JPH02279522A - Production of zirconia - Google Patents

Abstract

PURPOSE:To obtain high-purity ZrO2 excellent in sintering property at low cost by melting zircon sand with CaO-contg. raw material by heating, then rapidly cooling, concentrating the Zr component from the product, leaching, precipitating, refining by a specified method, sintering and pulverizing. CONSTITUTION:Zircon sand and Cao-contg. material are mixed and molten by heating and then rapidly cooled to obtain a molten product which is soluble in acid. From the product, calcium silicate is selectively leached with dil. hydrochloric acid and then zirconium component is leached with concd. hydrochloric acid. The leaching liquid with recovered to precipitate zirconium oxychloride crystal. The crystals isolated from the liquid, while the liquid is recovered to the preceeding process for recycle. The crystal is dissolved in water to precipitate insoluble zirconium salt. The precipitate is then isolated, dried, sintered and pulverized to obtain zirconia powder.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to a method for producing zirconia, and more specifically, to a method for producing zirconia, and more specifically to a method for producing fine zirconia powder from calcium zirconate obtained by melting zircon sand and calcium raw materials. The present invention relates to a manufacturing method.

[Prior art] Zirconium fine powder has conventionally been used in ferroelectric materials, piezoelectric materials, catalyst carriers, solid electrolytes, heat-resistant materials, wear-resistant materials, etc. 1 Fla! raw materials for sintered bodies such as materials, optical glass additives, thermal spraying materials, etc.
It is used in a wide range of fields such as pigments. The zirconia fine powders used for these purposes include those consisting of zirconia as a single component and those consisting of multiple components containing stabilizers such as magnesia, calcia, and ittria.

On the other hand, as research and development related to fine ceramics has become more active in recent years, the excellent properties of zirconia ceramics have attracted attention, and their use as high-performance electronic ceramic materials, high strength, high toughness ceramic materials, etc. is expanding. Demand for high-quality zirconia fine powder, which is the raw material for these products, is increasing.

Conventionally, the general method for producing high-purity zirconia for use in fine ceramics has been to use zirconium salts such as zirconium oxychloride and zirconium sulfate as starting materials, and to process an aqueous solution of these salts through a neutralization reaction or hydrolysis. A method has been proposed in which a reaction generates a precipitate of zirconium hydroxide or hydrate, and the precipitate is dehydrated, dried, and calcined. A specific method involves adding an alkali such as aqueous ammonia to an aqueous solution of zirconium oxychloride to neutralize it to generate a hydroxide, which is then filtered, washed,
A method of drying and then firing is used.

In this method, when neutralizing with alkali to produce a zirconium hydroxide precipitate, Fe, AI, Ti, Si, etc. present as impurities in zirconium oxychloride are entrained as hydroxides in the zirconium precipitate. Refined raw materials must be used for adulteration.

Zirconium oxychloride is produced by melting zircon sand in an alkali together with caustic soda, washing the melt with water, dissolving and separating sodium zirconate with hydrochloric acid, separating and removing insoluble materials, and concentrating the solution. It is manufactured by precipitating zirconium chloride crystals.

Further, the aqueous zirconium oxychloride solution is produced by hydrolyzing zirconium tetrachloride with water or dissolving zirconium carbonate in hydrochloric acid.

Zirconium oxychloride obtained by the caustic soda melting method usually contains a large amount of impurities, and unless the impurities are removed by repeated recrystallization, it cannot be used for fine ceramics or for the production of other high-purity zirconia compounds II.
It cannot be used as a K material, and it requires a large amount of cost to obtain highly pure zirconium oxychloride.

On the other hand, a method has been proposed in which zirconia is produced by pelletizing a mixture of zircon sand and calcareous powder, firing it, dissolving the resulting clinker in relatively concentrated hydrochloric acid, and then neutralizing it (Japanese Patent Publication No. 1986- 25658).

However, the purpose of this method is to economically produce zirconia in large quantities with a high recovery rate, and since the recovered zirconia is accompanied by impurities in the zircon sand ore, its separation is difficult. However, it has the disadvantage that it is not possible to obtain satisfactory results in terms of purity.

[Problems to be Solved by the Invention] The present invention overcomes the drawbacks of the conventional methods as described above, and produces particles with a particle size that can be used for the various uses mentioned above, including fine ceramics, through normal industrial operations. The object of the present invention is to provide an industrially advantageous method for producing high-purity zirconia fine powder that does not contain small, hard secondary aggregates, has good dispersibility, and has excellent sinterability.

[Means and effects for solving the problem] As a result of intensive research to solve the drawbacks of conventional methods, the present inventors mixed zircon sand with a calcium source such as lime and electromagnetically quenched it. The resulting zirconium-containing product is leached with hydrochloric acid, zirconium oxychloride crystals are precipitated from the obtained zirconium-containing leachate, and a zirconium compound precipitate is generated from the solution in which the zirconium oxychloride crystals are dissolved, which is then washed, dried, and calcined. The present invention was completed by discovering that, by doing so, it is possible to obtain fine zirconia powder of high purity, small particle size, and good dispersibility that does not contain any hard aggregates and can be used as a raw material for fine ceramics.

That is, the present invention provides (a) a melt generation step in which a raw material mixture of zircon sand and a CaO-containing raw material is heated and melted, and then rapidly cooled to obtain an acid-soluble melted product; (b) the acid-soluble melted product and dilute hydrochloric acid; a step of concentrating the zirconium component in which the calcium silicate component is selectively eluted and separated by contacting with an aqueous solution; (c) a leaching step of contacting and dissolving the zirconium component with an aqueous hydrochloric acid solution to recover a zirconium leachate; (d) a step of recovering the zirconium leachate. (e) a crystallization separation step in which crystals of zirconium oxychloride are precipitated from the aqueous solution, the resulting crystals are separated and recovered, and part or all of the recovered mother liquor is used in the previous step; a zirconium recovery step of producing a zirconium compound precipitate, and (f)! ! The present invention relates to a method for producing zirconia characterized by comprising a zirconia production step of drying, firing and pulverizing an insoluble zirconium compound to obtain zirconia powder.

The present invention will be explained in detail below.

In the method for producing zirconia according to the present invention, first, in the melt generation step, a raw material mixture of zircon sand as a starting material and a CaO-containing M material is heated and melted, and then rapidly cooled to obtain an acid-soluble molten product.

The Kf4 zircon sand used in the present invention can be used as a commercially available product, but may be subjected to a pulverization operation if necessary.

In addition, quicklime, slaked lime, various types of calcium carbonate, etc. can be used as CaO-containing raw materials, and if necessary, coarsely crushed or
Alternatively, it can be used after being granulated.

In the present invention, the mixing ratio of zircon sand and CaO-containing raw material is important and needs to be determined taking into account the composition of the molten product. The raw materials are mixed and then melted and rapidly cooled. The reaction within the molten product in this case is considered to basically follow the reaction shown in the following formula (H).

Zr5iOa+3CaO-CaZrOs+2CaO-S
iOz --- (1) As shown in the above formula (1), the ratio of zircon sand and quicklime is 3 mol of CaO to 21 mol of Zr, but in the actual reaction, impurities contained in the raw materials, Since there is some non-uniformity in the raw material mixture, it is desirable that the amount of CaO is 2.5 moles or more, preferably 2.8 to 4 moles, per mole of Zrozl.

Next, the raw material mixture is heated and melted at 1500 to 2600°C, preferably 1700 to 2400°C, and then the molten product is rapidly cooled by pulverization or the like. This operation usually uses an arc furnace equipped with a tap, through which the molten product flows out and is quenched by water pulverization by being blown with a high-pressure water stream.

By quenching by water pulverization, the zirconia component in the molten product can be rendered acid-soluble, and quenched amorphous or acid-soluble calcium zirconate (CaZrL) can be obtained.

According to the research of the present inventors, zircon sand and quicklime are used to melt a mixture of 2.5 mol or more, for example 3 mol, of CaO per 21 mol of Z r 0, and the molten product is pulverized. When rapidly cooled, xi diffraction analysis shows CaZr0z
(JCPDS Card 35-790.1985) only the X-ray diffraction peak appears, and 2CaO.5iOz is amorphous. On the other hand, when the molten product is gradually cooled, in addition to the Carry X-ray diffraction peak, 0.
85ZrOz ・0.15CaO (JCPDS card
28-341.1976) or Z r O2 (JC
PDS Card 17-923.1967) Similar x
AIA fold peak appears.

On the other hand, when less than 2.5 mol of CaO is mixed with 1 mol of ZrO and melted, and the molten product is pulverized and rapidly cooled, CaZr03(7) and other 0.852 rOz ・0
, 15CaO1 or ZrO2-like peaks appear. In addition, when 2 mol of CaO is mixed and melted with 21 mol of Z, the quenched product no longer contains C.
The X-ray diffraction peak of aZrOs does not appear, and 0.85Zr
02.0.15CaO or Z r O2-like peaks only.

Here, 0.85ZrOz・0.15CaO and Zr01 show almost similar X-ray diffraction patterns, and in reality, a solid solution of 0 to 0.15 mol of CaO is produced with respect to ZrOz. It is estimated that

Furthermore, the present inventors investigated the solubility (elution) of the zirconia component in hydrochloric acid for various melted products. As a result, X-ray diffraction analysis revealed that CaZr0! It was found that almost 100% of the zirconia component was eluted in the melted product in which only 2 mol/1 of hydrochloric acid was observed. In contrast, X-ray diffraction analysis revealed that CaZr0. Besides 0.
The melted product in which 85ZrOt-0,15CiO or ZrOt was observed is 0.85Zr02・0.15
It was found that the elution rate of the zirconia component decreased as the peak intensity of CaO or Z r O2 increased. And CaZr0. No diffraction peak < + 0.85ZrOz・0.15CaO or Z
r In the case of only the diffraction peak of O2, 2 to 11 mol/
Even when dissolved in hydrochloric acid (1), the elution rate of the zirconium component was 50% or less.

Based on the above findings, in order to melt a mixture of zircon sand and a CaO-containing raw material and make the zirconia component in the melted product acid-soluble, it is necessary to make the melted product in an amorphous or CaZrO2 crystalline phase as determined by X-ray diffraction analysis. It is particularly important to create a composition in which only ZrO is obtained;
0.85ZrOt J, 15
It is necessary to prevent the formation of CaO or ZrO2.

The acid-soluble molten product thus obtained is desirably pulverized to a powder having a particle size of 150 microns or less, preferably 100 microns or less.

If the particle size exceeds 150 μ-, colloids of SiO2 will aggregate on the particle surface during the next step of elution treatment with dilute hydrochloric acid, resulting in poor elution rate and separation performance.

Next, in the step of concentrating the zirconium component, the calcium zirconate component and the calcium silicate component are selectively eluted and separated from the acid-soluble molten product slurry produced by bringing the acid-soluble molten product into contact with an aqueous hydrochloric acid solution. By performing elution under conditions where the HCI concentration in the slurry of the acid-soluble molten product dispersed in an aqueous hydrochloric acid solution is less than 2 mol/1,
It is possible to elute as much calcium and silica as possible from the acid-soluble molten product. The reaction formula is as shown in the following formula (II).

CaZr0z + 2CaO・5iOt+4HC4-C
aZrO1+2CaC12+ 5ins +2H20・
...(11) Specifically, an amount of 1.0 to 1.2 times the equivalent of HCl in the reaction formula shown in the above formula (■) is used,
Elution is performed by diluting with water to prepare an aqueous hydrochloric acid solution having a concentration of less than 2 mol/l, and the calcium zirconate component of the elution residue is separated and recovered.

In addition, in the method of the present invention, the mother liquor obtained by separating the crystals in the subsequent crystallization step of zirconium oxychloride can be used as part or all of the aqueous hydrochloric acid solution in the step of concentrating the zirconium component, which is economical. It is also a very advantageous method.

Next, in a zirconium leaching step, the calcium zirconate obtained in the leaching step is dissolved in contact with an aqueous hydrochloric acid solution to recover a zirconium leaching solution. Calcium zirconate is immersed in an aqueous hydrochloric acid solution to remove H in the slurry.
Leaching is carried out under conditions where the CI concentration is 2 mol/1 or more,
Leaches out zirconium.

Specifically, an amount of 1.0 to 1.2 times the equivalent of HCI in the reaction formula represented by the following formula ([[I) Leaching is carried out using a hydrochloric acid concentration of 2 mol/1 or more.

In the method of the present invention, a mother liquor obtained by separating crystals in the subsequent crystallization step of zirconium oxychloride can be used as part or all of the aqueous hydrochloric acid solution used in this step.

Furthermore, in both the concentration step and the leaching step, there is no particular limitation on the slurry concentration in the eluate or leachate, as long as it satisfies a predetermined hydrochloric acid concentration.

Although there are no particular limitations on the elution or leaching in this case, the elution or leaching rate is generally faster when heated, and a temperature of 50 to 100°C is suitable.

In addition, when leaching the acid-soluble molten product with hydrochloric acid,
It is also possible to perform leaching in one step with 2 mol/1 or more hydrochloric acid, but in this case, calcium and silica are also leached together with zirconium into the leaching solution, and the silica that is once dissolved in the leaching solution is hydrated. Decomposition leads to insoluble silica precipitates, making subsequent solid-liquid separation extremely difficult.

Therefore, when leaching an acid-soluble molten product with hydrochloric acid,
As in the present invention, zirconium is preliminarily leached with less than 2 mol/e of hydrochloric acid to elute as much calcium and silica as possible in the molten product, and then the leaching residue is dissolved in 2 mol/e or more of hydrochloric acid. The two-step leaching method is industrially advantageous and is one of the features of the present invention.

Next, in the zirconium oxychloride crystallization step, zirconium oxychloride (ZrOClz.8LO) crystals are precipitated and separated into layers from the zirconium leachate obtained in the leaching step. For the precipitation of zirconium oxychloride crystals, a method is generally adopted in which a soluble zirconium solution is evaporated, but this method requires special equipment and requires a large amount of energy and cost, so it is industrially disadvantageous. have.

In order to overcome the drawbacks of conventional methods such as evaporative concentration, the present invention
This method uses an operation that easily and efficiently precipitates high-purity zirconium oxychloride crystals by adding hydrochloric acid to the zirconium eluate obtained as described above.

First, according to the literature, the solubility of zirconium oxychloride in hydrochloric acid is as shown in the figure. According to the figure, the solubility of zirconium oxychloride is 8.
It can be seen that a curve with a minimum value is drawn at ~9 mol/1.

Therefore, according to this solubility curve, in order to maximize the recovery rate of zirconium, the hydrochloric acid concentration should be 8 to 9 mol/1
It is advantageous to carry out the crystallization of zirconium oxychloride in such a manner that the zirconium solution in the solution is ZrO
2, it becomes 10y/1 or less.

On the other hand, according to the results of measurements made by the present inventors, it was found that when calcium chloride coexists with zirconium oxychloride, the hydrochloric acid concentration at which the solubility of zirconium oxychloride becomes minimum shifts to the lower concentration side. It was also found that as the concentration of calcium chloride increases, the concentration of 1 degree hydrochloric acid, at which the solubility of zirconium oxychloride becomes minimum, becomes lower. In this way, when attempting to efficiently recover zirconium by adding hydrochloric acid to a zirconium oxychloride solution to precipitate zirconium oxychloride crystals, in a system where calcium chloride is present in the zirconium oxychloride solution,
This is because the concentration of hydrochloric acid, where the solubility of zirconium oxychloride becomes minimal, shifts to the lower concentration side.

The amount of hydrochloric acid to be added is small, and furthermore, since the liquid from which the crystals have been separated is small in volume and has a low acid concentration, there are advantages such as ease of treatment of the waste liquid.

The zirconium leaching solution according to the method of the present invention is obtained by eluting zirconia a#1, which is mainly composed of zircon/calcium oxide, with an aqueous solution of hydrochloric acid, so calcium chloride is inevitably present. By precipitating zirconium oxychloride crystals and efficiently recovering zirconium, the amount of hydrochloric acid used can be reduced as described above.

Various embodiments can be considered for the operation of adding hydrochloric acid to the zirconium leachate to precipitate zirconium oxychloride crystals according to the method of the present invention. There is a method in which the crystals of zirconium oxychloride are precipitated by slow cooling after addition of calcium oxychloride.Next, the crystals of calcium oxychloride are separated from the mother liquor by a conventional method, and dissolved in a predetermined amount of water to form zirconium oxychloride. Obtain an aqueous solution. The impurity I in the zirconium oxychloride solution obtained in this way is reduced to about ]-/10 in terms of ZrO2 compared to the amount of impurities in the zirconium leaching solution, and Ti, Si-Ai!
, Fe and other impurity concentrations are Z ro 210 as oxides.
It has been purified to less than 500pp compared to 0%.

Furthermore, the mother liquor from which the zirconium oxychloride crystals have been separated can be recycled as part or all of the hydrochloric acid aqueous solution used in the previous step of concentrating the zirconia component and the step of leaching the zirconia in the method of the present invention. This is a major factor in realizing economically advantageous processes such as effective use of hydrochloric acid and reduction in waste liquid treatment, and is one of the characteristics of the present invention.

The zirconium oxychloride crystals obtained in this step can be further purified by conventional industrial operations such as washing or recrystallization.Next, the obtained zirconium oxychloride crystals are dissolved in water, The zirconium C supercompound is precipitated and used as a raw material for the next step of recovering zirconium.

Various embodiments can be considered for the method of producing a precipitate of a zirconium compound from a solution in which zirconium oxychloride is dissolved and recovering this precipitate, but the method of the present invention is not particularly limited, and various methods may be adopted. be able to. Among them, Japanese Patent Application Laid-Open No. 6
The precipitation method disclosed in Japanese Patent No. 164918 is superior.

That is, an insoluble zirconium salt is precipitated by contact mixing of an aqueous zirconium oxychloride solution and sulfuric acid.

Next, the zirconium salt slurry, which has been layered and washed for 1 minute, is neutralized with aqueous ammonia to convert it into zirconium hydroxide.

Through this series of steps, a highly produced zirconium precursor can be obtained even if the aqueous zirconium oxychloride solution is crude.

The zirconium precursor thus obtained is then dried, calcined, and pulverized to obtain zirconia powder by a known method.

Firing is usually performed at a temperature of 200 to 1000°C for 30 minutes to several hours.

The zirconia fine powder obtained by the method of the present invention can be used as it is as a raw material for various sintered bodies, but it is also possible to improve the powder properties by pulverizing it. The pulverization method may be either a dry method or a wet method, and other known methods may be used as desired.

[Examples] The present invention will be specifically described below with reference to Examples, but the method of the present invention is not limited thereto.

Example I Z r The molar ratio of O2 and CaO is 1=3.
After weighing 3 pieces of zircon sand and quicklime and mixing them uniformly,
Melted in an electric furnace. The heating melting temperature of the molten material at this time is 2
First, the temperature was 300° C., and then the melt was quenched with a water stream, dried and ground to obtain a molten product. As a result of analyzing this melted product, ZrO234°85!6, Ca047.7
%, S r Oz 16.9%, and the particle size was found to be less than 150 μι by sieving. Further, in the X-ray diffraction analysis, only the diffraction peak of CnZr0t was identified.

Next, 450 g of water 7.51.35% hydrochloric acid was added to a 101 glass beaker, and while stirring, the molten product was crushed.
0g was added and heated, and kept at 25°C for 2 hours.Next, this slurry was sent door to door, and the ZrO2 concentration in the P solution was measured, and it was 250 pp. Based on the composition analysis result of the molten product. When calculated, the leached form of ZrO2 was 18%.

The leaching residue obtained from each house is mixed with water for 21 hours! Rinse into a beaker, add 450g of 35% hydrochloric acid, and add 500ml of the total amount.
The slurry was then heated with stirring and held at 90°C for 2 hours.Then, the slurry was distributed door to door, and the filter cake was washed to obtain 120On+4 of a zirconium-containing (r;2) effluent. It was measured to be 92%, and calculated from the composition analysis results in the molten product.
The O2 leaching 1- was 98.0%. Note that the leachate contains C8, Fe, A1. (Ti and Si$ impurities are combined)
As a result of quantitative determination, the oxide IQ for Zr○
Ai by calculation! 2oz 0.47%, FC20s 0, 0
8%, Na200.01%, SiO□0.38%,
T i O20 was 34%.

Next, 850 g of 35% hydrochloric acid was added to the leachate while heating it to 75°C in a beaker, and the mixture was heated to 75°C while stirring.
The mixture was gradually cooled to 0.degree. C. to precipitate crystals of zirconium oxychloride. The obtained crystals of zirconium oxychloride were separated from the mother liquor by Buchner filtration, and then dissolved in water to obtain Zr.
A solution of 600 mN with an O□ concentration of 11.20≦ was obtained. As a result of quantifying impurities in the liquid containing this zirconium oxychloride, it was found that Alzo was 0.0 in terms of oxide relative to ZrO2.
4%, ``?c20, 0.01%, Nazo 0, 0
02%, Si○2004%, and TiO20.03%.

Next, put 325 g of this solution and 200 g of water in beaker 11.
Add g and heat while stirring, and when the temperature reaches 50℃,
9g of 98% sulfuric acid was added. When heating was further continued and the temperature reached 80°C, an insoluble precipitate of zirconium was formed. Furthermore, after holding at 80 to 90°C for 1 hour, the reaction was stopped. After solid-liquid separation, ZrO2 in the P solution was analyzed and found to be 11001, indicating that 97.5% of the dissolved zirconium was precipitated.

The insoluble precipitate is separated into solid and liquid, the filter cake is repulped in water, and 13 g of 25% ammonia water is added to neutralize it. The obtained zirconium hydroxide is separated into solid and liquid, and the sulfuric acid that adheres is washed. Roots removed.

Zirconium hydroxide filter cake is 1 in electric open
It was dried at 10°C for 8 hours. The dry powder was loosely aggregated and bulky, and could be easily loosened by finger pressure. This dried product was baked at 850°C for 2 hours. The obtained fired product does not contain any hard agglomerates and is monoclinic zirconia with good dispersibility.The crystal grain size determined by X-ray diffraction is approximately 197 g/cna', and the bulk density is 0.74 g/cna'. The tap density was 1.29 g/cm" and the specific surface area was 23a+2/y.

In addition, the main impurity in Z'02 is ALOt13pp transfer F.
e2Q s 20 ppm, TiO+130 ppm,
There were 10 ppm of CaO and 2220 ppm of Sio.

In addition, the hydrochloric acid concentration of the mother liquor from which the zirconium oxychloride crystals were separated in this operation cycle was 57 mol/l.

Next, in the same manner as in the above operation cycle, zircon sand and quicklime were weighed and mixed uniformly so that the molar ratio of Z r O2 to CaO was 1.3, and then melted in an electric furnace. The heating melting temperature of the molten material at this time was 2300°C.8 Next, a stream of water was applied to the molten material! , quench and dry 25)
A molten product was obtained by crushing.

As a result of analyzing this melted product, Zr02B4.806
, Ca:047.7%, S:0216.9%, and the particle size was 150 μm or less when sieved.

Further, in the X-ray diffraction analysis, only the diffraction peak of CaZrO3 was identified.

Next, add 7.01 g of water to a 101 beaker and 950 g of the above mother liquor.
322 g of the pulverized molten product was added thereto while stirring, and the mixture was kept at 25° C. for 2 hours, and then heated with P.

Transfer the filter cake obtained by door to door to a 21 beaker, add 790g of the above I\: liquid and water to make a total of 2k.
The solution was heated with stirring and held at 90° C. for 2 hours.Then, the treated solution was thoroughly filtered to remove the decomposed product, and 40 g of zirconium-containing leachate 11 was obtained. The Z'0. concentration in the leachate is 9.7%, the leaching rate of zirconia is 98.2% with respect to the molten product, and the zirconium oxychloride concentration in the method of the present invention is It was found that the mother liquor recovered in the crystallization operation could be used in place of 35% hydrochloric acid and would not cause any problems in carrying out the process.

Thereafter, fine zirconia powder was obtained in the same manner as in the operation cycle described above.

The obtained fine powder does not contain any hard agglomerates and is monoclinic zirconia with good dispersibility.The crystal grain size determined by X-ray diffraction is about 215, and the bulk specific gravity is 0.80 g/
cod', tap density 1,30 y,/cm', and specific surface f121 m2/y. In addition, the main impurities in ZrO7 are ALo 320 ppm, Fe20s
1.3 ppm, Ti0zl 30ppm, CaO62
ppm, Sio+200pp-.

[Effects of the Invention] As explained above, the method for producing zirconia of the present invention is to produce zirconia containing hard secondary aggregates with a small particle size by normal industrial operations from the raw material zircon sand containing impurities. There is an excellent effect that high-purity zirconia with good dispersibility and excellent sinterability can be provided industrially at low cost.

High-purity zirconia produced by the method of the present invention can be used for various purposes including as a raw material for fine ceramics, and is extremely useful.

[Brief explanation of drawings]

The figure is a graph showing the solubility of zirconium oxychloride in hydrochloric acid. Patent Applicant: Nihon Kagaku Kogyo Co., Ltd. Melt MJi (23°C) HCD of λ xyzirconium chloride (ZrOCb'8H20). Piutno

Claims (4)

[Claims] 1. (a) A melt generation step of heating and melting a raw material mixture of zircon sand and a CaO-containing raw material and then rapidly cooling it to obtain an acid-soluble melted product; (b) bringing the acid-soluble melted product into contact with a dilute aqueous hydrochloric acid solution; (c) a leaching step in which the zirconium component is dissolved in contact with an aqueous hydrochloric acid solution to recover a zirconium leachate; (d) zirconium oxychloride is extracted from the zirconium leachate. a crystallization separation step of precipitating crystals, separating and collecting the obtained crystals, and recycling a part or all of the recovered mother liquor to the previous step; (e) producing a precipitate of an insoluble zirconium compound from an aqueous solution in which the crystals are dissolved; and (f) a zirconia production step of drying, firing and pulverizing the insoluble zirconium compound to produce zirconia powder. 2. 2. The method for producing zirconia according to claim 1, wherein the step of crystallizing and separating zirconium oxychloride is performed by adding hydrochloric acid to the zirconium leachate. 3. In the zirconium recovery process, the molar ratio H_2SO_4/Z
The method for producing zirconia according to claim 1, wherein sulfuric acid is added so that rO_2 is in the range of 0.2 to 0.6 to insolubilize the zirconium content. 4. 2. A method according to claim 1, wherein part or all of the mother liquor from which the crystals are separated in the zirconium oxychloride crystallization separation step is recycled as part or all of the hydrochloric acid aqueous solution in the zirconium concentration step and/or the zirconium leaching step in the previous step. method for producing zirconia.