DK152807B - PROCEDURE FOR PREPARING BASIC Zirconium Carbonate - Google Patents

Abstract

1. Process for the preparation of an acid soluble and basic zirconium carbonate calcinable to a pure highly dispersed zirconium oxide from pure zirconium salts by reaction of the solid salts with ammonium hydroxide solution, separation of the basic zirconium salts obtained and conversion to the basic zirconium carbonate, characterised in that the carbonization is carried out in a urea solution undergoing hydrolytic decomposition thereof.

Description

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DK 152807B

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a process for preparing, from pure zirconium salts, an acid-soluble basic zirconium carbonate which can be calcined into a pure, high-dispersed zirconia by reacting the solid salts with an ammonia solution. basic zirconium salts and converting them to the basic zirconium carbonate.

The use of zirconia in special ceramic materials places great demands on the purity and dispersity of the raw material.

This is especially true if the material is to be processed into electronic components, such as piezoelectric ceramic components or oxygen measuring probes. In such cases, the requirements for a high degree of purity include not only metallic contaminants but also non-metallic contaminants, such as e.g. chloride or sulphate. This is of particular importance since salts such as the oxychloride ZrOCl2.8H2O or the acidic sulphate ZrOSO4.1.1 SO2 .3H2O are the usual starting products for the preparation of other zirconium chemicals, in particular the oxide.

20 Both salts generally appear in mineral extraction and can be recovered in the pure state by recrystallization under certain conditions (J. Am. Ceram.

Soc. 21 (1952) 2104).

If these salts are subjected to pyrolysis at high temperature, then oxides which are pure in terms of metallic contaminants appear, but the process is subject to considerable disadvantages and, as a rule, results in a highly sintered product to be subjected to grinding with its the following risk of subsequent pollution.

30 At least in the case of sulphate, this roasting is not complete to the extent required. It is therefore a matter of the state of the art to convert the known salts into basic carbonate, from which It is possible to produce salts of other acids again, but it is first and foremost possible to pour this basic carbonate into a high-dispersed pure zirconia.

Precipitation of the basic carbonate from an aqueous solution leads to poorly filterable and poorly washable precipitates, which is why it has already been proposed to perform this reaction as a slurry reaction. For this purpose, e.g. it is possible to introduce the pure acidic sulphate in solid form into an ammonium carbonate solution (Keram. Zeitschr. 33 (1981) 94), or the contaminated product can only be purified by repeated reaction as basic sulphate (molar ratio 10 ZrO 2: 80 ^ -2: 3 ) and then reacted in suspension with ammonium carbonate and carbonic acid, respectively, ammonium hydrogen carbonate (DE-PS 28 54 200 and DE-PS 29 27 128). In the known literature (Jr. H. Bastius, cited in Keram. Zeitschr. 33; (1981) 98, Ref. 17), this process step is unanimously referred to as critical, and it is this process step which the invention relates to, the purpose of the invention being the preparation of a pure, high-dispersed zirconia.

The correct dosage of the scavenger is of crucial importance in obtaining a good filterable and well washable precipitate as well as the avoidance of excess for a yield-reducing complex formation (cf. the above quotation from H. Bastius).

The stated object is achieved by a method which according to the invention comprises the measures specified in claim 1.

It has been found that this problem, which is particularly critical in the heterogeneous reaction, can be solved by the use of urea as the bulking agent instead of ammonium hydrogen carbonate and combinations of ammonium carbonate and carbonic acid, respectively. For carrying out the proposed process, purified solid zirconium salt, e.g. acidic zirconium sulfate or zirconium oxychloride, first in a hot ammonia solution and digested as granular suspension until constant pH. After this initial 3

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acidification, the well-deposited solid can be readily isolated from the solution of the ammonium salt by decantation, filtration or centrifugation and optionally washed free of soluble sulfate.

5 As can be seen from the following examples, it is possible to exclude these undefined basic salts for oxide of sufficient dispersion, but too high anions content. The resulting granular basic products are therefore resuspended in water, 10 urea added and digested in the solution at temperatures sufficient for hydrolytic cleavage of the urea.

In that case, both the ammonia solution and the urea solution are preferably present in a stoichiometric excess with respect to the zirconium sulfate or zirconium oxychloride used.

The filtered and washed product is acid-soluble in a filter-moistened state and, after annealing, provides a loose, open oxide which is also pure in anions and whose dispersion can be adjusted by changing the annealing temperature and annealing time.

The method according to the invention is illustrated by the following examples.

Example 1.

A commercially available technically acidic zirconium sulfate 25 was purified by recrystallization using a combination of processes known per se. To this end, 710 g of crude zirconium sulfate (about 2 moles) was introduced into the same amount of cold water, 71 g of aqueous 3 HCl (specific weight 1.19 g per cm) and 0.7 g of polyethylene glycol were added and stirred. ca. 1 hour at 50 ° C. The undissolved was filtered off using a dense filter, and to the clear filtrate was added 710 g of concentrated sulfuric acid (specific 3 weight 1.84 g per cm), increasing the temperature of the mixture to about 100 ° C. The mixture was kept warm for approximately

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4 20 to 30 minutes and cooled slowly (~ 0.5 ° C / min) to room temperature with slight stirring. The well crystallized salt can be impeccably isolated from the mother liquor by centrifugation and, in the unwashed state, is sufficiently pure for further reaction, as is evident from the comparison of the analyzes of crude sulphate and pure sulphate (with respect to ZrO 2 ~ annealing residue) in the following table:

Zr (SO 2) 2 * 2H 2 O (annealed at 1000 ° C for 10 hours) Crude salt Recrystallized salt 10 Wt% by weight Pwt% by weight

SiO2 0.02 <0.01

TiO2 0.24 <0.05

Fe2 O3 0.16 0.069

CaO 0.031 0.028 Al2 O3 0.02 0.02

The loss through the mother liquor amounts to approx. 5% by weight, based on the crude sulphate supplied.

710 g of purified zirconium sulfate (~ 2 mole) is then introduced with vigorous stirring into a mixture of 2 liters of H 2 O 3 and 1 kg of concentrated NH an NH3 solution of approx. 8.5% by weight.

The temperature of the mixture rises to approx. 50 ° C and the mixture is digested at this temperature for about 90-120 minutes until an approximately constant pH of 8-9 is obtained. The granular ammonia product from the heterogeneous reaction settles well and is filtered and washed once with cold water. Then it was suspended again for approx. 3 liters of H 2 O, the mixture was added 240 g of urea (~ 4 moles) and heated to near the boiling point and digested at this temperature for 90-120 minutes. The dense reaction product was excellently filtered and washed free of sulfate,

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5 as the reaction, as determined on annealed zirconia, was practically quantitative, calculated on the amount of zirconium sulphate supplied.

The result of the acid exchange, ie. the substitution of sulfate 5 with carbonate is completely what appears from the SO3 values of annealed sample portions.

However, when treated exclusively with NH 2, a product is obtained which, at a similar annealing, exhibits a substantially higher residual content of SO 2. However, the dispersion (specific surface area) of the resulting annealing products is quite similar.

Treatment with NH ^ + Treatment with NH ^ urea (according to the (comparative) finding) 15 Annealing SO ^ Specific Annealing- SO ^ Specification (wt%) Surface (wt%) Surface (° C / 3h) (G 2 m2) 600 0.033 22.2 --- --- --- 0.035 9.4 800 0.80 8.9 L000 0.030 2.9 1000 0, 3.5

Example 2.

With a zirconium oxychloride which was purified by recrystallization from 8 N HCl, a reaction similar to that of Example 1 was carried out, i. a dispersion of the solid salt in NH 4 solution and, subsequently, in hot urea solution, the chloride exchange was continued after both process steps by annealing the product (700 ° C and 3 hours) and determining residual Cl in zirconia to 0 , 02 wt.% (NH 2 treatment) and <0.005 wt. 30 percent (according to the invention NH 3 ~ + urea treatment).

In this case, too, the dispersions of the products were approximately equal: 11.6 and 16.7 m / g, respectively.

Claims (4)

A process for the preparation of a basic zirconium carbonate which is soluble in acid and can be calcined to a pure, high-dispersed zirconia, from pure zirconium salts by reacting the solid salts with an ammonia solution, isolating the basic zirconium salts and transfer them to the basic zirconium carbonate, characterized in that the carbonization is carried out in a urea solution under hydrolytic decomposition thereof. Process according to claim 1, characterized in that both the ammonia solution and the urea solution are used in stoichiometric excess with respect to the zirconium salts used. A process according to claim 1 or 2, characterized in that acid sulfate, Zr (SO 2) 2 ^ 41, 0 which is purified by recrystallization is used as the zirconium salt. Process according to claim 1 or 2, characterized in that, as zirconium salt, purified zirconium oxychloride, ZrOC 2, S 2 O, is used.