SK283913B6 - Method of purifying solutions containing alkali-metal aluminates - Google Patents

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

Technical field

The invention relates to a process for purifying and concentrating alkali aluminate solutions found in the aluminum processing industry. The invention also relates to the processing of aluminum hydroxide sludge and filter cakes into liquid or solid alkali aluminates.

I. Sodium aluminate waste solutions

1.1

The surface of the metal aluminum is protected by anodizing before being used as a material. Prior to anodizing, the aluminum components are cleaned and free of surface irregularities such as depressions, grooves and irregularities. The first cleaning or pickling is carried out in the hot baths of caustic soda, into which the components are immersed. This also dissolves some of the aluminum metal and creates sodium aluminate in the bath. When the aluminum content reaches approximately 60 g / l, such baths are drained or regenerated. As a material for the process according to the invention, these worn-out pickling baths containing sodium aluminate are particularly well suited. In further rinsing operations through which the pickled parts pass, waste liquids (rinses) are formed which also contain dissolved sodium aluminate and are thus usable within the meaning of the invention.

1.2

The aluminum-containing waste solutions are also formed in the re-preparation of aluminum-containing catalysts, for example in platform catalysts and in addition to the production of Raney-nickel, which is a particularly pyrophoric form of nickel and is used as a catalyst in numerous chemical processes.

Raney nickel is prepared by first alloying nickel with metals such as aluminum, silicon, magnesium or zinc and then treating the alloy after mechanical comminution with sodium or potassium hydroxide solution. In doing so, the catalytically inactive metal is leached, leaving a black metal sponge as "active nickel". The waste solutions which are formed in this case when the aluminum alloy is part of the alloy are usable as starting materials for the purposes of the invention.

I. 3

Among the aluminum forming techniques, extrusion is of great importance for the production of profiles from blocks and rods. During the pressing, aluminum residues are attached to the pressing device and must be removed. It is best to dissolve with caustic soda. The alkaline solutions which are formed in this case are nothing but more or less contaminated sodium aluminate solutions and are also suitable in the process according to the invention.

II. Solid residues containing aluminum

Alkaline aluminates are generally formed by dissolving aluminum-containing solid residues in aqueous alkaline lyes. According to the invention, all aqueous alkaline liquors, for example sodium or potassium hydroxide solutions, are useful for dissolving aluminum-containing solid residues.

II. I Aluminum hydroxide sludges

According to the invention, all sludges and filter cakes containing aluminum hydroxide resulting from the neutralization of alkaline or acidic waste solutions containing aluminum can be treated, for example when the alkaline anodizing liquors are mixed together with the sulfuric acid electrolyte from the aluminum anodization process (U.S. Pat. 3,909,405).

II. 2

Suitable aluminum hydroxides are further formed in the regeneration of the pickling bath according to DE OS 4008379, where the aluminum hydroxide is precipitated in situ.

III. Aluminum oxides

Alumina belonging to the gamma group of low temperature forms is also suitable for the process of the invention. It is formed from aluminum hydroxide by heating to 400 to 750 ° C and, due to its large pore volumes and large specific surfaces, finds application as a catalyst in the dehydrogenation of alcohols, as a catalyst support, desiccant and column chromatography column for separating natural substances. The contaminated materials from the above applications dissolve in hot concentrated alkaline liquors and are suitable as raw materials for the process of the invention. Partially dissolved material can also be used in the process of the invention.

IV.

Naturally, all combinations and mixtures which result from the above solutions with solid residuals containing hydroxide or alumina are also suitable for the process according to the invention.

This list of materials useful in the present invention is not exhaustive and is not intended to limit the invention in any way.

BACKGROUND OF THE INVENTION

The treatment of an aluminum pickling liquor is already described in U.S. Pat. No. 4,226,863. An integrated process for the treatment of waste water from anodizing plants is described, where two types of waste solutions are used, namely alkaline leptadio and aqueous sulfuric acid, the treatment comprising three progressive paths.

1. Preparation of aluminum sulphate by treating one part of the anodizing waste water by evaporation and crystallization or one part of aluminum hydroxide formed in the second operation.

2. Preparation of precipitated aluminum hydroxide and sodium sulfate solution by treating a portion of the anodizing waste water not consumed in the first operation with one portion of the waste etching agent.

3. Preparation of the sodium aluminate solution by reacting one part of the waste etching agent with the aluminum hydroxide prepared in operation 2 at the outlet of water to finally obtain the sodium aluminate as a concentrated solution as a powder or as a granulate.

A very important prerequisite that must be fulfilled is that the outlet solutions according to paragraph 11 from line 5 must not contain any organic or mineral impurities, as otherwise the procedure is not applicable successfully. Therefore, this procedure does not involve any purification of the solutions used, since it is designed only for "clean" solutions.

All of the solutions that arise or fall off in the processes of paragraphs I to IV are in common that they have a varying concentration of alkali aluminate, are alkaline and contain unwanted accompanying substances such as heavy metals, solids and sediment that limit or prevent further use for their contamination as well as their coloring and toxicity.

It is, however, an object of the present invention to provide a generally applicable process by which aluminate-containing contaminated alkaline waste solutions, optionally solid aluminum-containing residues, alkali aluminates in solution or powder form can be prepared. According to this process, it should also be possible to produce different alkali aluminates with different consistencies and with different molar ratios of alkali oxide to alumina and with different alumina contents.

This object could be solved by a combined process which is essentially characterized in that it treats aluminum containing waste solutions and possibly sludges by an integrated process into an alkali aluminate solution or a solid alkali aluminate.

U.S. Pat. No. 4,226,958 relates to a process for purifying solutions resulting from the treatment of nepheline mineral with sodium hydroxide and lime. This mineral has been used in the past to produce clay hydrate and highly active silica gels. In this process, no purification is carried out, but both essential components are separated. The purification steps are therefore only optional, that is to say they are used only when necessary.

WO-A 8701107 relates to a drying process for obtaining solid sodium aluminate. Solid sodium aluminate is known to be more stable than liquid aluminate. The method is based on the use of products resulting from the so-called Bayer process, i.e. it is applicable only in analogous cases.

Czech patent specification CS 144015 relates to a process for the special purification of sodium aluminate solutions which are produced in the Bayer process. For purification, tetravalent manganese compounds are added in combination with oxygen and calcium carbonate. This method makes it possible to remove, by precipitation, impurities contained in the solution, for example iron or silicates. Its use is limited to the Bayer process.

There is therefore a need to develop a process to purify any contaminated aluminum compounds and obtain pure end products. The invention solves this object.

SUMMARY OF THE INVENTION

Process for producing pure alkali aluminate solutions having an alkali oxide to alumina molar ratio greater than 1.0 from an alkaline waste solution having a molar ratio of alkali oxide to alumina of less than 5.0 and having an alumina content of 3 to 20% by weight in several stages according to the invention, the mole ratio of alkali oxide to alumina is adjusted to 1 to 5, preferably 1 to 2, by addition of alkaline liquor and / or alumina, and the solutions thus obtained are oxidized with an oxidizing agent and subjected to heating after heating to 50 to 100 ° C, preferably to 70 to 80 ° C, the first purification by mechanical separation with adjuvants and then concentrated to 10 to 25% alumina by weight, and finally these solutions are subjected to a second purification with adjuvants and a second oxidation.

In general, the process according to the invention is characterized by the following operations.

(la) When solid aluminum-containing waste material is available, it is dissolved in hot alkaline caustic liquor first. These solutions are then introduced into the first oxidation.

Ib) When starting from liquid waste solutions, these solutions can be subjected to the first oxidation immediately. Optionally, an alkaline liquor may be added to bring the aluminum contained in the precipitate, possibly deposited in the sludge, into solution in order to adjust the molar ratio of alkali oxide to alumina of 1 to 5, in particular 1 to 2.

Prior to the first oxidation, the solutions of operations 1a) and 1b) have a molar ratio of alkali oxide to alumina of less than 5, preferably 0.9 to 3, in particular 1.2 to 2, and an alumina content of 3 and 20% by weight.

2. The contaminated waste solutions are oxidized with an oxidizing agent, preferably hydrogen peroxide, to decolourize the solutions. The oxidation is carried out depending on the stability or resp. the range of activity of the oxidizing agent at an appropriately suitable temperature, preferably room temperature. Suitable oxidizing agents are all conventional oxidizing agents, for example hydrogen peroxide and sodium perborate. Depending on the degree of soiling, 0.05 to 0.5% by weight of oxidizing agent, based on the amounts used, is added. Decolourisation of the solutions can be carried out additionally by adsorption of the coloring impurities on activated carbon.

3. Prior to the first mechanical cleaning now occurring, the solution is heated to a temperature of 50 to 100 ° C, preferably a temperature of 70 to 80 ° C, to reduce the viscosity. Mechanical separation removes residual hydroxide-containing sludges. All separation processes can be combined, for example by sedimentation with pre-filtration with centrifugation and with countercurrent membrane filtration. In order to improve mechanical cleaning, it has proved particularly advantageous to add auxiliary substances, such as trimercapto-sym-triazine (TMT) or di-2-ethylhexyldithiophosphate, for the precipitation and / or complexing of heavy metals and / or to add organic flocculants, polyelectrolytes together with activated carbon.

4. After this separation, the mother liquor is concentrated by evaporation to 10 to 25% by weight of alumina, preferably to 15 to 25% by weight. In this operation it is possible to mix with aluminum hydroxide or aluminum oxide, for example according to paragraphs II to III. The ratio of alkali oxide to alumina must be maintained greater than 1, preferably 1.2 to 2.0.

5. The thus-obtained intermediate, intermediate 1, is subjected to a second mechanical treatment, which removes any residues from the first treatment by concentrating the precipitated sludge and any undissolved portions of the substances added in the fourth operation. This operation can be carried out similarly to the first mechanical cleaning using the auxiliary substances and using the various separation methods referred to in paragraph 3.

6. Intermediate 1 may optionally be discolored prior to treatment 5 by oxidizing agents if such components still exist or are introduced in the operation of paragraph 4. However, the coloring constituents may also be removed with activated carbon.

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

Further operations according to the invention serve to produce a solid alkali aluminate with an alumina content of 36 to 62% by weight, preferably 45 to 55% by weight.

7. The end product, end product 2, can be concentrated to a solid by evaporation of water. Depending on the degree of evaporation and the ratio of alkali oxide to alumina, products with different alumina contents can be prepared.

8. By evaporating water, the end product 1 can be concentrated to an alumina content of 25-35% by weight and then dried in a nozzle dryer or other suitable aggregate. The advantage of this process is that a solid end product of semolina consistency with a low bulk density is obtained. This may be advantageous in some applications, for example in the construction industry.

9. As a further variant, calcination is possible. The end product solution 1 is evaporated to a solid by removal of water and then calcined in a tubular rotary kiln.

The invention is illustrated by the following non-limiting examples.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

Production of sodium aluminate from anodizing lyes and wet hydrate

The black colored anodizing liquor containing particulate matter, as detailed in Table I, is reacted in two portions in a 25 m ³ tank at temperatures above 30 ° C with 0.15% hydrogen peroxide (30% solution additive) and the solution was stirred for an additional hour to complete the reaction. The anodic liquor is then heated to about 80 ° C with a flocculating excipient (8 ppm Alclar ^R W5, Allied Colloids GmbH, Hamburg) and treated with a 0.1% trimercapto-S-triazine trinium salt solution (TMT 15, Degusa AG, Hanau) ) and allowed to settle for 12 hours. The extract is concentrated in a one-stage expansion evaporator to give intermediate 1, having the following composition: Al ₂ O ₃ : 16.27%, Na ₂ O: 18.46%.

Intermediate 1 is then treated with 1.24 t of aluminum hydroxide (wet hydrate corresponding to 0.719 t of alumina) to a final content of 18.4% alumina. The solution was treated with a polymeric flocculation auxiliary ^(R 8 ppm Alclar W5, Allied Colloids GmbH, Hamburg), allowed to settle overnight (12 hours) and the supernatant is subjected to a clarifying filtration using a filter with a filter layer deposited auxiliary based on cellulose. The solution, which is still yellow after clarifying filtration, is again oxidized with 0.15% hydrogen peroxide (30% solution additive) and is then clear as slightly yellowish water.

The product is a clear, slightly yellowish, but already very thick liquid solution at room temperature. The analysis is in Table I.

Table I

Analysis of the starting material and the product in the preparation of the sodium aluminate solution from the anodizing liquor

entry Anodizing solution homogenized solution Product Filtrate sodium oxide % 13.35 18,30 aluminum oxide % 11.77 18.40 Na / Al nol / tna'- 1.87 1.63 iron PP® 3 005,00 140.00 arsenic ppm 0.04 0.03 chrome ppm 387.00 8.00 nickel ppm 26.00 0 honey ppm 137.00 4.50 lead ppm 5.30 C mercury ppm 0.21 about cadmium ppm 0 0 silicon ppm 2,172 548.00

Example 2

Production of a sodium aluminate solution using aluminum-containing solid residues

The aluminum hydroxide-containing residue, as defined in Table II, obtained by the method described in paragraph II.2, is dissolved in the reactor by direct heating with 50% sodium hydroxide solution. The strongly colored, still hot product containing solids was reacted with a polymeric flocculating aid (8 ppm Mikrosorban ^R 502, Giulini Chemie GmbH, Ludwigshafen), allowed to settle overnight (12 hours) and the supernatant was clarified by filtering with a cellulose-based filter-aid applied thereto. The solution, cooled after filtration to approximately 40 ° C, is treated with 0.15% hydrogen peroxide (30% solution additive) for decolourisation. The product is a clear, almost colorless thick solution.

Table II

Analyzes of aluminum-containing residual substance and sodium aluminate solution produced therefrom

entry Residual substance Product humidity % 16,00 __ sodium oxide % 0.66 19.70 aluminum oxide % 52.42 19.60 Na / Al ntol / mol - 1.65 iron ppm 740.00 16,00 chrome ppm 2.00 1.00 nickel ppm 760.00 1.00 copper ppm 30.00 0 lead ppm 5.00 0 zinc ppm 30.00 2.00

Example 3

Three-stage production of calcined solid sodium aluminate from a solution of residual aluminum-containing substances

A solution of the alkaline black gray of residue further characterized in Table III, resulting from the production of Raney nickel and containing solids, in a container containing 25 ^m3 of oxidation of 0.15% hydrogen peroxide (addition as a 30% solution) heated to ca. 80 ° C and then freed from solids similar to Example 1. The supernatant is concentrated in a one-stage evaporator to approximately 82% by weight to yield intermediate 1.

The concentrate from the evaporator is pumped into an open heated reactor, mixed with aluminum hydroxide and concentrated by evaporating water to approximately 77% by weight (intermediate 2). After solidification, intermediate 2 is introduced into a rotary tube furnace, calcined and finally ground. The solid sodium aluminate produced is an egg-shell hygroscopic powder having an apparent density of approximately 0.8 g / cm ³ and having very good water solubility. The characteristics of the individual stages are summarized in the table

III.

Table III

Analysis of the starting material, intermediates and product in the three-step production of solid sodium aluminate from the caustic soda

entry Inlet: solution containing Al Hcdaiprodukt 1 intermediate product 2 Product sodium oxide % 23.9 25.2 26.0 4C, 5 aluminum oxide% 16.2 20.0 37.1 54, 6 Na / Al no1 / mol 2.1 2.1 1.2 1.2 iron ppm 52 G 30.0 30.0 4b, 0 nickel ppm 43.0 11.0 12.0 17, 0

SK 283913-6

Example 4

Two-stage production of solid sodium aluminate from alkaline solutions of aluminum-containing residuals Up to 500 kg of the black-colored, cold anodizing liquor, as detailed in Table IV, are added, with stirring, 2.5 kg of 30% hydrogen peroxide in a two-jacketed stirred tank. After stirring for approximately one hour, the liquor was heated to 80 ° C. This hot suspension is cleanly filtered on a drum suction filter with a filter layer applied by scraping and discarded. Cellulose is used as the filter layer.

Suction drum filtration characteristics

Liquor temperature during filtration: 80 ° C.

Filter layer applied: 1 cm thick cellulose. The layer is applied to a filter of 2.5% suspension. The continuous collection of the filter cake is carried out by hydraulic scraping.

Drum speed: 0.3 to 1 per minute.

Filtrate flow: 250 l / (m ² h).

The still hot, clear, slightly yellowish filtrate was then concentrated in the reactor for three hours with stirring. The characteristics of the concentrate thus obtained are shown in the table

IN.

12.4 kg are obtained from this solution by spraying and drying in a spray dryer.

Spray dryer data:

Electrically heated, air inlet temperature: 350 ° C, air outlet temperature: 200 ° C, dried solution amount: 3 kg / h.

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

The characteristics of the starting material, intermediate and product are shown in Table IV.

Table IV

Characteristics of the starting material, intermediate and product in the two-stage production of solid sodium aluminate from the alkaline lye of aluminum-containing residues

entry A starting solution containing Al Concentrated intermediate Solid product aluminum oxide % 12.50 28.9 48.3 sodium oxide % 9.00 20.9 34.9 Fixed share substances 1.80 - - Na / Al nol / mol 1.19 1.19 1.19

Example 5

Separation of solid from anodizing lye by flow microfiltration

Because some anodizing lyes cannot be filtered by dead-end filtration, cross-flow filtration experiments are underway. The procedure is as follows.

The residual solution, which is very difficult to filter, is the anodizing liquor sludge described in Example 1. Heat in a tank to about 80 ° C and filter in a flow-through microfiltration-ultrafiltration unit. The intermembrane pressure, permeate and retentate streams can be measured using appropriate gauges. In the example of sludge filtration described in Table V, a 0.8 µm pore size alumina ceramic module is used.

The sludge used has the following composition:

19.3% sodium oxide,

14.3% alumina.

The permeate obtained is a clear, yellowish, thick liquid solution which can be further processed by evaporation and purification. By backwashing the membranes with permeate or dilute sodium hydroxide solution, it is possible to achieve longer membrane durability between individual cleaning intervals.

Table V

Filtration characteristics of the flow filtration of the sediment residue according to Example 1.

Flow rate: 3.5 m / s

Pore size: 0.8 pm

Time temperature Inter-membrane pressure solids loading in the retentate tin • c MPa 1 / oA) 9/1 3 ARE U 0.23 90 17.5 30 82 0.21 75 38.5 300 82 0.23 Θ5 37.8 355 88 0.23 69 234, 1

Industrial usability

A process for the multi-stage purification and concentration of alkali aluminate solutions that are waste in the aluminum, sludge, filter cake and aluminum-containing solid residue industries to obtain alkali aluminate or solid alkali aluminate solutions.

Claims (6)

PATENT CLAIMS A process for producing pure alkali aluminate solutions having an alkali oxide to alumina molar ratio greater than 1.0 from an alkaline waste solution having a molar ratio of alkali oxide to alumina of less than 5.0 and having an alumina content of 3 to 20 weight percent % by means of a multi-stage refining and concentration process, characterized in that the molar ratio of alkali oxide to alumina is adjusted to 1 to 5, preferably 1 to 2, by addition of alkaline liquor and / or alumina, and the solutions thus obtained are oxidized with an oxidizing agent and heating to 50 to 100 ° C, preferably to 70 to 80 ° C first cleaning by mechanical separation with adjuvants and then concentrated to a weight of 10 to 25% alumina, and then these solutions are subjected to a second cleaning with adjuvants and a second oxidation . Method according to claim 1, characterized in that the solid residues containing solid aluminum hydroxide and / or aluminum oxide and the filter cakes containing aluminum hydroxide are first dissolved in hot alkaline liquor. Method according to claim 1 or 2, characterized in that the solutions are concentrated by further evaporation of water to obtain a solid, the evaporation being carried out in a spray dryer or in another suitable aggregate to obtain solid alkali alumina containing 36 to 30% alumina. 62%, preferably 45 to 55%. Method according to claims 1 to 3, characterized in that the mechanical cleaning is carried out by sedimentation, filtration through a filter element, membrane filtration with a cross-flow through the membranes or by centrifugation and / or a combination of these methods. Method according to claims 1 to 4, characterized in that organic complexing agents, organic or inorganic flocculants such as celluloses, diatomaceous earth and activated carbon are used as auxiliaries. Method according to claims 1 to 5, characterized in that solids containing aluminum hydroxide or alumina are added to increase the concentration, wherein the ratio of alkali oxide to alumina is set to greater than 1, preferably 1.2 to 2.