DE3521632A1 - Process for treating an aqueous solution containing iron chloride and hydrochloric acid - Google Patents

Abstract

The aqueous solution contains from 10 to 30% by weight of iron chloride and from 15 to 25% by weight of hydrochloric acid. The solution is mixed, wholly or partially, with concentrated HCl gas in a crystallization zone at temperatures of from approximately 20 to 60 DEG C, and as a result a concentrated solution is generated which contains crystallized iron chloride and comprises at least 30% strength hydrochloric acid. A first separation device is employed to extract therefrom a salt slurry containing crystallized iron chloride and hydrochloric acid having an HCl content of at least 30% by weight. The remainder of the aqueous solution to be treated is mixed, in an evaporation zone, with flue gas which contains HCl gas and has temperatures of from 750 to 950 DEG C. The flue gas originates from a thermal dissociation process. From the evaporation zone, an HCl-containing gas phase and a liquid phase are drawn off separately. Concentrated HCl gas is extracted from the HCl-containing gas phase and is passed into the crystallization zone. The liquid phase is mixed with the salt slurry from the first separation device, the mixture being separated into a concentrated salt slurry and a liquid phase. The concentrated salt slurry is fed to the thermal dissociation process and the liquid phase is fed to the evaporation zone.

Description

Method of treating a ferric chloride and hydrochloric acid

containing aqueous solution The invention relates to a method for treating an aqueous solution containing ferric chloride and hydrochloric acid, wherein water is partially evaporated from the solution, and hydrous iron chloride is separated off and in an incinerator at temperatures ranging from 750 to 95t "Thermally splits C into iron oxide and * HCl gas, the HCl gas mixed with flue gas brings in direct contact with ferric chloride-containing solution in an evaporation zone and water partially evaporates in the process.

Such methods are from DE-PS 16 67 195 and DE-PS 22 61 083 and the corresponding US Patents 3,578,401 and 4,049,788 known. The invention is based on the object of further developing the known methods in such a way that that hydrochloric acid in a concentration of at least 30% by weight is obtained as the product and the process is carried out inexpensively and with less fault-prone equipment can be.

According to the invention the object is achieved in that (A) the to treating aqueous solution containing 10 to 30% by weight of ferric chloride and 15 to 25% by weight Contains hydrochloric acid, 70 to 100% in a crystallization zone at temperatures mix from about 20 to 60 "C with concentrated HCl gas and make a concentrated solution produced, which contains crystallized iron chloride and of at least 30% strength Hydrochloric acid consists of the concentrated in a first separator Solution of a salt paste containing crystallized iron chloride and a hydrochloric acid with an HCl content of at least 30% by weight wins, (B) the remainder of the to be treated aqueous solution in the evaporation zone with the HC1 gas mixed with flue gas, which has temperatures of 750 to 950 "C and comes from the thermal gap, mixed and separated from the evaporation zone an HCl-containing gas phase and a The liquid phase is withdrawn, (C) concentrated HCl gas is obtained from the HCl-containing gas phase and passes into the crystallization zone, the HCl content in the concentrated HCl gas at least 80% by volume, based on HC1 and H20, and (D) the liquid phase from stage (B) mixes the mixture with the salt slurry from the first separator a second separation device gives up a concentrated one from the second separation device Salt slurry withdraws and gives up the incinerator for thermal cracking and supplying a liquid phase to the evaporation zone from the second separation device.

In the crystallization zone, where the temperatures are preferred are in the range from 30 to 50 "C, will be contained in the solution to be treated Hydrochloric acid strengthened by the concentrated HCl gas, at the same time causes the Supply of HCl gas that ferric chloride precipitates. It is useful to the crystallization zone to supply concentrated HCl gas in such an amount that that from the crystallization zone Concentrated solution withdrawn, calculated to be free of solids, contains 30 to 35% by weight of HC1.

According to a further development of the invention, one wins from the HCl-containing Gas phase from the evaporation zone in direct contact with water hydrochloric acid a Concentration of about 16 to 22% by weight, produced by extractive distillation this hydrochloric acid concentrated HCl gas and leads this HCl gas into the crystallization zone.

The method according to the invention finds application in, for example, recovery concentrated hydrochloric acid, which is used for the digestion of ilmenite. Made of ilmenite, a mineral consisting mainly of iron and titanium oxide, is solved with concentrated Hydrochloric acid iron oxide out to produce titanium dioxide. The solution to be regenerated then contains about 10 to 30% by weight FeCl2 and about 15 to 25% by weight HC1 and less Concentration of other impurities, especially TiO2 and All3. Through the procedure the invention enables the environmentally friendly regeneration of the used solution, HC1 gas is obtained from the iron chloride, which strengthens the hydrochloric acid serves.

The known method of DE-PS 15 67 195 can be so concentrated Don't process solutions.

Design options for the method are shown in the drawing. It shows: Fig. 1 shows a first variant of the process management in a schematic Representation, Fig. 2 shows a modification of the one above the dash-dotted line A-B Process part lying in FIG. 1.

3 shows a possibility of generating the concentrated HCl gas by extractive distillation.

The aqueous solution to be treated is fed in line 1, it contains about 10 to 30% by weight of Fell2 and about 15 to 25% by weight of HC1. The main part of the solution, namely about 70 to 100%, preferably 70 to 90%, is in the line 2 fed to a crystallizer 3, while the remaining solution is in the line 4 an evaporation zone 5 is given up. Through the line 6 is the crystallizer 3 concentrated HCl gas is supplied, the HCl content of which is at least 80% by volume and preferably at least 85% by volume, based on HC1 + H20. The crystallizer 3 includes a Liquid circulation with the cooler 7, which ensures that the temperatures in the crystallizer are in the range from 20 to 60 ° C. and preferably 30 to 50 "C. Under these conditions ferric chloride crystallizes out, while the hydrochloric acid is strengthened.

The HCl concentrated solution generated in the crystallizer 3 arrives in the line 9 to the separating device 10, which is preferably a thickener acts. The withdrawn from the separating device 10 as an overflow in the line 11 clear phase consists essentially of hydrochloric acid with a concentration of at least 30% by weight and also contains a maximum of 10% by weight and mostly a maximum of 6% by weight Fell2. This clear phase can be repeated e.g. for the Ilmenite digestion be used. The one at the lower end in line 12 from the separator 10 extracted salt paste contains precipitated Fell2 2H2 0 in a FeC12-saturated Solution with which a certain amount of concentrated hydrochloric acid is also removed will.

The line 12 opens into a mixing vessel 13, the one through the line 14 the liquid phase from the evaporation zone 5 is also supplied. The mixture arrives in line 16 to a separating device 17, which is preferred is also a thickener. The separating device becomes 18 in the line a concentrated salt paste is drawn off, the solids content of which is essentially made up Fell2 2H20 exists. The liquid of the salt porridge consists of a saturated one FeC12 solution with 2 to 5% by weight HC1 and 35 to 45% by weight FeC12. As both the water content and the hydrochloric acid content of the salt mash is relatively low, the thermal Cleavage in the reactor 20 takes place with a favorable use of energy. Fuel is in the line 21 and combustion air in the line 22 supplied. In reactor 20, which is expediently a known fluidized bed reactor, thermal cleavage of the iron chloride takes place with direct combustion in a fluidized bed at temperatures in the range of 750 to 950 and preferably 800 to 900 "C. The The resulting iron oxide can be used as a fluidized bed material, an excess is withdrawn in line 23. A mixture of flue gas containing water vapor and HCl gas leaves the reactor in line 25, it is roughly dedusted in a cyclone 26, deposited solids in line 27 are fed back to the reactor and hot gas mixture flows off in line 28.

The gas mixture in line 28 passes with that prevailing in the reactor Temperatures in the evaporation zone 5, the one through the line 30 also gives up the liquid phase from the separating device 17 with the aid of the pump 31. The evaporation zone 5 is expediently like a known Venturi scrubber designed for intensive contact between gases, vapors and liquids cares.

With the help of the sensible heat of the hot gas mixture from the pipe 28 a gas phase consisting mainly of HC1, H20 and flue gases is generated, which is discharged in line 33. The gas phase contains the gases passed through line 28 introduced smoke gases. The evaporation zone 5 ensures that the HC1 practically completely passes into the gas phase of the line 33 and therefore the salt paste in the line 18 has only a low HCl content. So that you get the ferric chloride content holds in the solution in the line 14 below the saturation value and thus buildup in the evaporation zone 5 avoids, it may be useful through the line 35 to add more water to the evaporation zone 5.

To from the HCl-containing gas phase of the line 33 concentrated HCl gas to win, is generated first in the packed column 36 with water from the Line 37 hydrochloric acid with a concentration of 16 to 22% by weight, each of which is partly through line 38 and line 43 passes. The smoke gases that are practically HCl-free are withdrawn from column 36 by fan 41. The partial flow that is withdrawn through line 38, one gives up a treatment in which after a concentrated HCl gas is generated in a process known per se. Preferably are the hydrochloric acid from line 38 in an extractive distillation 40. As An aqueous, concentrated iron chloride-containing extractant is preferably used Solution of a chloride mixture, which preferably consists of magnesium chloride. By the line 42 becomes this concentrated Solution of extractive Distillation 40 supplied.

This displaces the HC1 from the hydrochloric acid. Concentrated HCl gas with only a low water vapor content flows off in line 6 and is, as already explained, fed to the crystallizer 3. Details of an embodiment of the Generation of the concentrated HCl gas are described with the aid of FIG.

The method variant of FIG. 2 can take the place of the above the process part of the process of the figure lying on the dash-dotted line A-B 1 kick. According to FIG. 2, the one to be treated, containing hydrochloric acid and ferric chloride, comes aqueous solution from line 1 and is 70 to 100%, preferably 70 to 90% % abandoned through line 2a to a mixing container 50, the remaining solution flows in line 4 to evaporation zone 5, cf.

Fig. 1. As already explained together with Fig. 1, the flows in the crystallizer 3 strengthened solution in the LeituWg 9 to the separating device 10, whereby one in the Line 11 to be reused, mainly from hydrochloric acid of an HCl concentration subtracts from at least 30% by weight of existing solution. The one containing mainly ferric chloride Salt slurry is also added to the mixing vessel 50 in line 12a and the Mixture arrives in line 51 to a separating device 52, which is is preferably also a thickener. The in the separating device 52 separated phase low in solids is fed to the crystallizer 3 in line 53, while the likewise separated salt paste in the line 12 is transferred to the mixing vessel 13, see.

Fig. I, is supplied.

By the method of Fig. 2 it is possible in the line 12 a To supply salt paste for further work-up, which contains a little less hydrochloric acid than the salt slurry from the separating device 10 of FIG. 1.

In the process part of Fig. 3, the hydrochloric acid substream from the Line 38 of the distillation column 40 abandoned, in which with the addition of hot, concentrated MgCl2 solution from line 42 an extractive distillation takes place, with concentrated HCl gas being drawn off overhead. The column 40 is known in Wise energy supplied via a heat exchanger 49. The temperature of the solution in the line 42 is in the range from 130 to 160 "C, it has a MgCl2 concentration in the range from 35 to 45% by weight. The used and therefore somewhat diluted MgCl2 solution is conducted in line 44 to an evaporator 45 which has a steam heating 46, with the help of which the solution is concentrated again. Leave the vapors the evaporator through line 47. The concentrated MgCl2 solution is from the Pump 48 is fed to column 40 through line 42.

The hydrochloric acid of the substream of line 43 is isothermal Absorption column 50 with concentrated HC1 gas, which via line 51 from the Column 40 is brought up, concentrated. The rest of the concentrated HCl gas reaches the crystallization zone 3 in line 6 (see FIG. 1). Column 50 has one or more coolers 52, the product, the iron chloride-free hydrochloric acid with an HCl content of 30-35 total 96, is withdrawn in line 53, and exhaust gas leaves the column through line 54 and can undergo further treatment, not shown are fed.

Example: In a process procedure corresponding to FIGS. 1 and 3 150,000 kg of solution worked up per hour, which in the management 1 comes from the digestion of ilmenite for the extraction of TiO2. In table 1 are the contents of FeC12, HC1 and H20 (in kg / h) in the liquids for the respective lines or suspensions indicated.

Table 1 Line FeC12 HC1 H20 1 29 000 29 000 92 000 2 21 000 21 000 67 000 4 8 000 8 000 25 000 11 2 700 26 900 49 000 12 12 18 300 7 600 18 900 18 26 300 1 000 17 500 The H20 content in the flow of line 12 contains moisture and Crystal water.

In the crystallization zone 3, FeC12 2H20 falls in crystalline form at 40 "C. from, while via line 6 concentrated HCl gas at 13,500 kg per hour HC1 and 1500 kg of H20 introduced and circulating liquid in the cooler 7 with water is cooled. The thickener 10 is supplied through line 9 with 124,000 kg / h of crystal suspension fed.

In line 11 is a 34% hydrochloric acid, which is still 3.4 wt.% Contains FeC12, deducted. In the mixing zone 13 becomes the suspension mixed from line 12 with 500,000 kg / h of solution from line 14, the mixture is added to the thickener 17, from which the liquid phase in line 30 is returned to the venturi scrubber, which forms the evaporation zone 5, flows.

The line 18 carries the same total mass flow as the line 12, but the stream of line 18 contains more FeCl2 and less HC1 and water than the stream in line 12. About 3 5000 per hour are fed to reactor 20 kg of heating oil and through line 22 75,000 Nm of combustion air. From the reactor 20 16,000 kg / h of iron oxide are withdrawn through line 23.

Table 2 A B C flue gases (kg / h) 90 000 90 000 90 000 HC1 (kg / h) 16 000 30 600 H20 (kg / h) 21 000 57 400 70 000 A gas mixture leaves via line 25 with a temperature of 820 "C and the composition according to Table 2, column A, the reactor 20 and is first dedusted before it is given up to the venturi scrubber 25 will. To regulate the concentration, the washer also receives around 10,000 kg / h Water supplied from line 35, this water is rinse water from the ilmenite outcrop. the Temperatures in the lines 14 and 33 are about 100 "C. The gas phase in line 33 has a composition according to Table 2, column B, it is in the column 36 with 127,000 kg / h of water in brought into direct contact, with a temperature of 84 "C at the top of the column. The composition of the gases withdrawn at the top of column 36 is given in Table 2, Column C again.

From the column 36 come a total of 14,500 kg / h hydrochloric acid with 21 wt. % HCl, of which 10 500 kg / h are in line 38 of the distillation column 40 and 40,000 kg / h of the isothermal absorption column 50 are supplied in line 43.

The MgCl2 solution in line 42 has a temperature of 150.degree and a MgCl2 concentration of 40% by weight, the amount of the solution is 600,000 kg / h.

From the hydrochloric acid substream of the line 43 are at 8700 kg / h concentrated HCl gas (concentration = 90 wt.%) in the column 50 at temperatures from 40 ° C. 49,000 kg / h hydrochloric acid with 35% by weight HC1 is generated.

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Claims (5)

Claims 1. A method for treating a ferric chloride and Aqueous solution containing hydrochloric acid, some of the water being extracted from the solution evaporated, hydrous ferric chloride separated and in an incinerator at temperatures in the range from 750 to 950 "C to form iron oxide and HCl gas thermally splits the HCl gas mixed with flue gas in an evaporation zone in direct Brings into contact with solution containing ferric chloride and partially evaporates water, characterized in that (A) the aqueous solution to be treated, the 10 to Contains 30% by weight ferric chloride and 15 to 25% by weight hydrochloric acid, 70 to 100% in a crystallization zone at temperatures of about 20 to 60 "C with concentrated HCl gas mixes and creates a concentrated solution that crystallizes iron chloride contains and consists of at least 30% hydrochloric acid, with one in a first Separating device from the concentrated solution a crystallized iron chloride containing salt paste and a hydrochloric acid with an HCl content of at least 30 % By weight wins, (B) the remainder of the aqueous solution to be treated in the evaporation zone with the HCl gas mixed with flue gas, which has temperatures of 750 to 950 "C. and comes from the thermal crack, mixed and separated from the evaporation zone a gas phase containing HCl and a liquid phase are withdrawn, (C) off The HCl-containing gas phase wins concentrated HCl gas and enters the crystallization zone conducts, the HCl content in the concentrated HCl gas being at least 80% by volume, based on on HC1 and H20, and (D) the liquid phase from stage (B) with the salt paste mixes from the first separation device, the mixture from a second separation device gives up, withdraws a concentrated salt paste from the second separator and gives up the incinerator for thermal cracking and a liquid Phase feeds from the second separation device to the evaporation zone. 2. The method according to claim 1, characterized in that one from the HCl-containing gas phase from the evaporation zone in direct contact with water Hydrochloric acid with an HCl concentration of about 16 to 22% by weight is generated and from this Hydrochloric acid obtained by extractive distillation concentrated HCl gas, which one passes into the crystallization zone. 3. The method according to claim 1 or 2, characterized in that 70 up to 90% of the solution containing ferric chloride and hydrochloric acid to be treated as first partial flow into the crystallization zone and the remaining solution as the second Partial flow are passed into the evaporation zone. 4. The method according to claim 1 or 2, characterized in that one 10 to 30% of the solution to be treated passes into the evaporation zone, the rest Solution mixes with the salt slurry from the first separator, the mixture one third separation device gives up the low-solids phase from the third separation device the crystallization zone and the salt slurry from the third separator mixed passes with the liquid phase from the evaporation zone into the second separating device. 5. The method according to claim 2 or one of the following, characterized in, that with a partial stream of hydrochloric acid the HCl concentration of about 16 to 22% by weight and a partial stream of the concentrated HCl gas from the extractive distillation Iron chloride-free hydrochloric acid with an HCl concentration of 30 to 35% by weight is generated.