DE2124593A1 - Disposal of waste acid ferrous sulphate from titanium - dioxide mfr - by selective evaporation,oxidn and formation of double - Google Patents

Abstract

Ferrous sulphate and sulphuric acid are produced by evaporation and cooling from the three-component system H2O:FeSO4:H2SO4 of compsn. defined by the area enclosed by (a), (b) and (c) on a triangular diagram, where (compsn. in wt.%) (a) is 90 H2O, 2 FeSO4, 8 H2SO4, (b) is 75 H2O, 17 FeSO4, 8 H2SO4, (c) is 68 H2O, 6 FeSO4, 26 H2SO4. The ferrous sulphate, in the form of its monohydrate, heptahydrate, or in aq. soln. is oxidised, esp. by air, to neutral or acid ferrisulphate and reacted with KCl to produce the potassium ferrisulphate double salt, which is isolated from the mother liquor which contains FeCl3. Other possible products are K2SO4, KHSO4, and HCl.

Description

Process for the processing of mixtures of substances from water, ferrous sulphate and sulfuric acid "In the production of titanium dioxide pigment fall significant Men- | gen hydrolysis waste acids ant the essentially ferrous sulfate and sulfuric acid contain. In the absence of economic usability, these are preferred sunk in the sea. A work-up fails due to the great costs of the separation, which is connected with a very complex to operate dehydration. This Effort is considerably reduced by using the invention; also avoids this harmful side effects from the discharges of waste acid.

While the introduction of gypsum or sodium chloride is not alien to the system Substances represent, it is known that with waste sulfuric acid a pH shift into the acidic area and, in addition, a withdrawal of what is necessary for marine ecology Oxygen enters. iFor procedural reasons, the hydrolysis to TiO2 is with reducing agents absolutely to drive on Fe2 +. The discharge of the hydrolysis waste mixtures is at least the conversion of FeSO4 to Fe2 (SO4) 3 is an additional consumer of dissolved oxygen in sea water and has a negative influence on | the life processes.

For example, it is possible to greatly narrow the waste acid that recovered FeSO4 7H2Q and FeSO4 IH2O to separate from the H2SO4 and all of the iron sulfate to be converted into the form of the monohydrate and with sulfur to Fe2O3 (FeO (OH) pigment or to decompose combustion and SO2 (H2SO4) that are just barely suitable for blast furnaces. This way of working often fails because investments are required in roasting capacities. It would also be possible after oxidizing the waste acid mixture this to ammonize and produce ammonium sulfate. It interferes with the costly fe (OH) 3 filtration.

The implementation of ferrous sulphate FeSO4 with potassium chloride KCl is still ongoing by the French patent specification 1,544,116 on ferrochloride FeCl2 and potassium sulfate K2S04 has been proposed.

For this purpose, FeSO4 must first be isolated, that is, the complex one Separation task is not bypassed. The narrowing is made even more difficult by the fact that an oxidation to Fe3 + is to be avoided.

In addition, the actual conversion of FeS04 and KCl is then below a non-oxidizing gas atmosphere, for example nitrogen (in F. Pat. 1.544.116 p. 2, first column last | Row, 2nd column, first 4 rows). This one The invention described below avoids effort and disadvantage.

There has now been a process for working up mixtures of substances Water, ferrous sulphate and sulfuric acid with mixtures of raw materials used in the area of the three-component system through the corner points wt.% H2O FeSO4 H2SO4 a) 90 2 8 b) 75 17 8 c.) Ód 6 26 are defined, where ferrous sulfate and sulfuric acid are dehydrated generated, cooled and separated, characterized in that the delimited Ferrous sulfate in the form of its hydrates or its aqueous solution to neutral or acidic ferric sulfate is preferably oxidized with air, with potassium chloride to form potassium iron sulfate implemented and separated from the FeOl -containing final liquor.

It has also been found that the dehydration can be achieved by indirect heating is carried out up to a residual water content of 16 to 23 wt.% H20, to 20 to 350 C, especially 250C, cooled, the crystallized FeSOt HO from the sulfuric acid is separated and oxidized.

It has also been found that the dehydration can be achieved by indirect heating is carried out up to a residual water content of 47 to 50 wt.% H2O, to 20 to 35 ° C, especially 25 ° C, and the crystallized FeSO4. 7H2O from the aqueous | FeSO4-containing sulfuric acid is separated and in this by indirect Heating, further dehydration up to a residual content of 22 to 23 Wt.% H2O made, cooled to 20 to 350 C, in particular 250 C, the crystallized Salt FeS04 1 1 H20, from which sulfuric acid is separated and oxidized.

It was further found that at a weight ratio of 2.1 FeSO 4 : 1H2SO4 in the initial mixture up to a residual water content of 16% by weight H20, from 0.23 FeSO4: 1H2SO4 up to 23% by weight H20 and those in this range FeSO4: H2SO4 weight ratios of the starting material mixtures up to the corresponding Remaining contents indirectly removed from water, cooled to 20 to 350 C, which crystallized FeS04. 1H2O is separated from the sulfuric acid and oxidized.

It was found that at a weight ratio of 2.1 FeS04: @ H2SO4 in the starting mixture up to a residual water content of 47% by weight H2O, of 0.23 FeSO4: 1 H2SO4 up to 50 wt.% H2O and in this range FeS04 H2SO4 ratios of the raw material mixtures up to the corresponding residual content indirectly removed water, cooled to 20 to 3500, the crystallized FeSO4 7 7 H20 is separated from the sulfuric acid and oxidizes.

It was also found that those with starting mixtures with weight ratios Mixtures of ferrous sulphate and sulfuric acid produced from more than 1.4 FeS04: 1 H2S04 Directly heated and oxidized, evaporated to 20 to 40% by weight of residual water, cooled to 500C and below, preferably to room temperature and the crystallized salt Fe2 (SO4) 3. H2SO4. 2H2O is separated from the sulfuric acid.

It was also found that starting mixtures with weight ratios Mixtures of ferrous sulphate and sulfuric acid made from less than 1.4 FeSO4: 1H2S04 up to 30 to 45 wt.

Residual water evaporated in an oxidizing manner, down to 500C and below, preferably be cooled to room temperature and the crystallized ferric sulfate of the sulfuric acid is separated.

Then it was found that in part of the starting mixture below non-oxidizing dehydration to 47-50 wt.% H20 evaporated and to 500 C and below, preferably cooled to room temperature and the crystallized FeSO4 7H20 is separated off with adhering sulfuric acid, the other part of the starting mixture warmed to 80 to 90 ° C and the equivalent of the double salt to be obtained Mix the amount of KOl, mix both parts of the starting mixture in the same proportion that a weight ratio of 2.1 to 1.5 FeSO4: 1H2SO4 and 65 to 70 % By weight H20 is set, the mixture is preferably oxidized by blowing in air, cooled to 50 ° C. and below, preferably to room temperature, which crystallized Doppelsal Be2 (S04) 3 2K2SO4 is separated from the FeCl3-containing final liquor.

It was then found that Be2 (S04) 3 H2S04 H20 in part of the oxidized starting mixture dissolved in the heat with one of the double salts to be obtained approximately equivalent amount of KCl stirred, to 500 C and below, preferably to room temperature, cooled and the crystallized double salt Fe2 (S04) 3 2K2S04 from the FeCl3-containing Final liquor is separated.

Finally it was found that the sulfuric acid evaporated and with potassium chloride to form potassium sulfate or potassium hydrogen sulfate and hydrogen chloride is processed.

Dehydration, separation and oxidation are unavoidable. By the use of ECl and conversion to iron (III) potassium double sulfates or potassium sulfate can save a considerable evaporation effort according to the method of the invention will. The main problem of FeSO4 or the residues is caused by discarding as FeCl3 dissolved. The S04 residue in Fe2 (S04) 3 serves as a sulphate source to the Extraction of potassium sulphate from KCl, which is compared to the usual production becomes available with, for example, MgSO4.

The remaining sulfuric acid can either be used as digestion acid can be used or for the conversion of further KCl to K2S04. or K11504 and hydrogen chloride.

The waste sulfuric acids used are shown in the isothermal triangle diagram FeS04-H2S04-H20 (250) shown in Fig. 1; the points a-c mark the protection area the feedstock mixtures that can be assumed.

It is the binary heptahydrate FeS04 7H2O (solid) with solutions efghi coexistent at 250 G. i is eutectic double saturation with, hepta- and monohydrate, from i (79 H20, 10 FeS04, 11 H2S04) to the corner point H2S04 the limit curve hugs to the binary system i-k-l-H2S04. When evaporating the solutions from a b c - e.g. with indirect heating - e-i is exceeded at higher temperatures between f and h, on removal of water to 47-50% by weight K20, cooling to 250 ° C., result in precipitation of FeS0 7 H2O liquids between g-h. With withdrawal up to, for example, 30 % By weight H20 in the remaining liquid and cooling to 250C result from g and h the liquids k and 1 with simultaneous precipitation of solid FeSO4 . 1H2O.

In Fig. 1 are the concentration paths of conversion example A and the Separation examples 1 + 2 can be seen in dashed lines, thin lines denote individual traces Borderline mixtures, strong delimitations are phase fields. Is dash-dotted the triangle a) b) c) denotes the scope of protection of the starting mixtures represents, the three hatched individual areas in this triangle indicate which Separation operations are to be performed in accordance with this invention.

The relationships in the oxidized system Fe203-S03-H20 are shown in Fig. 2 graphically represented. The conversion results for the starting mixtures: Weight% H2O FeSO4 H2SO4 or H2O Fe2O3 SO3 a) 90 2 8 "91.3 1.1 b) 75 17 8" 75.7 9.8 14.5 c) 68 6 26 @ 72.5 3.5 24.0 It was also found that starting with water removal of compositions according to a) -b) -c) (and therein d) for the following example A) because - the area g-h-i with high solubilities should be avoided, - the state point trace should be clearly to the right of 1.37 = Fe203 3 S03 (with higher Fe contents - left of which - unwanted Fe2 + salt can reappear) and - the range 1.37-e-f-1.38 (Precipitation area of Fe2 (S043. XH2O) in reproducible proportions is to be cut, a division of the appropriate cutting operations is advantageous is, namely A) Area with weight ratio FeS04: H2S04 1.4: 1 and larger or Fe2O3: SO3 0.55: 1 and larger (coincidentally identical to d) i.e. the area triangle b-bd 'in Fig. (diagram) 2.

Process stages: evaporation, cooling, separation of the FeS04 7 H2O at approx. 250 C and further evaporation of the solution with oxidation according to the separation example 3 (Points 3.0 and 3A in Fig. -1 and 2) B) The largest area in terms of area in parts by weight FeS04: 112S04 1.4: 1 to 0.5: 1 (d-a-H2O) or Fe203: SO3 0.55 : 1 to 0.22: 1 i.e. the area square a b '(d) d'c' in Fig. 2.

The following process stages are advantageous: Oxidising evaporation of the Fe203-rich starting solutions up to 40-45 total H2O in the residual mixture, the Fe203-poor Starting solutions up to 59-53 total H2O in the residual mixture, cooling to approx. 500 C and underneath, separating the Fe2 (S04) 3 x1120 from the residual acid to the extent that a Fe-rich phase still remains with the relative composition Fe2 (SO4) 3 1H2SO4. In addition to those already mentioned in example A (point 5 in Fig. 1 and 6 in Fig. 2) as well as in the separation examples 3 + 4 (Fig. 2). essential; for process economy, if necessary, excess H2SO4 has to be separated off, to set the mentioned Fe203: S03 ratio - or equivalent FeSO4 : H2S04 - to carry out the reaction with KCl.

C) Range FeSO4: H2S04 0.5: 1 parts by weight and smaller or Fe2O3 : SO3 0.22: 1 and smaller i.e. the triangle ac'c The following process steps are advantageous evaporation, cooling, separation of the FeSO4 '1 H20 at about 250 C, as one-step process; approx. 1/6 (and less) solid form in the remaining quantity Salt (see Fig. 1, there h '), separation of the main amount of H2S04, FeSO4 1H20 with more Process the raw mixture as in B) In Fig. 2, the protection area a-b-c is dash-dotted delimited with hatched individual fields for the separating operations to be used. Example A and separation examples 3 + 4 are dashed, thick, solid lines --ghief - denote the limit of coexisting phases (solid-liquid) at 500 C, the thinner solid lines either traces of individual mixtures or coexistence conodes for eutectic and transition points with the corresponding fixed Fabrics. The latter are simplified by numerals indicated moles Fe203, SO3, H20, for example the liquid point i is doubly saturated with 2.5.17 (= 2Fe2O3 5 S03. 17 H20) and 1.37 (= Fe203 3S03. 7 7 H2O).

Example A raw mixture, part I: 829 g with 630 K20, 115.5 FeS04, 83.5 H2SO4 (d, Fig. 1) are concentrated: 398 g "199", "", "" (1.0 Fig. 1) the latter were cooled to approx. 250C and separated only superficially, resulting in residual solution 1.t (in Fig. 1) as in the following separation example 1, namely 171 g with 91 K20, 19 FeS04, 61 H2S04 (this is processed further as in example 1 or 3) and a Salt slurry 1.1 '(in Fig. 1) with adhering H2SO4 with 227 g with 108 K20, 96.5 FeS04, 22.5 H2S04, this is stirred with further crude mixture, part II: 762.6 g with 578 H20, 103 FeS04, 81.6 H2SO4 (d, Fig. 1) with heating and oxidizing air blowing, The mixture 1.1 '+ II warm resulted in 989.6 g with 686 20, 199.5 FeSO4, 104.1 S03 (5, Fig. 1) which then oxidizes a solution point 6 Fig. 2 results in 1000 g with 705 H20, 105 Fe203 and 190 S03 or with 26.25% Fe2 (SO4) 3 and 4% fr.H2SO4 in these Fe2 (SO4) 3-rich Solution are heated at approx.

90 ° C stirred in 118 g of KCl, the resulting hot solution mixture Has now 63% by weight of H2O and separates on cooling to 250 ° C. 320 g of Fe2 (S04) 3 2K2S04 14H2O and 798 g of a final liquor containing FeCl3. The latter can be concentrated on potassium sulfate and FeC13 can be processed or discarded. The double salt results in getrock net 239 g with 25.2% K20 and 53.3 96 SO3.-It can therefore be made from 1591 g of waste mixture under evaporation of 430 g of H20, separation of 171 g of approx. 40 of the above H2SO4, which still contains some FeS04 contains, oxidation of FeS04 and use of 118 g KCl 239 g anhydrous Fe-K double sulfate with approx. 25% K20 are produced with an accumulation of 798 g of a ferrichloride-containing Final liquor. At the same time compared to the previous discharge into waters or the sea avoided the otherwise occurring biological oxygen deficit.

Example A corresponds in particular to claims 1 and .9.

The separation examples listed below show the solution to this Task, the progress made by the use of potassium chloride in terms of savings at evaporation work is achieved and finally that, depending on the other wishes, which one sets with regard to the recovery of by-products, the process can be varied.

Separation example 1 (two-stage, without oxidation, according to claim 2 and 3) There should be a separation in 2 stages with considerable dehydration and without Oxidation takes place for a mixture according to point d) in Fig. 1.

100 parts by weight with 76 H20 + 14 FeS04 + 10 H2S04 in solution become 52 parts by weight H20 evaporates to a residual content of 50% H2O, and it is cooled to 2596.

The result: in GT tot. H20 FeSO4 H2S04 and in% H20 FeS04 H2S04 1.0) 48 24 14 10 50 29 21 Mixture and separated from it 1.1) 19.5 8.8 10.7 45.3 54.7 solid: FeSO4 .7H2O 1.2) 28.5 15.2 3.3 10 54.3 10.6 35.1 Residual solution from 1.2 after evaporation of further 11.45 GT H20 to 22% H2O residual content, cooling to 250 C results 2.0) 17.05 3s75 3.3 10 22 19.3 58.? Mixture and separated from it: 2.1) 3.5 (>) 0.35 3.15 - 10.6 89.4 - solid: FeSO4. 1H2O 2.2) 13.55 3.4 (<) 0.15 10 25.1 1.1 73.8 Acid The course can be seen in Fig. 1 (diagram) with d- 1.0, 1.1, 1.2-2.0, 2.1, 2.2. Essential must be adapted to the position of point i in the first stage, the | dehydration, i.e. at the specified concentration range and the selected cooling 250 C to Concentrate to 47 - 50 wt. 96 residual H20.

Separation example 2 (one-stage, without oxidation, corresponding to claim 2) From same composition as separation example 1 - point d Fig. 1 - starting should now - but through a one-step procedure - be separated up to the same residual amount of H2S04 will. The course can be seen from Fig. 1.

A mixture of 100 GT with 76 H20, 14 FeSO4, 10 H2S04 (like example 1) is evaporated to 71.1 GT H20 (in example 1: 63.45) on: in GT total H2O FeSO4 H2SO4 or in% H2O FeSO4 H2SO4 3.0 28.9 4.9 14 10 17 48.4 34.6 separated from it at 250 C: 2.1 ') 15.3 1.45 13.85 10.6 89.4 -2.2') 13.6 3.45 0.15 10 25.1 1.1 73.8 Separation example 3 (two-stage, of which 2nd stage with oxidation, corresp. Claim 6) In the case of two-stage separation, the first stage is indirectly heated and in the 2nd process step with the immersion burner, possibly with air being blown in All FeSO4 still present in the last separation step is processed in Fe2 (S04) 3 converted with H2S04 and the separation then carried out at 500 C. Of the The second process step can be seen in Fig. 2 (point 3 A).

The mixture before the 2nd separation stage from Example 1 contains starting from an application of 1 kg with 760 g H20, 140 g FeS04 and 100 g H2SO4 total H2O FeS04 H2S04 process, state in g: 170.5: 37.5 33 100 = 2.0 in example 1 mixture before 2nd trenine mole: 2.085 0.217 1.021 voltage and without oxidation (requirement mole 02) (0.054) To departures moles + 0.047 - 0.109 / oxidation H2O ½Fe2 (SO4) 3 H2SO4 3.A mole result 2.132 0.217 0.922 g mixture 171.1: 38.4 42.3 90.4 mixture after oxidation H2O Fe2O3 SO3 also g, converted g: 55.0 17.35 98.75 "" "and in% by weight 32.1 10.2 57.7 see Fig. 2 separation separation at 500 C liquid / solid salt contains rel. % 10.1 30 59.9 Fe2O3.4SO3.3H2O solution "" "42.6 0.4 57 or g on 1 kg insert: 3.1 Salt 59.6 g = 7.5 + 16.9 + 35.2 = Fe2 (SO4) 3.H2SO4.2H2O | 3.2 Solution 111.5 g = 47.5 + 0.45 + 63.55 = 112504 5?, 3 96 with 0.25% Fe separation example 4 (single-stage and oxidizing, according to claim 7) Based on the use as in the previous examples as in Example 2, but in an oxidizing manner, concentrated. 711 g of H2O are extracted from 1000g, The following are then available: total H2O FeSO4 H2SO4 process, condition in g 289 g: 49 140 100 = 3.0 Example 2 in moles 2.725 0.921 1.021 Mixture before separation and without oxidation to / outlets moles + 0.23 - 0.461 / oxidation H2O ½Fe2 (SO4) 3 H2SO4 4th A. mole result 63.4 0.921 0.56) Mixture after Mixture g 53.3 184.1 54.9) Oxidation 292.3 g: H20 Fe203 503, likewise, convert. g 63.4 73.7 155.2 mixture after oxidation and in% by weight 21.7 25.2 53.1 see Fig. 2 Separation% wt. Relative% H2O Fe2O3 SO3 Separation solid / liquid at 50 ° C 4.11) Fe2 (SO4) 3.H2SO4. 2H2O 29.7% 10.1 29.0 61.0 4.12) Fe2 (SO4) 3.H2SO4 . 8H2O 66.5 96 16.8 16.6 33.1 4.1) solid salts 96.2% 20.6 26.1 53.3 (4.11 + 4.12) 4.2) Solution 3.8 50 1.5 48.5 or g on 1 kg insert: sat. gH2O gFe2O3 g SO3 4.1 Salts 181.2 g = 57.85 + 73.54 + 149.81 = Fe2 (S04) 3 112504 3H2O and with 9H2O; approx 1: 2 GT 4.2 solution 11.1 g = 5.55 + 0.16 + 5.39 It results for the rational separation, that in the pure separation examples 1-4 to withdraw significantly higher amounts of water are as in Example A; points 1.0, 2.0 and 3.0 in Fig. 1 are essential farther from point H20 than point 5 and in Fig. 2 points 3A and 4A substantially continue as point 6 for example A.

A quantitative comparison shows this: To point 1.0 in separating, example 1 theoretically, you have to use 520 g 1120 per kg of input (760 g H2O, 140 g FeS04 and evaporate 100g H2SO4 according to d), by 107 g Fe04 (phase 1.1) at all to be able to separate, this is 56 g SO3. In example A, partial amounts are made with the raw mixture I performed the same operations, but under technical conditions (Salt slurry 1.1 '). According to separation example 1, a water removal of 520 g H2O / 56 g is achieved S03 or 9.3 g H20 / g S03 (as FeS04 7 H20) required. However, according to example A. 430 g H2O can be withdrawn from 1591 g input or 270 g per kg input can be obtained 128 g SO3 or the actual evaporation effort is 2.1 g H20 / g SO3 (as E-Fe double sulphate), is therefore much cheaper.-Depending on the composition of the raw mixes available H2O-FeSO4-H2504 fall after the main reaction to E-Fe sulfates has been carried out in excess whose quantities are also varied according to the chosen separation path and so the other needs can be adapted, that is, the separation task is with coupled to the main reaction. A sulfuric acid obtained as an excess can, for example in the conventional way for the production of further K2S04 or KHSO4 and HCl Use of KCl or used in other conventional areas of application will. An excess of ferrous sulfate can according to other proposals that have come to light processed further with KCl to form K2S04-containing salts or with sulfur processed into iron oxides and SO2 (and from it sulfuric acid), if still there is an additional interest.

Claims (9)

PATENT CLAIMS 1. Process for the processing of mixtures of substances from water, ferrous sulphate and sulfuric acid with mixtures of raw materials used in the surface area of the three-component system through the corner points wt /% H20 FeSO4 H2SO4 a) 90 2 8 b) 75 17 8 c) 68 6 26 are defined, with ferrous sulfate and sulfuric acid with dehydration generated, cooled and separated, characterized in that the delimited Ferrous sulfate in the form of its hydrates or its aqueous solution to neutral or acid ferric sulphate, preferably oxidized with air, with potassium chloride to form potassium iron sulphate implemented and-is separated from the FeCl3 -containing final liquor. 2. The method according to claim 1, characterized in that the dehydration is carried out by indirect heating up to a residual water content of 16 to 23 wt. 96 K20, cooled to 20 to 35 ° C, in particular 250 C, the crystallized FeS04. H2O is separated from the sulfuric acid and oxidized. 3. The method according to claim 1, characterized in that the dehydration is carried out by indirect heating up to a residual water content of 47 up to 50 wt. 96 H2O, cooled to 20 to 350 C, in particular 25 ° C, and the crystallized FeS04 7H2O is separated from the aqueous FeSO4-containing sulfuric acid and in this further dehydration through indirect heating up to a residual content made from 22 to 23.Gew.96 H20, cooled to 20 to 3500, especially 25 ° C, the crystallized salt FeSO4. 1H2O separated from the sulfuric acid and oxidized will. 4. The method according to claims 1 to 3, characterized in that that with a weight ratio of 2.1 FeSO4: 1 H2S04 in the starting mixture up to a residual water content of 16 wt. 96 H20, from 0.23 FeSO4: 1 H2SO4 up to 23% by weight H20 and FeSO4: H2S04 weight ratios in this range water is indirectly withdrawn from the raw material mixtures up to the corresponding residual content, cooled to 20 to 350 C, the crystallized FeSO4 '1H20 from the sulfuric acid is separated and oxidized. 5. The method according to claims 1 to 3, characterized in that that at a weight ratio of 2.1 FeSO4: 1112504 in the starting mixture up to to a residual water content of 47 wt. 96 H20, of 0.23 FeSO4: 1 H2SO4 up to 50 % By weight H20 and FeSO4: H2SO4 ratios in this range | the Raw material mixtures indirectly removed water up to the corresponding residual content, cooled to 20 to 350C, the crystallized FeSO4 7H20 separated from the sulfuric acid and is oxidized. 6. The method according to claims 1 to 5, characterized in that that those with starting mixtures with weight ratios of more than 1.4 FeSO4 : 1 H2S04 produced mixtures of ferrous sulphate and sulfuric acid directly heated and oxidizing, evaporated to 20 to 40 wt. 96 residual water, cooled to 50 ° C C and below, preferably to room temperature and the crystallized salt Fe2 (S04) 3 H2S04. 2H20 is separated from the sulfuric acid. 7. The method according to claims 1 to 5, characterized in that that starting mixtures with weight ratios of less than 1.4 FeSO4: 1 H2SO4 manufactured mixtures of ferrous sulfate and sulfuric acid up to 40 to 45% by weight of residual water evaporated in an oxidizing manner, down to 500C and below, preferably down to room temperature be cooled and the crystallized ferric sulfate separated from the sulfuric acid will. 8. The method according to claims 1 to 7, characterized in that that in part of the starting mixture with non-oxidizing dehydration 47-50 wt.% H20 evaporated and to 500 C and below, preferably to room temperature cooled and the crystallized FeSO4 7H2O separated with adhering sulfuric acid the other part of the starting mixture is warmed to 80 to 90 ° C and placed in it the approximately equivalent amount of KCl to the double salt to be obtained is stirred, both parts the starting mixture are mixed in the ratio that a weight ratio the mixture is adjusted from 2.1 to 1.5 FeS04 1 H2SO4 and 65 to 70% by weight of H20 preferably oxidized by blowing air, to 500 C and below, preferably cooled to room temperature, the crystallized double salt Fe2 (SO4) 3 @ 2K2S04 of the FeOl3-containing final liquor is separated. 9. The method according to claims 1 and 6, characterized in that that Fe2 (SO4) 3. H2SO4. H2O dissolved in part of the oxidized starting mixture, in the heat with an amount of KCl which is approximately equivalent to the double salt to be obtained stirred, cooled to 500 ° C. and below, preferably to room temperature, and that Crystallized double salt Fe2 (SO4) 3 2K2S04 from the final liquor containing FeCl3 is separated. 10, method according to claim 1, characterized in that the sulfuric acid evaporated and combined with potassium chloride to form potassium sulfate or potassium hydrogen sulfate and Hydrogen chloride is processed.