AU2004279711B2

AU2004279711B2 - Method for producing aqueous solution of chlorination product of zirconium

Info

Publication number: AU2004279711B2
Application number: AU2004279711A
Authority: AU
Inventors: Atsushi Kumakura; Yasushi Nakajima; Hiroshi Sugii
Original assignee: Daiichi Kigenso Kagaku Kogyo Co Ltd
Current assignee: Daiichi Kigenso Kagaku Kogyo Co Ltd
Priority date: 2003-10-14
Filing date: 2004-10-12
Publication date: 2009-05-28
Anticipated expiration: 2024-10-12
Also published as: JP2005119895A; WO2005035446A1; JP4403451B2; ZA200603819B; AU2004279711A1

Description

-1 SPECIFICATION METHOD FOR PRODUCING AQUEOUS SOLUTION OF CHLORINATION PRODUCT OF ZIRCONIUM 5 TECHNICAL FIELD The present invention relates to a method for producing an aqueous solution of zirconium chloride. BACKGROUND OF THE INVENTION 10 Aqueous solutions of zirconium chloride can serve as a starting material for zirconium compounds such as zirconium oxychloride, zirconium hydroxide, basic zirconium sulfate, etc. Among these, zirconium oxychloride (hereunder sometimes referred to as "ZOC") are particularly useful as starting materials for 15 zirconia ceramics. An aqueous solution of zirconium chloride is usually produced by heat-melting or hydrothermally treating zircon sand together with an alkali agent, subjecting the resultant reaction product (mixture) to immersion in water to dissolve mainly alkali 20 silicate in water, filtering the resultant solution to obtain a cake (dehydrated cake) comprising zirconium hydroxide as a main ingredient, subjecting the resultant cake to extraction using hydrochloric acid to obtain an aqueous solution of zirconium chloride, rendering remaining silica components insoluble, and 25 filtering this remaining silica components. An example of a modification of this production method includes dissolving the cake in concentrated hydrochloric acid at 60*C to 100*C, adding 0.2 to 1.0 g/l gelatin to coagulate and precipitate gelated silica, and filtering silica components. 30 However, this method has drawbacks such as the hydrated silica (gelated silica, insoluble silica) has poor filterability, and dissolved silica components remain in the zirconium chloride aqueous solution. Since it is in a form of gel, the insoluble silica has a large volume, and contains not a little zirconium 35 components. This results in a low recovery of zirconium -2 components. Techniques for overcoming the above problem are disclosed in, for example, Patent Documents 1 and 2. Patent Document 1, discloses a method for producing zirconium 5 oxychloride comprising the steps of i) mixing zirconium silicate fine particles with an alkali and subjecting the resultant to hydrothermal treatment at boiling point or higher temperatures; ii) subjecting the slurry obtained in the hydrothermal treatment step to solid-liquid separation, returning the separated liquid 10 contents to the step in i), dispersing the separated solid contents into water, and conducting heat treatment; iii) dispersing the solid contents obtained by subjecting the heat treated slurry to solid-liquid separation, and neutralizing the solid contents using acid; iv) treating the solid contents 15 obtained by subjecting the neutralized slurry to solid-liquid separation with hydrochloric acid to elute the soluble contents; v) subjecting the slurry that was treated with hydrochloric acid to solid-liquid separation to obtain an acidic aqueous solution of zirconium oxychloride as a separated liquid; and vi) 20 concentrating the acidic aqueous solution to obtain zirconium oxychloride octahydrate by crystallization. Patent Document 2 discloses a method for producing an aqueous solution of zirconium chloride comprising the steps of subjecting a material obtained by treating zircon sand with 25 alkali to immersion in water, and subjecting the cake obtained by filtration to extraction using hydrochloric acid. This method is characterized in that a slurry is obtained by adding water to the cake, hydrochloric acid is added to the slurry while stirring in such a manner that the zirconium chloride concentration in the 30 liquid phase of the resultant suspension calculated as Zr0 2 is 9 to 16 wt %, and the free HCl concentration is 1 to 7 wt %, and filtration is then conducted. By employing the techniques disclosed in these documents, it is possible to obtain an aqueous solution of 35 zirconium chloride or zirconium oxychloride containing little 3 silica. However, the techniques disclosed in these documents have room for further improvement. For example, in the technique disclosed in Patent Document 1, the dispersion cake that has 5 been subjected to alkali decomposition is neutralized using hydrochloric acid, subjected to solid-liquid separation, and then the solid contents thereof is treated with hydrochloric acid to elute the soluble contents by redispersion. Therefore, filtration is conducted three times, this elongates production .0 time, and reduces the yield of product. In the technique disclosed in Patent Document 2, an aqueous solution of zirconium chloride is obtained by neutralizing the dispersion cake that had been subjected to alkali decomposition by slowly adding hydrochloric acid to the dispersion cake at a fixed rate, .5 maintaining the pH of the dispersion cake at neutral, further adding hydrochloric acid, and then subjecting the dispersion cake to solid-liquid separation. The thus-obtained aqueous solution of zirconium chloride contains little silica components and has a high production yield; however, a long time is !0 required to add the hydrochloric acid and extract zirconium. Furthermore, both the techniques disclosed in Patent Documents 1 and 2 require a long time for obtaining an aqueous solution of zirconium chloride and have low production efficiency. [Patent Document 1] Japanese Unexamined Patent Publication 25 No.1991-265519 [Patent Document 2] Japanese Patent No. 3427211 SUMMARY OF THE INVENTION The present invention relates to a method for producing an aqueous solution of zirconium chloride from a material obtained 30 by treating zircon sand with alkali (may be referred to as alkali-treated zircon sand), wherein the aqueous solution of 4 zirconium chloride has less silica content and requires less time for its production than conventional methods. In other words, the present invention relates to a method for producing an aqueous solution of zirconium chloride as 5 described below. 1. A method for producing an aqueous solution of zirconium chloride from a material obtained by treating zircon sand with alkali, wherein the method comprises the steps of: (1) a first step of obtaining a cake by subjecting the LO material to immersion in water and filtration; (2) a second step of preparing a dried intermediate by adding hydrochloric acid to the cake and drying the resultant gel, or adding hydrochloric acid to the cake and spray-drying the resultant slurry before gelling; L5 (3) a third step of preparing a suspension by adding hydrochloric acid to the dried intermediate, wherein the hydrochloric acid is added in such a manner that the liquid phase of the resultant suspension has a zirconium chloride concentration of 5 to 16 mass % calculated as Zr02, and a free 20 HCl concentration of 1 to 10 mass %; and (4) a fourth step of preparing an aqueous solution of zirconium chloride by filtering the above suspension. 2. A method for producing an aqueous solution of zirconium chloride according to Item 1, wherein, in the second step, a 25 dried intermediate having a moisture content of 0 to 15 mass % is prepared by spray drying a slurry at 100 to 300 0 C. 3. A method for producing an aqueous solution of zirconium chloride according to Item 1, wherein, in the second step, a dried intermediate having a moisture content of 0 to 15 mass % 30 is prepared by drying a gel while stirring at 60 to 150 0

C.

-5 4. An aqueous solution of zirconium chloride obtained by the method of any one of Items 1 to 3. The method for producing an aqueous solution of 5 zirconium chloride of the present invention is explained in detail below. The method for producing an aqueous solution of zirconium chloride of the present invention comprises Steps 1-4 as below. 10 (1) A first step of obtaining a cake (dehydrated cake) by subjecting a material (alkali-treated zircon sand) to immersion in water and filtration; (2) a second step of preparing a dried intermediate by 15 adding hydrochloric acid to the cake and drying the resultant gel, or adding hydrochloric acid to the cake and spray-drying the resultant slurry before gelling; (3) a third step of preparing a suspension by adding hydrochloric acid to the dried intermediate, wherein the 20 hydrochloric acid is added in such a manner that the liquid phase of the resultant suspension has a zirconium chloride concentration of 5 to 16 mass % calculated as Zr0 2 , and a free HC1 concentration of 1 to 10 mass %; and (4) a fourth step of preparing an aqueous solution of 25 zirconium chloride by filtering the above suspension. The production method of the present invention is explained in detail by being broken into each step. [The first step] In the first step, a cake is prepared by subjecting a 30 material obtained by treating zircon sand with alkali to water leaching and filtration. There is no limitation to the types of alkali-treated zircon sand (hereunder may be referred to as "alkali-treated substance"), but typically usable are those obtained by 35 subjecting a mixture of zircon sand (Zr-containing sand) and -6 sodium hydroxide (caustic soda) and/or sodium carbonate to a high temperature treatment (alkaline fusion) or hydrothermal treatment. Ingredients of the alkali-treated substance vary depending on the conditions of the alkali treatment, however, in 5 many cases, at least one member selected from the group consisting of sodium zirconate, sodium zirconium silicate, sodium silicate and unreacted zircon sand is used. The reactions presumably caused by the alkali treatment are described below. 1) ZrSiO 4 + 6NaOH Na 2 ZrO 3 + Na 4 SiO 4 + 3H20 10 2) ZrSiO 4 + 2NaOH -+ Na 2 ZrSiO 5 + H 2 0 3) ZrSiO 4 + 2Na 2

CO

3 - Na 2 ZrO 3 + Na 2 SiO 3 + 2CO 2 I 4) ZrSiO 4 + Na 2

CO

3 Na 2 ZrSiO 5 + C02 7 The production method of the present invention can be suitably employed to any type of alkali-treated zircon sand 15 prepared under any alkali treatment conditions. In other words, the production method of the present invention can be suitably employed . to alkali-treated substances other than those exemplified above. The method for leaching alkali-treated substance using 20 water is not limited as long as the alkali silicate contained in alkali-treated substance can be dissolved in water. Examples of such methods include dipping an alkali-treated substance in water, mixing an alkali-treated substance with water, etc. The amount of water used is not limited as long as the alkali silicate can be 25 dissolved to a sufficient degree. The temperature of the water is also not limited and can be suitably selected depending on the type of alkali-treated substance, method of leaching, -amount of water, etc. A cake (dehydrated cake) can be obtained by conducting 30 leaching, and filtering the leached-out substance (a mixture of alkali-treated substance and water) to separate the water in which alkali silicate is dissolved. The components of the resultant cake vary depending on the components of the alkali treated substance as described below. 35 For example, in the case of an alkali-treated substance -7 obtained by the reactions shown by Formula 1) and/or 3), sodium zirconate can be hydrolyzed due to the leaching treatment using water, and zirconium hydroxide and sodium hydroxide (caustic soda) are formed. The amount of water used for leaching is not 5 limited as long as the sodium zirconate can be hydrolyzed to a sufficient degree. Sodium silicate and excess alkali are removed by filtration, obtaining a cake comprising zirconium hydroxide as a main ingredient. The filtration method is not limited and a generally-used methods using a filter press, decompression 10 suction filter, precoat pressure filter, etc., can be employed. A batch operation-type filter and/or continuous filter can be used. If the alkali-treated substance is obtained by the reactions shown in Formula 2) and/or 4), sodium silicate and 15 excess alkali are dissolved in water by conducting water leaching. The amount of water used for leaching is not limited as long as the sodium silicate and excess alkali can be dissolved to a sufficient degree. By conducting filtration, sodium silicate and excess alkali are removed and a cake comprising sodium zirconium 20 silicate as a main ingredient can be obtained. The filtration method is the same as that described above. The resultant cake generally comprises at least one member selected from the group consisting of zirconium hydroxide, sodium zirconium silicate, sodium zirconate and unreacted zircon 25 sand. The ratio of its constituent components is not limited, but generally is about 30 to 50 mass % Zr0 2 , about 3 to 10 mass % Na 2 0, and about 1 to 8 mass % SiO 2 . The water content of the cake is not limited but is generally about 10 to 50 mass %, and preferably about 15 to 40 30 mass %. In the production method of the present invention, it is also possible to obtain an aqueous solution of zirconium chloride by preparing cakes other than those exemplified above and subjecting such cakes to postprocessing. 35 [The second step] -8 In the second step, a dried intermediate is obtained by adding hydrochloric acid to the cake obtained in the first step and drying the resultant gel, or adding hydrochloric acid to the cake and spray-drying the resultant slurry before gelling. In 5 either case, it is also possible to add the cake to hydrochloric acid. As described above, in the second step, a dried intermediate can be obtained by i) adding hydrochloric acid to the cake obtained in the first 10 step and drying the resultant gel, or ii) adding hydrochloric acid to the cake and spray-drying the resultant slurry before it becomes a gel. In either case, the hydrochloric acid concentration is not particularly limited, but it is preferable that the 15 hydrochloric acid be diluted with water. In this case, the concentration of hydrochloric acid is generally about 5 to 16%, and preferably about 8 to 15%. Having a hydrochloric acid concentration of below 5% or over 16% is not preferable because the zirconium extraction ratio (yield) decreases at such 20 hydrochloric acid concentrations (see Fig. 1). The amount of hydrochloric acid to be added is not limited but generally the HCl/Zr0 2 molar ratio is about 1.5 to 2.5, and preferably about 2 to 2.2. When its molar ratio is below 1.5, the SiO 2 /ZrO 2 ratio (i.e., a measurement of the content of SiO 2 , 25 which is an impurity) of the ZOC prepared using an aqueous solution of zirconium chloride obtained by employing the method of the present invention decreases; however, the zirconium extraction ratio (yield) also decreases and is therefore not preferable. When the molar ratio is over 2.5, the SiO 2 /ZrO 2 ratio 30 of ZOC prepared using an aqueous solution of zirconium chloride obtained by employing the method of the present invention decreases and the zirconium extraction ratio increases, but is uneconomical since excess hydrochloric acid remains (see Fig. 2) . In the case of i), as a method for drying the gel, it 35 is preferable to employ a method that can uniformly dry silica -9 sols. Therefore, a method in which the gel is dried while stood still is not preferable because the surface and inside of the gel are dried nonuniformly, and this may result in a low zirconium yield in the later extraction step using hydrochloric acid. In 5 other words, it is preferable that silica sol be uniformly dried and drying methods such as using paddle-type driers, fluid bed type driers, Nautor-type driers, etc., may be employed. It is preferable that the gel be dried while agitating (e.g., stirring). The drying temperature is not limited and is generally 10 about 60 to 150 0 C, and preferably about 80 to 110 0 C. When the drying temperature is unduly low, drying may be unsatisfactory. When the drying temperature is too high, the Zr extraction ratio (yield) in the later extraction step using hydrochloric acid may be diminished. 15 The water content of the dried intermediate obtained by the drying step is not limited but is generally 0 to 15 mass % and preferably about 2 to 8 mass %. When the water content is over 15 mass %, the filterability in a later step is unsatisfactory and therefore not preferable. 20 The drying time is not limited and may be suitably controlled depending on the drying method, drying temperature, etc., so that a dried intermediate having a desirable water content can be obtained. It is preferable that the thus-obtained dried 25 intermediate be pulverized into particles having a particle diameter of about 10 to 200 pm. By pulverizing, it is possible to increase the zirconium extraction ratio by adding hydrochloric acid in the third step. In the case of ii), a slurry is prepared by adding 30 hydrochloric acid to the cake. The concentration of the hydrochloric acid and added amount are as in i). Spray-drying is conducted before the slurry becomes a gel. The spray-drying conditions are not limited and conventional methods can be employed. An example of such conditions are an inlet port 35 temperature being about 100 to 3000C and preferably about 150 to -10 2500C, the number of revolutions of the disc being about 30000 to 50000 rpm, and an outlet port temperature being about 75 to 115 0 C. The average particle diameter of the obtained dried intermediate (fine particles) is not limited but is generally in 5 the range of about 10 to 200 pm. The water content of the dried intermediate is same as in the method i). Note that the method ii) is suitable for industrial production since it can obtain dried intermediate in a shorter time than the method i). In the production method of the present invention, 10 because gel or slurry is once dried to obtain a dried intermediate in the second step, it is possible to increase the deposition ratio of silica in the hydrochloric acid extraction solution and the filterability of the deposited silica particles, etc., in the third step described below. As a result, it is 15 possible to obtain an aqueous solution of zirconium chloride of high purity with little dissolved silica in the fourth step. The reason for this is presumably that polymerization, coagulation, dehydration, etc., of the silica component are accelerated by once forming a dried intermediate, and a SiO 2 polymer having 20 excellent deposition properties and filterability is formed whose structure is different from that of silica particles (SiO 2 - nH 2 0) deposited by employing an extraction conventional method using hydrochloric acid. [The third step] 25 In the third step, a suspension is obtained by adding hydrochloric acid to the dried intermediate. Specifically, hydrochloric acid is added in such a manner that the zirconium chloride concentration in the liquid phase of the resultant suspension is 5 to 16 mass % calculated as ZrO 2 , and the free HCl 30 concentration is 1 to 10 mass %. In the third step, zirconium is extracted by adding hydrochloric acid to the dried intermediate (it is also possible to add the dried intermediate to hydrochloric acid). There is no limitation to the hydrochloric acid 35 concentration; however, it is preferable that the hydrochloric -11 acid be diluted with water. In this case, the hydrochloric acid concentration may be generally about 5 to 16%, and preferably about 8 to 15%. Having a hydrochloric acid concentration in this range can increase the zirconium extraction ratio. 5 There is no limitation to the amount of hydrochloric acid added as long as the zirconium chloride concentration calculated as ZrO 2 in the liquid phase of the resultant suspension is 5 to 16 mass %, and the free HCl concentration is 1 to 10 mass %. If the zirconium chloride concentration is below 5 mass % 10 calculated as ZrO 2 , the volume of the liquid is increased and is therefore not preferable. If the zirconium chloride concentration is over 16 mass % calculated as ZrO 2 , there is a possibility that ZOC crystals are deposited when the liquid temperature is lowered and is therefore not preferable. If the concentration of free HCl 15 is below 1 mass %, the zirconium extraction efficiency is unsatisfactory. If the concentration of free HCl is over 10 mass %, excess hydrochloric acid remains and is therefore uneconomical. The thus-obtained suspension may be directly forwarded 20 to the fourth step (filtration step); however, it is preferable that the suspension be subjected to a heat treatment before filtration. By conducting heat treatment, the zirconium extraction ratio can be increased. The conditions for heat treatment are not limited; 25 however, the temperature of heat treatment is preferably not less than 800C, and more preferably not less than 900C. When the temperature is below 80*C, zirconium extraction ratio may be unsatisfactory. The heating time is preferably not less than 30 minutes and more preferably not less than 1 hour. When the 30 heating time is below 30 minutes, the zirconium extraction ratio may be unsatisfactory. There is no upper limitation to the heating time; however, even if the heating time is prolonged to 2 hours or more, further improvement in the effects cannot be obtained, and therefore the upper limit to the heating time may 35 be about 2 hours from the viewpoint of productivity.

-12 It is preferable that the suspension be cooled to not greater than 70*C after the heat treatment. Cooling the suspension is effective from the viewpoint of decreasing the amount of silica dissolved in the suspension. The lower the 5 cooling temperature, is the lower the solubility of silica. However, if the cooling temperature is too low, ZOC may be deposited, and the viscosity of the suspension becomes high and its filterability may be reduced. Therefore, it is preferable that the cooling temperature be in the range of about 50 to 60*C. 10 [The fourth step] In the fourth step, an aqueous solution of zirconium chloride is obtained by filtering the suspension. In other words, in the fourth step, the suspension is subjected to solid-liquid separation to remove suspended 15 components such as silica, zircon sand (Zr-containing sand), etc. The solid-liquid separation method is not limited and a generally used method using such as a filter press, decompression suction filter, precoat pressure filter, etc., can be employed. A batch operation-type filter and/or continuous filter can be used. 20 The suspension temperature during filtration is not limited but is preferably not greater than 700C and more preferably about 50 to 60'C. For example, in the third step, a suspension is prepared, subjected to a heat treatment, and cooled 25 to not greater than 70*C and preferably about 50 to 600C. The resultant suspension may be subjected to a filtration process in the fourth step while maintaining the same temperature as in the third step. Note that filtration (solid-liquid separation) and 30 removal of silica can be effectively conducted by adding a polymer flocculant to the suspension. Examples of polymer flocculants are cationic esters of polymethacrylic acid, polyamines, nonionic polyacrylamide, polyethylene oxides (hereunder referred to as "PEO"), polyvinyl alcohol, etc. The 35 amount of polymer flocculant added is not limited but is -13 preferably 0.5 to 5 parts by weight relative to 100 parts by weight of SiO 2 . There is no limitation to the method for adding such polymer flocculant, but it is preferable that the polymer flocculant be added in the form of an aqueous solution from the 5 view of dispersibility. The method of the present invention makes it possible to produce an aqueous solution of zirconium chloride with reduced silica content from alkali-treated zircon sand in an effective and efficient manner. 10 In particular, according to a preferable embodiment of the present invention, the time required in producing an aqueous solution of zirconium chloride from alkali-treated zircon sand can be reduced to about 1/3 that of prior art techniques, and therefore the production efficiency (process capability) of the 15 aqueous solution of zirconium chloride can be significantly improved. This method achieves a high zirconium extraction ratio (yield) and the volume of the filtered substance (solid) containing silica is reduced to about 1/5 to 1/3 that of prior 20 art techniques. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows the relationship between Zr extraction ratio (yield) and hydrochloric acid concentration when the 25 hydrochloric acid concentration in the first step is changed to 10, 15 and 25% under the conditions of Example 1. Fig. 2 shows the relationship between the HCl/Zr0 2 molar ratio, when the amount of hydrochloric acid added in The first step under the conditions of Example 1 is changed to 2, 2.1, 2.2 30 and 2.3 in terms of HCl/ZrO 2 molar ratio, and the Si0 2 /ZrO 2 ratio of the ZOC solution obtained by using the resultant aqueous solution of zirconium chloride. Examples 35 The present invention is explained detail below with -14 reference to Examples and Comparative Examples. However, the present invention is not limited to the following Examples. Example 1 5 Frits comprising alkali-treated zircon sand were subjected to leaching using water and then filtered, giving 1000 g of cake (comprising 45 mass % of Zr0 2 and 4.3 mass % of unreacted Zr-containing sand). Subsequently, a diluted solution was prepared by adding 10 1366 g of water to 1634 g of 18% hydrochloric acid (8.06 mol), and the cake obtained by subjecting a material to immersion in water was added to the diluted solution and then stirred, giving a uniform slurry. The slurry was placed in a spray-dryer (hereunder 15 referred to as "SD") at 4 kg/h and dried. The conditions for operating the SD were such that the inlet port temperature was 2000C, the number of revolutions of the disc was 40000 rpm, and the outlet port temperature was 75*C. Thereby, 1183 g of dried intermediate was obtained. The dried intermediate had a moisture 20 content of 4 mass % and a particle diameter of 20 to 30 pm. Water (534 g) and 36% hydrochloric acid (229.7 g) were sequentially placed in a 1 L beaker, and 400 g of dried intermediate (ZrO 2 : 142.2 g) was added thereto in such a manner that the mixture had an HCl/ZrO 2 molar ratio of 2. The mixture 25 was stirred, maintained at 960C for one hour, cooled to 58.50C, and a 5% PEO aqueous solution (55.8 g) was then added thereto. The mixture was stirred for about 10 minutes and subjected to suction filtration using a Buchner funnel (inside diameter of 11 cm). 30 The resultant filtered cake was washed with 9% hydrochloric acid (200 g), collecting 265 g of residue containing silica particles and unreacted Zr-containing sand, and 12-95 g of zirconium chloride aqueous solution comprising 10.95 mass % ZrO 2 wherein SiO 2 /ZrO 2 (weight ratio) was 0.0013, and 3.8 mass % free 35 HCl. The Zr extraction ratio (yield) was 99.7%. Table 3 shows -15 the results. Example 2 After subjecting alkali-treated zircon sand frits to 5 water leaching, the resultant was filtered, obtaining 1000 g of cake (comprising 45 mass % Zr0 2 , and 4.3 mass % unreacted Zr containing sand). Subsequently, 1634 g of 18% hydrochloric acid (8.06 mol) was diluted by adding 1300 g of water, and the cake was 10 added to the resultant diluted solution and then stirred, preparing a gelated product. The resultant gelated product was placed on a hot plate, and dried while stirring at 110*C, giving 1163 g of dried intermediate. The dried intermediate had a moisture content of 15 4.8 mass %. Water (520 g) and 36% hydrochloric acid (226.4 g) were sequentially placed in a 1 L beaker, and 400 g of dried intermediate (Zr0 2 : 137.6 g) was then added thereto in such a manner that the mixture had an HCl/ZrO 2 molar ratio of 2. The 20 mixture was stirred, maintained at 96*C for one hour, cooled to 58.50C, and a 5% PEO aqueous solution (55.8 g) was added thereto. The mixture was stirred for about 10 minutes and subjected to suction filtration using a Buchner funnel (inside diameter of 11 cm). 25 The resultant filtered cake was washed with 9% hydrochloric acid (200 g), collecting 265 g of residue containing silica particles and unreacted Zr-containing sand, and 1239 g of zirconium chloride aqueous solution comprising 11.05 mass % Zr02 wherein SiO 2 /ZrO 2 (weight ratio) was 0.0012, and 3.8 mass % free 30 HCl. The Zr extraction ratio (yield) was 99.5%. Table 3 shows the results. Comparative Example 1 In a 2 L beaker were placed 1000 g of cake (comprising 35 37 mass % Zr0 2 , 41.5 mass % H 2 0, and 9.1 mass % unreacted Zr- -16 containing sand) that had been obtained by subjecting alkali treated zircon sand frits to water leaching and filtration, and 680 g of water, giving a slurry having a pH .of 13 (at 33 C) . To the resultant slurry was added 1215 g of 36% hydrochloric acid at 5 16 g/min while stirring. When the pH of the mixture became 6, addition of hydrochloric acid was stopped, and only stirring was continued for 30 minutes. Thereafter, addition of hydrochloric acid was resumed, and the temperature of the slurry was raised to 90*C when addition of hydrochloric acid was completed. The slurry 10 was maintained at 900C and stirred for 8 hours, and then cooled to 600C. To the heat-treated slurry was added 135 g of 0.5 mass % PEO aqueous solution, the mixture was stirred for 2 hours and then subjected to suction filtration using a Buchner funnel (having an inside diameter of 20 cm). 15 The filtered cake was washed with 550 ml of hot water, giving 457 g of cake comprising silica particles and unreacted Zr-containing sand, and 3344 g of an aqueous solution of zirconium chloride comprising 11 mass % ZrO 2 and 4 mass % free Hl wherein the ratio of SiO 2 /ZrO 2 (weight ratio) was 0.0016. The Zr 20 extraction ratio (yield) was 99.4%. Table 3 shows the results. Comparative Example 2 To a 2 L beaker were sequentially placed alkali treated zircon sand frits, 1000 g of cake (comprising 37 mass % 25 ZrO 2 , 41.5 mass % H 2 0, and 9.1 mass % unreacted Zr-containing sand) that had been obtained by conducting water leaching and filtration, and 500 g of water. The mixture was dispersed and neutralized (pH 6) by hydrochloric acid. Subsequently, the resultant dispersion was subjected to a heat treatment for 2 30 hours and suction filtration using a Buchner funnel (inside diameter of 11 cm), giving 938 g of neutralized cake. The neutralized cake was added to 1290 g of 20% hydrochloric acid solution, and stirred at 90'C for 1 hour. The resultant slurry was cooled to 60 0 C and subjected to suction filtration using a 35 Buchner funnel (inside diameter of 20 cm). The filtered cake was -17 washed with 500 ml of hot water, obtaining 487 g of cake comprising silica particles and unreacted Zr-containing sand, and 2191 g of an aqueous solution of zirconium chloride comprising 10.3 mass % ZrO 2 and 3 mass % free HCl wherein the ratio of 5 SiO 2 /ZrO 2 (weight ratio) was 0.0021. The Zr extraction ratio (yield) was 61%. Table 3 shows the results. Comparative Example 3 To 1215 g of 35% hydrochloric acid were added a slurry 10 prepared by dispersing 1000 g of cake (comprising 37 mass % ZrO 2 , 41.5 mass % H 2 0, and 9.1 mass % unreacted Zr-containing sand) into 680 g of water. The cake had been obtained by subjecting alkali treated zircon sand frits to water leaching and filtration. The resultant mixture was stirred at 900C for 8 hours and cooled to 15 60*C. 135 g of 0.5 mass % PEO aqueous solution was added thereto and the resultant slurry was subjected to filtration under the same conditions as in Example 1. After about 20 g of liquid had been obtained, further filtration became impossible. 20 Examples 3-7 Table 3 shows the results of experiments (Examples 3 and 4) wherein the drying conditions of Example 1 were changed as in Table 1. [Table 1] Moisture content (%) SD drying of Experiment temperature* dried intermediate Example 3 150 5 Example 4 250 1 25 * SD drying temperature indicates "SD inlet port temperature". Table 3 also shows the results of experiments (Examples 5 to 7) wherein the drying conditions of Example 2 were changed as in Table 2. 30 -18 [Table 2] Drying Drying Moisture content Experiment temperature method (%) of dried intermediate Example 5 150 Stirred on 4.8 hot plate Stood on hot Example 6 100 plate 4.6 plate Example 7 80 Stirred on 4 hot plate (Temperature unit: *C) [Table 3] r2Si2ZrO 2 Extraction Relative Experiment concentration SiOt/Zro) time (mass %) (weight ratio) yield () required Example 1 10.95 0.0013 99.7 1 Example 2 11.05 0.0012 99.5 1.6 Example 3 10.87 0.0014 99.6 1 Example 4 11.34 0.0011 99.0 1 Example 5 10.23 0.0010 98.7 1.6 Example 6 10.2 0.0018 92.4 1.6 Example 7 10.31 0.0025 90.5 1.7 Comparative 11 0.0016 99.4 3.4 Example 1 Comparative 10.3 0.0021 61 1.7 Example 2 1 1 5 * Relative time required was calculated by defining the time required in Example 1 as being 1. Industrial applicability The present invention relates to a method for producing 10 an aqueous solution of zirconium chloride having low silica content from alkali-treated zircon sand in an effective and efficient manner. In particular, in a preferable embodiment of the present invention, the time required in producing an aqueous 15 solution of zirconium chloride from alkali-treated zircon sand can be reduced to about 1/3 that of conventional techniques, and therefore the production efficiency (process capability) of aqueous solutions of zirconium chloride can be significantly increased.

19 The present invention exhibits high zirconium extraction yields and can reduce the volume of the filtered substance (solid) containing silica to about 1/5 to 1/3 that of conventional techniques. 5 The aqueous solution of zirconium chloride of the present invention can be suitably used as a material for zirconium oxychloride (ZOC) , which is of use as a starting material for zirconia ceramics. As used herein, except where the context requires otherwise, LO the term "comprise" and variations of the term, such as "comprising", "comprises" and "comprised", are not intended to exclude other additives, components, integers or steps. Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment, or any form of L5 suggestion, that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art.

Claims

1. A method for producing an aqueous solution of zirconium chloride from a material obtained by treating zircon sand with alkali, 5 wherein the method comprises the steps of: (1) a first step of obtaining a cake by subjecting the material to immersion in water and filtration; (2) a second step of preparing a dried intermediate by adding hydrochloric acid to the cake and drying the resultant LO gel, or adding hydrochloric acid to the cake and spray-drying the resultant slurry before gelling; (3) a third step of preparing a suspension by adding hydrochloric acid to the dried intermediate, wherein the hydrochloric acid is added in such a manner that the liquid L5 phase of the resultant suspension has a zirconium chloride concentration of 5 to 16 mass % calculated as ZrO2, and a free HC1 concentration of 1 to 10 mass %; and (4) a fourth step of preparing an aqueous solution of zirconium chloride by filtering the above suspension. 20

2. A method for producing an aqueous solution of zirconium chloride according to Claim 1, wherein a dried intermediate having a moisture content of 0 to 15 mass % is prepared by conducting spray drying of a slurry at 100 to 300 0 C in the second step. 25

3. A method for producing an aqueous solution of zirconium chloride according to Claim 1 wherein a dried intermediate having a moisture content of 0 to 15 mass % is prepared by drying a gel while stirring at 60 to 150 0 C in the second step.

4. An aqueous solution of zirconium chloride obtained by 30 the method of any one of Claims 1 to 3. 21

5. A method according to claim 1, substantially as hereinbefore described with reference to the examples, excluding the comparative examples. 5