SK125995A3 - 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

Process for producing pure alkali aluminate solutions

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. Waste sodium aluminate solutions

1.1. stains

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 hot liquor baths in 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. These spent mordant baths containing sodium aluminate are particularly well suited as material for the process according to the invention. In other 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 Raneynikl, 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 this process, the catalytically inactive metal is leached, leaving a black metal sponge as the active nickel. The waste solutions which are formed in this case when aluminum is part of the alloy are useful as starting materials for the purposes of the invention.

1.3

Among the aluminum forming techniques, extrusion is of great importance for the production of profiles from blocks and rods. When pressing, aluminum residues are attached to the pressing tool and must be removed. It is best to dissolve with caustic soda. The alkaline solutions which are formed in this case are no more than 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.1. 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, in which 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 400-750 ° C and, due to its large pore volumes and large specific surfaces, finds its application as a catalyst in the dehydrogenation of alcohols, as a catalyst support, desiccant and chromatographic column packing for the separation of natural substances. The contaminated materials from the above applications dissolve in hot concentrated alkaline liquors and are useful 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. 4,226,663. An integrated process for the treatment of waste water from anodizing plants is described, wherein two types of waste solutions are used, namely an alkali etching agent and an aqueous sulfuric acid solution, the treatment comprising three progress paths:

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

2. Preparation of the 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. Thus, this process does not involve any purification of the solutions used, since it is designed only for pure solutions.

All of the solutions that arise or fall off in processes according to paragraphs I to IV are in common that they exhibit fluctuating concentrations of alkali aluminate, are alkaline and contain undesirable accompanying substances, such as heavy metals, solids and sediment, that limit or prevent further use for their contamination as well as their color and toxicity.

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

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

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 an alkali oxide to alumina molar ratio of less than 5.0 and an alumina content of 3 to 20% by weight 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 after heating to 50 to 100 ° C, preferably to 70 to 80 ° C, first cleaned 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 second oxidation .

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

L.A.)

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

I.b)

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, optionally settled in the sludge, into solution so as to adjust the molar ratio of alkali oxide to alumina of 1-5, in particular 1-2.

Prior to the first oxidation, the solutions of operations 1.a) and b.) 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 activity range 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 the mechanical purification, it has proven to be particularly advantageous to add, in the first mechanical purification, an adjuvant, such as trimercapto-sym-triazine (TMT) or di-2-ethylhexyl dithiophosphate for precipitation and / or complexation of heavy metals and / or , 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 alkali oxide to alumina ratio must be maintained at a level of greater than 1, preferably 1.2 to 2.0.

5)

The thus obtained intermediate, Intermediate 1, is subjected to a second mechanical treatment in which any residues from the first treatment are removed 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)

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

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

For the production of a solid alkali aluminate with an alumina content of 36 to 62% by weight, preferably 45 to 55% by weight, further operations according to the invention serve:

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 jet 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 another variant, calcination is possible. The end product solution 1 is evaporated to a solid by removing water and then calcined in a tubular rotary kiln.

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

Examples . 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 was then heated to about 80 ° C with a flocculating aid (8 ppm Alclar ® W5, Allied Colloids GmbH, Hamburg) and treated.

0.1% Trimercapto-S-triazine trinitrate 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 yield 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 polymer flocculation auxiliary ^(R 8 ppm Alclar W5, Allied Colloids GmbH, Hamburg), allowed to settle overnight (12 hours) 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 a 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 product in the production of sodium aluminate solution from the anodizing liquor

entry Anodizing solution homogenized solution Product The filtrate sodium oxide % 13.35 18,30 aluminum oxide % 11.77 18.40 Na / Al mol / mol 1.87 1.63 iron ppm 3 006,00 140.00 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 0 mercury ppm 0.21 0 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 subjected to a clear filtration through a filter. with a cellulose-based filter-aid applied thereto. The solution, cooled after filtration to approximately 40 ° C, is treated with 0.15% hydrogen peroxide (additive 30% solution) for decolourisation. The product is a clear, almost colorless thick solution.

Table II

Analysis of the 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 mol / 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 ^e C and then freed from solids similar to Example 1. The supernatant is concentrated in a one-stage evaporator to approximately 82% of its weight to yield intermediate 1.

The concentrate from the evaporator is pumped into an open, heated reactor, mixed with aluminum hydroxide, and concentrated by evaporation of 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 eggshell hygroscopic powder having an apparent density of approximately 0.8 g / cm ³ , which exhibits very good water solubility.

The characteristics of the individual stages are summarized in 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 input: solution containing Al intermediate product 1 intermediate product 2 Product sodium oxide % 20.9 25.2 26.0 40.5 aluminum oxide% 16.2 20.0 37.1 54.6 Na / Al mol / mol 2.1 2.1 1.2 1.2 iron ppm 52.0 30.0 30.0 45.0 nickel ppm 43.0 11.0 12.0 17.0

Example 4

Two-stage production of solid sodium aluminate from alkaline solutions of aluminum containing residues

To a 500 kg black colored cold anodizing liquor, as detailed in Table IV, was added 2.5 kg of 30% hydrogen peroxide in a double-walled, stirred tank heated with stirring. After about one hour of stirring the liquor heated to 80 ^e C The hot suspension is filtered to clean the filter drum aspiration applied to the filter layer by means of scraper, the collection and discarded. Cellulose is used as the filter layer.

Suction drum filtration characteristics:

Liquid 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 Table V.

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

Spray dryer data:

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

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 product firm product aluminum oxide % 12.50 28.9 48.3 sodium oxide % 9.00 20.9 34.9 Fixed share substances % 1.80 - - Na / Al mol / mol 1.19 1.19 1.19

Example 5

Separation of solid from anodizing liquor by flow microfiltration

Since some anodizing lyes cannot be filtered by dead-end filtration, cross-flow filtration experiments are carried out. Here's how:

The residual solution, which is very difficult to filter, is the anodizing liquor sludge described in Example 1. It is heated. in a tank at a temperature of about 80 ° C and filtered in a flow-through microfiltration-ultrafiltration unit. The intermembrane pressure, permeate and retentate streams can be measured with appropriate gauges.

In the example of sludge filtration described in Table V, a ceramic module of alumina with a pore size of 0.8 μιη 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 sedimentation residue flow filtration according to Example 1.

Flow rate: 3.5 m / s

Pore size: 0.8 μιη

Time temperature Intermembrane pressure ^v permeate Fixed load substances in the retentate min "C. MPa l / (m ² h) g / l

3 81 0.23 90 17.5 30 82 0.21 75 38.5 300 82 0.23 85 87.8 • 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% by weight. % by means of a multi-stage refining and concentration, 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 lye and / or alumina, and the solutions thus obtained are oxidized with an oxidizing agent and subjected after heating to 50 to 100 ° C, preferably to 70 to 80 ° C, first cleaned by mechanical separation with adjuvants and then concentrated to 10 to 25% alumina by weight, and then these solutions are subjected to a second cleaning with adjuvants and 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 and the solutions thus formed are further processed according to the process of of claim 1. Method according to claim 1 or 2 for the production of solid alkali aluminates with an alumina content of 36 to 62% by weight, preferably 45 to 55%, characterized in that these solutions are concentrated by further evaporation of water to obtain a solid, It is carried out in a spray dryer or in another suitable aggregate. Method according to claims 1 to 3, characterized in that the mechanical cleaning is carried out by sedimentation, filtration through a filter element, membrane cross-flow filtration or centrifugation and / or a combination of these methods. - 17 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 from 1.2 to 2.