WO1992015663A1

WO1992015663A1 - Detergents

Info

Publication number: WO1992015663A1
Application number: PCT/EP1992/000390
Authority: WO
Inventors: Horst Upadek; Jörg Poethkow; Rainer Salz; Hans-Jürgen Riebe; Wolfgang Seiter
Original assignee: Henkel Kommanditgesellschaft Auf Aktien
Priority date: 1991-03-05
Filing date: 1992-02-25
Publication date: 1992-09-17
Also published as: ES2079858T3; EP0574436B1; EP0574436A1; DE59204203D1; ATE129743T1; JPH06505045A; DE4106880A1

Abstract

Detergents which contain 30 to 65 wt. % of a fine-particle, hydrated zeolite with a mean particle size of 1 to 5 $g(m)m and 1 to 15 wt. % of a solid alkali silicate with a molar composition M2?O:SiO2? of 1:2.0 to 1:3.0 and are free from water-soluble organic complex builders from the group of the substituted phosphonates, free from polymeric polycarboxylates and substantially free from alkali carbonates can be used as substitutes for ordinary commercial detergents which contain large amounts of phosphonates, polymeric polycarboxylates and/or alkali carbonates, without any loss of detergency. The proportion of organic synthetic compounds in detergents can thus be reduced.

Description

laundry detergent

The invention relates to a phosphate-free detergent based on zeolite and alkali silicate and a process for its production.

In practice, zeolite, in particular zeolite NaA, and in particular mixtures of zeolite with alkali silicates and alkali metal carbonates and polymeric polycarboxylates were used as phosphate substitutes in washing and cleaning agents. In addition there are complexing agents such as the salts of nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA) and phosphonic acids. The mostly selective complexing agents have the task of eliminating heavy metal ions, which in trace amounts can have a very negative effect on the washing process, in particular on the bleaching process (Ullmann, 1987, Vol. 8, pp. 351 to 354) . It is known that the phosphonates also counteract the precipitation of poorly soluble calcium salts and thus the incrustation caused by poorly soluble calcium salts and the graying of the fabric ("Use of phosphonates in heavy duty liquid detergents", M. Paladini, G. Schnorbus, soap oil fats - Waxes, 115th year (1989), pp. 508 to 511). Finally, the combined use of phosphonates and copolymers based on acrylic acid and maleic acid, in comparison with formulations which contain only one of these two constituents, results in a higher degree of whiteness of the textiles ("Use of phosphonates in household detergents with a low phosphorus content (1%) ", M. Paladini, G. Schnorbus, Soap-Oil-Fat-Waxes, 114th year (1988), pp. 756 to 760). European patent application 291 869 (Henkel) describes phosphate-free builders combinations of zeolite and aminoalkane polyphosphonate and / or polymeric polycarboxylate and l-hydroxyethane-l, l-diphosphonate (HEDP), certain weight ratios of the last three components show a synergism with regard to the prevention of the formation of fiber incrustations.

Crystalline, layered sodium silicates have also been described as substitutes or as partial substitutes for phosphates and zeolites. European patent application 164 514 (Hoechst), for example, discloses a phosphate-free builder combination which mainly contains crystalline sheet silicates of the formula (I) aMSi _x θ2 + ι * yH2Ö, where M is sodium or water serstoff means, x is a number from 1.9 to 4 and y is a number from 0 to 20 and preferred values for x 2, 3 or 4. These layered silicates can be used as water softeners both separately and in detergents and cleaners together with other builders such as phosphates, zeolite, other silicates, phosphonates and polycarboxylates.

German patent application 24 12837 (Henkel) already describes detergents which, in combination with zeolite, contain various complexing agents such as polymeric polycarboxylates and phosphonates and alkaline framework substances which are not capable of complex formation, such as carbonates and silicates. In this case, “microcrystalline” zeolites are preferably used, which are at least 80% by weight of particles between 10 and 0.01 μm in size and in particular between 8 and 0.1 μm.

From the German patent application 25 25 778 (P&G), washing and cleaning agents are known which contain 0.5 to 3% by weight of alkali silicate (calculated as a solid). These agents are produced either by a customary mixing process in which the solid silicates or a corresponding amount of a water glass solution are mixed together with the other main constituents, or by a spray drying process in which the slurry contains both zeolite and the corresponding amount of alkali silicate . The alkali silicates serve as corrosion inhibitors.

A detergent is known from German patent application 26 56 009 (Colgate) which contains 12 to 25% by weight of zeolite, in particular of type 4A, 5 to 20% by weight of a sodium silicate having the composition a2θ: Siθ2 of 1: 1 to 1 : 3.2, in particular from 1: 2.0 to 1: 2.6, and contains a peroxy bleach. According to the information in this reference, undesired deposits of the water-insoluble zeolite particles on the laundry are to be prevented by 0.3 to 3% by weight of a polymer from the group carboxymethyl cellulose, lower alkyl cellulose, hydroxy-lower alkyl-lower alkyl cellulose, Polyvinyl alcohol, polyvinyl acetate and polyvinylpyrrolidone are used. The zeolite has an average particle diameter of 0.5 to 12 μm, preferably 5 to 9 μm. European patent application 10 247 (Henkel) describes a detergent which contains surfactants in conventional amounts, zeolite, alkali silicate and, if appropriate, a peroxy bleach. The addition of water-soluble organic complexing agents from the group of the substituted alkanedi- and alkanetri-phosphonic acids, which are present in the form of their alkali and / or alkaline earth salts, gives a detergent which not only has a good primary washing action, but also the formation reduced by fiber incrustations. In addition, the addition of these phosphonates results in increased bleaching stability despite the absence of conventional stabilizers such as magnesium silicate and aminopolycarboxylate. The composition contains 20 to 65% by weight of a finely divided zeolite, as described in German patent application DE 24 12837, and 1 to 7% by weight of solid, powdered sodium silicate with the molar composition Na2θ: SiÜ2 of 1 : 2 to 1: 2.2. The composition consists of a mixture of at least 2 powder constituents, the first of which is obtained by spray drying an aqueous slurry which contains the zeolite, surfactants and optionally the water-soluble organic complex-forming framework substances, and the second powder constituent from the sodium Likatpulver and optionally from the water-soluble phosphonates and other detergent additives, which are sensitive to hydrolysis and / or temperature.

From European patent application 240356 (Unilever), detergents are known which, in addition to zeolite and water-soluble sodium silicates, as described in European patent application 10247, contain polyer polycarboxylates and their derivatives, for example polyacrylates and salts of copolymers of acrylic acid and maleic acid. These polymeric polycarboxylates are spray dried together with the zeolite during the production of the detergent.

From European patent applications 337217 and 337 219 (Hoechst), builder combinations for detergents are known which contain crystalline layered silicates and optionally phosphates and polycarboxylates such as citrates, glykonates, NTA and / or iminodiacetates, but no zeolite. The agents which contain 10 to 50% by weight of crystalline layered silicate are distinguished by a storage-stabilized bleaching system. European patent application 405 122 (Hoechst) specifies a builder combination for textile detergents, the builder combination consisting of a mixture of zeolite and crystalline layered sodium silicate in a ratio of 4: 1 to 1: 4. The incrustation of the fabric can be reduced by using a textile detergent that contains this builder combination.

The object of the invention was to further develop the field of phosphate-free builders combinations for use in textile detergents with the aim of reducing the proportion of organic synthetic compounds. Surprisingly, it has now been found that detergents which contain a special combination of finely divided zeolite with a relatively narrow particle size spectrum and alkali silicate as builders meet the high demands placed on modern detergents.

The invention relates to a detergent which contains surfactants, zeolite, alkali silicate and optionally a peroxy bleach and which is characterized in that it comprises 30 to 65% by weight of a finely divided, hydrated zeolite with an average particle size of 1 to 5 microns, 1 to 15 wt .-% of a solid alkali silicate of the molar composition M2O: Si2θ from 1: 2.0 to 1: 3.0, wherein M is sodium and / or potassium, with the proviso that the agent is free of water-soluble organic complexing agents from the group of the substituted phosphonates, free of polymeric polycarboxyates and essentially free of alkali carbonates.

The finely divided, hydrated zeolite generally has a water content of 17 to 25% by weight. However, the quantities for zeolite relate to the anhydrous active substance. Suitable zeolites are those of the zeolite A type. Mixtures of zeolite NaA and NaX can also be used, the proportion of zeolite NaX in such mixtures expediently being less than 30%. Preferred zeolites have an average particle size between 1.8 and 4.5 μm, in particular between 2.0 and 4.0 μm (measurement method: Fraunhofer diffraction; mean value of the distribution of voltages). The content of the agents in finely divided tigers, in particular crystalline, hydrated zeolite is preferably 30 to 55% by weight and in particular 32 to 54% by weight, based on the anhydrous active substance.

The solid alkali silicates can be amorphous or crystalline, as powder or as granules, for example as roller-compacted chip granules, or as a spray-dried compound. Preferred alkali silicates are the sodium silicates, in particular the amorphous sodium silicates, with a Na2O: SiO2 molar ratio of 1: 2 to 1: 2.8. Such amorphous ATkaTisiTkate are commercially available for example under the name Portil ( ^R ) (Henkel). Crystalline layered silicates of the formula (I) NaMSi _x 02+ yH20, in which M is sodium, x is 2 or 3 and y is a number of, are preferably used as crystalline silicates, which may be present alone or in a mixture with amorphous silicates Is 0 to 20. Both β- and fr-sodium disilicate Na2Si2Ü5 are particularly preferred. The content of alkali silicates in the compositions is preferably 2 to 10% by weight and in particular 3 to 10% by weight, based on the anhydrous substance. In particular, the amorphous sodium silicate content of the agents is 3.5 to 8% by weight, based on the anhydrous substance. The weight ratio of zeolite: amorphous silicate, in each case based on anhydrous substance, is preferably 4: 1 to 10: 1. The crystalline layered silicates are preferably used in amounts of 2 to 7% by weight, the weight ratio of zeolite to crystalline layered silicate, in each case based on anhydrous substance, being at least 5: 1. In compositions which contain both amorphous and crystalline alkali silicates, the weight ratio of amorphous alkali silicate: crystalline alkali silicate is preferably 1: 2 to 2: 1 and in particular 1: 1 to 2: 1.

The agents do not contain any water-soluble organic complexing agents from the group of the phosphonates, so that the agents have a calculated phosphorus content of 0%.

Polymeric polycarboxylates, for example polyacrylates, polyethacrylates, polymaleates or copolymers of acrylic acid with maleic acid or maleic anhydride, which are usually used in combination with zeolite, are also not present in the product according to the invention, since they do not have its primary and secondary washing power improve. The agents are also essentially free of ATkaTicarbonates, which means that they contain no more than about 5% by weight, preferably no more than 4% by weight and particularly advantageously no more than 3% by weight of alkali carbonates, in particular of sodium carbonate. Depending on the recipe, it cannot be ruled out that an alkali carbonate content in the range mentioned also contributes to increased incrustation. In the context of this invention it is therefore provided that alkali carbonate may only be added in the amounts in which it does not contribute to increased incrustation.

Preferred detergents contain peroxy bleach and in particular peroxy bleach in combination with bleach activators. Among the compounds which serve as bleaching agents and deliver H2O2 in water, the sodium perborate tetrahydrate and the sodium perborate monohydrate are of particular importance. Other bleaches that can be used are, for example, peroxycarbonate or peracidic salts of organic acids, such as perbenzoates or salts of diperdodecanedioic acid. Suitable bleach activators for these peroxy bleaching agents are, for example, the N-acyl or O-acyl compounds which form organic peracids with H2O2, preferably N, N'-tetraacylated diamines such as N, N, N'N'-tetraacety-methylenediamine. The content of peroxygen pond middleT in the middle T is preferably 12 to 30% by weight, in particular in combination with 1 to 10% by weight, preferably 2 to 8% by weight, of a bleach activator.

The detergents according to the invention are not only characterized by a reduced formation of fiber incrustations compared to agents of the prior art, which usually contain polymeric polycarboxylates and / or ATkaTicarbonate in larger quantities. Surprisingly, they also have an improved pond effect or an improved stabilization of the peroxy bleaching agent, although they contain no conventional stabilizers such as phosphonate, magnesium silicate or other complexing agents such as the salts of nitrilotriacetic acid and ethylenediaminetetraacetic acid.

The detergents and cleaners contain known compounds from the group of anionic, nonionic and zwitterionic surfactants as further constituents. In particular, sulfonates come as anionic surfactants and sulfates and soaps from preferably natural fatty acids or fatty acid mixtures. Cg-Ci3-alkylbenzenesulfonates, olefin sulfonates, esters of oc-sulfofatty acids or α-sulfofatty acid disalts are used as surfactants of the sulfonate type. Suitable surfactants of the sulfate type are the Schwefelsäuremonoester of primary alcohols natür¬ or synthetic origin, ie of C - ^ -. CISS fatty alcohols or ^'length from Ci0 "-20-0 ^χoa koho1en ^ _f and those of secondary alcohols also Ketten¬ the sulfuric acid monoesters of the alcohols reacted with 1 to 6 moles of ethylene oxide (EO) are suitable as addition products, preferably addition products of preferably 2 to 20 moles of EO to 1 mole of an aliphatic compound having essentially 10 to 20 carbon atoms from the group of alcohols, carboxylic acids, fatty amines, carboxamides and alkanesulfonamides are of interest, but in addition to the water-soluble nonionic surfactants, it is also important to have water-insoluble or not completely water-soluble polyglycol ethers with 2 to 7 ethylene glycol ether residues in the molecule, especially if they are used together with water-soluble ones nonionic or anionic surfactants can also be used Onic surfactants also alkyl polyglycosides of the general formula R-0- (G) _x are used, in which R is a primary straight-chain or aliphatic radical branched in the 2-position with 8 to 22, preferably 12 to 18 carbon atoms, G is a symbol , which stands for a glycose unit with 5 or 6 carbon atoms, and the degree of oligomerization x is between 1 and 10.

The total content of surfactants in the compositions is generally between 5 and 40% by weight. It is preferably 5 to 30% by weight and in particular 8 to 25% by weight.

The other detergent and cleaning agent components, the proportion of which, depending on the composition of the detergent, is up to 40% by weight, preferably 5 to 30% by weight and in particular 8 to 20% by weight, include foam inhibitors, optical brighteners, enzymes and textile-softening agents Substances, dyes and fragrances as well as neutral salts, solvents and water. The use of graying inhibitors, which are usually used in modern textile detergents, is not necessary and, in particular, is not preferred. Suitable enzymes are those from the K-cup of proteases, lipases, CeTTuTases and Ayytases or their mixtures. Enzymatic active ingredients obtained from bacterial strains or fungi such as Bacillus subtilis, Bacillus licheniformis and Streptomyces griseus are particularly suitable. Proteases of the sub-lisin type and in particular proteases obtained from Bacillus lentus are preferably used. The enzymes can be adsorbed on carriers and / or embedded in protective substances in order to protect them against premature decomposition.

Suitable non-surfactant-like and preferably used foam inhibitors are OrganopoTysiToxane and their mixtures with microfine, optionally siliconized silica. Mixtures of different foam inhibitors are also advantageously used, e.g. B. from silicone and paraffins or waxes. The foam inhibitors are preferably bound to a granular, water-soluble or dispersible carrier substance.

In a preferred embodiment, powdery or granular detergents contain 10 to 30% by weight of surfactants, 30 to 45% by weight of a finely divided, hydrated zeolite with an average particle size of 2.0 to 3.8 μm, 2 to 10 wt .-% of amorphous Natriumsil cat with a molar ratio Na 2 O: SiO 2 from 2.0 to 2.8 or a mixture of the ge called amorphous sodium silicate having a crystalline layered silicate, preferred wise ß-NatriumdisiTikat or δ ^{'-NatriumdisiTikat} and 18 to 30% by weight of peroxygen pond, preferably perborate, and 2 to 8% by weight of a Pond activator, preferably TAED.

The detergents according to the invention can be prepared in a conventional manner, for example by mixing, granulating and / or by spray drying. It is possible to incorporate the builders zeolite and solid alkali metal acetate into the middle in a conventional manner and with a large number of rows.

The pourable powder-form or granular preparations preferably consist of a dry homogeneous mixture of at least 2 powder components, at least the first of which is in the form of spray-dried granules. It is done by a conventional way Spray drying of a slurry available which contains at least the anionic surfactants and optionally nonionic surfactants.

This slurry preferably additionally contains at least part of the zeolite and / or the silicate. In the event that the slurry contains zeolite, the slurry can partly, but not more than 3% by weight and in particular not more than 2% by weight, in each case based on the total, finished agents containing amorphous silicates. The rest of the amorphous alkali silicates present as powder or granules, like the crystalline layered silicates which may be present, which are in granular form or adsorbed on a carrier consisting, for example, of sodium sulfate, are subsequently mixed into the spray product. In particular, however, it is preferred that the zeolite-containing slurry be free of amorphous alkali silicates and that these are added to the spray-dried product altogether.

However, if the slurry does not contain zeolite, it is possible to incorporate the entire proportion of the amorphous alkali silicates into the slurry and to spray-dry them. In this case, however, the crystalline layered silicates which may be present are preferably not spray-dried, but are added subsequently in granular form or adsorbed onto a support. The zeolite is then also incorporated into the compositions as a powder or, preferably, as a commercially available compound, for example as Wessalith ( ^R ) CS or Wessalith ( ^R ) CB (commercial products from Degussa, Federal Republic of Germany).

It is also possible for a zeolite-containing and a silicate-containing slurry to be spray-dried separately and then mixed. However, it is particularly advantageous if the zeolite-containing slurry and the silicate-containing slurry are introduced into a spray tower at the same time.

Bleaching agents such as perborate, as usual, are not spray-dried together with the constituents of the first powder component because of their thermal sensitivity, but are also only added to the spray product subsequently. Examples

Granular detergents of the following composition were produced and tested. The perborate, the bleach activator, the alkali silicate and enzyme granules and silicone oil granules were subsequently mixed into the spray-dried product from a slurry which contained the remaining constituents. The test was carried out under practical conditions in household washing machines (Miele W 717). The washing conditions are specified in more detail in the individual examples. The degree of whiteness was measured in a Zeiss reflectometer at 460 nm (suppression of the AufheT-ter effect). Remission differences of 2% and more are significant and can be traced directly by the consumer.

The center T E according to the invention and the comparing center T V had the following composition:

Cχ2-ATkyTbenzoTsuTfonat- 8.0 8.0

Sodium sets

Cχ2-Ci8-FettaTkohoT with 5.5 5.5

5 EO

C ^ -Ci _β -fatty acid soap- 1.5 1.5

Sodium sets

Zeolite NaA (anhydrous AS) - 24.0 average particle size 4.2 μm

ZeoTith NaA (anhydrous AS) 38.0 mean particle size 3.3 μm amorphous sodium 5.5

Na2θ: Siθ2 = 1: 2.0 amorphous sodium silicate - 3.5

Na2θ: Siθ2 = 1: 3.3

Sodium carbonate (anhydrous) - 12.5

Acrylic acid-maleic acid - 3.5

CopoTy er sodium set

(SokaTan CP5 ( ^R ), hand product from BASF, Germany) (Continued composition)

Sodium perborate tetrahydrate

TAED

1-hydroxyethane-l, 1-diphosphonate

Magnesium silicate

Rest (enzyme, perfume, silicone

oil, optical brightener, sodium sulfate, water)

Example 1: Stabilization of the peroxy bleach using washing conditions: tap water of 17 ° d (equivalent to 170 mg Ca0 / 1),

Main wash at 25 - 90 ° C (heating up time 60 minutes, 15

Minutes at 90 ° C),

Fleet ratio (kg of laundry: 1 wash liquor in

Main wash) 1: 4, δ repeated rinsing with tap water, spinning and

Dry; Dosage of the detergent: 146 g.

The machines were loaded with 3.5 kg of normally soiled household linen (bed linen, table linen, underwear) and 0.5 kg of test fabric. Strips of standardized cotton fabric (laundry research institute Krefeld), of refined cotton fabric and of a mixed fabric of polyester and refined cotton were used as the test fabric.

Soiling: grease / pigment soiling and bleachable

Soiling such as red wine, tea, cocoa, wild berries

The experiment was repeated three times. The specified reflectance values reflect the average values across all measurements.

In two further test series, 5ppm and 10ppm divalent copper ions (Cu2 ⁺ in the form of copper sulfate) were added to the wash liquor added. The specified reflectance values also correspond to the average values across all measurements.

From TabeTle 1 it can be seen that in the test series a) (washing agent T without addition of copper) the middle TE and V have comparable performances. In the test series b) (washing agent T and 5ppm Cu2 ⁺ ), the washing agent E according to the invention performed significantly better than V in the case of aTT soiling. In the test series c) (washing agent T and 10ppm Cu2 ⁺ ), the difference in performance between E and V was in favor of E. even bigger.

Table 1% remission for detergent test series E V

a) Detergent T 73.9 74.4

b) Detergent 68.1 63.3 + 5ppm Cu2 ⁺

c) Detergent 53.3 47.7 + lOpp Cu ²⁺

Example 2: secondary effects

Washing conditions: tap water of 23 ° d, 3.5 kg of clean laundry, dosage of detergent 146 g, 25 washes; aTTe further parameters as in example 1.

From TabeTTe 2 it can be seen that both the ash content (measured on terry tissue) and the incrustation (measured weight increase on bleaching nettle tissue) turn out to be higher in the comparison agent V than in the agent E. Table 2

Medium% ash incrustation (terry cloth) (white nettle)

E 1.37 2.54 V 2.82 3.40

Comparable results were achieved in remission measurement if instead of 5.5% by weight of an amorphous sodium silicate with the molar ratio Na2θ: Siθ2 of 1: 2.0, an amorphous sodium silicate with a molar ratio of 1: 2, 6, a crystalline β-disilicate or a mixture of 3.5% by weight of an amorphous sodium silicate and 2% by weight of a crystalline δ ^" disilicate were used.

Claims

1. Detergent containing surfactants, zeolite, alkali silicate and optionally a peroxy bleach, characterized in that it contains 30 to 65% by weight of a finely divided, hydrated zeolite with an average particle size of 1 to 5 μm, 1 to 15% by weight. -% of a solid alkali silicate with the molar composition M2θ: Siθ2 from 1: 2.0 to 1: 3.0, where M is sodium and / or potassium, with the proviso that the agent is free of water-soluble organic Complexing agents from the group of substituted phosphonates, free of polymeric polycarboxyates and essentially free of alkali carbonates.

2. Composition according to claim 1, characterized in that it is 30 to 50 wt .-%, preferably 32 to 45 wt .-% of a finely divided, hydrated zeolite, with an average particle size of 1.8 to 4.5 μm, preferably 2.0 to 4.0 microns, and 2 to 10 wt .-%, preferably 3 to 8 wt .-% of sodium silicate with a molar ratio Na2θ: Siθ2 of 1: 2.0 to 1: 2.8 contains.

3. Composition according to claim 1 or 2, characterized in that it contains 12 to 30 wt .-% of a peroxy bleach, preferably in combination with 1 to 5 wt .-% of an activator for the peroxy bleach.

4. Composition according to one of claims 1 to 3, characterized in that it contains 2 to 7 wt .-% of a crystalline layered silicate of the formula Na2Si2θ5- H2θ, where y is a number from 0 to 20, and the ratio of zeolite to crystalline layered silicate is at least 5: 1.

5. Composition according to one of claims 1 to 3, characterized in that it contains zeolite and amorphous alkali silicate in a weight ratio of 4: 1 to 10: 1.

6. Agent according to one of claims 1 to 5, characterized in that it is amorphous alkali silicate and crystalline alkali silicate in one Contains weight ratio of 1: 2 to 2: 1 and preferably from 1: 1 to 2: 1.

7. Composition according to one of claims 1 to 6, characterized in that it contains not more than 4 wt .-% and preferably not more than 3 wt .-% of alkali carbonates, especially sodium carbonate, with the proviso that the alkali carbonate only is added in the amounts in which it does not contribute to increased incrustation.

8. A process for the preparation of an agent according to any one of claims 1 to 7, characterized in that a slurry containing the anionic surfactants, at least part of the zeolite, part, but not more than 3% by weight, preferably not more than 2% by weight, based on the total finished agent, which contains amorphous silicates and optionally nonionic surfactants, is spray dried.

9. The method according to claim 8, characterized in that the zeolite-containing slurry is free of amorphous alkali silicates and these are added to the spray-dried product together with the crystalline layered silicates which may be present.

10. A process for the preparation of an agent according to any one of claims 1 to 7, characterized in that a slurry containing the anionic Tensi¬ de, amorphous alkali silicates and optionally nonionic surfactants is spray-dried and the zeolite is added to the spray-dried product subsequently.

11. A process for the preparation of an agent according to any one of claims 1 to 7, characterized in that a zeolite-containing slurry and a silicate-containing slurry are simultaneously introduced into a spray tower.