SE452481B - METHOD OF REGULATING BEDBATH AND REGENABLE SOLUTION FOR BETTING IRON AND STEEL FORM - Google Patents

Description

452 481 and hydrogen chloride. The latter is absorbed during recycling of betsyran. One must expect a certain loss of hydrogen chloride, because the residual acid also enters the furnace.

It is also theoretically possible to regenerate the beet bath by electrolysis. The iron in the beet bath is then precipitated at cathode of the electrolytic cell. In order to be able to implement this electrolysis must consist of the beet bath (electrolyte) an almost neutral solution of ferrochloride. Since the beet bath, however, contains a relatively high content of residual acid one obtains mainly hydrogen evolution at the cathode, i.e. the metal precipitation becomes small in relation to it consumed electricity.

A neutral solution can be obtained by evaporation of bath and crystallization of ferric chloride and separation of the excess acid, which can then be returned to bet processes.

However, since ferric chloride is very easily soluble, one is required vigorous evaporation of the bath, to crystallize out should be able to happen. The subsequent electrolysis requires in addition, a lot of electrical energy, because a large part of the chloride consumed through chlorine gas evolution, while oxidizing occurs at the anode of ferrochloride to ferric chloride. The degree show the concentration of Fe III changes the polarity, leading to the precipitation of alkaline salts below sharply decreasing power output.

A conventional electrolytic cell for recycling beet acid must therefore be of the diaphragm type with ion exchange membrane as a partition between the anode and cathode compartments, to the acid formed at the anode should not prevent iron precipitation at the cathode.

A conventional beet bath with good beet effect contains usually 100-200 g of free hydrochloric acid per liter of beet bath with 0-80 g Fe2 + and attacks the base material strongly. When pickling iron and steel parts with embers, normally consisting of FeO'Fe2O3 oxides are therefore obtained point corrosion, due to the fact that the oxide has a high potential in relation to the iron in the current solution and is cathodic to the base material, which becomes the solution electrode, due to its 452 481 anodic potential. The scale is thus not dissolved in the acid, but rather "exploded" away, by the acid penetrating underneath the ember shell and lifts this off. The Fe304 oxide collects bottom of the acid bath as a pickle sludge. In order to limit corrosion the damage to the base material is used beta inhibitors. The object of the present invention is to achieve a process for pickling iron and steel objects, which during a high power output enables a sufficient fermentation of the pickling acid, whereby the pickling can take place in a closed process where the residual products are pickled iron and steel objects and pure electrolyte iron.

The method according to the invention is characterized in that the objects are placed in a beet bath with a temperature above 25 ° C, and containing a low ferric chloride solution content of free hydrochloric acid, which beet bath is regenerated continuously. in a circulatory system with cells which are connected electrically in series with a direct current source and in parallel in in relation to the beet bath flow, for electrolytic precipitation iron and free acid recovery.

Preferably, the beet bath contains at least 300 g of FeCl 2 per liters and not more than 50 g of free acid calculated as HCl per liter.

Suitably the ferrochloride content is reduced by a maximum of 10 g per liters of solution, during its passage through any of the the light cells and the current at resp. cathode in these are preferably between 0.2 - 10 A per dm 2 of the cathode surface.

A solution for pickling iron and steel objects, which are intended to undergo a subsequent surface treatment or mechanical processing, comprising: FeCl2, Fe and HCl suitably shows the following levels: FeCl2 between 250 and 450 g / l, Fe between 110 and 200 g / l and HCl between 5 and 50 g / l.

Because the pickling according to the invention takes place at high altitudes levels of iron and thus low levels of free acid as well as at elevated temperature, good dissolution of the oxides is obtained, without corrosion on the basic material. The good effect despite the high the iron content of the beet bath depends on the complex formation of the chloride ability. A large part of the iron in the beet bath is bound in anion form according to: (Fec14) 2 ' 452 481 This complexion is in equilibrium with the other ions in the bath due to the elevated temperature of the beet bath, which causes one higher content of free hydrogen ions.

Because the iron ionization pressure is relatively low in a ferrochloride solution with low content of free acid it is possible to precipitate the iron electrolytically with high current yield, disk in a simple electrolytic cell, without ion-exchange diaphragm between anode and cathode.

The invention will be explained in more detail below reference to an embodiment and the accompanying drawing which schematically shows a pickling plant for pickling according to the procedure and with regeneration of the pickling acid in a closed system.

The figure shows a pilot plant for pickling castings. iron and hot-rolled goods before hot-dip galvanizing. With 10 has designated a tank containing beet baths. Goods represented of the arrow 11 is conveyed by means of conveyor down into the beet bath after preparatory degreasing and rinsing. It grazed the estate represented by arrow 12. I The beet bath is continuously pumped from the tank 10 by means of a pump 13, via five electrodes connected in parallel with the pump flow. listening cells 14 and back to the tank 10 by means of a return pump 15. The electrolyte cells are electrically series-connected added with positive and negative poles 16 resp. 17 to one direct current source. Each electrolyte cell 14 contains on known insert an anode 18 and a cathode 19.

The following conditions apply: In the bath 3 Volume: 10 m Freight flow: 2 tonnes / h Triggered iron: 10 kg / h Theoretical amount of acid consumed per hour 15 kg HCl 100% 50 kg acid 30% Concentration: FeCl2 340 g / l Fe 150 g / l free HCl 20 g / l Temperature: 40 ° In the betbad takes place i.a.

In regeneration part Dim.

Electrode system: Voltage drop per cell: Current density: Converters: Current per cell: Total amount of current: 452 481 5 the following reactions: Feo -> Fe2 + Fe3 + 5Fe2 + l500xl000Xl200 mm 5 cells with bipolar electrodes anode: graphite cathode: stainless, acid-proof 2.5 V 2 A / dm2 16 V, 1000 A 900 A 4500 Ah Theoretical amount of precipitated Fe: 4680 g Actual amount of precipitated Fe: Estimated power output: Recovered acid: 4300 g 91% 22 kg 30% -ig The following reactions take place in the electrolytic cells: Cathode Fe2 + - 9Fe0 Anode Fe2 + - §Fe3 + The cathode plates 19 consist of 0.1 mm stainless, acid-resistant plate. At regular intervals, the cathodes in the cells 14 are replaced.

The electrolyte precipitate deposited on the cathodes can in this case easily removed by folding the plates.

During the electrolysis the system with a flow means that the difference the beet bath circulates through the cell of about 30 liters per minute. This in concentration of iron in in- and the starting solution is between 2.0 - 2.5 g / l. In the present case, with an iron solution in the beet bath of 10 kg / h, is obtained thus a 40% recovery of the acid.

In order to obtain a complete recovery is required thus a cell system with a total current of 10,000 A.

This means that the inverter must be dimensioned for for example 16 V and 2000 A or 24 V and 1000 - 1500 A. 452 481 The latter option is more advantageous because the cost of a converter mainly depends on current capacity and not on power or voltage.

The regeneration cells can be built in a modular system, which can be adapted to most existing beta plants, at transition to the beet process of the present invention.

The above dimensions and values can be varied within the scope of the appended claims. The bite method according to the invention can be used in combination with conventional beet procedures. To the beet bath described above, put an activator, a surfactant with high affinity to the metal surface, which facilitates the penetration of the beet bath between the shell and the metal surface. Furthermore, electrolytic current but between the poles 16, 17 is pulsed low frequency, giving a lower polarization and thus a higher current yield.

Claims (5)

452 481 PATENT REQUIREMENTS A process for regenerating pickling baths (10) for pickling iron and steel articles intended to undergo subsequent surface treatment or mechanical processing, characterized in that the pickling bath is maintained at a temperature between 25 and 50 ° C, and contains Fe with a content of 110-200 g / l and free hydrochloric acid, HCl with a content of 5-50 g / l beet bath, which is regenerated continuously in a circulation system with cells (14), which are connected to a direct current source (16, 17), for reducing the content of Fe in the beet bath by electrolytic precipitation of iron and increasing the content of free acid, HCl. Process according to Claim 1, characterized in that the beet bath (10) contains at least 300 g of ferrochloride per liter. 3. Process according to claims 1 or 2, characterized in that the ferrochloride content, during the passage of the solution through the respective electrolytic cell, is reduced by a maximum of 10 g per liter of solution. 4. A method according to any one of the preceding claims, characterized in that the current at resp. cathode (19) in the electrolytic cells (14) is between 0.2 - 10 A per dm 2 of cathode surface. Regenerable solution for pickling iron or steel articles, which are intended to undergo a subsequent surface treatment or mechanical processing, comprising: FeCl2, Fe and HCl, characterized in that the FeCl2 content in the solution amounts to between 250 and 450 g / l, that the Fe content in the solution is between 110 and 200 g / l, and that the content of free acid, HCl is between 5 and 50 g / l. . ._ ... n-. fi ... a-e- »a fl v- _..--.