DE19611454A1 - Mineral filler and building material additive based on calcium aluminum sulfate and their manufacture and use - Google Patents

Abstract

The invention concerns a process for preparing a precipitate based on calcium aluminium sulphate (CASUL), optionally mixed and/or chemically bonded with silicate. According to the invention, a dilute aqueous sulphate-containing solution and one or a plurality of reactive calcium compounds and optionally one or a plurality of silicate compounds are added to a dilute aqueous alkali sodium aluminate solution. The resultant crystalline precipitate is separated by sedimentation, optionally dehydrated, optionally washed with water, optionally dried and optionally calcined. The resultant products can be used as follows: the suspension can be used as gloss-white in paper manufacture; the precipitate dried at less than 80 DEG C can be used as a flame-retardant filler for fire-proofing construction materials; the precipitate calcined at less than 500 DEG C can be used as a filler for producing plaster panels; and the precipitate calcined at above 500 DEG C can be used as a hydraulically active additive for producing expanding cement, expanding gypsum and the like.

Description

The invention relates generally to a new mineral filler or Building material additive based on calcium aluminum sulfate (CASUL) if in a mixture and / or in chemical bonding with calcium carbonate (CARBOSUL), and its manufacture and use; it affects in particular a process for the production of a mineral filler or construction Additive based on calcium aluminum sulfate (CASUL), if necessary in a mixture and / or in a chemical bond with calcium carbonate (CARBOSUL), as well as the products obtained and their use in the manufacture of cellulose, paper, cardboard or cardboard as filler or Coating pigment suspension and its use in the dewatered Zu stood as a general filler, e.g. B. for plastic production, as well as in ent watered, calcined and ground state as a setting accelerator for hydraulic building materials such as cements or gypsum, as well as for use this process for cleaning sulfate-containing process water.

The chemical composition of the mineral according to the invention Filler based on calcium aluminum sulfate (CASUL) or invented Mineral building material additive according to the invention based on calcium aluminum niumsulfate in a mixture and / or in a chemical bond with calcium carbonate (CARBOSUL) corresponds to multi-component systems with the following formula

CASUL xCaO · yAl₂O₃ · zCaSO₄ · βH₂O x = 2-4, y = 1-2, z = 3-4, β = 25-35
CARBOSUL xCaO · yAl₂O₃ · zCaSO₄ · aCaCO₃ · βH₂O x = 2-4, y = 1-2, z = 2-4, a = 1-3, β = 10-30

Fillers, especially mineral fillers, are used on a large scale among others in the plastics, paint, tire and ceramic industries as well used especially in the pulp and paper industry.

Paper, cardboard and cardboard, for example, are made from an aqueous suspension (Fabric) mainly produced by dewatering, drying and pressing. In addition to fiber materials such as cellulose and wood pulp, among other things Fillers, preferably the natural minerals kaolin (aluminosilicates) and Chalk (calcium carbonate) used. Depending on the requirements of the paper or cardboard quality (printability, whiteness, gloss, strength and the like) however, the quantitative use of fillers is limited. Usually lies he at 10 to 25 wt .-%, based on the paper weight. In Germany who the approximately 3 million tons of fillers used in the paper industry each year needs.

Mineral natural fillers must be mined, cleaned (e.g. washed) and ground. Higher quality requirements of the filler processors have led to the fact that synthetic precipitates, preferably calcium carbonate, are increasingly used. Attempts have also been made several times to use gypsum (calcium sulfate) as a filler, in particular the large quantities of reaction products from the flue gas desulphurization plants of power plants (REA gypsum). This has so far failed because calcium sulfate is water-soluble up to a concentration of about 2 g SO₄ ^2- per liter and insufficient "whiteness" has been achieved. In papermaking, there is an accumulation of dissolved calcium sulfate in the process water cycle and therefore undesirable deposits and microbiological problems (for example due to bacteria such as Desulfovibrio or Desulfazomaculum).

A calcium aluminum sulfate precipitate is already being used in the paper industry the name "satin white" or "gloss pigment" as a coating pigment for high quality papers used. This product is made from the raw materials  Aluminum sulfate and hydrated lime according to the following reaction equation won:

Al₂ (SO₄) ₃ + 6Ca (OH) ₂ + 25H₂O → Ca₆Al₂ ((OH) ₄) SO₄) ₃ _* 5H₂O {satin white}

However, this creates a suspension with a low solids content and the Manufacturing is complex and expensive.

On the other hand, precipitation processes have already been developed for the sulfate to reduce content in process and waste water. It is with the addition of Lime and aluminates poorly soluble calcium aluminum sulfate (ettringite) gebil det. A disadvantage of this process is that the precipitation reaction at high pH values from 11.5 to 12.5 must take place. Hence the wastewater or process water has a high pH value and can be used without subsequent new talization to pH values below 9.0 not derived and reused will. Furthermore, the problem arises with these known methods that About 4.5 g of solid are formed from 1 g of sulfate, which previously ent ent high costs had to be taken care of, so that the sulfate precipitation for cost reasons so far could not establish.

The object of the invention was to provide a new mineral filler or Building material additive with improved properties to develop the (that) on produced economically and ecologically sensible and to the users conditions can be adjusted.

It has now been found that this object is achieved in accordance with the invention can be that for the separation of sulfate from process and waste water also known sulfate precipitation, which is carried out at high pH values must be combined with a neutralization, a precipitate with particularly advantageous properties, which is a valuable filler represents. This is especially true for the suspended form of the thickened pre zipitats because the pH value of about 10 conforms to the application.  

According to a first aspect, the invention relates to a method for Production of a mineral filler or building material additive based on Calcium aluminum sulfate (CASUL), optionally in a mixture and / or in chemical bond with calcium carbonate (CARBOSUL), thereby known is that you have a sulfate-containing medium with at least one reactive Calcium compound and at least one reactive aluminum compound combined with a pH of <11, optionally calci umcarbonate adds and introduces carbon dioxide to carry out a part new stabilization up to a pH of 8 to 11, preferably 9.5 to 10.5, and the resulting amorphous to fine crystalline precipitate is separated off and added if necessary drained.

If desired, the precipitate can be removed and drained also dried, calcined at 200-1000 ° C and ground.

Dilute sulfur is preferably used as the sulfate-containing medium acid, especially waste acid, or a sulfate-containing solution, in particular sulfate-containing water, waste water or process water. Particularly suitable a solution or suspension of gypsum is available as the sulfate-containing medium preferably gypsum from flue gas desulphurization plants (REA gypsum).

Lime milk is preferably used as the reactive calcium compound (Hydrated lime or Ca (OH) ₂) or calcium carbonate, especially ground or calcium carbonate suspended in water.

Water-soluble aluminum is used as the reactive aluminum compound. Salts, preferably a water-soluble alkaline aluminum salt, esp special sodium aluminate. A particularly well suited active aluminum compound is an alkaline sodium aluminate solution, especially a waste pickle alkali, as obtained in the surface treatment of aluminum metal becomes. The effective components of the alkaline sodium aluminate solution  or waste pickling solution Na₂O and Al₂O₃ are preferably in a molver Ratio of (1.2 to 5.0): 1, in particular of (1.4 to 2.5): 1.

An acidic aluminum salt can also be used as the reactive aluminum compound solution, preferably an aluminum sulfate, aluminum chloride and / or aluminum minium nitrate solution can be used.

Carbon is preferably used to carry out the precipitation reaction Dioxide-containing smoke or exhaust gases, especially those from plants for ver burning fossil fuels, especially from power plants.

The reactive (n) aluminum compound (s) is (are) preferably used in an amount of 0.1 to 1.0, in particular 0.2 to 0.4 g of aluminum (Al) per g of precipitated sulfate (SO₄ ^2- ) .

The reactive calcium compound (s) is (are) preferably in an amount of 0.5 to 5.0 g, in particular 0.5 to 1.5 g calcium (Ca) per g precipitated sulfate (SO ( ^2- ) used.

Reactive carbon dioxide is preferably used in an amount to achieve a pH from 8 to 11, preferably from 9.5 to 10.5, is used.

To carry out the precipitation according to a preferred embodiment of the Invention is preferably submitted to the sulfate-containing component and the other reactants are reactive aluminum compound in the order, reactive calcium compound and reactive carbon dioxide added. To Her position of a particularly finely dispersed precipitate, however, it is preferred that Submit reactive calcium compound and then the reactive aluminum admit connection.

The precipitation reaction is preferably carried out in a treatment zone, in particular in a stirrer tank with stirring, or in several treatments  development zones, in particular in three containers connected in series Stir continuously.

The precipitation is preferably within a reaction time of 1 to 300 min, in particular 10 to 30 min.

According to a preferred embodiment of the invention, the precipitate after sedimentation and thickening, especially in one Settlement pool, subjected. To carry out sedimentation and indentation The precipitate is preferably given a solution of at least one organic polyelectrolyte, especially one based on Po ly (meth) acrylates or poly (meth) acrylamides. The poly (meth) acrylate or Poly (meth) acrylamide is preferably used in an amount of 5 to 20 ppm added.

According to a further preferred embodiment of the invention, the Mechanically dewatered precipitate, preferably using a Chamber filter press or a vacuum belt filter, and then given if necessary, dried and ground.

The dewatered and optionally dried and ground precipitate is preferably resuspended in water and used as a filler slurry turns.

However, it is also possible for the dewatered precipitate to be preferably at 200 to Calcine 1000 ° C, especially at 400 to 900 ° C, and then to Manufacture of a setting accelerator for hydraulic building materials, e.g. B. for Cements and gypsum to grind.

According to a further aspect, the invention relates to the use of the pre zipitates as described above or produced as a filler or Coating pigment suspension for the production of cellulose, paper, cardboard or  Cardboard as well as a general filler, e.g. B. in the production of plastic fen.

In another aspect, the present invention relates to uses Formation of the precipitate in the dewatered, calcined and ground state as a setting accelerator in the building materials industry. Currently Abbin accelerator for cements, e.g. B. for Portland cement or for shotcrete, Calcium aluminates or sodium aluminates are used. These connections be accelerate the reaction with Tri that is important when setting cement mortar calcium aluminate for the final cement product "monosulfate".

The precipitate CASUL obtained according to the invention corresponds to the Calcination at over 200 ° C an ettringite dehydrate and reacts violently with strong heat again with water. The one today as an obstruction less commonly used calcium aluminates react far more sluggishly and are expensive due to complex manufacturing processes (lime + aluminum hydrate). The product manufactured according to the invention can thus be technical-like economic benefits can also be achieved.

Finally, the invention also relates to the application of the above Written method for the purification of waste water, preferably sul wastewater containing waste, and for cleaning process water, preferably of sulfate-containing process water from the pulp and paper industry.

The method according to the invention is ecologically significant because of the profit a valuable material with the solution of a waste water and exhaust gas problem can be coupled. Process and wastewater containing sulphate and coal-di According to the invention, oxide-containing exhaust gases can be cleaned in an environmentally friendly manner the. This recycling process is primarily for the paper and building materials industry significant.  

According to the invention, the solution of a wastewater problem is not in the foreground reason, but the extraction and commercialization of a new minerali filler or building material additive. In addition, with the invent precipitation process according to the invention enables the use of gypsum as a filler light because invented the problem of sulfate redissolution in process cycle water is solved accordingly. In addition, additional uses open up Possibilities for the flue gas cleaning of flue gas Sulfur plants (REA) resulting gypsum (REA gypsum).

In the practical implementation of the method according to the invention Filler obtained as a precipitate of a precipitation reaction in which the sulfate term component in the form of, for example, dilute sulfuric acid or submitted to process or waste water containing sulfate or a gypsum suspension, with reactive calcium and aluminum compounds to a pH of <12 set and, depending on the use of the precipitation product, simultaneously with Calcium carbonate mixed with carbon dioxide up to a pH of 9 to 12, preferably from 9.5 to 10.0, is partially neutralized. This creates a Amorphous to fine crystalline white precipitate, which is preferably used as a filler can be used in the pulp and paper industry. This precipitate but can also be dried and calcined after dewatering Production of a building material additive with particularly advantageous properties.

The invention is illustrated by the following examples, but without to be limited to that.

example 1

Waste water from a paper and pulp mill with a sulfate content of 1208 mg / l was used. The following were introduced into a reactor with stirring:
1000 l process waste water with 1208 mg / l SO l (= 1.2 kg sulfate load)
4.3 kg of sodium aluminate solution with 7% by weight Al and 18% by weight Na₂O (corresponding to 0.25 g Al per 1 g SO₄ ^2- )
2.0 kg calcium hydroxide with 52 wt .-% Ca (corresponding to 1.04 g Ca per 1 g SO₄ ^2- ).

A white calcium aluminum sulfate was formed at a pH of 12.1 (CASUL) precipitation. After a reaction time of 15 min, the fil a residual sulfate content of 168 mg / l was measured, d. H. the sulfate concentration had decreased by 86%.

The white ultrafine crystalline CASUL precipitate was by adding an anio African polyelectrolyte solution of a copolymer of acrylamide + Na acrylate brought to sedimentation, thickened and on the reactor floor as a suspension deducted. The suspension was used directly as a filler at papermaking lung used.

Example 2

The same process waste water as in Example 1 was burst with 2 kg of calci umcarbonate per 1 m³ of wastewater and then be according to Example 1 acts. A precipitate was formed in which the calcium carbonate particles in the CASUL crystals that formed were stored. The sulfate content of Process wastewater was increased from 1208 mg to 184 mg / l, i.e. H. reduced by 87%.

The resulting white, very fine crystalline CARBOSUL precipitate was through Addition of a polyelectrolyte solution brought to sedimentation, thickened and withdrawn as a suspension from the reactor bottom. The suspension became direct used as a filler in papermaking. The one containing calcium carbonate Filler showed a significantly better opacity and an improved Printability of the paper.  

Example 3

A suspension of FGD gypsum was mixed with lime and sodium aluminate solution in a stirred kettle as follows:
1000 l process wastewater with 1208 mg / l SO ( ^2- (corresponding to 1.2 kg sulfate load)
100 kg REA gypsum
100 kg of sodium aluminate solution with 7 wt .-% Al and 18 wt .-% Na₂O
10 kg calcium oxide (quicklime)
The addition of quicklime gave rise to heat, so that the chemical reaction and recrystallization to CASUL was accelerated and completed within 5 hours. The result was a creamy, settling-stable suspension that was used as a coating pigment in papermaking.

Example 4

The suspension obtained in Example 3 was on a chamber filter press dewatered and dried at 550 ° C (calcined). The calcined product was de ground and used as a setting accelerator for cement. By Adding 8% CASUL made it easier for Portland cement to set the. The setting time was reduced from 30 h to 5 min.

Claims (25)

1. A process for the preparation of a mineral filler based on calcium aluminum sulfate (CASUL), optionally in a mixture and / or in a chemical bond with calcium carbonate (CARBOSUL), characterized in that a sulfate-containing medium with at least one reactive calcium compound and at least one reactive aluminum compound combined with adjustment of a pH value of <11, optionally adding calcium carbonate and introducing carbon dioxide to carry out a partial neutralization up to a pH value of 8 to 11, preferably 9.5 to 10.5, and the resulting amorphous to fine crystalline precipitate separated by sedimentation and dewatered if necessary. 2. The method according to claim 1, characterized in that as medium containing sulfate, dilute sulfuric acid, preferably waste acid, or a sulfate-containing salt solution, preferably sulfate-containing water, Ab water or process water used. 3. The method according to claim 1 and / or 2, characterized in that a solution or suspension of gypsum as the sulfate-containing medium preferably REA gypsum (gypsum from flue gas desulfurization plants), or Chemical gypsum used. 4. The method according to at least one of claims 1 to 3, characterized ge indicates that lime milk (hydrated lime or Ca (OH) ₂) or calcium carbonate, preferably ground or in what suspended calcium carbonate used. 5. The method according to at least one of claims 1 to 4, characterized ge indicates that a reactive aluminum compound is a water-soluble alkaline aluminum salt, preferably sodium aluminate, used.   6. The method according to claim 5, characterized in that as acti ve aluminum compound an alkaline sodium aluminate solution, in particular a waste pickling liquor used as in the surface treatment of Aluminum metal is obtained. 7. The method according to claim 6, characterized in that the effective Components of the alkaline sodium aluminate solution or waste stain Ge Na₂O and Al₂O₃ in a molar ratio of (1.2 to 5.0): 1, preferably from (1.4 to 2.5): 1. 8. The method according to at least one of claims 1 to 5, characterized ge indicates that an acidic aluminum is used as the reactive aluminum compound Salt solution, preferably an aluminum sulfate, aluminum chloride and / or aluminum nitrate solution used. 9. The method according to at least one of claims 1 to 8, characterized ge indicates that for the precipitation reaction carbon dioxide-containing smoke or exhaust gases, preferably those from plants for burning fossil fuels Fuels, especially from power plants, are used. 10. The method according to at least one of claims 1 to 9, characterized in that the sulfate-containing component is presented to carry out the precipitation and the other reactants are added in the following sequence and quantity balance:

• a) reactive aluminum compound: 0.1 to 1.0, preferably 0.2 to 0.4 g of aluminum (Al) per g of precipitated sulfate (SO) ^2- );
• b) reactive calcium compound: 0.5 to 5.0 g, preferably 0.5 to 1.5 g, calcium (Ca) per g of precipitated sulfate (SO₄ ^2- ) and
• c) reactive carbon dioxide in an amount to achieve a pH of 8 to 11, preferably from 9.5 to 10.5.

11. The method according to at least one of claims 1 to 9, characterized ge indicates that one produces a particularly finely dispersed precipitate tats the reactive calcium compound and then the reactive aluminum redirection admits. 12. The method according to at least one of claims 1 to 11, characterized ge indicates that the precipitation reaction takes place in a treatment zone preferably in a stirred tank with stirring, or in several Be action zones, preferably in three cascaded containers with stirring, carried out continuously. 13. The method according to at least one claims 1 to 12, characterized ge indicates that the precipitation within a reaction time of 1 to 300 min, preferably from 10 to 30 min. 14. The method according to at least one of claims 1 to 13, characterized ge indicates that the precipitate is precipitated after sedimentation and thickening, preferably in a sedimentation basin. 15. The method according to claim 14, characterized in that one for Carrying out the sedimentation and thickening of the precipitate a solution at least one organic polyelectrolyte, preferably copolymers Basis of poly (meth) acrylates or poly (meth) acrylamides, admits. 16. The method according to claim 15, characterized in that one Poly (meth) acrylate or poly (meth) acrylamide in an amount of 5 to 100 ppm admits. 17. The method according to at least one of claims 1 to 16, characterized ge indicates that the precipitate is mechanically dewatered, preferably using a chamber filter press or a vacuum belt filter, and then optionally drying and grinding.   18. The method according to at least one of claims 1 to 17, characterized ge indicates that the dehydrated and optionally dried and ground precipitate resuspended in water and as a filler slurry used. 19. The method according to at least one of claims 1 to 17, characterized ge indicates that the dewatered precipitate at 200 to 1000 ° C, before preferably at 400 to 900 ° C, calcined and then ground so that a particularly reactive setting accelerator for hydraulic building materials (Cements, gypsum) arises. 20. Mineral filler based on calcium aluminum sulfate (CASUL), optionally in a mixture and / or in a chemical bond with calcium car bonat (CARBOSUL), characterized in that it is in amorphous to fine crystalline stallin form and by the method according to at least one of the Claims 1 to 19 is available. 21. Use of the mineral filler according to claim 20 in the Manufacture of cellulose, paper, cardboard or cardboard as filler or Coating pigment suspension. 22. Use of the mineral filler according to claim 20 in the drained Serten condition for the production of plastics. 23. Use of the mineral filler according to claim 20 in the drained Serten, calcined and ground state as a setting accelerator for hydraulic building materials (cements, gypsum). 24. Application of the method according to at least one of claims 1 to 19 for the purification of waste water, preferably of sulfate-containing waste water ser.   25. Application of the method according to at least one of claims 1 to 19 for cleaning process water, preferably sulfate-containing Process water for the pulp and paper industry.