EP0523507A1 - Dilutable aluminium-triformiate tanning agents in highly concentrated water-solved and storage stable form and their use - Google Patents

Abstract

The invention describes the use of supersaturated and acid-adjusted aqueous solutions, which are at least largely storage-stable, of mixtures of aluminium triformate with alkali metal and/or alkaline earth metal formate as a concentrated supply form of a water-dissolved mineral tanning agent based on aluminium triformate for chromium-free or low-chromium tanning of leather and/or skins. The invention in this case relates particularly to storage-stable finished supersaturated and acid-adjusted aqueous solutions of this type, which additionally contain small amounts of stabilisers, preferred stabilisers being 1,2,3,4-butanetetracarboxylic acid and/or xanthan gum. The invention finally relates to the use of these stabilised supersaturated aqueous supply forms of aluminium triformate solutions for use as tannery auxiliaries having fixing and/or tanning action in the tanning and/or finishing of leather and fur skins.

Description

The invention relates to and describes a new, highly concentrated form of aluminum triformate in supersaturated, but nevertheless storage-stable, aqueous solution which is particularly suitable for use in the field of chrome-free or low-chrome mineral tanning of leather and / or furs. Compared to the commercial forms of mineral tanning agents based on aluminum that are commercially available today, the aqueous high concentrates according to the invention are not only distinguished by the fact that the active ingredient component aluminum triformate is already predefined in the state of the aqueous solution, it has also been shown that a plurality of mineral tanning agents in this form of supply Improvements and simplifications for the field of tanning, finishing and finishing of leather and fur are given.

The use of mineral tanning agents or auxiliaries such as aluminum-based fixing aids is becoming increasingly important in the manufacture and finishing of leather and skins. This is due to the not inconsiderable concerns from an ecological point of view of the chromium-based work equipment or auxiliary materials that are mainly used to date. In practice, aluminum-based mineral tanning agents are used in particular in two forms, both of which are in solid form: On the one hand solid basic aluminum chloride and, on the other hand, finely crystalline solid aluminum triformate is offered and used as a feedstock in the leather and fur industry. For the adjustable work results, the advantages are known which result from the simultaneous use of aluminum and lower carboxylic acids, for example in the form of the aluminum triformate. A disadvantage in this connection is the comparatively low solubility of the pure crystalline aluminum triformate in aqueous solutions, which is below 5% by weight at usual tanning temperatures. This is probably the key to the fact that, up to the present day, watery forms of aluminum triformiate as feedstock for the leather and fur industry have not gained any practical importance.

The invention is based on the object of making available aqueous concentrates which contain the aluminum triformate in active ingredient concentrations well above its solubility in water, are nevertheless sufficiently stable in storage and, in leather-producing operation, by simple dilution into the concentration ranges of the aluminum material required in each case can be brought. The solution to the problem according to the invention is based on the finding that under certain conditions which are described in detail below, highly concentrated aqueous active substance concentrates based on aluminum triformate can be prepared which contain this valuable substance in a supersaturated but nevertheless storage-stable form. It has also been shown that the use of such forms of preparation of the mineral tanning agents or auxiliary substances can have further advantages which are noticeable, for example, in an unprecedented degree of liquor depletion.

The teaching of the invention

A first embodiment of the invention accordingly relates to the use of aqueous solutions of mixtures of aluminum triformate with alkali metal and / or alkaline earth metal formate, which are at least largely storage-stable and acidified, and are acidic - hereinafter also referred to as "formate salts" - as a concentrated form of an aqueous dissolved mineral tanning agent based on aluminum triformate for chrome-free or low-chrome leather and / or fur tanning.

In an important embodiment of the invention, these supersaturated aqueous solutions of formate salts contain small amounts of selected acid-stable stabilizers. The addition of butanetetracarboxylic acid as a stabilizer of the supersaturated active ingredient solutions is of particular importance in this context, but selected organic polymer compounds are also suitable for the storage stabilization of these supersaturated formate salt solutions which is virtually unlimited in time.

Accordingly, in a further embodiment, the invention relates to supersaturated and acidic aqueous solutions of aluminum triformate in a mixture with sodium formate with solids contents of the formate salt mixtures of at least 35% by weight, preferably at least 40% by weight, which are stable in storage and which contain small amounts contain butane tetracarboxylic acid and / or xanthan gum as stabilizers.

Finally, the teaching according to the invention comprises, in a further embodiment, the use of these stabilized supersaturated aqueous formate salt solutions as water-thinnable, but already aqueous-dissolved aluminum triformate preparation for use as a tanning aid with fixing and / or tanning effect in the tanning and / or dressing of leather and fur skins.

Details of the teaching according to the invention

The teaching of the invention is based on the knowledge and details of the older but not prepublished German patent application P 40 10 930.5 (DE 40 10 930), the details of which are hereby expressly made the subject of the present disclosure of the invention.

This earlier application describes a process for producing an alkali and / or alkaline earth-containing aluminum triformate solution from an aluminate solution with formic acid, the process being characterized in that an aqueous alkali and / or alkaline earth metal containing alkali solution with a formic acid present neutralized and the precipitated solid transferred into an aluminum triformate solution while increasing the temperature. Aqueous sodium aluminate lyes are preferably used in the reaction. Weight ratios of sodium oxide / aluminum oxide can be used in a wide range of, for example, 5: 1 to 1: 5 in these aluminate solutions. Ranges from 2: 1 to 1: 2 are preferred here.

The following reaction parameters can be important for the preparation of a supersaturated aluminum triformate solution on this basis: It is usually necessary to add the formic acid and to add the aluminate solution dropwise. The reaction proceeds in two steps. During the addition of lye, a gelatinous, easily movable precipitate increasingly forms in an exothermic reaction. In a second step, this can be brought back into solution by heating - after cooling, there is little or no re-precipitation. In the implementations Formic acid and aluminate used in the formation of sodium formate and aluminum triformate in stoichiometric ratios.

In particular in the production of corresponding supersaturated solutions with high contents of formate salts, which are preferably above 40% by weight and particularly preferably above 50% by weight, it has proven to be important to remove the heat of reaction which occurs during the neutralization. Internal temperatures of the reaction mixture of about 25 to 30 ° C. are to be avoided as far as possible in the neutralization stage. After the addition of aluminate has ended, the crude product solution must be heated in a second step to dissolve the precipitate formed as an intermediate until a clear solution is obtained, for example to temperatures between about 60 ° C. and 80 ° C. After the subsequent cooling to room temperature, the product solution initially remains clear. With longer standing times - a few weeks or months - a slight cloudiness can recede, but the state of the supersaturated solution remains.

The teaching of the earlier application cited here provides for the use of the aluminum triformate solutions containing alkali and / or alkaline earth metal for different purposes. These include the impregnation of textiles, the use in disinfectants and cleaning agents or as a coagulant for paints. Finally, their use as fixing aids in leather processing is also mentioned. The use of such supersaturated aqueous aluminum triformate solutions directly as a mineral tanning agent for the production of chromium-free or at least low-chromium leather is not disclosed in the earlier application.

The meaning and chemical nature of tanning agents on the one hand and fixing aids on the other hand in leather extraction or leather finishing are not congruent terms. Is It is known that selected tanning agents can also be used as fixing aids in leather finishing, but the term fixing auxiliary for leather finishing does not normally cover the field of tanning agents for leather production from suitably prepared natural skins. To this extent, the teaching according to the invention goes beyond the teaching of the earlier application mentioned with the application concerned here for the highly concentrated supersaturated aqueous formate salt solutions based on aluminum triformate.

In the preferred embodiment of the invention, as stated, small amounts of selected acid-resistant stabilizing agents are used, the butane tetracarboxylic acid - in particular 1,2,3,4-butane tetracarboxylic acid - being of particular importance. Even extremely high concentrations of the formate salts in the supersaturated aqueous solution, which are particularly preferably in the range above 50% by weight and in particular in the range from approximately 55 to 60% by weight, are stabilized by adding small amounts of this stabilizer, that a month-long storage of the supersaturated concentrates is also possible using temperature fluctuations that are common in practice. Not only is there a decisive advance in the field of mineral tanning agents based on aluminum triformate, but also the area of fixing aids for leather dressing already mentioned in the earlier application is substantially promoted by these tools in the sense of the invention, so that the Teaching according to the invention also extends to the field of leather finishing already mentioned in the earlier application.

The supersaturated aqueous solutions of the formate salts described in accordance with the invention and to be used in accordance with the invention contain aluminum triformate in combination with in particular sodium formate. Salt mixtures of this type can be started easily of the inexpensive sodium aluminate solutions and their reaction with formic acid. The formate salt solids content in the aqueous concentrates is at least about 35% by weight, preferably at least about 40% by weight. In the embodiments of particular interest according to the invention, the formate salt contents are above 50% by weight and in particular in the range from about 55 to 60% by weight.

Although the mixing ratios of aluminum triformate to sodium formate can fundamentally fluctuate within a wide range, as is disclosed in the previously mentioned older application DE 40 10 930, however, mixing ratios of aluminum triformate to sodium formate are preferred for the teaching according to the invention , which are in the range of about 0.5 to 2, based on the weight ratio of the two components as oxide, ie based on the weight ratio of Al₂O₃ to Na₂O.

The proportions of formic acid on the one hand and formate-forming metal components on the other - in particular, therefore, aluminum and sodium - are chosen in the preferred production in a practically stoichiometric ratio. A control of the pH of the supersaturated aqueous concentrates is expedient or necessary to ensure the storage stability of the supersaturated solutions in the sense according to the invention. In the preferred embodiment, the pH values of the concentrates are weakly acidic values and in particular in the range not above pH 5. The pH range from about 3 to 4 can be particularly suitable with regard to the degree of acidity of the aqueous concentrates.

The stabilizing agents according to the invention are, on the one hand, the 1,2,3,4-butanetetracarboxylic acid already highlighted, but also acid-stable, water-soluble and / or water-swellable polymer compounds, with the xanthan gum being of particular importance here comes to. The stabilizing agents are expediently used in amounts below 5% by weight, based on the aqueous concentrate, and in particular in amounts of about 0.1 to about 2% by weight in the aqueous concentrate. It may be expedient to add these stabilizers in the form of aqueous solutions - for example about 10% by weight aqueous solutions - or also after pre-swelling in, for example, isopropanol in the formate salt-containing active ingredient mixture.

Particularly suitable for the use of the concentrates according to the invention as mineral tanning agents for the production of chromium-free or low-chromium leathers and furs is the use of butanetetracarboxylic acid as a stabilizer, which here is preferably present in amounts of about 0.5 to 1% by weight on aqueous concentrate - to which formate salt concentrates can be added. Aqueous active substance preparations of this type show a practically unlimited storage stability even when the formate salt concentrations are at or above 50% by weight.

The stabilizing agent, for example butane tetracarboxylic acid, can be added in the course of the preparation of the aqueous concentrates, for example before the final heating of the primary reaction mixture for the preparation of the supersaturated aqueous solutions. Likewise, the stabilizer can also be added to the finished concentrates subsequently in a final process step.

The forms of mineral tanning agents based on aluminum triformate described according to the invention are notable for outstanding tanning advantages in the tanning and dressing of leathers and skins. Here, for example, the good meterability, the easy distribution of the mineral tanning agent in the tanning liquor, the neutral odor, above all are to be listed But also the good Al₂O₃ absorption of the skin. Extensive comparative tests, which will be dealt with in the examples, have shown that when using comparatively lower aluminum triformate concentrations in the tanning liquors, comparable results are obtained with regard to the product properties as are known from the previously known processes for mineral aluminum tanning with those described corresponding products can be set on a solid basis. Associated with this is, however, a significantly better exhaustion of the liquors, whereby not only the percentage exhaustion of the liquor is significantly increased compared to the prior art processes, in particular the residual aluminum content in the liquor can be significantly reduced by the teaching according to the invention.

Details can be found in the following examples.

Examples

In the following Examples 1 and 2, the preparation of characteristic representatives for the supersaturated concentrated formate salt solutions to be used according to the invention is first described.

example 1

To 1210 g of an 85% aqueous formic acid (or 1030 g of pure formic acid), 2000 g of sodium aluminate (14.3% by weight Na₂O and 11.3% by weight Al₂O₃) were added dropwise within 30 minutes. A temperature rise of up to 80 ° C and precipitation occurred. The mixture was then heated under reflux until a clear solution was obtained. The yellow product solution contained 23.0 wt .-% (or 24.3 wt .-%) aluminum triformate (corresponding to 7.3 wt .-% Al₂O₃ or 7.6 wt .-% Al₂O₃) and 19.5 wt. -% (or 20.7% by weight) sodium formate.

To increase the aluminum triformate concentration, a more concentrated aluminate solution was used in further work. It was used under the trade name "DYNAFLOCK L" from the company Hüls AG sodium aluminate solution with 19 wt .-% Na₂O and 25 wt .-% Al₂O₃. In the neutralization reaction of this aluminate solution with formic acid under the abovementioned conditions, it was found that no clear products were initially to be produced. However, further tests then showed that the desired storage-stable, clear, highly supersaturated aqueous solutions could also be obtained by carefully controlling the temperature. In detail, the following was true:
When the concentrated aluminate solution was added dropwise to formic acid, a white, gelatinous and easily mobile precipitate was obtained in the first step. To obtain a clear product solution later, it was necessary to remove the heat of reaction. Avoid internal piston temperatures above approximately 25 ° C. The dropping rate was therefore dependent on the effectiveness of the cooling. After the addition of the aluminate had ended, the crude product solution had to be heated at 60 ° C. in order to dissolve the precipitate until a clear solution was obtained. After the subsequent cooling to room temperature, the product solution remained clear. Details are shown in Example 2 below.

Example 2

To 2260 g of an 85% aqueous formic acid, 2000 g of DYNAFLOCK L (sodium aluminate solution: 19% by weight Na₂O and 25% by weight Al₂O₃; Hüls AG) were added dropwise with vigorous stirring while cooling with cold water. The dropping rate depended on the temperature of the reaction solution, which should not exceed 25 ° C. The mixture was then stirred at 60 ° C. until a clear solution was obtained (about 10 minutes). The clear, colorless solution contained 37.3% by weight aluminum triformate (corresponding to 11.75% by weight Al₂O₃) and 19.6% by weight sodium formate.

By adding 1,2,3,4-butanetetracarboxylic acid (BTCA) a permanent stabilization of the supersaturated solution could be achieved. BTCA was used in amounts of 0.1 to 1.5% by weight, based on the aqueous concentrate, as a pure substance or in the form of an aqueous solution, preferably as a 10% by weight aqueous solution. BTCA levels of 0.5 to 0.7% by weight led to stable, easily movable systems. A 1.0% by weight BTCA provided a pseudoplastic system. Storage tests under changing climate conditions (-30 to 60 ° C) with the BTCA-stabilized solutions showed that these withstood the extreme temperature fluctuations for more than 6 weeks.

In a series of application studies, the concentrates according to the invention were used as tanning agents and compared with commercial products based on basic aluminum chloride or solid, fine-crystalline aluminum triformate.

The comparative products were the basic aluminum chloride complex salt sold by the applicant under the trade name "Pellutax ALP" with an aluminum content (Al₂O₃) of 16 to 18% by weight and a basicity of approx. 20%, and the product sold by Zschimmer and Schwarz " Novaltan AL "(about 23% Al₂O₃) used.

Details of the comparison tests are given below. In summary, the following can be said in advance:
When using the examined mineral tanning agents on pickled German sheepskins, no differences were found with regard to the evaluation criteria of feel, softness, fullness and color tone of wool and leather. The aluminum tannins stabilized according to the invention with BTCA initially contained significantly less active substance (aluminum compounds). However, these agents were better available for the tanning process. This resulted in cheaper fleet wasting. The difference between the aluminum triformate range in the fleet and the aluminum absorbed by the sheepskin is smaller than that of the comparison products.

The tanning trials

Together with the commercial products mentioned, two tanning agents based on aluminum triformate / sodium formate, designed as a liquid product, stabilized with BTCA. The formate mixture EP-1 according to the invention produced according to Example 2 contained - based on aqueous concentrate - 0.5% by weight BTCA. The formate mixture EP-2 according to the invention produced according to Example 2 contained 1.0% by weight of BTCA, based on the aqueous concentrate. The two products were each stabilized with a 10% by weight aqueous BTCA solution.

The mineral tannins to be compared were used in the same amount by weight. In detail, the following was true: The tests were carried out with German pickled fur sheepskins. Before tanning, the corresponding skin halves were shaved to a wool height of 20 mm, then trimmed and the weights of the skin halves adjusted.

In order to complete the test series and to test the behavior of the tanning agents on leather, the corresponding pimple pelvis halves, which originated from the same raw material and were specially softened, shredded, unwrapped, ashed, stained, degreased and unwound, ran in the same series were. The weights of the spots were set to the same value. The starting point for the calculation of the fleet quantity was the pimple weight of the skins. The liquor ratio was 1:10. The use of the chemicals was fixed at g / l and calculated accordingly.

The following products were tested against each other in equal quantities: 1. Pellutax ALP 17 wt .-% Al₂O₃ 2. Novaltan AL 23.5 wt .-% Al₂O₃ 3. EP-1 11.2 wt .-% Al₂O₃ 0.5 wt .-% 1,2,3,4 butanetetracarboxylic acid 4. EP-2 10.6 wt .-% Al₂O₃ 1 wt .-% 1,2,3,4 butanetetracarboxylic acid

• a) vor Zugabe des Al-Gerbstoffes;
• b) 30 Min. nach Zugabe des Al-Gerbstoffes;
• c) 4 Stunden nach Zugabe des Al-Gerbstoffes;
• d) 14 Stunden nach Zugabe des Al-Gerbstoffes;
• e) 4 Stunden nach Abstumpfen des Al-Gerbstoffes

gemessen. Die Werte sind aus nachstehender Tabelle 1 ersichtlich.

Tabelle 3 Aufnahme der Haut an Al₂O₃ eingesetzter Gerbstoff Pellutax ALP Novaltan AL EP-1 EP-2 Anfangsmenge g/l Al₂O₃ 2,55 3,52 1,59 1,59 Auszehrungsgrad in % nach 3 Min. 0 0 0 0 Aufnahme in g/l nach 30 Min. 0,35 0,52 0,19 0,19 Auszehrungsgrad Aufnahme in % nach 30 Min. 13,72 14,77 11,94 11,94 Aufnahme in g/l nach 6 h 0,55 0,72 0,59 0,59 Auszehrungsgrad Aufnahme in % nach 6 h 21,56 20,45 37,10 37,10 Aufnahme in g/l nach 14 h 0,75 0,82 0,59 0,59 Auszehrungsgrad Aufnahme in % nach 14 h 29,41 23,29 37,10 37,10 Aufnahme in g/l nach 4 h abstumpfen 0,85 1,12 0,69 0,69 Auszehrungsgrad Aufnahme in % nach 4 h abstumpfen 33,3 31,8 43,4 43,4 The liquor pH of the various tanning procedures was electrometric

• a) before adding the Al tanning agent;
• b) 30 minutes after adding the Al tanning agent;
• c) 4 hours after adding the Al tanning agent;
• d) 14 hours after the addition of the Al tanning agent;
• e) 4 hours after the Al tanning agent has been blunted

measured. The values are shown in Table 1 below.

Table 3 Absorption of the skin on Al₂O₃ tanning agent used Pellutax ALP Novaltan AL EP-1 EP-2 Initial amount g / l Al₂O₃ 2.55 3.52 1.59 1.59 Degree of exhaustion in% after 3 min. 0 0 0 0 Absorption in g / l after 30 min. 0.35 0.52 0.19 0.19 Degree of exhaustion in% after 30 min. 13.72 14.77 11.94 11.94 Admission in g / l after 6 h 0.55 0.72 0.59 0.59 Degree of exhaustion in% after 6 hours 21.56 20.45 37.10 37.10 Admission in g / l after 14 h 0.75 0.82 0.59 0.59 Degree of exhaustion in% after 14 h 29.41 23.29 37.10 37.10 Blunt the absorption in g / l after 4 h 0.85 1.12 0.69 0.69 Degree of exhaustion in% blunt after 4 h 33.3 31.8 43.4 43.4

Tabelle 6 Der Al₂O₃-Gehalt der korrespondierenden Fellhälften (Al₂O₃-Gehalt bei 0% H₂O) ist aus nachstehender Tabelle 6 ersichtlich. Fell-Nr. Gerbstoff Gew.-% Al₂O₃ Fell-Nr. Gerbstoff Gew.-% Al₂O₃ 61 Pellutax ALP 1,30 61 A Novaltan AL 1,90 62 Pellutax ALP 1,60 62 A Novaltan AL 2,00 63 Pellutax ALP 1,30 63 A EP-2 1,30 64 Pellutax ALP 1,80 64 A EP-2 2,00 69 Pellutax ALP 1,40 69 A EP-1 1,50 79 Pellutax ALP 1,80 70 A EP-1 1,80 65 Novaltan AL 2,00 65 A EP-2 1,60 66 Novaltan AL 1,60 66 A EP-2 1,10 71 Novaltan AL 1,90 71 A EP-1 1,70 72 Novaltan AL 1,90 72 A EP-1 1,50 In a large number of comparative tests, the product properties were assessed in accordance with Table 4 below. The following applies to the numerical values in this table: grade 10 = very good, grade 1 = very bad

Table 6 The Al₂O₃ content of the corresponding skin halves (Al₂O₃ content at 0% H₂O) is shown in Table 6 below. Fur no. Tannin Wt .-% Al₂O₃ Fur no. Tannin Wt .-% Al₂O₃ 61 Pellutax ALP 1.30 61 A Novaltan AL 1.90 62 Pellutax ALP 1.60 62 A Novaltan AL 2.00 63 Pellutax ALP 1.30 63 A EP-2 1.30 64 Pellutax ALP 1.80 64 A EP-2 2.00 69 Pellutax ALP 1.40 69 A EP-1 1.50 79 Pellutax ALP 1.80 70 A EP-1 1.80 65 Novaltan AL 2.00 65 A EP-2 1.60 66 Novaltan AL 1.60 66 A EP-2 1.10 71 Novaltan AL 1.90 71 A EP-1 1.70 72 Novaltan AL 1.90 72 A EP-1 1.50

The evaluation of the fur skins and leather showed no quality differences in terms of feel, softness, fullness and whiteness of the leather and the wool. Compared to Pellutax ALP, the good binding and absorption of the fur leather to Al₂O₃ of the two products according to the invention were found to be advantageous. When using Pellutax ALP (17 wt .-% Al₂O₃), no more Al₂O₃ was stored in the fur leather despite the higher concentration. The Al₂O₃ content of the fur skins, which were tanned with the products EP-1 and EP-2 according to the invention, was above the values achieved for the goods produced with Pellutax ALP.

Claims (13)

Use of at least largely storage-stable supersaturated and acidic aqueous solutions of mixtures of aluminum triformate with alkali and / or alkaline earth formate as a concentrated form of an aqueous mineral tanning agent based on aluminum triformate for chrome-free or low-chrome leather and / or fur tanning . Embodiment according to claim 1, characterized in that there are mixtures of aluminum triformate with sodium formate, which have been prepared in particular by reacting aqueous sodium aluminate solution with formic acid. Embodiment according to claims 1 and 2, characterized in that the solids contents of the formate salt mixtures in the aqueous concentrates are at least 35% by weight, preferably at least 40% by weight and particularly preferably above 50% by weight. Embodiment according to claims 1 to 3, characterized in that the mixing ratios of aluminum triformate to sodium formate are in the range from 0.5 to 2 - based on the weight ratio of Al₂O₃: Na₂O. Embodiment according to claims 1 to 4, characterized in that the aqueous concentrates have pH values not above 5, preferably pH values between 3 and 4. Embodiment according to claims 1 to 5, characterized in that they are formed as concentrates which are free-flowing, storage-stable, supersaturated and at least largely segregation-free and problem-free water-dilutable concentrates, which are preferably prepared by reacting an aqueous aluminate solution with formic acid. Embodiment according to claims 1 to 6, characterized in that the aqueous concentrates contain acid-resistant stabilizing agents which are preferably present in the aqueous concentrate in amounts below 5% by weight, particularly preferably in amounts of 0.1 to 2% by weight. Embodiment according to claims 1 to 7, characterized in that butanetetracarboxylic acid and / or acid-stable water-soluble and / or water-swellable polymer compounds, preferably butanetetracarboxylic acid, are used as stabilizers. Embodiment according to claims 7 and 8, characterized in that the aqueous concentrates contain butanetetracarboxylic acid in amounts of 0.5 to 1% by weight, based on the aqueous concentrate. Embodiment according to claims 1 to 9, characterized in that the aqueous concentrates have been prepared as follows:

Addition of an aqueous aluminate liquor with cooling to formic acid in a stoichiometric ratio, the temperature of the reaction mixture preferably not exceeding 25 ° C., subsequent heating of the reaction product to temperatures in the range from about 60 to 80 ° C. and subsequent cooling, the stabilizing agent, preferably butane tetracarboxylic acid, may have been added before or after heating. Super-saturated and acidified aqueous solutions of aluminum triformate in a mixture with sodium formate with a solids content of the formate salt mixture of at least 35% by weight, preferably at least 40% by weight, which are stable in storage, and which contain small amounts of butanetetracarboxylic acid and / or xanthan Gum included as stabilizers. Supersaturated aluminum triformate solutions according to claim 11, characterized in that they have pH values not above 5, preferably pH values between 3 and 4. Use of the supersaturated aluminum triformate solutions according to claims 11 to 12 as a water-thinnable, but already water-soluble aluminum triformate preparation for use as a tannery aid with a fixing and / or tanning effect in the tanning and / or dressing of leather and Fur skins.