EP0693040A1

EP0693040A1 - Method of purifying soluions containing alkali-metal aluminates

Info

Publication number: EP0693040A1
Application number: EP94916913A
Authority: EP
Inventors: Istvan Potencsik; Reinhold Sedelies; Hubert DÖRRER; Johannes Breker; Detlev Roggenkamp
Original assignee: Giulini Chemie GmbH
Current assignee: BK Giulini Chemie GmbH
Priority date: 1993-04-08
Filing date: 1994-04-07
Publication date: 1996-01-24
Also published as: SK283913B6; CZ261395A3; PL310826A1; SK125995A3; DE4311716C1; CZ290971B6; WO1994024050A3; WO1994024050A2

Abstract

The invention concerns a multi-stage method for the purification of the alkali-metal aluminate solutions arising as wastes in the aluminium processing industry, as well as the processing of solid aluminium-containing residues to give purified alkali-metal aluminate solutions or solid alkali-metal aluminates.

Description

METHOD FOR CLEANING ALKALIA UMINATENT HOLDING SOLUTIONS

The present invention relates to a method for cleaning and concentrating alkali aluminate solutions which are obtained in the aluminum processing industry. The invention further relates to the processing of aluminum hydroxide-containing sludges and filter cakes to give liquid or solid alkali aluminates. The following sections provide examples of some materials that can be used for the present invention.

I. Sodium aluminate waste solutions:

1.1. Pickling liquors: The surface of aluminum metal is protected from its final use as a material by anodizing. Before anodizing, the aluminum workpieces are cleaned and any irregularities such as abrasions, scratches and bumps on their surface are removed. The first cleaning or pickling is carried out in hot sodium hydroxide baths in which the workpieces are immersed. Part of the aluminum metal also dissolves and sodium aluminate is formed in the bath liquid. After reaching an aluminum content of approx. 60 g / 1, these baths are discarded or replaced. These used sodium aluminate pickling baths are particularly preferred as material for the process according to the invention. In further rinsing processes which pass through the workpieces so pickled before they are immersed in the sulfuric acid anodizing liquids, waste liquids (standing rinses) are obtained which also contain dissolved sodium aluminate and thus in the sense of the present invention

SPARE BLADE (RULE 26) - __ - can be used.

1.2. Aluminum-containing waste solutions also arise during the reprocessing of aluminum-containing catalysts and e.g. in platforming catalysts and also in the production of Raney nickel, which is a particularly pyrophoric form of nickel and is used as a catalyst in many chemical processes.

Raney nickel is made by first nickel with metals, e.g. is alloyed with aluminum, silicon, magnesium or zinc and then this alloy is treated with sodium hydroxide solution or potassium hydroxide solution after mechanical grinding. This removes catalytically inactive metal, leaving a black metal sponge as "active nickel". The waste solutions resulting from this process, provided aluminum is an alloy component, can be used as a starting material in the sense of the present process.

.3. Among the technical deformation processes of aluminum, extrusion plays a major role in the production of profiles from blocks and bars. During the pressing process, aluminum residues remain in the pressing tool, which must be removed. The best way to dissolve them is with sodium hydroxide solution. The alkaline solutions obtained here represent nothing other than a more or less contaminated sodium aluminate solution and can therefore also be used for the purposes of this invention.

II. Solid aluminum-containing residues

Alkali aluminates generally arise from the dissolution of solid ones

E EL26 aluminum-containing residues in aqueous alkali lyes. According to the invention, all aqueous alkali solutions, for example sodium hydroxide or potassium hydroxide, can be used for the dissolution of the solid aluminum-containing residual substances.

11.1. Aluminum hydroxide slurries

According to the invention, all aluminum hydroxide-containing sludges and filter cakes can be used which result from the neutralization of alkaline or acidic aluminum-containing waste solutions, e.g. if you combine alkaline anodizing eyes with sulfuric acid electrolyte from the aluminum anodizing process (USP 4,265,863 / USP 3,909,405).

1 .2. Suitable aluminum hydroxides also arise during the regeneration of the pickling bath according to DE OS 40 08 379, in which aluminum hydroxide is precipitated in situ.

III. Aluminum oxides

The low-temperature forms of aluminum oxide belonging to the gamma group are also suitable for the process according to the invention. They arise from the aluminum hydroxides by heating to 400 to 750 ° C and, due to their large pore volumes and their large specific surfaces, are used as catalysts in the dehydrogenation of alcohols, as catalyst supports, drying agents and as chromatography column fillings for the separation of natural products. Contaminated materials from the uses mentioned above dissolve in hot concentrated alkali lyes and are the raw material for this method according to the invention suitable. Also only partially resolvable

Material can be used in the process according to the invention.

IV. All combinations or mixtures which arise from the aforementioned solutions with the solid aluminum hydroxide or aluminum oxide-containing residues are of course also suitable for the process according to the invention.

This list of the materials which can be used according to the invention is not complete and should in no way limit the present invention.

State of the art

The preparation of alkaline aluminum pickling liquors has already been proposed in US-A 4,265,863. Accordingly, an integrated process for the treatment of waste water from anodizing plants is proposed, which uses two types of waste solutions, namely the alkaline etching solution and the aqueous sulfuric acid solution, the treatment comprising three process routes:

1. Production of aluminum sulfate by treating a part of the anodizing waste water throughput by evaporation and crystallization or with a part of the aluminum hydroxide formed in step 2.).

2. Preparation of precipitated aluminum hydroxide and a sodium sulfate solution by treating the part of the anodizing waste water throughput that is not consumed in step 1.) with part of the caustic waste water throughput.

3. Preparation of a sodium aluminate solution by reacting the part of the etching water throughput with aluminum hydroxide produced in step 2.) with the escape of a quantity of water in order finally to obtain the sodium aluminate as a concentrated solution, as a powder or as granules. A very important requirement that must be met is that according to column 11, lines 5 ff, the starting solutions used must not contain any organic and mineral impurities, otherwise the process cannot be used successfully. This process therefore does not include cleaning of the solutions used here, since this process is only designed for "clean" solutions.

According to US-A 4,265,863, it is necessary that the starting solutions used contain no organic and mineral contaminants. Otherwise the procedure cannot be used successfully. The known method therefore does not include cleaning of the solutions used in it, since it is only designed for "clean" solutions.

It is common to all the solutions that arise or arise in Sections I to IV that they have fluctuating concentrations of alkali aluminate, are alkaline and that they contain some undesirable accompanying substances, such as heavy metals, solids and sediment, etc., which result in their further use limit or prevent these impurities, as well as their color or toxicity. It is therefore the object of this invention to be generally applicable

To provide a process according to which, from contaminated alkaline waste solutions containing aluminate or solid residues containing aluminum, alkali aluminates in the form of a solution or

Powders can be produced. According to this process, it should also be possible to use several alkali aluminates with different consistencies and different molar ratios of alkali oxide to Al O and Al O

Held to manufacture.

This object could be achieved by a combined process which is essentially characterized in that the waste solutions and / or sludges containing aluminate are worked up in an integrated process to form alkali aluminate solution or to solid alkali aluminates. In particular, the method according to the invention is characterized by the following steps:

l.a. ) If solid aluminum-containing material is available, this is first dissolved in hot alkali lye. These solutions are then fed to the first oxidation.

1. b. ) If you start with liquid waste solutions, these solutions can be subjected to the first oxidation immediately. Optionally, alkali metal hydroxide solution is used to dissolve the aluminum contained in the sediment or added sludge, and thus to set the alkali oxide / Al O molar ratio in the range from 1 to 5, preferably 1 to 2.

The solutions in la) and b.) Show before the first Oxidation has an alkali oxide / Al O molar ratio of less than 5, preferably 0.9 to 3, in particular 1.2 to 2, and an Al O content of 3 to 20% by weight.

2. The contaminated waste solutions are oxidized with an oxidizing agent, preferably hydrogen peroxide, in order to decolorize the solutions. Depending on the stability or range of action of the oxidizing agent, the oxidation is carried out at the appropriate temperature, preferably at room temperature. All common agents are suitable as oxidizing agents, e.g. H O, sodium perborate and others Depending on the degree of contamination, 0.05 to 0.5% by weight of oxidizing agent, based on the amounts used, are added. The solutions can also be decolorized by adsorbing the coloring impurities on activated carbon.

3. Before the first mechanical cleaning now taking place, the solution is heated to 50 to 100 ° C., preferably 70 to 80 ° C., in order to lower the viscosity. The mechanical separation removes any remaining cloudy turbidity. All separation processes can be used individually or in combination, e.g. Sedimentation with precoat filtration, with centrifugation and "cross-flow" membrane filtration. It has proven to be particularly advantageous to use auxiliary substances, e.g. Trimercapto-s-triazine (TMT) or di-2-ethylhexyl dithiophosphate for precipitating and / or complexing heavy metals, and / or adding organic flocculants or polyelectrolytes in conjunction with activated carbon to improve the mechanical separation.

4. After this separation, the mother liquor is evaporated to 10

SPARE BLADE (RULE 26) to 25 wt.% Al O, preferably 15 to 25 wt.%, concentrated. In this step, aluminum hydroxide or aluminum oxide, for example those mentioned in Sections II or III, can also be added. The alkali oxide / Al O ratio must be above

1, preferably kept at 1.2 to 2.

5. The intermediate product ZP 1 thus formed is now subjected to the second mechanical cleaning, whereupon residues from the first cleaning, turbidity precipitated by concentration, and any undissolved parts of the substances added under 4. are removed. This step can be carried out in the same way as for the 1st mechanical cleaning, using auxiliaries and using the various separation processes already mentioned under point 3.

The intermediate product ZP 1 can optionally be decolorized before step 5 with the aid of oxidizing agents if such constituents should still be present or have been introduced in step 4. You can also remove the coloring components with activated carbon.

After these steps, the first end product EP 1 is already available in the form of a bright and clear solution and can be used for all known purposes. It has an alkali oxide / Al O molar ratio of at least 1 to 2 and an Al O content of 10 to 25% by weight.

According to the invention, there are several further process steps for the production of solid alkali aluminate with an AlO content of 36 to 62% by weight, preferably 45 to 55% by weight:

ERSATZBLÄTT REGEL26) 7.) The end product EP 1 can be evaporated up to

Evaporate solid. Depending on the degree of evaporation and

Alkaline oxide / Al O ratio can be used with different products

AI o produce content.

8.) The end product EP 1 can be concentrated to an AlO content of 25 to 33% by weight by water evaporation and then this solution can be dried in a spray dryer or in another suitable unit. The advantage of this method is that the solid end product EP 2 is produced in a free-flowing consistency with a low bulk density. This can have advantages in some applications, e.g. in the building materials industry.

9.) Calcination is another option. Solution EP 1 is evaporated to a solid by water evaporation and then calcined in a rotary kiln.

In the following examples, the performance of the process according to the invention is demonstrated on the basis of the analysis results which had been achieved with the various starting materials before and after cleaning.

26 Example 1: Production of sodium aluminate from anodized eyes and moist hydrate

Which characterized in more detail in Table 1, black-colored, solid-containing Eloxallauge was divided into two batches, in a 25 m ³ tank, at temperatures not above 30 ^* C with 0.1 5% hydrogen peroxide (added as a 30% solution) was added and the Mix the solution for another hour so that the oxidation reaction can proceed completely. Subsequently, the anodized eyes were heated to approx. 80 "C, with flocculant (8 ppm Alciar W5, Allied Colloids GmbH, Hamburg) and with 0.1% trimercapto-S-triazine-trisodium salt solution (TMT 1 5, Degussa AG , Hanau) and sedimented for 1 to 2. The supernatant was thickened in a one-stage expansion evaporator to form intermediate 1. Intermediate 1:

Al ₂ 0 ₃ : 1 6.27% Na ₂ 0: 18.46%

The intermediate product 1 was then increased with 1, 24 1 aluminum hydroxide (moist hydrate, corresponding to 0.719 t Al ₂ 0 ₃ ) to the final content of 18.4% Al ₂ 0 ₃ . This

<D

The solution was treated with a polymeric flocculant (8 ppm Alciar W5, Allied Colloids GmbH, Hamburg), sedimented overnight (12 h) and the supernatant was subjected to clarification by means of a filter with a washed filter aid layer made of Celiulose. The solution, which is still yellow after clear filtration, is oxidized again with 0.15% hydrogen peroxide (added as a 30% solution) and is then water-clear with a slight yellow tinge.

The product is a clear, slightly yellowish solution that is already viscous at room temperature. The analysis is shown in Table 1 below.

ERSÄΓZBLÄΓT (RULE 26) Table 1: Analyzes of the educt and product in the production of sodium aluminate solution from anodized aluminum

Anga¬ anodizing solution; Product; be homogenized filtrate in solution

Na ₂ 0% 13.35 18.3

Al ₂ 0 ₃ % 1 1, 77 18.4

Na / Al mol / mol 1, 87 1, 63

Iron ppm 3 006 140

Arsenic ppm 0.04 0.03

Chromium ppm 387 8

Nickel ppm 26 0

Copper ppm 137 4.5

Lead ppm 5.3 0

Mercury ppm 0.21 0

Cadmium ppm 0 0

Silicon ppm 2,172,548

RULE 2b Example 2: Preparation of sodium aluminate solution using solid aluminum-containing residues

The aluminum hydroxide-containing residue characterized in more detail in Table 2, which is obtained by the process described in Chapter 11.2, was dissolved in 50% sodium hydroxide solution in a reactor heated directly with steam. The strongly colored, solids-containing, still hot product was mixed with a polymeric flocculant (8 ppm Mikrosorban 502, Giulini Chemie GmbH, Ludwigshafen), sedimented overnight (1 2 h) and the supernatant, using a filter with a washed-on filter auxiliary layer made of Celiulose, subjected to a clear filtration. The solution, which was cooled to about 40 ^° C. after the filtration, was treated with 0.15% hydrogen peroxide (added as a 30% solution) for decolorization. The product is a clear, almost colorless, viscous solution.

Table 2: Analyzes of the aluminum-containing residue and the sodium aluminate solution prepared from it

Anga residue; Product; be in

Humidity% 16 - -

Na ₂ 0% 0.66 19.7

Al ₂ 0 ₃ % 52.42 19.6

Na / Al mol / mol - - 1.65

Iron ppm 740 16

Chromium ppm 2 1

Nickel ppm 760 1

Copper ppm 30 0

Lead ppm 5 0

Zinc ppm 30 2

SPARE BLADE (RULE 26) Example 3: Production of calcined, solid sodium aluminate from a solution containing aluminumium in three stages.

The aluminum-containing, alkaline, black-gray, solid-containing residue solution solution, characterized in more detail in Table 3, from the Raney nickel production was placed in a 25 m ³ container according to which. Oxidation with 0.15% hydrogen peroxide (addition as a 30% solution), heated to about 80 ^° C. and then freed from the solids in accordance with Example 1. The supernatant was thickened to about 82% of its mass, to intermediate 1, in a single-stage expansion evaporator. The concentrate from the evaporator was pumped into an open, heatable reactor, aluminum hydroxide was added there and the mixture was evaporated to about 77.4% of its mass (intermediate product 2). After solidification, the intermediate product 2 was placed in a rotary kiln, calcined and then ground. The solid sodium aluminate produced is a hygroscopic, eggshell-colored powder with a bulk density of approx. 0.8 g / cm ³ , which has a very good solubility in water. The contents of the individual levels are listed in Table 3.

Table 3: Analyzes of starting material, intermediate products and product in the production of solid sodium aluminate from residual aluminum hydroxide solution in three stages

Anga¬ entrance; Zwischenpro¬ Zwischen¬ product; be alumini¬ duct 1; product 2; in a concentrated concentrated solution

Na ₂ 0% 20.9 25.2 26.0 40.5

Al ₂ 0 ₃ % 16.2 20.0 37.1 54.6

Na / Al mol / mol 2.1 2.1 1, 2 1, 2

Iron ppm 52 30 30 45

Nickel ppm 43 1 1 12 17 Example 4: Preparation of solid sodium aluminate from aluminum-containing, alkaline residues solutions in two stages.

2.5 kg of 30% hydrogen peroxide were added to 500 kg of the dark black colored, cold anodizing solution, which is characterized in more detail in Table 4, in a double-walled, steam-heated stirred tank. After stirring for about an hour, the alkali was heated to 80 ^° C. This hot suspension was clarified by a precoat suction cell rotary filter with precoat scraper removal and stored temporarily. Celiulose was used as the precoat. Filtration data of the precoat rotary cell suction filtration:

Lye temperature during filtration approx. 80 ° C.

Precoat layer: Celiulose, 1 cm thick, the precoat layer was applied to the filter from an approx. 2.5% suspension. The continuous acceptance of the fitter cake was carried out with a hydraulic scraper acceptance.

Drum speed: 0.3 to 1 rpm.

Fiitrate flow: 250 l / (m ² h). The still hot, clear, slightly yellowish filtrate was then concentrated in the reactor for about 3 hours with stirring. The concentrate thus obtained has the contents listed in Table 5.

12.4 kg of this solution were sprayed and dried in a spray dryer. Spray dryer data: electrically heated,

Air inlet temperature: 350 "C

Air outlet temperature: 200 ^* C

Throughput of solution to be dried: 3 kg / h

The solid sodium aluminate produced by spray drying is a hygroscopic, eggshell-colored, fine powder whose bulk density is about 0.1 g / cm ³ and which dissolves very well in water.

The contents of starting material, intermediate product and product are summarized in Table 4.

Claims

EXPECTATIONS

1. A process for the preparation of pure alkali aluminate solutions with a molar ratio of alkali oxide to Al O of greater than 1.0, starting from alkaline waste solutions with a molar ratio of alkali oxide to Al O of less than 5.0 and an Al O content of 3 to 20 % By weight, these solutions being subjected to a multi-stage cleaning and concentration, characterized in that the alkali oxide to Al O molar ratio is adjusted by adding alkali metal hydroxide solution and / or aluminum oxide or aluminum hydroxide in the range from 1 to 5, preferably 1 to 2, and the solutions thus obtained are oxidized with an oxidizing agent and, after heating to 50 to 100.degree. C., preferably 70 to 80.degree. C., are cleaned by mechanical separation processes with the addition of auxiliaries and then concentrated to 10 to 25% by weight of Al 2 O and then these Solution subjected to a second cleaning with the addition of auxiliaries and a second oxidation.

2. The method according to claim 1, characterized in that solid aluminum hydroxide and / or aluminum oxide-containing residues and aluminum hydroxide-containing filter cake are first dissolved in hot alkali solution and the solutions thus obtained are further processed according to claim 1.

3. The method according to claim 1 or 2 for the preparation of solid alkali aluminates with an Al O content of 36 to 62 wt.%, Preferably 45 to 55 wt.%, Characterized in that these solutions are concentrated to further form a solid by further water evaporation, the Evaporation in a spray tower or other suitable Aggregate is carried out.

4. The method according to claims 1 to 3, characterized in that the mechanical cleaning by sedimentation, precoat filtration, cross-flow membrane filtration and centrifugation, and / or in combination of these methods.

5. The method according to any one of claims 1 to 4, characterized in that organic complexing agents, inorganic and organic flocculants such as cellulose, diatomaceous earth and activated carbon are used as auxiliaries.

6. The method according to any one of claims 1 to 5, characterized in that solids containing aluminum hydroxide or aluminum oxide are added to the concentration, an alkali metal oxide / Al O ratio of over 1, preferably 1.2 to 2 being set.