CN1114564C

CN1114564C - Technological process of preparing pure cerium hydroxide

Info

Publication number: CN1114564C
Application number: CN99114762A
Authority: CN
Inventors: 张其春
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-04-01
Filing date: 1999-04-01
Publication date: 2003-07-16
Anticipated expiration: 2019-04-01
Also published as: CN1269327A

Abstract

The present invention relates to a technical process for preparing cerium hydroxide (IV). Mixed rare earth chlorides are used as raw materials, and the process comprises the following steps of depositing RE<3+> into RE(OH)3 by adding alkali, oxidizing Ce(OH)3 in mixed rare earth hydrate into Ce(OH)4 by adding oxidizing agents, completely dissolving and converting the depositions of the mixed rare earth hydrate by adding hydrochloric acid into the chloride solution of mixed rare earth, separating cerium hydroxide (IV) grains by adding precipitating agents and/or heating the chloride solution, and filtering and separating the cerium hydroxide (IV) grains to obtain pure cerium hydroxide (IV), wherein the chloride solution contains cerium which is a cerium (IV) compound in a dissolving state. The cerium hydroxide (IV) prepared with the process has the advantages of favorable dissolving performance in nitric acid, low impurity content, high cerium partition larger than 99%, and high oxidation rate larger than 99%.

Description

Process for preparing pure cerium (IV) hydroxide

The invention relates to a process for preparing cerium (IV) hydroxide, in particular to a process for preparing pure cerium (IV) hydroxide with high oxidation rate by taking mixed rare earth chloride containing cerium (III) and non-cerium rare earth as raw materials and carrying out a wet chemical process.

The existing preparation process for extracting cerium from mixed rare earth mainly comprises a process method for separating cerium based on an extraction technology using an organic extractant and a cerium oxidation separation method belonging to a conventional wet chemical process.

The process method for separating cerium from mixed rare earth based on the extraction separation technology using the organic extractant is far from the process method of the invention, and has the problems of needing to use expensive extractants and consuming a large amount of acid.

The basic principle of the cerium oxidation separation method belonging to the conventional wet chemical process is as follows: after the trivalent cerium is oxidized into tetravalent cerium, the tetravalent cerium is much less alkaline than trivalent rare earth ions, so that the tetravalent cerium salt is extremely easy to hydrolyze, and is hydrolyzed into cerium hydroxide to be separated out at the pH value of 0.7-1.0, and other trivalent rare earth ions are precipitated into hydroxide to be separated out at the pH value of 6-8. In addition, tetravalent cerium has a great tendency to form a complex. These characteristics are greatly different from those of trivalent rare earth elements. The existing oxidation separation method for rapidly separating cerium utilizes the characteristics of cerium, firstly, trivalent cerium in mixed rare earth is oxidized into a tetravalent state, and then, tetravalent cerium is separated from trivalent rare earth elements by other chemical methods by utilizing the obvious difference between the chemical properties of tetravalent cerium and trivalent rare earth elements. Common oxidants for oxidizing trivalent cerium include air, chlorine, hydrogen peroxide (i.e., aqueous hydrogen peroxide solution), potassium permanganate, and the like. The oxidation separation method of cerium, which has been adopted in production, includes a wet air oxidation method, and a chlorine oxidation method (see document 1, Zhaoju birch: "rare earth element chemistry", Tianjin scientific and technical Press, 1987: p266-p 268.2 "rare earth" write group: rare earth "book on, Metallurgical Press, 1978: p315-p 328.):

(1) the mixed rare earth hydroxide is mixed into slurry by a wet air oxidation method, the slurry is heated to 85 ℃, compressed air is introduced for oxidation, and Ce (OH) in the slurry is oxidized₃Oxidation to Ce (OH)₄While the hydroxide of the non-cerium rare earth keeps the trivalent valence unchanged. After filtering and washing, the hydroxide of non-cerium rare earth is dissolved preferentially by 10% dilute nitric acid, and the pH value of the solution is controlled to be 4-5 in the dissolving process. Via a solid-liquidSeparating to obtain cerium hydroxide with non-cerium rare earth distribution of 3% -4% and non-cerium rare earth solution with cerium distribution less than 2% -3%.

Obtained Ce (OH)₄By dissolving the above-obtained cerium hydroxide in nitric acid, heating and then adding ammonium nitrate to precipitate ammonium cerium (IV) nitrate [ (NH)₄)₂Ce(NO₃)₆]Thereby further separating from the included non-cerium rare earth; it is also possible to use solvent extraction methods, e.g. with TBP or P_2O4Equal extractant for extracting Ce⁴⁺，The cerium salt obtained is further purified.

(2) Chlorine oxidation processes are commonly used in the industry as an oxidizing agent. The mixed rare earth hydroxide containing trivalent cerium is suspended in water, chlorine is introduced to oxidize the trivalent cerium into tetravalent cerium, and the suspension is changed from weak alkalinity to weak acidity. Due to Ce (OH)₄The alkaline property of the rare earth hydroxide is weak, the rare earth hydroxide is not dissolved in a weak acidic solution, and the rest of the trivalent rare earth hydroxide is gradually dissolved by acid. When the pH value of the solution is controlled to be proper (the pH value is 3.5-4.0), Ce (OH) can be obtained₄Remaining in the precipitate, the remaining trivalent rare earths are dissolved into solution.

The method can also be directly used for separating cerium from mixed rare earth chlorides: when chlorine is introduced into the mixed rare earth chloride solution, the following reactions can occur:

NaOH solution should be added during the reaction process to neutralize HCl generated in the reaction, so that the pH value of the reaction system can be maintained at 3.5-4.0. After long-time chlorine gas oxidation, the trivalent cerium can be basically completely oxidized, and finally a cerium product with the cerium distribution of 90-94% is obtained.

The above-mentioned method for the separation by oxidation of cerium has the disadvantages that the obtained cerium hydroxide product is difficult to filter and the purity of the product is low.

The process for preparing pure cerium hydroxide related to Chinese patent CN1048239A comprises the following steps: using acid aqueous solution containing cerium and rare earth except cerium as feed liquid, firstly adding potassium permanganate as oxidant, and adding carbonate of alkali metal and ammonium or its hydrogen carbonateTo a pH of 1-6, precipitating cerium as cerium (IV) hydroxide; separating the cerium hydroxide from the non-cerium rare earth solution, pulping, adding sodium sulfite and sulfuric acid to reduce and dissolve the cerium hydroxide into Ce₂(SO₄)₃Then adding NaCl or Na₂SO₄With Ce in solution³⁺Combining to generate sodium cerium (III) sulfate double salt precipitate; finally, the separated sodium cerium (III) sulfate double salt alkali is converted into cerium hydroxide by using hot NaOH solution. The processing principle and steps of the process are different from those of the present invention. Because the method uses potassium permanganate as an oxidant and finally uses NaOH to convert the sodium cerium (III) sulfate double salt into cerium hydroxide, the generated cerium hydroxide product can carry and wrap Na⁺、Mn²⁺And SO₄ ^2-So that the cerium hydroxide product obtained by the method cannot be used in occasions with high requirements on the content of impurities, such as the preparation of catalysts for purifying automobile exhaust. In addition, when the sodium cerium sulfate double salt is alkali-converted with NaOH, the resultant cerium hydroxide product is a mixture of cerium (IV) hydroxide and a small amount of cerium (III) hydroxide, and the oxidation rate of cerium is difficult to further increase.

In addition, cerium is separated from raw ore containing rare earth (light rare earth) of cerium group by sodium sulfate fractional precipitation method in production, and the final cerium product is cerium dioxide. The method is to mix the mixed light rare earth concentrate and powdered carbon in advanceThe mixture of sodium acid is roasted, and then leached by dilute sulfuric acid, so that the quadrivalent cerium and otherlight rare earth are dissolved into the obtained acidic leaching solution (the similar method is to directly roast bastnaesite, and then leach by dilute sulfuric acid, and also can obtain similar sulfuric acid solution of light rare earth). In the sulfuric acid solution of the light rare earth, cerium is basically Ce⁴⁺Are present. Due to Ce⁴⁺The precipitate is not easy to form double salt with sodium sulfate, so when sodium sulfate is added into the leaching solution, trivalent rare earth is mainly precipitated in the form of double salt of rare earth sodium sulfate, but a small part of Ce is also generated at the same time⁴⁺Forming double salt precipitate with trivalent rare earth, and mixing with sodium sulfate double salt of trivalent rare earth to form primary double salt (acid leaching-sulfur in the presence of calcined bastnaesite as raw material)In the sodium acid fractional precipitation process, when the method is operated, the cerium partition of the formed primary double salt (namely sigma Ce)_xO_y/∑RE_mO_nThe ratio of) can be controlled to be about 20%). Most of the Ce in the original sulfuric acid leaching solution⁴⁺The filtrate is left after the separation of the primary double salt. Then, ferrous sulfate or hydrogen peroxide is added into the filtrate to obtain Ce in the filtrate⁴⁺Reduction to Ce³⁺Ce as reduction product³⁺Then combined with sodium sulfate in the solution and precipitated as a sodium cerium (III) sulfate double salt, which is called a secondary double salt. The secondary double salt base can be converted into crude cerium hydroxide by the action of hot NaOH solution. The crude cerium hydroxide contains non-rare earth impurities such as iron, thorium, manganese, phosphorus and the like, and cannot be directly utilized. For this purpose, the crude cerium hydroxide is reduced and dissolved by adding hydrogen peroxide to concentrated hydrochloric acid to dissolve the cerium hydroxide into CeCl₃(ii) a The pH of the solution obtained is then adjusted upward with ammonia in order to bring the CeCl₃Fe in solution³⁺、Th⁴⁺Precipitating to obtain hydroxide, filtering, and separating to obtain CeCl₃A solution; from the CeCl with oxalic acid₃In solution, Ce³⁺Precipitating to obtain cerium (III) oxalate, and burning to obtain cerium dioxide. The primary double salt obtained by the fractional precipitation method needs to be subjected to alkali conversion-optimum solution treatment, and a mixed rare earth chloride solution with medium cerium partition (the cerium partition is about 20%) is prepared from the primary double salt. The use of such mixed rare earths with a medium cerium partition is not very large because of their high cerium content. It is also common in industry to subject the solution to a cerium extraction treatment by means of a hydrogen peroxide oxidation process combined with the addition of ammonia, to precipitate the cerium contained therein, so as to reduce the cerium partition of the solution to the permissible range of low-cerium lanthanum-rich rare earth chlorides (. sigma.Ce)_xO_y/∑RE_mO_nLess than 5%). However, since part of the trivalent rare earth is also precipitated by ammonia water during the cerium extraction by oxidation, the loss of the trivalent rare earth is large, the obtained precipitate is a cerium-enriched product with relatively low cerium partition, and the filtering performance of the precipitate is poor.

In view of this, the present invention aims to provide a process for preparing pure cerium (IV) hydroxide which is high in purity, high in oxidation rate, and easily soluble in nitric acid, from a mixed rare earth chloride containing cerium (III) and a non-cerium rare earth, wherein the process is short in process flow, low in treatment cost, easy to operate, and good in separation effect.

The invention adopts a non-extraction wet chemical process, and separates cerium contained in the mixed rare earth chloride in a pure cerium (IV) hydroxide form through precipitation-oxidation-dissolution-reprecipitation steps to achieve the aim.

The technological process of preparing pure cerium hydroxide (IV) with mixed RE chloride solution containing Ce (III) and non-Ce as material liquid includes the following steps:

(1) adding alkali to the feed solution under stirring to include Ce³⁺Inner RE³⁺Precipitate is RE (OH)₃To obtain a solution containing Ce (OH)₃The suspension of (a) is,

(2) adding an oxidizing agent under stirring to oxidize Ce (OH) therein₃Is Ce (OH)₄To obtain a solution containing Ce (OH)₄And a suspension of a mixed rare earth hydroxide precipitate of non-cerium rare earth hydroxide,

(3) slowly adding hydrochloric acid under stirring to gradually decrease the pH value of the suspension until the mixed rare earth hydroxide precipitate is completely dissolved by hydrochloric acid and converted into a mixed rare earth chloride solution, wherein the cerium is a dissolved cerium (IV) compound,

(4) adding a precipitating agent, which is a weakly basic substance, or a weak base, or a salt, to the solution obtained in step (3) under stirring, and/or heating the solution to destabilize the cerium (IV) -containing compound in the acidic solution and gradually separate it out of the solution in the form of cerium (IV) hydroxide particles, thereby finally obtaining a suspension of precipitate of cerium (IV) hydroxide particles,

(5) and (4) filtering the suspension generated in the step (4), obtaining filtrate which is low-cerium lanthanum-rich rare earth chloride solution, and washing a filter cake to obtain a pure cerium (IV) hydroxide product.

The invention described above adds ammonia to a mischlorinated rare earth containing cerium (III) and a non-cerium rare earthIn the feed liquid, the Ce is included³⁺All trivalent rare earth ions in the interior are precipitated in the form of mixed hydroxides of trivalent rare earths to precipitate all RE³⁺Is RE (OH)₃. Then adding an oxidant to oxidize Ce (OH) in the mixed rare earth hydroxide₃Is Ce (OH)₄While the hydroxides of other rare earths than cerium continue to be present in the form of RE (OH)₃The form exists. When hydrogen peroxide is used as the oxidant, Ce (OH) contained in the mixed rare earth hydroxide is used₃Oxidation to cerium (IV) peroxide, followed by decomposition of the peroxide by heating to convert it to Ce (OH)₄. On the basis of this, hydrochloric acid is added to the suspension system, so that when the pH of the solution is lowered to about 2.0, the cerium contained therein is converted into Ce (OH)₄The mixed rare earth hydroxide in the form is completely dissolved and converted into clear and transparent bright red solution. Preferably, hydrochloric acid is further added to adjust the pH of the solution to 0.5-2.0, preferably 0.8-1.2. The cerium contained in the solution is present in the form of a cerium (IV) compound. The solution has certain stability, and can be stored for a long time without turbidity. Adding precipitant into the solution, or heating the solution, or adding precipitant and heating to destroy the stability of cerium (IV) -containing compound in the solution, so that the cerium (IV) contained in the solution is converted into Ce (OH)₄The particles are precipitated from the solution, the solution is made turbid, and the other non-cerium rare earths continue to be in RE³⁺Shape ofThe formula (II) is stably retained in solution. In the subsequent continuous heating process, the conversion process to the cerium (IV) hydroxide gradually becomes complete along with the gradual increase of the pH value of the solution, the cerium content of the solution gradually decreases, and the generated particles of the cerium (IV) hydroxide gradually grow up. When the cerium partition of the solution is reduced to the allowable range of the low-cerium lanthanum-rich rare earth chloride, the reaction is stopped. Filtering to remove non-cerium rare earth solution, and washing the obtained filter cake to obtain pure cerium (IV) hydroxide product. Thereby realizing separation of cerium from non-cerium rare earth and obtaining pure cerium (IV) hydroxide with high oxidation rate.

The alkali in the step (1) is at least one of ammonia water, sodium hydroxide and potassium hydroxide, wherein ammonia water is preferred.

The oxidant in the step (2) is one of air, oxygen, potassium permanganate, potassium chlorate and hydrogen peroxide (namely aqueous solution of hydrogen peroxide), or more than one of the oxidants is used in combination. Wherein, the hydrogen peroxide is the best, because the oxidation effect of the hydrogen peroxide is good and impurity ions can not be introduced.

The weak alkaline substance used for destroying the stability of the solution in the step (4) is urea, or hexamethylenetetramine, or ammonium bicarbonate, the weak base is ammonia water, the salt is sodium sulfate, or potassium sulfate, or ammonium sulfate, and any one of the weak alkaline substance, the weak base and the salt can be used. Wherein, the best is urea, because the price of the urea is lower, the precipitation process of cerium (IV) hydroxide caused by adding the urea into the solution obtained in the step (3) is slow and stable, so that finally formed precipitate particles are compact, the solid content is high, and the purity is good.

In the above-mentioned process of the present invention, in order to reduce the content of impurity ions in the finally obtained cerium (IV) hydroxide product and obtain high-quality cerium (IV) hydroxide, all RE is added in step (1)³⁺When the precipitate is precipitated in the form of hydroxide of trivalent rare earth, it is preferable to use ammonia water; in the step (2), hydrogen peroxide is preferably used as an oxidant, but oxygen or air can also be used as the oxidant, however, in order to enable the oxidation reaction to reach a high oxidation rate, a small amount of hydrogen peroxide is preferably added as a supplementary oxidant even after the oxygen or air is used for oxidation; in step (4), it is preferable to use urea as a precipitant for destabilizing the solution in combination with heating to promote hydrolysis of the urea, thereby ensuring complete precipitation of cerium (IV) and good performance of the resulting cerium (IV) hydroxide product.

In the above-described process of the present invention, step (1) is used for precipitating RE³⁺The amount of the alkali in step (2), the amount of the oxidizing agent in step (2), the end point pH value when the mixed rare earth hydroxide is dissolved in the hydrochloric acid in step (3), and the amount of the precipitating agent for destroying the stability of the solution in step (4) are key parameters. Wherein, when the total amount of rare earth in the mixed rare earth chloride feed liquid is expressed by a form of REMOn and is recorded as TREO, the weight of ammonia water (calculated by 20 percent of ammonia content, the same below) is usedThe amount is 0.5-3.0TREO, preferably 1.2-1.4 TREO. The weight of the hydrogen peroxide (concentration of 28%, the same applies below) is usedThe amount is 0.1-2.0TREO, preferably 0.35-0.40 TREO. When the reaction conditions are optimized, ammonia water and TREO are usedaccording to the weight ratio of 1.2: 1, hydrogen peroxide is used according to the stoichiometric value required for oxidizing all cerium (III) into cerium (IV), namely, when the hydrogen peroxide and TREO are used according to the weight ratio of 0.37: 1, trivalent rare earth ions in the mixed rare earth chloride solution can be completely precipitated into hydroxide of trivalent rare earth, and further Ce (OH) contained in the mixed rare earth hydroxide is added₃Oxidation to cerium (IV) peroxide. When the dosage proportion exceeds the proper dosage proportion, the dosage of the ammonia water and the hydrogen peroxide is further increased, and no adverse effect is caused on the reaction result. When hydrochloric acid is added in the step (3) to dissolve the mixed rare earth hydroxide precipitate in the suspension, hydrochloric acid is preferably continuously added after the dissolution is clear until the pH value of the solution is adjusted to be between 0.5 and 2.0, preferably between 0.8 and 1.2, so that high-quality cerium (IV) hydroxide can be finally prepared. In step (3), the pH value of the solution can also be adjusted without adding hydrochloric acid after the mixed rare earth hydroxide precipitate is completely dissolved by using hydrochloric acid, but the cerium partition of the cerium (IV) hydroxide prepared by the subsequent steps and the CeO of the wet filter cake₂The contents are all lower than the product obtained when the pH is adjusted down to 0.8-1.2. In step (3), the pH of the solution can also be adjusted to below 0.8, which also enables cerium (IV) hydroxide to be obtained via step (4), but with higher precipitant levels and/or longer heating times. The precipitating agent used in step 4 is preferably urea, which is used in an amount of 0.01-0.50TREO, preferably 0.08-0.10TREO, by weight. When combined with heating and urea is used as a precipitator, the obtained cerium (IV) hydroxide has good filtering performance, the solid content of a wet filter cake is high, thecerium partition is high, and the cerium partition of the filtered low-cerium lanthanum-rich rare earth chloride solution also completely meets the requirement (Sigma Ce)_xO_y/∑RE_mO_n＜5％)。

Compared with the prior art, the invention has the following advantages and remarkable effects:

the invention relates to a process for preparing cerium (IV) hydroxide from cerium (III) and cerium (III) hydroxideThe mixed rare earth chloride of cerium rare earth is used for separating out cerium contained in the mixed rare earth chloride in the form of cerium (IV) hydroxide. The process method comprises the following steps: firstly, precipitating mixed rare earth chloride into mixed rare earth hydroxide by using ammonia water; oxidizing the mixed rare earth hydroxide with an oxidizing agent to obtain Ce (OH)₃Oxidation to Ce (OH)₄When hydrogen peroxide is used as the oxidizing agent, Ce (OH) is used₃Oxidizing to cerium peroxide, and heating to decompose and convert the peroxide to Ce (OH)₄(ii) a Then the cerium contained is reacted with Ce (OH) using hydrochloric acid₄Completely dissolving the mixed rare earth hydroxide in the form; finally, the stability of the cerium (IV) -containing compound in the obtained solution is destroyed by a precipitant, and a cerium (IV) hydroxide product with good filtering performance and high purity is precipitated from the cerium (IV) -containing compound, and meanwhile, the obtained filtrate is lanthanum-rich rare earth chloride which does not contain cerium basically. The method has good adaptability to the change of the cerium distribution of the mixed rare earth chloride, and can separate cerium contained in the mixed rare earth chloride with the cerium distribution of 5-75%.

Secondly, when the process is carried out in the step (1), the RE is dissolved fromthe mixed rare earth chloride solution by using ammonia water³⁺When precipitated, obtained RE (OH)₃An amorphous structure, and oxidizing the amorphous structure in step (2) to obtain cerium (Ce), (OH)₄The mixed rare earth hydroxide precipitate in the form of the precipitate maintains the original amorphous structure and has high dissolving activity, so when hydrochloric acid is used for dissolving the mixed rare earth hydroxide obtained in the step (2) in the step (3), when the pH value of the solution is reduced to about 2.0, the cerium contained in the mixed rare earth hydroxide can be dissolved in Ce (OH)₄The mixed rare earth hydroxide precipitate in the form is completely dissolved and converted into bright red clear solution, and then the pH value of the solution is continuously reduced to about 1.0 according to the optimized process conditions. In the dissolving process, hydrogen peroxide is not required to be added, and the solution can contain Ce (OH) with high proportion₄The mixed rare earth hydroxide precipitate is completely dissolved, the acidity of the system is only changed from near neutrality to weak acidity in the process, and the system does not need to enter the range of strong acidity, so that the acid consumption in the dissolving process is small, and the rationality of the process is reflected.

Third, in this bookThe stable solution of cerium (IV) -containing compound obtained in process step (3) of the invention exhibits instability with respect to temperature increase, to pH increase of the solution and to the addition of sulfates, as a result of which Ce (OH) precipitates from the solution₄. When urea is used as a precipitating agent, the urea will slowly hydrolyze as the temperature of the solution increases according to the following formula:

NH formed₃·H₂And O gradually raises the pH value of the solution, so that a compound containing cerium (IV) in the solution is unstable, cerium hydroxide particles are precipitated, the solution is turbid, the bright red clear solution is changed into a reddish brown suspension, and the bright yellow suspension is changed after a short time. After 0.5-2 hours of boiling reaction, the pH value of the solution is increased from about the original pH1 to 2-3, the cerium content of the solution is reduced to below 2%, and in the process, the particles of cerium (IV) hydroxide grow up and the filtering performance is obviously improved.

Among the precipitants used in step (4) of the present invention, urea has outstanding advantages: on heating, the urea is slowly hydrolyzed, and the pH value of the system is gradually increased by the hydrolysis products, thereby destroying the stability of the compound containing cerium (IV) in the solution, and enabling the cerium (IV) to be gradually added with Ce (OH)₄The particles are precipitated from the solution and grow up through a nucleation growth mechanism, so that the product has high purity and good filtering performance. In step (4), NH is introduced into the system by hydrolysis of urea₄ ⁺But NH₄ ⁺NH that has been previously present in the system and is entrained by the cerium (IV) hydroxide product₄ ⁺The use property of the product is not influenced.

Fourthly, because in the step (4), when the cerium contained in the solution is almost completely separated out in the form of cerium (IV) hydroxide, the pH value of the solution is still 2-3 which is far lower than that of rare earth which is not cerium and is precipitated into RE (OH)₃The required pH value, in this case, metal ions such as sodium, calcium, magnesium, aluminum and the like are also stably present in the non-cerium rare earth solution. Due to the hydrogen and oxygen generated by the processEasy filtration and washing of cerium (IV) product to make the non-cerium rare earth solution and metal ion contained in it easy to be filtered and washedThe washing is removed from the filter cake, thereby ensuring a high purity of the cerium (IV) hydroxide product obtained by the present process. Under the optimized condition, the content of metal oxides such as sodium, calcium, magnesium, aluminum and the like in the cerium (IV) hydroxide product obtained by the process is only classified by one hundred thousand. In addition, the cerium (IV) hydroxide product prepared by the method has the advantages of high cerium partition, high cerium oxidation rate, easy dissolution by nitric acid and the like. Under optimized conditions, the CeO of the wet filter cake prepared by the method is utilized₂The content is more than 50 percent, the cerium distribution is more than 99 percent, and the oxidation rate (namely Ce)⁴⁺/(Ce⁴⁺+Ce³⁺) The ratio) is greater than 99%. Drying the obtained wet filter cake at 110 ℃ to obtain light yellow cerium (IV) hydroxide powder, the CeO of the cerium (IV) hydroxide powder₂The content reaches more than 70 percent. An important indicator of the quality requirements of the user for pure cerium (IV) hydroxide is its solubility in nitric acid, which, according to the test standard for the nitric acid solubility of cerium (IV) hydroxide, should be completely clear within 24 hours, by dissolving 50 g of cerium (IV) hydroxide in 88ml of 67% strength nitric acid at 90-100 ℃. Under the above test conditions, cerium (IV) hydroxide prepared using the process of the present invention was dissolved and was completely dissolved when the external heating water bath just boiled.

By way of comparison, in the cerium oxidative separation process which has been adopted in production, the oxidation product is subjected to selective dissolution, i.e., the pH of the solution is adjusted downward to dissolve the non-cerium hydroxide, leaving ce (oh) insoluble under the selected pH conditions of the solution (pH 3.5-4.0)₄Thus, the obtained cerium hydroxide is colloidal and difficult to filter, so that the obtained cerium hydroxide filter cake can wrap a considerable amount of non-cerium rare earth solution and other components which are difficult to remove in the subsequent washing process, and the purity of the cerium hydroxide product obtained by selective preferential dissolution is relatively low.

And fifthly, pure cerium (IV) hydroxide is extracted from the mixed rare earth chloride by a wet chemical preparation technology, the related process flow is short, the equipment is simple, the operation condition is easy to control, the auxiliary materials used in the process are all cheap and easily available common industrial raw materials, and the production cost is reduced. The process method avoids the problems of using expensive extracting agent and consuming a large amount of acid in the organic solvent extraction process, and also overcomes the defects of difficult filtration and low product purity of the cerium hydroxide product obtained by the cerium oxidation separation method adopted in the production. In the occasion of needing cerium dioxide product, the cerium (IV) hydroxide product prepared by the process method is directly calcined to obtain the powdery cerium dioxide, thereby avoiding the trouble that the cerium oxalate is precipitated from the extract liquor by using high-price oxalic acid in the extraction process and then the cerium oxalate is decomposed by calcination to prepare the cerium dioxide.

The cerium (IV) hydroxide product prepared by the method has high purity and high oxidation rate, and the X-ray diffraction pattern of the cerium (IV) hydroxide product is the diffraction characteristic of an amorphous substance, which shows that the cerium (IV) hydroxide productis an amorphous substance, so that the cerium (IV) hydroxide product has good nitric acid solubility and can meet the quality requirements of users on the cerium partition, the oxidation rate, the purity and the nitric acid solubility of the pure cerium (IV) hydroxide. The cerium (IV) salt of the corresponding acid, for example, cerium nitrate, cerium sulfate, etc., can be prepared by dissolving the cerium (IV) hydroxide product with an acid. At the same time, directly burning the cerium (IV) hydroxide product to obtain the cerium dioxide product with high cerium distribution.

The present invention will be further described with reference to examples.

Example 1

The invention relates to a process method for preparing pure cerium (IV) hydroxide, which takes mixed rare earth chloride containing cerium (III) and non-cerium rare earth as raw materials, and the total amount of rare earth in mixed rare earth chloride feed liquid is RE_mO_nThe form is expressed and recorded as TREO, the main rare earth components of the mixed rare earth chloride comprise lanthanum, cerium, praseodymium, neodymium and samarium, and the distribution of the cerium is 47.7 percent. The process comprises the following steps:

firstly, dissolving mixed rare earth chloride in water, wherein the total amount of rare earth in the mixed rare earth chloride solution is RE_mO_nExpressed formally, denoted TREO, formulated as RE_mO_nFeed solution with a concentration of 150 g/l.

(1) Under stirring, 1.2TREO ammonia water is added to precipitate mixed rare earth chloride as mixed rare earth hydroxide.

(2) Then, 0.37TREO hydrogen peroxide is added to oxidize Ce (OH) in the mixed rare earth hydroxide₃Is a reddish brown peroxide. The suspension obtained is heated until the suspension turns from reddish brown to yellow.

(3) Hydrochloric acid is slowly added to the suspension under stirring to dissolve the mixed rare earth hydroxide, during which the turbidity of the suspension gradually decreases, the pH gradually decreases and the color gradually turns red. When the suspension had completely turned clear, the solution had already appeared bright red and had a pH of 1.90. Hydrochloric acid was added to the solution to lower the pH of the solution to pH 1.12.

(4) Adding 0.08TREO urea into the solution under stirring, heating the system, and turning the color of the suspension from red to yellow before and after the solution is boiled. The turbidity deepened during the heating. After about 2 hours of boiling reaction, the pH value is raised to 2.28, and sampling analysis shows that the cerium partition of the filtrate is reduced to 1.66 percent, which belongs to qualified rare earth chloride solution with less cerium and rich lanthanum, and the cerium in the solution is nearly completely precipitated.

(5) The suspension was filtered. The filter cake was then washed with hot water, previously adjusted to a pH of about 2. What is needed isCeO for obtaining wet filter cake of cerium hydroxide₂The content is 55.8 percent, the distribution of cerium is 99.6 percent, and the oxidation rate is more than 99.5 percent.

In this example, the reaction conditions for preparing pure cerium hydroxide from mixed rare earth chlorides as raw materials through precipitation-oxidation-dissolution-reprecipitation steps were tested, and it was found that:

(1) in the presence of ammonia for precipitating RE³⁺Is RE (OH)₃Then, the Ce (OH) in the mixture is oxidized by hydrogen peroxide₃In the case of cerium (IV) peroxide, the reaction medium isalkaline. Converting the peroxide to Ce (OH) upon heating₄Thereafter, the reaction medium is already in near neutral conditions, with a pH value of 5 to 8 and in most cases in the range of pH5.80 to 6.80.

(2) The invention uses hydrochloric acid to dissolve Ce (OH) in the process step (3)₄When the rare earth hydroxide is mixed, the rare earth hydroxide is uniquely dissolvedThe pH value of the solution is reduced to a lower range (about 2.0) to achieve the aim of completely dissolving the mixed rare earth hydroxide prepared in the step (2), and then hydrochloric acid is continuously added to reduce the pH value of the solution to about 1.0. In the pH range of the solution, Ce (OH)₄Cannot be dissolved as Ce⁴⁺Is stable in solution because, under the relevant conditions of the solution, Ce is present in solution⁴⁺The simple ions must be converted thermally according to one of the following two equations:

the first equation shows that Ce is present in the presence of a reducing agent⁴⁺Will be reduced to Ce³⁺. The second reaction reflects Ce⁴⁺Is easily hydrolyzed when the pH value of the solution is 0.7-1.0, and generates Ce (OH)₄And (4) precipitating. However, in step (3), the cerium contained in the cerium-containing solution is dissolved in hydrochloric acid to form Ce (OH)₄In the form of mixed rare earth hydroxides, despite Cl^-Reducing at low pH, but no Cl is present during the dissolution₂The bright red clear solution containing cerium (IV) obtained after dissolution still has sufficient stability at pH>1. Once a solution of this type with a pH of 1.86 was sealed, after 30 days of storage, the solution remained without any clouding and any change in color. The above-mentioned stability of the cerium (IV) -containing solution obtained in step (3) negates Ce (OH)₄Is Ce⁴⁺The simple ionic form of (a) is present in the solution.

It now appears that the cerium present as Ce (OH) for the cerium prepared in step (2)₄The mixed rare earth hydroxide exists in the form that in the clear solution obtained after dissolving the mixed rare earth hydroxide with hydrochloric acid in the step (3), the compound containing cerium (IV) may exist in two forms: ce⁴⁺Or cerium (IV) hydroxide sol particles. The numerous phenomena associated with this observed in the individual experiments cannot simply support which form of presence.

(3) Under the conditions adopted in step (4), the pH value of the solution is gradually increased due to the decomposition of urea, the stability of the cerium (IV) -containing compound in the solution is destroyed, and cerium (IV) -containing compound is gradually precipitated from the solution in the form of cerium hydroxide particles, so that the cerium partition of the solution is gradually reduced. In the early stage of the reaction in this step, the precipitated cerium (IV) hydroxide particles are fine and very difficult to filter. Along with the increase of the heating time, the particles of the cerium (IV) hydroxide grow gradually, and the sedimentation performance of the particles is improved. When the cerium partition of the solution falls below 5% during the reaction, the cerium (IV) hydroxide particles formed are sufficiently coarse that they rapidly settle once agitation is stopped. Therefore, when the optimum conditions are adopted, the cerium (IV) hydroxide product finally obtained in step (4) is excellent in filtration performance and easy to wash.

(4) The cerium (IV) hydroxide product obtained in step (5) is washed with aqueous ammonia,and may have Cl^-The content is reduced to below 0.01%. After washing, the CeO of the wet filter cake is obtained here₂The content was 64.7%. Drying the filter cake at 110 deg.C to obtain light yellow loose cerium (IV) hydroxide powder, CeO₂The content reaches 74.3 percent. The cerium (IV) hydroxide powder has good solubility in nitric acid.

Example 2

The invention discloses a process for preparing pure cerium (IV) hydroxide, which has the raw materials and process steps similar to those of example 1, but in step (2), firstly, a steel cylinder is used for oxygen bubbling oxidation for 4 hours under the stirring condition, and then, hydrogen peroxide which is 0.1 time of TREO is added for supplementary oxidation so as to improve the Ce (OH) content₃The oxidation rate of (c).

CeO of the obtained wet cake₂The content is 56.2%, the distribution of cerium is 99.4%, and the oxidation rate is more than 99.5%.

Example 3

The raw materials and the process steps of the process for preparing pure cerium (IV) hydroxide are similar to those of example 1, but ammonium sulfate is used as a precipitating agent in the step (4). Immediately after the addition of ammonium sulfate, the solution clouded and the suspension turned yellow in color. AddingThe suspension was heated, and after maintaining the boiling state and reacting for 2 hours, it was filtered. The filtration rate was much lower than in example 1. The obtained filtrate is a rare earth chloride solution with less cerium and rich lanthanum, and the cerium distribution of the rare earth chloride solution is 2.15 percent. CeO of the wet cake₂The content is 22.6 percent, and the distribution of cerium is 87.2 percent.

Example 4

The raw materials and the process steps of the process for preparing pure cerium (IV) hydroxide are similar to those of example 1, but the step (4) adopts sodium sulfate as a precipitator, and the solution immediately turns into yellow after the sodium sulfate is added. The suspension was heated, and after maintaining the boiling state and reacting for 2 hours, it was filtered. The obtained filtrate is a rare earth chloride solution with less cerium and rich lanthanum, and the cerium distribution of the rare earth chloride solution is 3.78 percent. CeO of the obtained wet cake₂The content is 34.9 percent, and the distribution of cerium is 94.7 percent.

Repeated experiments show that the sodium sulfate used as a precipitant has various effects (filtering performance of the product, cerium partition of the product, CeO of the wet filter cake)₂Content, etc.) are superior to those using ammonium sulfate, but still far inferior to those using urea as a precipitant. In addition, when sulfate is used as the precipitating agent, SO is brought into the cerium (IV) hydroxide product₄ ^2-It is difficult to elute. Due to the high required cerium (IV) hydroxide product vs SO₄ ^2-Is below 0.01%, and therefore, when it is desired to obtain cerium (IV) hydroxide products having the desired high purity, it is not desirable to use sulfate as a precipitating agent.

Example 5

The raw materials and the process steps of the process for preparing pure cerium (IV) hydroxide are similar to those of example 1, but the step (4) adopts (1+4) ammonia water as a precipitator. Upon addition of a small amount of ammonia, the solution immediately became cloudy and turned yellow. The pH of the solution was gradually adjusted to 4.16 by the addition of ammonia to enhance the filtration properties of the resulting suspension. After heating the suspension to boiling, a sample was taken and analyzed, andthe cerium fraction of the filtrate was 1.79%. The bulk suspension was filtered after about 2 hours of boiling reaction. This filtration rate was slower than in example 3. The obtained filtrate is low inThe cerium of the cerium-rich lanthanum rare earth chloride solution is 1.56 percent. The CeO of the wet filter cake is obtained after the filter cake is repeatedly dispersed and washed twice₂The content is 19.6 percent, and the distribution of cerium is 94.0 percent. This indicates that ammonia is not an ideal precipitant. The reason for this is that the alkalinity of ammonia is stronger than that of urea, the addition of ammonia will quickly raise the pH of the solution obtained in step (3), so that the cerium (IV) containing compound will be quickly destabilized, cerium (IV) will be precipitated from the solution in the form of cerium (IV) hydroxide particles, and since this action will tend to be complete in a short time, there is no proliferation growth process in which the particles gradually precipitate from the solution when urea is used as a precipitant and the precipitated particles are nuclei in the early stage, so that the cerium (IV) hydroxide particles formed therein will not easily grow, and thus the filtration performance of the suspension is poor and the moisture content of the filter cake is high.

Example 6

The raw materials and the process steps of the process for preparing pure cerium (IV) hydroxide are similar to those of example 1, but ammonium bicarbonate is adopted as a precipitating agent in the step (4). After a small amount of ammonium bicarbonate was added, the solution turned yellow-turbid immediately. And continuing to slowly add the ammonium bicarbonate until the suspension is light yellow and the pH value of the solution reaches 2.10, and continuing to supplement the ammonium bicarbonate until the pH value of the solution reaches 2.74. After heating the suspension, maintaining it at boiling for 2 hours,the pH of the solution rose to 3.29 during this time. The filtration rate was still slow this time, similar to example 5. The cerium content of the filtrate was 4.48%. After the filter cake is repeatedly dispersed and washed, CeO is obtained₂The content is 22.3 percent, and the distribution of cerium is 95.4 percent.

Example 7

The raw materials and the process steps of the process for preparing pure cerium (IV) hydroxide are similar to those of the example 1, but the precipitant is not added in the step (4), and the stability of the clear solution obtained by dissolving the precipitate in the hydrochloric acid in the previous step is destroyed only by heating. When the clear solution was heated to boiling, the solution turned yellow-turbid. After 2 hours of boiling reaction, the pH of the solution increased from 0.88 to 1.06. The filtrate was reddish yellow with a cerium partition of 12.9% being the highest in each example.The CeO of the wet filter cake is obtained after the filter cake is repeatedly dispersed and washed₂The content is 41.1%, the cerium distribution is 97.5%, and the oxidation rate is 99.3%. This example shows that heating alone is not sufficient to completely destabilize the cerium (IV) -containing compound in the solution obtained in step (3), and that after the same heating time as in the previous examples, a considerable amount of cerium still does not precipitate out of the solution.

This example relies on heating alone to destabilize the cerium (IV) containing compound in solution in step (4), also obtaining cerium (IV) hydroxide with a high oxidation rate; in examples 1, 2, the urea used as a precipitant in step (4) did not have any oxidizing property, and cerium (IV) hydroxide having a high oxidation rate was also precipitated from the solution. Considering that in step (4), no other oxidizing agent is added, except for the oxidizingproperty of the small amount of air brought in by the contact of the liquid surface with the atmosphere, and the lower pH range actually involved in step (4), these conditions are not favorable for oxidizing trivalent cerium into tetravalent cerium having a high oxidation rate. Therefore, the fact that the process is capable of producing in step (4) a cerium (IV) hydroxide product having a high oxidation rate is due to the fact that in step (3) the cerium contained is dissolved by hydrochloric acid to form Ce (OH)₄When the mixed rare earth hydroxide exists in the form, the cerium exists in the form of a cerium (IV) compound in the generated bright red clear solution, namely, after the cerium in the system is converted into the cerium (IV) valence state through hydrogen peroxide oxidation in the step (2), the existing form of the cerium (IV) -containing compound is changed in the steps (3) and (4), and the valence state of the formed cerium (IV) is not changed.

Example 8

The process for preparing pure cerium (IV) hydroxide of the invention has the process steps similar to example 1, but the mixed rare earth chloride raw material used is different from example 1, samarium and neodymium in the mixed rare earth chloride raw material are extracted, so that the mixed rare earth chloride only takes lanthanum, cerium and praseodymium as main rare earth components and has the composition of La, cerium and praseodymium₂O₃＞32％，CeO₂＞60％，Pr₆O₁₁3 to 7 percent. Because the cerium distribution of the mixed rare earth chloride is obviously increased, the steps are carried outThe amount of hydrogen peroxide used in step (2) is correspondingly increased to 0.5 times the total amount of TREO in the treated mixed rare earth chloride.

CeO of the obtained wet cake₂The amount was 52.7% and the cerium partition was 99.1%.

Example 9

The invention relates to a process method for preparing pure cerium (IV) hydroxide, which extracts cerium (IV) hydroxide from mixed rare earth chloride with medium cerium distribution through precipitation-oxidation-dissolution-reprecipitation steps and simultaneously obtains low-cerium lanthanum-rich rare earth chloride. The mixed rare earth chloride raw material used was different from that of example 1. The mixed rare earth chloride solution with medium cerium partition is obtained by hot-dipping and roasting bastnaesite with sulfuric acid, separating primary double salt from the obtained sulfuric acid leaching solution by adopting a sodium sulfate classification method, and then carrying out alkali conversion-optimum dissolution on the double salt. Since the cerium partition of the mixed rare earth chloride with the medium cerium partition is only 21.8%, in order to reduce the using amount of ammonia water, the steps (1) and (2) are changed into the following steps: according to a hydrogen peroxide oxidation method using ammonia water in combination, which is generally used in industry, hydrogen peroxide is added to a solution, and ammonia water is added to maintain the pH value of the solution at about 5, so that Ce contained in the solution is reduced³⁺Cerium peroxide, which oxidizes and hydrolyzes to reddish brown, precipitates, and when the cerium partition of the solution drops to 1.37%, the oxidation is stopped, and the suspension is heated to turn the reddish brown precipitate to yellow. Then, the cerium (IV) hydroxide is precipitated from the solution through dissolution-reprecipitation by sequentially treating according to the steps (3), (4) and (5) of the present process. The cerium content of the filtrate was 3.85%. CeO of the obtained wet cake₂The content is 54.5 percent, and the distribution of cerium is 98.9 percent. The method for extracting cerium from the mixed rare earth chloride with medium cerium distribution overcomes the defects of the existing hydrogen peroxide oxidation method, and the obtained precipitate has good filtering performance and high cerium product purity.

Claims

1. The technological process of preparing pure cerium hydroxide (IV) with mixed RE chloride solution containing cerium (III) and non-cerium RE as material liquid features the following steps:

(1) adding alkali into the feed liquid under stirring to obtain a solution containing Ce (OH)₃The suspension of (a);

(2) adding an oxidizing agent under stirring to obtain a mixture containing Ce (OH)₄And a suspension of a mixed rare earth hydroxide precipitate of a non-cerium rare earth hydroxide;

(3) slowly adding hydrochloric acid under stirring to gradually reduce the pH value of the suspension until the mixed rare earth hydroxide precipitate is completely dissolved by the hydrochloric acid and is converted into a chloride solution of the mixed rare earth;

(4) adding a precipitating agent into the solution obtained in the step (3) under stirring, and/or heating the solution, wherein the precipitating agent is a weak alkaline substance, a weak base or a salt, and finally obtaining a suspension containing the precipitate of the cerium (IV) hydroxide particles;

2. The process for preparing pure cerium (IV) hydroxide as claimed in claim 1, wherein said alkali in step (1) is at least one of ammonia, sodium hydroxide and potassium hydroxide.

3. The process for preparing pure cerium (IV) hydroxide according to claim 1, wherein the oxidant in step (2) is at least one of air, oxygen, potassium permanganate, potassium chlorate and hydrogen peroxide.

4. The process for preparing pure cerium (IV) hydroxide according to claim 1, wherein the oxidant added in step (2) is hydrogen peroxide, and then heating is carried out.

5. The process for preparing pure cerium (IV) hydroxide according to claim 1, wherein the weakly basic substance in step (4) is urea, hexamethylenetetramine or ammonium bicarbonate, the weak base is ammonia water, and the salt is sodium sulfate, potassium sulfate or ammonium sulfate.

6. The process for preparing pure cerium (IV) hydroxide according to claim 1, wherein the weight of the ammonia water (ammonia content: 20%) is 0.5-3.0% of the total amount of the rare earth, the weight of the hydrogen peroxide (concentration: 28%) is 0.1-2.0% of the total amount of the rare earth, the weight of the urea is 0.01-0.50% of the total amount of the rare earth, and the final pH value of the solution in the step (3) is 0.5-2.0, calculated on the basis of the total amount of the rare earth in the mixed rare earth chloride feed solution.

7. The process for preparing pure cerium (IV) hydroxide according to claim 1, wherein the weight of the ammonia water (ammonia content: 20%) is 1.2-1.4 of the total amount of the rare earth, the weight of the hydrogen peroxide (concentration: 28%) is 0.35-0.40 of the total amount of the rare earth, the weight of the urea is 0.08-0.10 of the total amount of the rare earth, and the end point pH value of the solution in the step (3) is 0.8-1.2, calculated according to the total amount of the rare earth in the mixed rare earth chloride feed liquid.