Method of Producing Basic Zirconium Carbonate

The present invention relates to methods of producing zirconium compounds, and more particularly to methods of producing basic zirconium carbonate.

At present basic zirconium carbonate, being readily soluble both in mineral and organic acids, finds an ever wider application in industry for producing various zirconium compounds, as well as in the textile industry for impregnating fabrics with a view to imparting fastness and waterproof properties to the latter. However, no method of producing basic zirconium carbonate has been found so far, which could be considered effective and economically expedient.

The known method of producing basic zirconium carbonate, which depends on the precipitation thereof from acidulous aqueous solution of zirconium oxychloride with ammonium carbonate, has a number of disadvantages.

1. The gelatinous precipitate of basic zirconium carbonate which forms is very slow to filter and difficult to wash with water.

2. In order to obtain basic zirconium carbonate of adequate purity, it is necessary to carry out preliminary purification of industrial zirconium oxychloride solutions from iron, titanium, aluminum, and other admixtures, by evaporating the solution, crystallizing the oxychloride with subsequent filtration and washing the zirconium oxychloride crystals with concentrated hydrochloric acid, this being associated with considerable gas evolution and corrosion of the equipment.

3. The process requires great consumption of ammonium carbonate, both for neutralization of the zirconium oxychloride solution, and for the formation of the basic zirconium carbonate.

The main object of the present invention is to provide an effective and commercially expedient method of producing basic zirconium carbonate.

Another object of the invention is to provide easily available and inexpensive stock material for producing basic zirconium carbonate.

Said and other objects are accomplished by a method which, according to the invention, is characterized in that basic zirconium sulfate is used as a stock material, said basic zirconium sulfate being reacted with ammonium carbonate or an alkali carbonate in an aqueous medium. Ammonium carbonate is preferable in this case, since it ensures greater purity of the resulting desired product. The reaction between the said compounds proceeds at normal temperature and pressure.

For attaining a maximum yield of basic zirconium carbonate, it is recommended that the starting reactants be taken in such a molar ratio, that there should be about 0.8 mole of ammonium carbonate or an alkali carbonate per mole of ZrO.sub.2 in the basic zirconium sulfate used as the stock material.

Greater quantities of ammonium carbonate or an alkali carbonate than those specified hereinabove may lead to losses of zirconium due to formation of complex zirconium carbonates which pass into the solution; in this connection considerable amounts of said carbonate prove to be undesirable.

The reaction of basic zirconium sulfate should be effected with an aqueous solution of said carbonate, the concentration of the latter being 9-10 wt.%. Such a concentration ensures the most favorable reaction conditions.

In the above-specified process the reaction of the formation of basic zirconium carbonate takes place in a solid phase, with the SO.sub.3 -group being substituted by the CO.sub.2 -group. The resulting product is a fine-crystalline precipitate of basic zirconium carbonate, which can be easily and rapidly separated by conventional filtration, the thus separated precipitate being then washed with water. The mother liquor remaining after the separation of the precipitate contains ammonium sulfate, which is used for obtaining basic zirconium sulfate.

Basic zirconium sulfate is an easily available stock material, and is an intermediate product of primary processing of zirconiferous ores to zirconium dioxide.

The herein-proposed method is expedient to be carried out in combination with a method of primary processing of zirconiferous ores to zirconium dioxide not only in view of the fact that the intermediate product of said processing, basic zirconium sulfate, is utilized, but also in view of the fact that the mother liquor after the separation of the basic zirconium carbonate precipitate is recycled to the process for the formation of basic zirconium sulfate. Hence, in the said process all the products are utilized, without any wastes.

The basic zirconium carbonate thus obtained is pure, since use is made of basic zirconium sulfate which is almost free from iron, titanium, and other admixtures. This can be explained by the fact that in the course of formation of basic zirconium sulfate said admixtures remain in solution, and the precipitate of basic zirconium sulfate is separated and washed with water. Such basic zirconium sulfate ensures the obtaining of basic zirconium carbonate, with not more than 0.6 wt.% of admixtures.

The main advantage offered by the method of the present invention consists in the obtaining of basic zirconium carbonate in a fine-crystalline form with a high content of ZrO.sub.2 of about 67 wt.%, whereas in accordance with the method known heretofore a gelatinous precipitate of basic zirconium carbonate is obtained containing 40 wt.% of zirconium dioxide.

Thus, the present invention features a number of advantages over the prior-art method. The method of the present invention can be easily carried out in industry on a large scale.

For a better understanding of the present invention, given hereinbelow is an example of a specific embodiment of the method proposed herein.

10 kg of wet basic zirconium sulfate, which in the air-dried state contains 55% of ZrO.sub.2, 21.4% of SO.sub.3 and 23.6% of H.sub.2 O, are charged in a tank equipped with a stirrer, and then an aqueous solution of ammonium carbonate with a concentration of 68.1 g/lit. is poured thereinto. The ammonium carbonate is taken in such a quantity that the molar ratio is 0.8 mole of ammonium carbonate per mole of ZrO.sub.2 in the stock material. After stirring at room temperature for 15 min., the pulp is filtered on a vacuum filtre, and the residue is washed free from SO.sub.4 .sup.-.sup.- ions with water. The content of ZrO.sub.2 in the mother liquor is 0.01 g, and in the washing water, 0.005 g/lit. The yield of the product is 99 percent. The obtained product is a white crystalline powder, completely soluble in acids and containing, in the air-dried state, 67% of ZrO.sub.2, 6% of CO.sub.2, and 27% of H.sub. 2 O, which approximately corresponds to the formula 4ZrO.sub.2.CO.sub.2. 11 H.sub.2 O.

The percentage of admixtures in the product is as follows:

TiO.sub.2, 0.13; Al.sub.2 O.sub.3, less than 0.015; CaO, 0.20; SiO.sub.2, 0.08; Fe.sub.2 O.sub.3, less than 0.01; MgO, less than 0.07 P.sub.2 O.sub.5, 0.07. No sulfur has been detected.