JPS5839897B2 - Desorption method of uranium and strontium - Google Patents

Description

Detailed Description of the Invention The present invention desorbs uranium and strontium separately from an adsorbent that has adsorbed uranium and strontium, and reuses the adsorbent after desorption to adsorb uranium and strontium. This invention relates to an adsorption/desorption method.

In recent years, research has been conducted on extracting uranium from seawater with the aim of stabilizing the uranium supply.

Various attempts have been made to extract uranium, including the foaming separation method, coprecipitation method, ion exchange resin method, and adsorption method.
Among these, much research has been conducted on adsorption methods, and of these, adsorption methods using titanic acid are considered to be the most promising.

However, when extracting uranium from seawater, it is preferable to collect not only uranium but also other useful substances, especially strontium, and from an industrial perspective, it is strongly desired to smoothly repeat the adsorption/desorption cycle of uranium and strontium. There is.

As a result of various studies on this point, the present inventors have found that by contacting the adsorbent after uranium desorption with an aqueous hydrochloric acid solution, not only can strontium be efficiently desorbed, but the adsorbent can also be regenerated to the extent that it can be reused. The present invention was completed by discovering that

The present invention is based on this knowledge, and involves contacting an adsorbent that has adsorbed uranium and strontium with an aqueous carbonate solution to desorb uranium, and then adjusting the adsorbent after uranium desorption to a pH of 1 to 1.
Strontium is desorbed by contacting with the hydrochloric acid aqueous solution in step 5,
This is a method for adsorbing and desorbing uranium and strontium, which is characterized in that the adsorbent after strontium desorption is reused for adsorbing uranium and strontium.

Although any adsorbent can be used, the titanic acid adsorbent obtained by the method described in Japanese Patent Application No. 53-31662 is particularly excellent.

In the present invention, an adsorbent that has adsorbed uranium and strontium is first contacted with an aqueous carbonate solution to adsorb and desorb uranium.

It is known that an aqueous carbonate solution desorbs uranium, and for example, it is preferable to use an aqueous solution of ammonium carbonate, soda carbonate, soda bicarbonate, or the like.

Its concentration is generally 0.4 to 2 monoL/e, preferably 0
．． It is 8 to 1.2 mol/e.

The rate of uranium desorption from an aqueous carbonate solution at room temperature is rapid up to 12 hours, but after that the increase in concentration is minute, so the desorption time is preferably within 12 hours.

In order to obtain a high desorption rate, for example, Japanese Patent Application No. 50-13213
It is necessary to heat the desorption liquid to a high temperature of 60 to 90°C as described in the specification.

However, this method has disadvantages both in terms of energy costs and the material of the equipment.

Furthermore, the present inventors desorbed uranium using a multi-stage contact method, in which the carbonate aqueous solution (desorption liquid) after desorbing uranium in the first adsorption/desorption cycle was used one step earlier in the next adsorption/desorption cycle. Alternatively, it has been found that a high desorption rate can be obtained even at room temperature by using it in the uranium desorption step that corresponds to several steps earlier.

It is preferable that the uranium desorption solution in the first stage in each cycle is concentrated and used for uranium extraction.

FIG. 1 is a flow sheet showing a preferred embodiment of this multi-stage contact system, in which uranium desorption is performed in three stages.

First, after the adsorbent has completed adsorption for a predetermined period of time, it is washed with water (pre-washing) to remove attached seawater, dirt, etc.

Next, desorption of uranium is carried out in three stages using a carbonate aqueous solution (desorption 1, desorption 2, desorption 3), followed by washing with water, and then transferred to hydrochloric acid desorption for strontium desorption.

The chronological sequence of these treatments that the adsorbent undergoes is shown vertically, with one cycle from adsorption to hydrochloric acid desorption.

In the first cycle of uranium desorption, desorption liquids A, B, and C are obtained through the first, second, and third desorptions, ie, "desorption 1,""desorption2," and "desorption 3," respectively.

The adsorbent that has undergone "desorption 3" is washed with water, and a carbonate as a desorbent is added to the obtained washing water to form a desorption liquid with a predetermined concentration, and strontium is desorbed from the adsorbent after washing with water.

Then, in the second cycle, after adsorption and water washing,
First and second stage uranium desorption “Desorption 1” and “Desorption 2”
” are desorption fluids B and C from the second and third stage uranium desorption “Desorption 2” and “Desorption 3” of the first cycle, respectively.
The desorption liquid C and C are obtained, respectively.

In the third stage of uranium desorption "Desorption 3" of the second cycle, the desorption liquid obtained from the post-washing of the first cycle is used,
A desorption liquid D' is obtained.

Next, the adsorbent is washed with water, and a absorbent is similarly added to the obtained washing water to prepare a desorption liquid E, and strontium is desorbed from the adsorbent after washing with water.

Then, in the third cycle, desorption 1, desorption 2, and desorption are carried out in the same manner as in the second cycle, that is, by using the desorption liquid obtained from each stage of uranium desorption in the second cycle one stage at a time. 3 is desorption liquid 0 respectively
', D' and E are used.

In FIG. 1, the flow of the desorption liquid in the second cycle is shown by a solid line, and that in the third cycle is shown by a wavy line.

A desired number of adsorption/desorption cycles can be performed by increasing the number of uranium desorption steps in one cycle.

The desorption liquid obtained from the first stage of uranium desorption of each cycle (e.g. A, B').

Uranium is recovered from uranium (such as C) through enrichment.

In preferred embodiments of the invention, multiple adsorbent beds may be used in parallel.

In this case, uranium is desorbed in multiple stages using different desorbents in the adsorption/desorption cycle of each adsorbent, and the desorption liquid after desorbing uranium in the first cycle is transferred to the second row of desorbents. It is used for the uranium desorption step corresponding to one or several steps earlier in the train cycle.

In this way, the desorption fluid is used sequentially between each cycle, and in each cycle, the desorption fluid obtained from the first desorption step is concentrated and used for uranium extraction, using a multi-stage countercurrent contact method to extract uranium. It can be harvested with industrial advantage.

FIG. 2 is a flow sheet showing a preferred embodiment of this multi-stage AC contact system, in which uranium desorption is performed in three stages.

To explain this, the adsorbent after adsorption for a predetermined period of time, preferably several days to several tens of days, is washed with water (pre-washing).
Adhering seawater, garbage, etc. are removed.

Next, desorption is carried out in three stages using an aqueous carbonate solution, followed by washing with water (after rinsing with water), followed by desorption with hydrochloric acid for the next strontium desorption.

The flow of these adsorbents over time is adsorption → water washing/desorption 1 →
It is shown as desorption 2 → desorption 3 → post-cleaning → hydrochloric acid desorption.

The drawing shows four columns or four parallel adsorbent beds.
is shown, but the number of adsorbent beds can be chosen arbitrarily.

The number of desorption stages in each row is also chosen accordingly.

To explain the flow of the desorption liquid, the desorption liquid adhering to the adsorbent is dissolved in the washing water after one row of washing, so the carbonate is dissolved in this washing water and the desorption liquid has a predetermined concentration. shall be.

This desorption liquid is first used for desorption in the third stage of desorption "Desorption 3" in the example ■, then in the second stage desorption "Desorption 2" in column ■, and finally in the first stage desorption "Desorption 2" in column ■. 1"
The three steps (three times) of attachment and detachment are completed.

The desorption liquid that has completed desorption in this manner is transferred to a conventional concentration process to recover uranium.

The desorption liquid that has completed desorption 1 in each row is concentrated.

The desorption liquid that has completed desorption 2 and desorption 3 is used as it is for the next stage of desorption in the next row, and the desorption is repeated in the same manner.

This is a multi-stage countercurrent contact method in which the desorption flow of the adsorbent and the desorption liquid contact each other in countercurrent flow in multiple stages. It goes without saying that appropriate changes and additions may be made when implementing the invention.

In the uranium desorption process of the present invention, the contact between the adsorbent and the desorption liquid varies depending on the contact mode adopted, but in the case of the multi-stage countercurrent contact method, which is a preferred embodiment of the present invention, the contact between the adsorbent and the desorption liquid is Particularly preferred is a method in which the liquid is circulated between the liquid tank and the liquid tank using a pump.

In this case, interference is not a particular problem, and 1I in the adsorbent bed.
About Z777/min is preferable.

Further, since the amount of desorption liquid does not particularly affect the desorption rate, it is advantageous to keep it as small as possible because the uranium concentration will be high and the amount of processing liquid will be small.

In the uranium desorption step using a carbonate aqueous solution, strontium is desorbed by leaving 11 of the strontium on the strontium 4-desorbing adsorbent and then contacting the hydrochloric acid aqueous solution.

It is preferable to circulate the aqueous hydrochloric acid solution while not adding it gradually, but keeping the pH of the solution at 5 or less.

Hydrochloric acid aqueous solution treatment not only desorbs strontium, but also decomposes and removes deposits such as calcium and magnesium carbonates attached to the adsorbent, and has the effect of forming bridges with the deposits and breaking apart the adsorbents that have stuck to each other. , and the treated adsorbent has an unexpected effect in that it has recovered adsorption capacity to approximately the same level as before adsorption.

This is extremely advantageous industrially because it eliminates the conventional problem of reducing uranium recovery efficiency due to clogging during adsorption in fixed bed adsorption beds, etc., and also eliminates the need for frequent regeneration of the adsorbent. be.

Thus, according to the method of the present invention, uranium and strontium can be desorbed separately in a series of steps.

Moreover, since the adsorbent has recovered its adsorption capacity after desorption, the adsorption/desorption cycle can be repeated smoothly.

When multi-stage countercurrent catalytic desorption is carried out on an industrial scale according to the present invention, it is preferable to carry out, for example, as follows.

Four group combinations of six adsorbent beds per group are used.

Adsorption of each adsorbent bed was carried out for 10 days, followed by water washing for 12 hours.
12 uranium desorption in the first to third stages each
After washing and desorption with hydrochloric acid for 12 hours, the adsorption/desorption cycle is 12 days.

In this case, the operation is performed so that the adsorption/desorption cycles in the six adsorbent beds of each group are delayed by a certain period of time,
Then, uranium is desorbed between the four groups using a multi-stage countercurrent contact method as shown in FIG.

That is, for example, if desorption 1 is completed on the first group of adsorbent beds I and desorption 3 is completed on the second group of adsorption beds The desorption liquid is supplied to the next desorption 2 on the adsorbent bed (1), and the desorption liquid is similarly supplied from one group to the other group with a further delay of a fixed time between the third and fourth groups.

Desorption rates of 80-100% are thus achieved.

On the other hand, the desorption liquid is used in countercurrent flow to desorption 3, desorption 2, and desorption 1, so its concentration increases sequentially.

The method of the invention can be used not only for the recovery of uranium and strontium from seawater, but also for other dilute solutions containing uranium and strontium.

Example 1 Diameter 0.3~o, s mTI mainly composed of titanic acid
Adsorbent 7612F granulated into L, diameter 30cIIT,
The layer thickness is 5□ with an interval of 10□□□ in the column.
□□ was packed and an adsorption bed was set up.

After flowing seawater through the adsorption bed at a flow rate of 20 cm and 7 minutes for 10 days, clean water 40e was passed through the adsorption bed at a flow rate of 5 cIn and 7 minutes for washing.

Uranium was desorbed using a three-stage contact method (see Figure 1).

1 mol/e ammonium carbonate aqueous solution as desorbent liquid 4
The first stage of uranium desorption was performed by circulating 06 through the adsorption bed for 24 hours to obtain Liquid A.

Next, second and third stages of uranium desorption were performed in the same manner to obtain liquids B and C, respectively.

After the third stage of uranium desorption, 5c of clean water 406 was
After washing, ammonium carbonate was added to the washing solution to give a concentration of 1 mol/e, and this was designated as Solution D.

Finally, in order to desorb strontium, an aqueous hydrochloric acid solution with a pH of 2 was circulated for 2 hours, and 6N hydrochloric acid was added dropwise so that the pH did not exceed 5.

The process from the above adsorption to desorption of strontium is the first cycle.

After completing the first cycle, a second cycle is performed in the same manner using the same adsorbent-packed column.

In this cycle, the first stage desorption of uranium is performed using liquid B, the second stage desorption is performed using liquid C, and the third stage desorption is performed using liquid D, to obtain liquids B', σ, and U, respectively.

Subsequently, post-cleaning was carried out in the same manner, and ammonium carbonate was added to the post-cleaning solution to obtain solution E having a concentration of 1 mol/e, and finally strontium was desorbed.

The third cycle was operated in the same manner, and the σ liquid was used for the first stage desorption of uranium, the d liquid was used for the second stage desorption, and the E liquid was used for the third stage desorption.

Amount of uranium desorbed in each cycle (total amount of uranium desorbed in three stages), uranium recovery rate (ratio of the amount of uranium desorbed to the amount of uranium contained in the circulating seawater), adsorption during adsorption Table 1 shows the pressure drop in the bed and the amount of strontium recovered.

For comparison, the results obtained when the same operation as above but without desorption of strontium using an aqueous hydrochloric acid solution are shown in the first table.
It is also shown in the table.

As is clear from the results in Table 1, according to the adsorption/desorption method of the present invention, uranium and strontium can be well desorbed from the adsorbent, and a high uranium recovery rate of 30% or more can be obtained.
Furthermore, since the pressure loss during adsorption is small, the adsorbent can be reused without reducing the amount of uranium and strontium recovered, which is economical.

On the other hand, in the case of the comparative example, the pressure loss gradually increases and the amount of uranium recovered also decreases significantly.

Example 2 37.8μ? Four columns (■ to ■), each with a diameter of 3 CIn, were packed with adsorbent 125P, which is mainly composed of titanic acid and has a particle size of 0.3 to 2 mm, adsorbing uranium from Al, as shown in Figure 2. Uranium was desorbed by sequentially passing the desorption solution through each column using a three-stage countercurrent contact method.

A 1 mol/e ammonium carbonate aqueous solution was used as the uranium desorbent solution, and the treatment was carried out for 24 hours at each stage.

Table 2 shows the uranium concentration in the desorption solution and desorption rate at each desorption stage for each column.

As is clear from the results in Table 2, this method reduces the general adsorption rate (desorption rate at the third stage) in each column to approximately 9.
It can be increased from 0% to 100%.

[Brief explanation of the drawing]

The drawings are process diagrams for explaining examples of embodiments of the present invention, in which FIG. 1 shows one adsorbent bed and FIG. 2 shows repeated adsorption/desorption cycles using several adsorbent beds. on how to do so.

Claims (1)

[Claims] 1. An adsorbent that has adsorbed uranium and strontium is brought into contact with an aqueous carbonate solution to desorb uranium, and then the adsorbent after uranium desorption is brought into contact with an aqueous hydrochloric acid solution of pH 1 to 5 to desorb strontium. and a method for adsorbing and desorbing uranium and strontium, characterized in that the adsorbent after strontium desorption is reused for absorption of uranium and strontium. 2 The uranium adsorption/desorption cycle is repeated multiple times using the same adsorbent, and in each cycle, uranium is desorbed in several stages using different desorption liquids, and the uranium obtained from the desorption process of the previous cycle is The desorption liquid obtained in the next cycle is used in a desorption step corresponding to the previous step, and in each cycle, the desorption liquid obtained from the first desorption step is concentrated and used for uranium extraction. The method described in Scope No. 1. 3 Adsorption and desorption of uranium is performed using multiple adsorbents in parallel, each in a separate cycle. At this time, the desorption of uranium in each cycle is performed in several stages using different desorption liquids, and the first column The desorption liquid obtained from the desorption process of the cycle is used in the desorption process corresponding to the previous stage in the second row of cycles, and the desorption liquid is sequentially carried forward between each cycle and used in the first desorption process in each cycle. 3. The method according to claim 1 or 2, wherein the desorption solution obtained from the desorption solution is concentrated and used for uranium extraction.