WO1992020834A1

WO1992020834A1 - Method for the desilification of aqueous inorganic solutions

Info

Publication number: WO1992020834A1
Application number: PCT/AT1992/000069
Authority: WO
Inventors: Werner Vlach; Dietfried Gamsriegler; Manfred Gamsriegler; Wolfgang Kladnig
Original assignee: Andritz-Patentverwaltungs-Gesellschaft M.B.H.
Priority date: 1991-05-13
Filing date: 1992-05-13
Publication date: 1992-11-26
Also published as: AT395408B; TW222610B; KR0138070B1; CN1037705C; EP0584146A1; ATA98191A; CN1068602A; JP2810234B2; JPH06507206A

Abstract

Proposed is a method for the desilification of aqueous inorganic solutions, in particular pickling solutions, and a method of producing iron oxide with a reduced silicic acid content. The aqueous inorganic solution to be processed is fed to a cross-flow filter and passed through the filter at a temperature of 60-90 °C. In order to produce oxide, the filtrate is then converted to the appropriate oxide by spray roasting.

Description

METHOD FOR PILIFYING INORGANIC AQUEOUS SOLUTIONS

The invention relates to a process for the silicification of inorganic aqueous solutions, in particular pickling solutions, and a process for the production of iron oxide with a reduced content of silica, in particular for the production. of ferrites.

In the technical field of regenerating used pickling solutions, it is known to use spray roasting technology. It is possible to extract iron (III) oxide (Fe ₂ 0,), which serves as a primary material for the electronics industry (ferrite construction). The electronic (electromagnetic) properties of these iron oxide ceramics are primarily dependent on the silica content of the materials. For example, the electronics industry is now demanding a maximum of 0.01% silica (SiC) in iron oxide for soft ferritic applications, whereas a few years ago this limit was 0.02%. The development in the iron oxide sector is expected to further lower this limit. Accordingly, the price for very pure iron oxide powder (ax. 0.01% Si0 ₂ ) can be estimated at about 4,900, - / t, while iron oxide with about 0.05% Si0 ₂ , as is produced in conventional plants, is only available at around € 700 to € 950 / t.

For the treatment of silicate-containing water, a device and a method is known from JP-PS 59-90688, in which the silicate-containing raw water is passed through two filter stages, the first filter stage containing a microporous membrane or an ultrafilter membrane, and the second filter stage a reverse osmosis membrane having. This method detects microparticles in water with a maximum size of one micrometer, and it is therefore not to be expected that silica in its conventional form can be separated off with it, since it is present in particle sizes below 0.02 micrometers. Furthermore, there is no indication that this process could also be applicable to the decilification of pickling solutions with their high content of additional ingredients. For this reason, processes for the silicification of pickling solutions have been proposed for some time and have also been used or tested in industrial plants. These processes, as described for example in AT-PS 380 675, are based on the precipitation of part of the iron chloride contained in the pickling acid (approx. 1 to 2%) as iron hydroxide and the associated adsorptive co-precipitation of colloidal silica. However, this method has the disadvantage that it requires a high level of technical equipment and that large amounts of sludge must be expected, which must be disposed of. In addition, the chemical consumption, for example of ammonia and flocculant, is relatively high, as a result of which the plant for carrying out the process is relatively expensive and not particularly economical. For example, the share of the total investment costs of the spray roaster is approx. 20 - 30%.

The object of the present invention was therefore a process which allows the silicic acid contained in any inorganic aqueous solutions to be separated off in a relatively inexpensive manner while avoiding chemicals and labor. Another task was to use this as a basis to specify a simple process for the production of iron oxide, this iron oxide not exceeding the limit values for silica required by the electronics industry. This process should also be suitable for incorporation into existing processes for the regeneration of used pickling solutions, in which iron oxide is preferably obtained.

To solve the first object, the invention provides that the supplied to a cross-flow filter solution to be treated and at a temperature of 60 - 80 ^* C is passed through the filter - 90 ^* C, preferably 70th

The silica present in the aqueous solutions is replaced by the Conditions in the cross-flow filter, mainly the prevailing temperatures, converted into micellar structures. These poly eren ^' structures are in hydrated form and are kept in suspension by electrostatic charges. Their diameter is several hundredths to tenths of a micron. This size of the micellar structures of the silica makes it also accessible for microfiltration.

By definition, the range of microfiltration for separable particle sizes is between 0.02 and 10 micrometers. Membranes for such filters are now made from a wide variety of materials, with cellulose derivatives being used for biochemical applications and, on the other hand, for the technology of cross-flow filtration as used in the process according to the invention, mainly plastic membranes made of polypropylene, polyethylene or polysulfones are used. Hollow fibers, foamed glasses or porous ceramic materials can also be used.

The principle of cross-flow filtration is also known per se for processing liquids with suspended or emulsified ingredients. The top layer of the filter cake on the filter element, which is constantly increasing in the case of static filtration and reduces the filtrate flow, is prevented in cross-flow filtration by a shear stress gradient which acts transversely to the direction of filtration beyond the associated equilibrium state. This allows long-term filtration at high filtrate flows. moreover, the cover layer can be largely detached from the surface of the filter element and removed by periodic backwashing, ie brief reversal of the filtration process, whereby the original filtration performance is restored. However, it was not from to be expected beforehand that the silica contained in aqueous solutions can be brought into a structure which permits the separation by means of a crossflow filter. Under the specified conditions, however, the already mentioned formation of micellar structures of over a few hundred angstroms of pressure gauge takes place, so that with conventional 0.2 micrometers

Polypropylene membrane hoses allow an almost complete separation of the silica.

In a particularly advantageous manner, the process according to the invention can be built into processes for the regeneration of used pickling solutions, the advantage here being that the iron oxide obtained from the pickling solution is largely free of silica and is therefore particularly suitable for the purposes of the electronics industry. For this purpose, it is provided according to the invention that an inorganic aqueous solution, in particular used pickling solution, which predominantly contain dissolved iron and silica, is passed through a crossflow filter at a temperature of 60 to 90 ^° C., preferably 70 to 80 ^° C., and the permeate is then passed by spray roasting in the corresponding oxides with max. 0.01% silica is transferred.

It is preferably provided in both described methods that the concentrate is cyclically returned to the cross-flow filter. This permits a further increase in the separation efficiency of the filter with an increased degree of purity of the permeate.

In the following description, a preferred embodiment of the process for the production of iron oxide from spent pickling acid will be explained in more detail with reference to the accompanying drawings. It shows

Fig. 1 in a schematic table a plant for

Pickling acid regeneration with built-in decalcification and 2 shows a schematic detailed illustration of the decalcification system with two filter units connected in series.

The solution to be prepared is subjected to a spray roasting in the spray roasting reactor 1 after passing through a preconcentrator 2 and the pre-flow container 3, which forms the pre-concentrator sump. The resulting solid reaction products, i. H. the metal oxides are drawn off by means of the discharge device 11, while the gaseous reaction products are preferably fed back to the preconcentrator 2 via an electrostatic filter 12. A line leads from the pre-concentrator 2, which can be from Lurji or Venturityp, to two droplet separators 4 and finally to absorber columns 5, 6, in which the pickling acid is recovered. The exhaust gas from these absorber columns 5, 6 is passed through two droplet separators 7 and then into the open.

From the flow tank 3, the on-center solution can also be fed to the crossflow filter 8 via a pump 31. A pump 81 is used for repeated circulation of the concentrate through said filter 8.

As shown schematically in FIG. 2, two (or more) filter units (8a and 8b) can be arranged in series one behind the other.

Exemplary embodiment;

Used pickling acid of the following composition (and the theoretical oxide composition resulting therefrom after the spray roasting process) was fed into a pickling acid regeneration plant, which was constructed according to the diagram in FIG. 1, for treatment. 1 ICP analysis:

: with it theoretically. Oxide composition

Fe203 99.16%

Cr203 352 ppm

NiO 204

A1203 760

Si02 289

MnO 2800

CaO 900

ZπO 598

MgO 2315

PbO 00

CuO 221

theor.max Cl 'value: 0.15% GEB.

The cross flow filter was directly integrated into the concentrate circuit. The delivery rate in the concentrate circuit was 2,800 1 / h and the delivery rate in the filter was 2,000 1 / h. After a running time of 13 or 17 hours, the following values for the concentration of iron ions or silicon oxide resulted:

a) = Fe (2+) in g / 1, b) = Fe (3+) in g / 1, c) = SiO «in mg / 1 concentrate permeate

(124-148 ppm / oxide)

(114-137 ppm / oxide)

In a subsequent test, pickling acid was treated, the concentration values of which were as follows: Fe (2+) 79.9 g / 1, Fe (3+) 5.6 g / 1, Si0 “38 mg / l (this corresponds to a theoretical maximum value of 337 ppm in the oxide ). Within an hour or after four This resulted in hours using crossflow filtration

(76-92 ppm / oxide)

(109-135 ppm / oxi

The cross flow filter was then switched off and after four hours the following values were obtained:

Concentrate permeate a) b) c) a) b) c)

4h 113.8 32.4 56.2 (1) 39 (350 ppm / oxide)

In the tables above, when silicon oxide was stated in the total oxide withdrawn, the solution was extrapolated to the oxide. Therefore, an analysis result for the spray roasting oxide is given here:

Claims

Claims:

1. A process for desilication inorganic aqueous solutions, in particular pickling solutions, characterized in that the fed to a cross-flow filter solution to be treated and at a temperature of 60 - 80 ^* C is passed through the filter - 90 ^* C, preferably 70th

2. Process for the production of iron oxide with a reduced content of silica, in particular for the production of ferrites, characterized in that an inorganic aqueous solution, in particular used pickling solution, containing predominantly dissolved iron and silica, at a temperature of 60-90 ° C., preferably

70 - 80 ^* C through a cross-flow filter and the permeate is then converted into the corresponding oxides with a maximum of 0.01% silica by spray roasting.

3. The method according to claim 1 or 2, characterized in that the concentrate is cyclically returned to the cross-flow filter.