge rates, either because of the acid content or the metal salt content. Without neutralization, the etching stains introduced into watercourses make it impossible to supply water to industrial plants located near the watercourse, mainly to the pulp and textile industry and to the production of large quantities of black ferrous sulphide bottom sludge. Fish in the watercourse migrate or die out due to acid. In the simplest case, slaked-lime neutralization is used to reduce the effects of environmental pollution, resulting in an insoluble precipitate. During the neutralization of exhausted etching stains, both the acid remaining in the staining and the ferrous sulphate in the solution are wasted.

A significant step forward is the Hungarian patent specification No. 169,344 of Dr. József Kerti et al., According to which iron powder and sulfuric acid are recovered from the purified iron sulphate solution by electrolysis.

In the Danube Ironworks by freezing method FeSO ₄ . 7H ₂ O crystalline material is recovered from some of the pickle juice.

The iron etching process is used throughout the world and, when sulfuric acid is used, large quantities of ferrous sulphate are produced as a by-product in the spent pickle solution. In our domestic plants - Borsodnádasd, Salgótarján, Csepel and Dunaújváros - this iron sulphate is produced in tens of thousands of tons. At this time, the sale of this material is essentially unsolvable, as the by-products are formed

80-85% of it is discharged unused partly into watercourses and partly - after neutralization - into vomiting.

The industry in the socialist countries has similar problems. In the Polish People's Republic, for example, at the Nova Huta iron plate pickling plant, approx. 30 000 tonnes of iron sulphate are produced each year, of which about 90% is sent to the Vistula after costly neutralization. In the GDR, the ferrous sulphate marinade solution is transported on board vessels designed for this purpose and poured into the sea. According to preliminary surveys, neighboring Czechoslovakia does not use iron sulphate either. According to the literature, most of the resulting marinade solution in the Federal Republic of Germany and in France is neutralized and transported to vomiting.

However, the latest technical solutions are already available to obtain a useful product from marinades. 525 625 is to be considered as such. (CH 01, G 49/10), which was filed in 1976. According to the description, the brine is treated with CaCl ₂ - gypsum is formed and the filtrate is electrolyzed. A procedure with a similar purpose is proposed in U.S. Patent No. 4,137,292. In U.S. Pat. A similar solution is found essentially in U.S. Patent No. 7,385,494. In the Japanese patent, which neutralizes the brine with limestone and bases the filtrate by precipitating the iron hydroxide - which is used for roasting. No. 993,115. According to British Patent Specification, essentially CaCl _{2 is used to} treat the pickle solution and to form gypsum a solution containing FeCl _{2 is} pyrolyzed at 350 ° C separated from the gypsum to produce Fe ₂ O ₃ and HCl.

By the process according to the invention, it is possible to sell the ferrous sulfate content of the spent pickle solution formed as a by-product of iron etching with sulfuric acid.

It is characterized by the efficiency of the process according to the invention that the utilized metal and sulphate radical which has been lost so far in the used pickling solution is completely utilized without any waste water being produced.

According to our procedure, we can make three marketable products from the used marinade solution:

- precipitated gypsum (calcium sulfuricum praecipitatum); ' - ferric hydroxide of technical purity (used as a clarifying agent in water purification and as a pigment in the manufacture of paints and rubbers);

- ammonium nitrate (an important fertilizer) containing magnesium nitrate.

Evaluating the most significant patent listed, the following can be stated:

- József Kerti's solution is technically good, but it is very expensive to produce iron powder in this way. Soviet specification products such as gypsum and iron powder with looks economically favorable in - but apparative ^gen costly and cause considerable disturbance to the equilibrium conditions do not or hardly can be controlled, - No. 4,137,292. It does not appear to be a good solution according to U.S. Pat. No. 7,395,494 as a result of the magnetic separation of a pure product which is insignificant. we have similar comments to the Japanese solution as in the previous US patent,

184,279 - The method proposed in British Patent No. 993,115 was tested on a laboratory scale. The equilibrium conditions are unfavorable - a significant excess of CaCl _{2 is} required when the sulphate radical is removed, and thus Fe ₂ O ₃ is contaminated with calcium. The production of hydrochloric acid is costly and significantly more expensive than conventional technology. The main advantages of the technology we have developed over the solutions described are:

- waste-free technology - Ca (NO ₃ ) _{3 and} Mg (NO ₃ ) ₂ solutions made from dolomite allow for the production of controllable granules and high purity gypsum, - iron oxide produced from nitrate and sulphate solutions is both highly filterable and highly pure in many areas, - compound fertilizer that can be made by evaporation of the final lye MgNH ₄ (NO ₃ ) ₃ , a useful fertilizer.

Ultimately, each of the components added to the process can be recovered in useful form - and at the same time all useful components of the brine are recovered. This is the main advantage of our process and it can be stated that this can only be achieved by the nitrate method.

Our process is completely novel because nitrate removal is not used anywhere in the world and the benefits of this method have not yet been recognized. It is not a minor circumstance, among the benefits of the process, that its investment in assets is not significant.

The essence of the procedure:

The used pickle solution contains iron sulfate, free sulfuric acid and impurities. In the first step, the free sulfuric acid is neutralized. In the second step, the pickling solution is reacted with a solution of dolomite digested in nitric acid in a suitable apparatus with stirring. The reaction results in the formation of calcium sulphate (gypsum) in the form of a precipitate; from the resulting solution, by adding nitric acid and ammonium hydroxide, heating the precipitated iron hydroxide or After evaporation, a fertilizer of magnesium ammonium nitrate is prepared.

Detailed description of the procedure:

1. Neutralization of free sulfuric acid

The free sulfuric acid in the used pickle solution reacts with calcium nitrate from nitric acid digestion to form calcium sulfate and nitric acid.

H ₂ SO ₄ + Ca (NO ₃ ) ₂ = CaSO ₄ + ₂ HNO ₃

Since, according to literature, 100 cm ^{3 of} normal strength nitric acid is ca. It would hold 1.52 g of gypsum in solution, so the presence of nitric acid in the system is undesirable. Therefore, the free sulfuric acid in the used pickling solution, which initiates the undesirable process, must be neutralized.

To neutralize the free sulfuric acid, metal acid, ammonium hydroxide or other alkalis may be used.

2. Preparation of a dolomite solution

When digging dolomite, it should be borne in mind that during dissolution, the carbon dioxide formed will be highly foamy, and therefore, the digester should be chosen taking into account that only one-fifth of the volume of dolomite can be contained.

Dolomites mined in Hungary can be used directly for the process. In the case of Pilisvörösvár dolomite, the utilization rates are as follows:

kg of 1-2 mm particle size dolomite is mixed with 1 liter of network-quality water and then a calculated amount of nitric acid (1.48 liter, 1.4% (65% concentration)) is added. After the foaming ceases, the solution is filtered through a vacuum or other filter to remove impurities. The resulting filtered solution had a volume of 1500 cm ³ and contained nitrates corresponding to 56.1% CaCO ₃ and 42.7% MgCO ₃ .

3. Separation of the sulfate content of the used pickle solution

To the neutralized spent pickle solution is added a solution of dolomite containing an amount of calcium salt corresponding to its sulphate content:

FeSO ₄ + Ca (NO ₃ ) ₂ = Fe (NO ₃ ) ₂ + CaSO ₄ . 2 H ₂ O

The calcium salt produces calcium sulfate, which is filtered after 10 to 15 minutes on a vacuum or other filter. The potassium sulphate is first washed with two to three percent sulfuric acid water to prevent the hydrolytic precipitation of iron, and then continued until acid free from tap water. . The calcium sulphate thus obtained corresponds to the form of CaSO ₄ · 2 H ₂ O, which can be converted to CaSO ₄ 1/2 H ₂ O by drying and heating to 120-170 ° C.

4. Obtaining additional products

The solution filtered from calcium sulfate contains iron and magnesium in the form of nitrate. The solution was strongly acidified by the addition of nitric acid and then heated to 70-75 ° C, with some foaming, to oxidize the ferric lake to ferric nitrate. The oxidized iron is precipitated by adding a calculated amount of NH ₃ or NH ₄ 0H from solution. The precipitated iron is obtained in the form of ferric hydroxide (Fe / OH / ₃ ). To separate this solution from the solution, approx. after five to six hours, vacuum or other filtration is applied. The filtered iron hydroxide is washed with alkaline water at 40-50 [deg.] C. and dried.

The solution remaining after filtration of the iron hydroxide contains most of the magnesium content of the nitric acid dolomite solution used, in the form of a complex, in the form of MgNH '(NO ₃ ) ₃ - (Mg / NO ₃ ) ₂ -NH ₄ NO ₃ calcium nitrate; and small amounts of ammonium sulfate formed as a result of sulfuric acid washing. Drying the solution in vacuo gives these compounds as a solid, some in crystalline form.

An example of economical processing of an iron sulfate-containing pickle solution.

Tools and compounds used in the extraction of ferrous sulphate content of spent pickle liquor from iron pickling.

Resources:

- Equipment for fine grinding of dolomite.

- Equipment for digestion of dolomite in nitric acid.

- Equipment (eg vacuum filter) for filtering off precipitates.

compounds:

- The iron solution containing iron sulphate used contains - g Fe ²⁺ / 1; 138 g Salt _4/1

Dolomite solution:

kg of 1-2 mm particle size dolomite is mixed with 10 liters of water and then 15 liters of 1.4 fs nitric acid is added in portions. This is how to prepare

After filtration of 184,279 solutions, 56.1% CaCO ₃ and

It contains 42.7% nitrates corresponding to MgCO ₃ . ammonium hydroxide:

0.91 fs .; With 26% NH ₃ content.

Detailed description of the procedure:

For the lab-size assay, 401 tired pickle solutions are weighed. Its iron, sulphate and free sulfuric acid content is as follows; Fe: 40x80 = 3.2 kg, SO ₄ : 40 x 138 = 5.5 kg, H ₂ SO ₄ : 40 x 10 = 0.4 kg.

The disturbance of 0.4 kg of free sulfuric acid is approx. Neutralize with 1 kg of sheet iron scrap. After standing for 4-5 hours, the solution is blown with hot water vapor for approx. Heat to 40-50 degrees Celsius. To the solution of iron sulphate thus prepared, a mixture of calcium nitrate (10 kg) and magnesium nitrate (10 kg) was added in portions under constant stirring. The calcium sulfate formed at this time was ca. After 10-15 minutes, filter through a vacuum filter and wash three times with 2% sulfuric acid, then wash with clean tap water until acid free. After drying at 100 ° C from the resultant calcium sulfate white, 9.5 kg weight of CaS0 ₄ .2H ₂ O.

In a solution filtered from calcium sulphate, the iron is ca. It is oxidized at 70-75 degrees C. The iron is precipitated with 23-241 with 25% ammonium hydroxide. After 3 to 4 hours, the resulting iron hydroxide is filtered off with suction and the filtered iron hydroxide washed with alkaline water at 40 to 50 degrees C. The weight of the iron hydroxide dried at 100 degrees Celsius is 6.1 kg Fe (OH) ₃ .

The solution filtered from the iron hydroxide contains the magnesium in the form of magnesium nitrate in the dolomite used and the ammonium nitrate precipitated in the iron removal. Drying the solution gives these compounds in solid form, by weight

Mg (NO ₃ ) ₂ 7.5 kg NH ₄ NO ₃ 13.8 kg

Mass Balance 401.80 g utilization pácoldat containing Fe / 1.138 g SO _4/1, when processing

use:

1. dolomite 10 kg

2. nitric acid 13.5 kg

3. ammonium hydroxide ₁₀ (25%) 12.8 L

formation:

CaS0 ₄ 9.5 kg Fe / OH ₃ 6.1 kg Mg (NO ₃ ) ₂ 7.5 kg NH ₄ NO ₃ 13.8 kg

Claims (2)

2Q is then filtered, and the clear solution is mixed with a solution of Ca (NO ₃ ) ₂ and Mg (NO ₃ ) ₂ and purely filtered from a mixture of dolomite and nitric acid and the resulting gypsum (CaSO ₄ .2H ₂ O) filtered separating, optionally drying - then adding HNO _{3 to} the filtrate until Fe (NO ₃ ) _{2 forms} Fe (NO ₃ ) ₃ - which is neutralized with NH ₃ or NH ₄ OH until Fe ( OH) ₃ formation holds, then the precipitate was removed by filtration and optionally dried, and the filtrate Q ₃ MgNH ₄ (N0 _{3) 3} salt mixture is crystallized by evaporation. 2. A process according to claim 1, wherein the CaSO ₄ .2H ₂ O and Fe (OH) _{3 are} dried.