GB1568349A

GB1568349A - Magnetic adsorbent and method for production thereof

Info

Publication number: GB1568349A
Application number: GB10116/78A
Authority: GB
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1977-03-15
Filing date: 1978-03-14
Publication date: 1980-05-29
Also published as: DE2810995C2; DE2810995A1

Description

(54) MAGNETIC ADSORBENT AND METHOD FOR PRODUCTION THEREOF (71) We, HITACHI, LTD., a corporation organized under the laws of Japan, of 5--1, l-chome, Marunouchi, Chiyoda-ku, Tokyo, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a magnetic adsorbent and a method for the production thereof, and more particularly to a magnetic adsorbent having a good magnetism, an easy separation of solid-liquid when employed in a slurry state, and a good adsorbability, applicable to removal or recovery of valuable metals in industrial waste water, or sea water by selective adsorption thereof, particularly to extraction of uranium from sea water.

Recently, demand for uranium as a nuclear fuel is increasing year by wear owing to the development of the atomic industry. However, the uranium resource in the earth's crust is not so abundant, and it is the doubtless fact that the continued expansion of the atomic industry will have consumed all the uranium resource within the near future. In this connection, various attempts have been made to establish a stable supply of uranium, among which a process for extracting uranium from sea water is the most promising one. That is, sea water contains about 3 ,ug/l of uranium, and there is 4,000,000 tons of uranium in total in the sea water on the earth. Thus, an efficient extraction of uranium from the sea water means that an endless uranium source has been assured. On the other hand, recovery of uranium from waste water in refinery plants or from effluent liquids from reprocessing plants is very useful from the viewpoint of environmental problems as well as resource problems.

Many processes have been proposed so far for extracting uranium from sea water or low concentration uranium solutions, for example, by adsorption, coprecipitation, bubbling separation, solvent extraction, or biological concentration, among which the adsorption process is deemed to be most practical. It is adsorbents that play an important role in the adsorption process. That is, the adsorbents must have such properties as have not been required in the ordinary adsorbents, for example, higher selectivity and higher adsorbability owing to the low uranium concentration of sea water. Thus, it is an important point to produce an adsorbent having a high selectivity and a high adsorbability.

As the uranium adsorbent, hydrous titanium oxide, galena, magnesium oxide, etc. have been so far proposed, and hydrous oxides such as said hydrous titanium oxide, are regarded as promising. However, these prior art adsorbents have a low adsorbability, making an adsorption apparatus larger in scale, or such other problems as lowering in percent adsorbability and dissolution of the adsorbents themselves due to the pH of the uranium solutions, or difficulty in preparing the adsorbents. In the case of the extraction from sea water, it is an important factor in view of the use of a large amount of an adsorbent that the adsorbent must be cheap.

In this connection, adsorbents comprising titanium as an essential component have been recently proposed for extraction of uranium and other heavy metals, for example: Japanese Kokai (Laid-open) Patent Application No. 54818/76 discloses the use of titanium compound in combination of pentavalent arsenic compound.

Japanese Kokai (Laid-open) Patent Application No. 28489/71 discloses the use of hydrous titanium oxide supported on a solid carrier of at least one of oxides, sulfide, or phosphate of Mg, Pb, Mn, Zn, Fe, Zr and Cb.

Japanese Kokai (Laid-open) Patent Application No. 29480/77 discloses a preparation of adsorbent comprising titanium compound on a carrier by treatment of the impregnated carrier in ammonia gas.

These prior arts have such disadvantages as use of toxic material, arsenic compound, and the amounts of uranium extracted are not so high.

Most of the adsorbents used in adsorption of metal ions in solutions, removal of heavy metals in waste effluent solutions and recovery of useful metals such as uranium from sea water are employed in a powdery state to enhance their adsorption rate. In that case, the largest disadvantage is an extreme difficulty in solid-liquid separation of slurry. That is, the powdery adsorbent is separated from the solution after the adsorption by settling or centrifuge, but the separation by settling requires much time and also an equipment of a larger size, whereas the separation by centrifuge requires a centrifugal separator of larger size, though the separation time is shortened. The settling or centrifuge can suffice, so long as the adsorption is carried out in a small amount, but an enormous amount of time and expense is required in the separation by settling or centrifuge when the adsorption is carried out in a very large amount such as is the case of the extraction of uranium from sea water. It has been deemed impossible to use powdery adsorbents in the adsorption in such a very large amount, and thus a fixed bed type process using larger particle sizes of adsorbent has been proposed.

However, the use of the adsorbent of larger particle size in the fixed bed type process reduces the adsorption rate, necessitating a larger amount of the adsorbent, and consequently making the apparatus larger in scale and the cost higher. Furthermore, the adsorbent is liable to be disintegrated in the course of its service owing to a low mechanical strength of the adsorbent and flow out together with sea water, eventually causing a problem of secondary environmental pollution.

An object of the present invention is to overcome said disadvantages of the prior art and provide an adsorbent having an easy separability of solid-liquid when used as a powdery adsorbent in a slurry adsorption process, and a higher adsorbability.

The present invention is based on such a finding that, as a result of search for excellent adsorbents for extraction of uranium from sea water, adsorbents prepared by coprecipitation from an aqueous solution of water-soluble ferrous salt and a water-soluble salt of such metal as titanium or aluminium, by addition of an alkali thereto have a high adsorbability and a good magnetism. That is, in the present invention, the adsorbent is used in a powdery state to increase an adsorption rate, and endowed with a magnetism to facilitate a solidliquid separation when used in a slurry state.

The present invention provides a magnetic adsorbent, which comprises a composite material of ferromagnetic oxide as a first component and at least one of hydrous oxides of titanium, aluminium, ferric iron, lead, manganese, zinc, tin, chromium, zirconium, silicon, and rare earth element as a second component, at least a portion of the ferromagnetic oxide being in a form of at least one of Foe, 04 and y-Fe2O,, and a method for the production thereof, which comprises mixing a water-soluble ferrous compound as a first component with at least one of watersoluble compounds of titanium, aluminium, ferric iron, lead, manganese, zinc, tin, chromium, zirconium, silicon, and rare earth element as a second component in the presence of water, adding an alkali to the resulting aqueous solution, thereby forming a magnetic material of ferromagnetic oxide and at least one of hydrous oxides of titanium, aluminium, ferric iron, lead, manganese, zinc, tin, chromium, zirconium, silicon and rare earth element by precipitation.

The water-soluble ferrous compound used in the present invention can be the ordinary ferrous salts, such as ferrous chloride, and ferrous sulfate, which can be converted to magnetic materials Fe304 and y-Fe203 by addition of an alkali. The water-soluble compounds of titanium, aluminium, ferric iron, lead, manganese, zinc, tin, chromium, zirconium, silicon, and rare earth element used in the present invention can be the ordinary chlorides, sulfates, or nitrate thereof, but the compounds having a higher solubility in water are desirable. That is, they include titanium tetrachloride, titanium sulfate, titanium tetrabromide, titanium alkoxide, aluminium chloride, ferric chloride, manganese chloride, lead nitrate, zinc chloride, stannic chloride, chromium nitrate, zirconium chloride, sodium silicate, lanthanum nitrate, and ceric nilrate.

As the alkali for forming precipitates of the present composite material of hydrous oxides, caustic soda, caustic potash, sodium carbonate, or ammonia, can be used.

The preferable rare earth elements in the present invention are lanthanum and cerium.

The preferable composite material in the present invention is a composite material comprising ferromagnetic oxide and hydrous titanium oxide, and more particularly a composite material having an atomic ratio of titanium to iron of 0.3-20:1 in view of their adsorbabilities. That is, it has been found in the adsorbent of the present invention comprising a composite material of ferromagnetic oxide and hydrous titanium oxide that a good adsorbability, especially a peculiarly distinguished selectivity and adsorbability for uranium, is obtained in an atomic ratio of titanium to iron of 0.3-20:1 in the composite material.

At least a portion of the ferromagnetic oxide in said composite material takes a form of at least one of Foe,04 and y-Fe20s, and thus the present adsorbent has a magnetism.

These facts are not observable in single oxide of titanium or iron, or a mere mixture thereof, and it seems that such peculiarly distinguished adsorbability can be obtained by forming the composite material.

The present composite material comprising ferromagnetic oxide and hydrous titanium oxide is prepared by mixing a water-soluble titanium compound with a water-soluble iron compound in an atomic ratio of titanium to iron of 0.3-20:1 in the presence of water, then slowly adding an alkali thereto, thereby precipitating a composite material thereof, filtering the resulting precipitates, and washing and air-drying the precipitates. The precipitates of the composite material have a magnetism, as described above, and are dense, so that they be readily separated from the solution such as sea water.

The water-soluble titanium compound used in the present invention includes, for example, titanium tetrachloride, titanium sulfate, titanium tetrabromide, and titanium alkoxide.

The adsorbability of the composite material comprising ferromagnetic oxide and hydrous titanium oxide depends upon the temperature and pH for the precipitation by alkali addition. That is, in mixing the water soluble titanium compound with the water-soluble iron compound in an atomic ratio of titanium to iron of 0.3-20:1 in the presence of water, and adding the alkali thereto, thereby forming the precipitates of the composite material of ferromagnetic oxide and hydrous titanium compound, it is necessary to maintain the pH at 7-12 and the temperature at 300--700C.

When ammonia is used as the alkali, it has been found that precipitates having a higher adsorbability can be obtained when an ammonia gas diluted with air or nitrogen is introduced as an alkali into an aqueous solution of water-soluble titanium compound and water-soluble ferrous compound than when other alkali is added thereto, under the same pH and temperature conditions as those for the addition of other alkali. It seems that this is because reaction of hydroxyl ions with metal ions takes place slowly as a result of gasliquid contact of the ammonia gas with the aqueous solution of water-soluble titanium compound and water-soluble ferrous compound, and consequently uniformly fine precipitates are formed in the aqueous solution and grow into crystalline particles having larger particle sizes.

The composite material of the present invention can be supported on an inert porous carrier. That is, since a specific surface area of metal oxide or hydrous metal oxide is usually so small that the adsorbability of the metal oxide or hydrous metal oxide is low, a distribution of the metal oxide or hydrous metal oxide can be improved by supporting it on a porous inert carrrier having a large specific surface area, thereby effectively utilizing the effective components and simultaneously improving its mechanical strength.

The adsorbent of the present invention in which the composite material is supported on a porous inert carrier is produced as follows: Finely pulverized porous carrier is dipped in an aqueous solution containing, for example, ferrous chloride as a first component and a water-soluble compound of other metal as a second component and left standing therein until it is impregnated with the solution thoroughly even to insides of pores. Then, the impregnated carrier is dipped in, for example, aqueous ammonia or an aqueous coustic soda solution to precipitate ferromagnetic oxide and hydrous oxide of the second component metal within the carrier, then washed with water, and air-dried or dried below 200"C. The resulting absorbent has a magnetism.

In place of dipping the carrier in the mixed aqueous solution of ferrous chloride and the water-soluble compound of the second component, the carrier can be dipped in an aqueous solution of ferrous chloride and successively in an aqueous solution of the watersoluble compound of the second component, separately. However, the resulting adsorbent has an adsorbability and magnetism substantially equal to those of the adsorbent prepared by the dipping in the mixed solution, and thus in view of the simplicity in operation, the dipping in the mixed solution is preferable.

Porous inert carrier having a large specific surface area, preferably 200 m2/g or higher, is used in the present invention, and includes commercially available alumina, silica, activated carbon, and zeolite. As the alkali, an aqueous solution of caustic soda, ammonia, or the like, can be employed, but a gas such as ammonia gas is preferable for the following reasons: The aqueous alkali solution occasionally fails to go into the pores of the carrier fully or forms precipitates only on the surface of carrier. That is, the active components are not deposited on the inside surfaces of the pores. On the other hand, ammonia gas can readily enter into pores of the carrier because of its smaller molecules, and thus the active components can be fully deposited even on the inside surfaces of pores.

The precipitating agent must be the alkali for the ferrous compound, but in case of other metal components, their activity can be endowed by hydrolysis or decomposition by heating, and thus the other metal components can be precipitated by steam blowing or only by heating in the solution.

When a hydrous oxide type adsorbent is desired, air drying is preferable.

The precipitates of hydrous oxides deposited by the alkali addition are filtered, washed with water, and air-dried, whereby an adsorbent having a magnetism can be obtained.

The water-washed precipitates can be aged in hot water under such a hydrothermal condition as 1500C and 6 atmospheres in an autoclave before the air drying, whereby the composite material can undergo crystallization to improve its adsorbability and lower its solubility in water. However, the ageing above 3000C is not preferable, because the composite material is completely crystallized and its adsorbability is lowered.

In the present invention, a ferromagnetic oxide such as y-Fe2O, or Fe,04 can be used as the carrier. That is, as the first component, ferrous component has a magnetism in the foregoing, but when a ferromagnetic oxide such as -Fe2O, or Fe,O4 is used as the carrier in place of said porous inert carrier, it is not necessary to coprecipitate said first and second components on a carrier. That is, an adsorbent having a good magnetism can be simply produced by depositing only the second component on the ferromagnetic oxide as the carrier. The ferromagnetic oxide as the carrier is, of course, in a powdery form in the present invention.

The adsorbent of the present invention comprising the ferromagnetic oxide carrier is produced in the following manner: Finely pulverized ferromagnetic oxide is dipped in an aqueous acidic solution containing at least one of water-soluble compounds of said second metal components, and thoroughly stirred. Then, an aqueous alkali solution is added to said acidic solution with stirring, or the impregnated ferromagnetic oxide is taken out of said acidic solution, placed in a beaker, and admixed with the aqueous alkali solution. After formation of the precipitates of the hydrous oxide on the ferromagnetic oxide, the precipitates on the carrier are sufficiently washed with water, and airdried. In this embodiment, it seems that a portion of ferromagnetic oxide as the carrier is dissolved in the acidic solution, and precipitated as the hydrous oxide on the carrier together with the hydrous oxide of the second metal component by the addition of the alkali thereto.

Typical of ferromagnetic oxide is magnetite (Fe,O4). In addition, the following ferrites, for example, y-Fe,O,, ZnFe2O,, Y,Fe,Ol,, CoFe2O4, NiFe2O4, CuFe2O4, BaFe,O -Mg2Fe204 and MnFe2O4 are applicable in the present invention.

The present invention will be described in detail below, referring to Examples and Comparative Examples, but the present invention is not restricted to these Examples.

Adsorbability of adsorbent is evaluated in Examples and Comparative Examples in the following manner, unless otherwise specified.

0.2 g of adsorbent pulverized to 100--200 mesh was added to 5 1 of sea water enriched to 10 ppb uranium, and stirred for 5 hours.

Then, the adsorbent was separated from the solution and the charge of the uranium concentration in the solution was measured, and an amount of uranium adsorbed per gram was determined by a difference in concentrations of uranium in the enriched sea water before and after adsorption operation.

Example 1.

200 ml of an aqueous 0.66M titanium chloride solution and 200 ml of an aqueous 4.66M ferrous chloride solution were mixed together, and the resulting mixed solution was heated to 50"C. Then, an aqueous 10% caustic soda solution was added thereto with sufficient stirring at a rate of 3-5 ml/minute by a pump, and precipitates formed at a pH each of 7, 9 and 12 are filtered separately, and washed with distilled water and air-dried to obtain composite material adsorbents. The resulting adsorbents had a magnetism and also had a diffraction peak identical with that of Fe304 by X-ray diffraction analysis. The amounts of uranium adsorbed on the adsorbents thus prepared at the different pH values are shown in Table 1.

Example 2.

200 ml of an aqueous 0.66M titanium tetrachloride solution and 200 ml of an aqueous 0.66M ferrous chloride solution were mixed together, and the resulting mixed solution was heated to a temperature each of 300, 500, and 70"C. An aqueous 10% caustic soda solution was added thereto in the same manner as in Example 1 to make pH 9. The resulting precipitates were filtered, and washed with distilled water and air-dried to obtain adsorbents of composite material. The resulting adsorbents had a magnetism. The amounts of uranium adsorbed on the adsorbents thus prepared at the different temperatures are shown in Table 1.

Example 3.

200 ml of an aqueous 0.66M titanium tetrachloride solution was mixed with 200 ml of an aqueous ferrous chloride solution having a different concentration, that is, 2.2, 1.65, 1.32, 0.825, 0.66, 0.33, 0.11, 0.066, 0.04 and 0.033M, to change an atomic ratio of titanium to iron, and the resulting mixed solutions were heated to 50"C. Then, an aqueous 10% caustic soda solution was added to each of the solutions with sufficient stirring at a rare of 35 /c ml/minute by a rating pump to make pH 9. The precipitates were filtered, and washed with distilled water, and air-dried to obtain composite material adsorbents. The amounts of uranium adsorbed on the adsorbents having different atomic ratios of titanium to iron are shown in Table 1.

In this connection, it was found that the adsorbents having the atomic ratios of titanium to iron of 0.4, 0.1, 2.0, 6.0, 10.0 and 20.0 had a magnetization intensity, cr, (emu/ g), of 13.3, 6.27, 4.53, 1.46, 0.6, and 0.015, respectively.

Then, the adsorbent having an atomic ratio of titanium to iron of 0.4 thus prepared was tested to determine a magnetic separation efficiency of adsorbent suspended in water by applying a magnetic field thereto under the following conditions: Absorbent: composite material of ferro magnetic oxide and hydrous titanium oxide having an atomic ratio of Ti/Fe of 0.4, a magnetization intensity of 13.3 emu/g and particle sizes of 20-40 m.

Concentration of adsorbent particles in water: 168 ppm.

Magnetic separator: High-gradient type.

Magnetic field intensity: 2300--2600 Oe.

Flow rate of test water: 0.18-0.2 m/sec.

The following separation efficiency was obtained with varying filter thickness of the magnetic filter: Filter thickness of magnetic separator (cm) Separation efficiency (%) 4 99.54 8 99.94 12 99.98 16 99.99 TABLE 1

Temp. at Uranium TiCl4 FeCl2 Atomic ratio pH at preparation absorbed (M) (M) of Ti/Fe (II) preparation ( C) ( g-U/g) Example 1 0.66 0.66 1 7 50 105 " " " " 9 " 150 " " " " 12 " 180 Example 2 " " " 9 30 95 " " " " " 50 150 " " " " " 70 110 Example 3 " 2.2 0.3 " 50 105 " " 1.65 0.4 " " 112 " " 1.32 0.5 " " 120 " " 0.83 0.8 " " 130 " " 0.66 1.0 " " 150 " " 0.33 2.0 " " 170 " " 0.11 6.0 " " 180 " " 0.066 10.0 " " 230 " " 0.044 15.0 " " 170 " " 0.033 20.0 " " 100 Comparative Example 1.

200 ml of an aqueous 0.66M titanium tetrachloride solution was admixed with an aqueous 10% caustic soda solution at a rate of 3-5 ml/minute by a rating pump to make pH of the solution 3, 5, 7, 9 and 12, individually. The precipitates formed at the individual pH values were filtered, and washed with distilled water, and air-dried to obtain adsorbents of single hydrous titanium oxide.

Amounts of uranium adsorbed on the adsorbents thus prepared at different pH values are shown in Table 2.

Comparative Example 2.

200 ml of an aqueous 0.66M titanium tetrachloride solution was heated to 30 , 50 , and 70"C individually, and then admixed with an aqueous 10% caustic soda solution at a rate of 3.5 ml/minute by a rating pump to make pH of the solution 5. The precipitates heated at the individual temperatures at the preparation were filtered, and washed with distilled water and air-dried to obtain adsorbents of single hydrous titanium oxide. The amounts of uranium adsorbed by the adsorbents thus heated at the individual temperatures at the preparation are shown in Table 2.

TABLE 2

Temp. at Uranium TiCI4 pH at preparation adsorbed (M) preparation (roc) (1lg-U ' g) Comp. Ex. 1 0.66 3 30 22 " 5 " 40 " 7 " 33 " 9 " 10 12 ,, , 1 2 Comp. Ex. 2 " 5 ,, 40 ,, ,, g 50 70 65 As is evident from comparison of Table 1 with Table 2, the present composite materials of ferromagnetic oxide and hydrous titanium oxide having an atomic ratio of 0.3-20:1 have a higher uranium adsorbability than the conventional adsorbents of single hydrous titanium oxide, which have been so far regarded as the best uranium adsorbent.

X-ray diffraction analysis revealed that sizes of the single hydrous titanium oxide most suitable for the uranium adsorption is about 50 A, whereas the size of hydrous titanium oxide in the present composite materials having said range of atomic ratio of titanium to iron prepared under the conditions of Examples 1 to 3 is around 50 A, but the hydrous titanium oxide takes an amorphous form outside said range of the atomic ratio, or its crystals grow extremely larger owing to crystal growth acceleration of hydrous titanium oxide by the ferromagnetic oxide, resulting in decrease in the uranium adsorbability.

The present adsorbent has a magnetism as shown in the foregoing Examples, and thus can undergo easy solid-liquid separation when used in a slurry state. That is, the present adsorbent having very small particle sizes can be employed.

Example 4.

500 ml of an aqueous 0.066M titanium tetrachloride solution and 500 ml of an aqueous 0.066M ferrous chloride solution were mixed together, and the resulting mixed solution was heated to 50"C. Then, an ammonia gas diluted to 20% by nitrogen was injected into the solution through a porous glass filter having pore sizes of 5-30 am at a rate of 1 I/minute until pH of the solution reached 9. The resulting precipitates were filtered, washed with distilled water, and air-dried to obtain an adsorbent of composite material.

The amount of uranium adsorbed by the adsorbent thus prepared was 190 ag-U/g, and the adsorbent had a magnetism.

Example 5.

20 g of y-alumina dried in air at 1200C for 2 hours was dipped in 50 ml of an equimolar (2.5M) solution of titanium tetra chloride and ferrous chloride, and left standing therein for 24 hours while being tightly sealed. Then, the y-alumina was transferred into water at 50"C and an ammonia gas diluted to 20% by nitrogen was injected therein until pH of the water reached 9. The y-alumina was filtered and washed with distilled water and air-dried to obtain an adsorbent of composite material. The y-alumina thus treated contained 180 mg Ti and 210 mg Fe(II)/g carrier. The amount of uranium adsorbed by the resulting adsorbent was 90 ag-U/g adsorbent, which corresponded to 500 ag-U/g Ti. This was due to an increased distribution of the composite material of ferromagnetic oxide and titanium oxide. The absorbent had a magnetism.

Example 6.

The adsorbents prepared in Example 1 were aged in hydrothermal condition at 1500C under 6 atmospheres in an autoclave, and then air-dried. The amounts of uranium of the aged adsorbents prepared in Example 1 at pH of 7, 9 and 12 were 128, 180, and 190 ug-U/g, respectively.

In the following Examples and Comparative Examples, the amounts of cobalt and potassium per gram of adsorbent were determined by differeneces in concentration of the solution containing cobalt and potassium before and after adsorption operation in the manner similar to the determination of uranium.

Comparative Example 3.

20 g of alumina dried in air at 1200C for 2 hours was dipped in 100 ml of an aqueous 3M ferrous chloride solution, and left standing therein until ferrous chloride went into the pores of the y-alumina fully. Then, the resulting alumina was brought in contact with an aqueous 10% caustic soda solution to precipitate iron (II) precipitates, and washed with distilled water and air-dried to

Example 14.

An adsorbent of composite material was prepared in the same manner as in Example 10, using commercially available powdery activated carbon as the carrier in place of the y-alumina.

Example 15.

An adsorbent of composite material was prepared in the same manner as in Example 7, using commercially available silica gel pulverized to 400 mesh as the carrier in place of the alumina.

Comparative Example 4.

An aqueous 10% caustic soda was added to an aqueous 1M ferrous chloride solution at a liquid temperature of 500C until pH reached 9, thereby obtaining an adsorbent of ferromagnetic oxide. The adsorbent had a magnetism.

Comparative Example 5.

An aqueous 10% caustic soda was added to an aqueous 1M titanium tetrachloride solution at a liquid temperature of 500C until pH reached 5, thereby obtaining an adsorbent of single hydrous titanium oxide.

Comparative Example 6.

An aqueous 10% caustic soda solution was added to an aqueous 1M aluminum chloride solution at a liquid temperature of 500C until pH reached 5, thereby obtaining an adsorbent of single hydrous aluminum oxide.

The adsorhents prepared in the foregoing Examples 7 to 1S and Comparative Examples 3 to 6 were subjected to uranium, cobalt and potassium adsorption tests individually.

Table 3 shows the test results of the absorbents prepared in Examples 7 to 9 and Comparative Examples 3 to 6: TABLE 3

Uranium Cobalt Potassium adsorbed adsorbed adsorbed Adsorbent (llg-U/g) (meq/g) (meq/g) Comp. Ex. 3 60 0.15 0.10 (Fe-Al2O,) Example 7 130 0.45 0.35 (Fe-A1,0, + Ti) Example 8 90 0.40 0.37 (Fe-Al2O3 + Al) Example 9 170 0.55 0.42 (FbA1,0, + Ti + Al) Comp. Ex. 4 20 0.12 0.08 (Fe) Comp. Ex. 5 50 0.39 0.34 (Ti) Comp. Ex. 6 40 0.32 0.30 (Al) As is evident from Table 3, the adsorbents of Examples 7 to 9 have a considerably higher adsorbability than those of the adsorbents of Comparative Examples 3 to 6, and this means than a combination of Fe (11) is effective upon the increase in the adsorbability, which is the peculiar feature of the binary and ternary composite materials of the present invention, as never seen in the adsorbents of single hydrous metal oxide. The higher adsorbability of the present composite materials supported on the carrier seems to be due to the finely powdery state of the adsorbent, the resulting increased specific surface area and better distribution of the active components, that is, the increased active surface area.

Table 4 shows the adsorbability of the adsorbents of Examples 10 to 12 prepared in the different manner as in Examples 7 to 9, though their respective compositions are corresponding to those of the adsorhents of Examples 7 to 9. It is evident that the adsorbabilities are substantially identical with those of Examples 7 to 9. Preparatory operation for the adsorbents of Examples 10 to 12 are simpler than that for those of Examples 7 to 9, and thus are more advantageous. All these adsorbents had a magnetism.

TABLE 4

Uranium Cobalt Potassium adsorbed adsorbed adsorbed Adsorbent ( g-U/g) (meq/g) (meq/g) Example 10 120 0.42 0.33 (Fe-Ti + Al2O3) Example 11 85 0.36 0.35 (Fe-Al + A1203) Example 12 165 0.50 0.40 (Fe-Ti-Al ffi A1203) Table 5 shows ahe adsorbabilities of the adsorbents of Examples 13 to 15, using activated carbon and silica as the carrier. As is evident from Table 5, the adsorbents have a high adsorbability, and of course they had a good magnetism.

TABLE 5

Uranium Cobalt Potassium adsorbed adsorbed adsorbed Adsorbent (Ag-U'g) (meq,'g) (meq,'g) Example 13 150 0.48 0.40 (Fe-C t Ti) Example 14 140 0.40 0.38 (Fe + Ti + C) Example 15 110 0.35 0.30 (Fe-SiO2 + Ti) The magnetic adsorbent based on the yalumina carrier prepared in Comparative Example 3 was subjected to deposition of hydrous oxides of manganese, zinc, lead, tin, chromium, zirconium, silicon and rare earth element and their uranium adsorbabilities were measured in the following Examples 16 to 25.

Example 16.

The adsorbent prepared in Comparative Example 3 was dipped in 100 m! of an aqueous 3M manganese chloride, and left standing therein until the solution thoroughly permeated into the adsorbent. Then, the dipped adsorbent was transferred to a platinum netting, and kept above a beaker containing 500 ml of 28% aqua ammonia as high as or higher than the liquid level of the beaker. The beaker was heated to introduce an ammonia gas into the adsorbent, thereby depositing hydrous manganese oxide onto the adsorbent to obtain an adsorbent of composite material.

Example 17.

An adsorbent of composite material was prepared in the same manner as in Example 16, using an aqueous 1.SM lead nitrate solution in place of the aqueous manganese chloride solution.

Example 18.

An adsorbent of composite material was prepared in the same manner as in Example 16, using an aqueous 3M zinc chloride solution in place of the aqueous manganese chloride solution.

Example 19.

An adsorbent of composite material was prepared in the same manner as in Example 16, using an aqueous 1M stannic chloride solution in place of the aqueous manganese chloride solution.

Example 20.

An adsorbent of composite material was prepared in the same manner as in Example 16, using an aqueous 3M chromium nitrate solution in place of the aqueous manganese chloride solution.

Example 21.

An adsorbent of composite material was prepared in the same manner as in Example 16, using an aqueous 1M zirconium chloride solution in place of the aqueous manganese chloride solution.

Example 22.

An adsorbent of composite material was prepared in the same manner as in Example 16, using an aqueous 1M sodium silicate solution in place of the aqueous manganese chloride solution.

Example 23.

An adsorbent of composite material was prepared in the same manner as in Example 16, using an aqueous 3M citric nitrate solution solution in place of the aqueous manganese chloride solution.

Example 24.

An adsorbent of composite material was prepared in the same manner as in Example 16, using an aqueous 3M ceric nitrate solution in place of the aqueous manganese chloride solution.

Example 25.

An adsorbent of composite material was prepared in the same manner as in Example 16, using an aqueous 3M ferric chloride solution in place of the aqueous manganese chloride solution.

The results of measuring the uranium adsorbabilities of the adsorbents prepared in the foregoing Examples 16 to 25 are shown in Table 6. The adsorbents had a high adsorbability and also a magnetism. Lanthanum and cerium are rare earth elements, and other rare earth elements are applicable to the present invention. TABLE 6

Uranium adsorbed Adsorbent OLg-U.'g) Example 16 Pb) 90 (Fe-Al,O3 + Example 17 80 (Fe-A12O3 + Mn) Example 18 85 (Fe-AI,O, + Zn) Example 19 73 (Fe-A1,0, + Sn) Example 20 70 (Fe-A120, + Cr) Example 21 80 (Fe-Al,O3 + Zr) Example 22 65 (Fe-Al2O3 + Si) Example 23 80 (Fe-Al2O, + La) Example 24 85 (Fe-Al2O3 + Ce) Example 25 80 (CFe-Al2O3 + Fe) Example 26.

10 g of y-Fe,O, having a particle size of 400 mesh was mixed with 50 ml of an aqueous 2M titanium tetrachloride solution with vigorous stirring, and then an aqueous 10% caustic soda solution was continuously added to the resulting mixture at a rate of 3.5 ml/ minute until precipitates of hydrous titanium oxide was completely formed on the surface of 7-Fe2O, and in the solution. Then, the 7-Fe,O, supporting the hydrous titanium oxide was separated from the solution by a magnet, and washed with distilled water and air-dried to obtain an adsorbent.

Example 27.

An adsorbent of y-Fe203 supporting hydrous aluminum oxide was prepared in the same manner as in Example 26, using an aqueous 3M aluminum chloride solution in place of the aqueous titanium tetrachloride solution.

Example 28.

An adsorbent was prepared in the same manner as in Example 26, using CoFe2O4 as the carrier in place of y-Fe203.

Example 29.

An adsorbent was prepared in the same manner as in Example 26, using NiFe2O4 as the carrier in place of y-Fe,Os.

Example 30.

An adsorbent was prepared in the same manner as in Example 26, using an aqueous solution of 2M each of titanium tetrachloride and ferrous chloride in place of the aqueous titanium tetrachloride solution.

The adsorbents prepared in the foregoing Examples 26 to 30 had a good magnetism and were easy to undergo solid-liquid separation.

The uranium adsorbabilities of the adsorbents are shown in Table 7.

TABLE 7

Uranium adsorbed Adsorbent (gg-U g) Example 26 150 Example 27 90 Example 28 115 Example 29 105 Example 30 120 .present magnetic absorbents have a -- bability as shown above, and are parated from the solution by apply -dc field to the solution when used in a slurry state, and thus can make the size of an adsorbing apparatus smaller and a recovery operation of the heavy metal as well as the absorbent itself from the solution simpler, making the adsorbing operation more economical.

Claims

WHAT WE CLAIM IS:

1. A magnetic adsorbent, which comprises a composite material of ferromagnetic oxide as a first component and at least one of hydrous oxides of titanium, aluminum, ferric iron, lead, manganese, zinc, tin, chromium, zirconium, silicon and rare earth element as a second component, the ferromagnetic oxide including at least one of Foe304 and y-Fe,O,.

2. A magnetic adsorbent according to Claim 1, wherein the composite material comprises ferromagnetic oxide and hydrous titanium oxide.

3. A magnetic adsorbent according to Claim 2, wherein the composite material has an atomic ratio of titanium to iron of 0.320:1.

4. A magnetic adsorbent, which comprises a composite material of ferromagnetic oxide as a first component and at least one of hydrous oxides of titanium, aluminum, ferric iron, lead, manganese, zinc, tin, chromium, zirconium, silicon, and rare earth element as a second component, the composite material being supported on a porous carrier, and the ferromagnetic oxide including at least one of Fe304 and y-Fe,O,.

5. A magnetic adsorbent according to Claim 4, wherein the composite material comprises ferromagnetic oxide and hydrous titanium oxide.

6. A magnetic adsorbent according to Claim 5, wherein the composite material has an atomic ratio of titanium to iron of 0.320:1.

7. A magnetic adsorbent according to Claim 4, wherein the porous carrier is selected from alumina, silica, activated carbon and zeolite.

8. A magnetic adsorbent, which comprises a composite material of at least one of hydrous oxides of titanium, aluminum, ferric iron, lead, manganese, zinc, tin, chromium, zirconium, silicon and rare earth element, supported on ferromagnetic oxide.

9. A magnetic adsorbent according to Claim 8, wherein the ferromagnetic oxide is selected from Fe,04, y-Fe,O, ZnFe2O 73FQ012, CoFe2O4, NiFe2O4, CuFe2O1, BaFe,O,, MgFe,04 and MnFe,04.

10. A method for producing a magnetic adsorbent according to either of Claims 1 and 4, which comprises mixing a water-soluble ferrous compound as a first component with at least one of water-soluble compounds of titanium, aluminum, ferric iron, lead, manganese, zinc, tin, chromium, zirconium, silicon, and rare earth element as a second component in the presence of water, and add ing an alkali to the resulting aqueous solution, thereby forming a magnetic composite material of ferromagnetic oxide including at least one of Fe,O, and y-Fe2Os and at least one of hydrous oxides of titanium, aluminum, ferric iron, lead, manganese, zinc, tin, chromium, zirconium, silicon, and rare earth element by precipitation.

11. A method according to Claim 10, wherein the water-soluble ferrous compound is ferrous chloride or ferrous sulfate.

12. A method according to Claim 10, wherein the water-soluble ferrous compound is mixed with at least one of titanium tetrachloride, titanium sulfate, titanium tetrabromide, titanium alkoxide, aluminum chloride, ferric chloride, manganese chloride, lead nitrate, zinc chloride, stannic chloride, chromium nitrate, zirconium chloride, sodium silicate, lanthanum nitrate, and ceric nitrate.

13. A method according to Claim 10, where the alkali is caustic soda, caustic potash, sodium carbonate, or ammonia.

14. A method according to Claim 10, wherein the water-soluble ferrous compound is mixed with water-soluble titanium compound in the presence of water at an atomic ratio of titanium to iron of 0.3-20:1.

15. A method according to Claim 14, wherein the alkali is added to the resulting aqueous solution at pH 7-12 and 30a 700C.

16. A method according to Claim 14, wherein an ammonia gas is added to the resulting aqueous solution as the alkali, thereby forming the magnetic composite material of ferromagnetic oxide and hydrous titanium oxide.

17. A method according to Claim 10, wherein the resulting magnetic composite material is aged by hydrothermal treatment.

18. A method for producing a magnetic adsorbent as claimed in either of Claim 1 and 4, which comprises impregnating a porous carrier with an aqueous solution of a watersoluble ferrous compound as a first component and at least one of water-soluble compounds of titanium, aluminum, ferric iron, lead, manganese, zinc, tin, chromium, zirconium, silicon, and rare earth element as a second component, and bringing the porous carrier in contact with an alkali, thereby forming a magnetic composite material of ferromagnetic oxide including at least one of Fe2Os and y-Fe,O, and at least one of hydrous oxides of titanium, aluminum, ferric iron, lead, manganese, zinc, tin, chromium, zirconium, silicon, and rare earth element on the porous carrier by precipitation.

19. A method according to Claim 18, wherein the water-soluble ferrous compound is ferrous chloride or ferrous sulfate.

20. A method according to Claim 18, wherein the aqueous solution comprises the water-soluble ferrous compound as the first component and at least one of titanium tetrachloride, titanium sulfate, titanium tetrabromide, titanium alkoxide, aluminum chloride, ferric chloride, manganese chloride, lead nitrate, zinc chloride, stannic chloride, chromium nitrate, zirconium chloride, sodium silicate, lanthanum nitrate, and ceric nitrate as the second component.

21. A method according to Claim 18, wherein the alkali is caustic soda, caustic potash, sodium carbonate, or ammonia.

22. A method according to Claim 18, wherein the porous carrier is selected from y-alumina, silica, activated carbon and zeolite.

23. A method according to Claim 18, wherein the porous carrier is dipped in an aqueous solution of a water-soluble ferrous compound and a water-soluble titanium compound at an atomic ratio of tiaanium to iron of 0.3-20:1.

24. A method according to Claim 23, wherein the alkali is added to the resulting aqueous solution at pH 7-12 and 30"--70"C.

25. A method according to Claim 23, wherein an ammonia gas is brought in contact the resulting porous carrier as the alkali, thereby forming the magnetic composite material of ferromagnetic oxide and hydrous titanium oxide on the porous carrier.

26. A method according to Claim 18, wherein the resulting composite material is aged by hydrothermal treatment.

27. A method for producing a magnetic adsorbent as claimed in either of Claims 1 and 4, which comprises impregnating a ferromagnetic oxide with an acidic aqueous solution containing at least one of water soluble compounds of titanium, aluminum, ferric iron, lead, manganese, zinc, tin, chromium, zirconium, silicon and rare earth element, and bringing the ferromagnetic oxide in contact with an alkali, thereby forming a magnetic composite material of ferromagnetic oxide including at least one of Foe304 and y-Fe,O,, at least one of hydrous oxides of titanium, aluminum, ferric iron, lead, manganese, zinc, tin, chromium, zirconium, silicon, and rare earth element on surfaces of the ferromagnetic oxide by precipitation.

28. A method according to Claim 27, wherein the ferromagnetic oxide is selected from Foe,041 y-Fe,O:,, ZnFe2O4, y3-Fe CoFeO4, NiFe2O4, CuFe2O4, BaFe,O,, MgFe2O4 and MnFe.O4.

29. A method according to Claim 27, wherein the aqueous solution comprises at least one of titanium tetrachloride, titanium sulfate, titanium tetrabromide, titanium alkoxide, aluminum chloride, ferric chloride, manganese chloride, lead nitrate, zinc chloride, stannic chloride, chromium nitrate, zirconium chloride, sodium silicate, lanthanum nitrate, and ceric nitrate.

30. A method according to Claim 27, wherein the alkali is caustic soda, caustic potash, sodium carbonate, or ammonia.

31. A method according to Claim 27, wherein the ferromagnetic oxide is in a powdery form.

32. A method according to Claim 18, wherein the porous carrier is in a powdery form.

33. A magnetic adsorbent according to Claim 1 substantially as hereinbefore described.

34. A method according to Claim 10 for producing a magnetic adsorbent substantially as hereinbefore described.

35. A magnetic adsorbent when produced by a method according to any one of Claims 10 to 32 or 34.