JPS6242973B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering heavy metals dissolved in seawater. More specifically, the present invention relates to a method for recovering heavy metals dissolved in seawater, which involves concentrating heavy metals by binding them to a matrix containing a substance that has the property of adsorbing heavy metals.

Since unprecedented amounts of heavy metals exist in seawater, many attempts have been made to recover heavy metals from seawater. It is based on the precipitation method and ion flotation method, and requires the use of chemicals. However, these methods generally have the disadvantage that large amounts of chemicals must be used, and furthermore, the processing costs increase proportionately as the chemicals are consumed. And preventing environmental pollution caused by the chemicals used requires a great deal of expense.

German Patent No. 2441479 describes cultivable mutants of seaweed.
A method for enriching uranium using a matrix consisting of Algen) is disclosed, and in this method, uranium can be recovered from seawater without using chemicals and there is no need to worry about seawater contamination. do not have. However, if it is desired to produce about 1 ton per day using this known method, a large amount of cultivation land is required to cultivate the required amount of seaweed, which requires a large amount of expense.

The object of the present invention is to find a method for recovering heavy metals, in particular uranium, from seawater that is easy to implement and does not cause environmental pollution by chemicals. Yet another object of the invention is to find a method by which the daily production of heavy metals can be increased to an economically viable amount.

The above objects of the present invention have been achieved by the method of the present invention, which includes the following steps.

(a) The presence in seawater of an adsorbent matrix containing biologically new humic acid as an adsorbent for the concentration of heavy metals and in which the substance used as a carrier for humic acid is present in an amount of up to 99% by weight in the dry state. (b) After concentrating the heavy metals in step (a), the heavy metal-containing adsorbent matrix is (c) A step in which the heavy metal-containing adsorbent matrix separated in step (b) is washed out with a diluent having a pH of 3 or less in order to elute the adsorbed heavy metals; (d) Step (c) (e) adding an alkaline solution to the heavy metal-containing acid separated in step (d) to obtain a heavy metal-containing acid with a pH of 4 to 8;
(f) contacting the heavy metal-containing solution obtained in step (e) with a substance that has chemical binding or adsorption binding properties to heavy metals in order to further concentrate the heavy metals; (g) (f) A process in which the biologically new humins contained in the adsorbent matrix used are concentrated by a chemically binding or adsorbing substance and then post-treated by a method known per se to produce heavy metal salts. By acid is meant humic acid, which is obtained from humic products produced over a period of up to several thousand years.

Humic acids are poorly soluble in water and biologically stable, especially against bacterial separation, so that they can be used for long periods in seawater. Its partition coefficient (ratio of heavy metal concentration in the adsorbent/heavy metal concentration in seawater under equilibrium conditions) is extremely high, and a high concentration is achieved despite the high pH of seawater.

When carrying out the method of the present invention industrially, it is of course necessary to set optimal conditions, and from the viewpoint of time saving and in consideration of the adsorption rate, the maximum concentration of heavy metals in seawater must be determined. It is preferable not to leave the adsorption matrix until enrichment has been achieved, but to remove it from the seawater and replace it with a new adsorption matrix before equilibrium is reached; on the other hand, the amount of adsorbent required per weight unit of heavy metal and the amount of heavy metal In order to keep the required acid consumption low in the case of relatively slow elution, it is preferred that the adsorption amount of heavy metals be as high as possible.

According to a highly preferred embodiment of the method of the invention,
Heavy metals are concentrated in a matrix of natural black peat. The degree of decomposition of black peat (a measure of the relative amount of humic products in the total material) is between 35 and 55.
%. The partition coefficient of black peat for uranium in seawater is of the order of 10 ⁴ , in this case:
Adsorbent matrices consisting of black peat accumulate not only uranium but also other heavy metals (eg vanadium, molybdenum). The ability to recover these heavy metals as a by-product when recovering uranium from seawater increases the economic efficiency of the present invention and becomes a factor in reducing costs. Since other components in black peat also exhibit similar stability to bacterial degradation in seawater as humic acids, adsorbent matrices made of black peat can be used for the extraction of heavy metals in seawater over long periods of time. can be used for. Therefore, this adsorbent matrix can be used repeatedly after eluting the heavy metals concentrated in the matrix. For this reason, and because black peat has a very good and commendable availability, the uranium production (which must be taken into account for the economic recovery of uranium) has been reduced to 1. This adsorbent matrix can be used insofar as it is in principle possible to obtain up to 1 ton per day. The amount of black peat required for this is approximately 5×10 ³ per day if the adsorbent matrix is reused at least 10 times.
less than a ton. Furthermore, it is another advantage of the invention that the black peat, after being used in the process of the invention, can be reprocessed and reused as peat coke.

The adsorbent matrix used for the concentration of heavy metals is composed of granular black peat with a particle size of 0.1 to 10 mm, which is produced by drying and then comminuting natural black peat. To manufacture this adsorbent matrix, naturally occurring black wet peat is used as a starting material and is dried on a large flat surface in the open air to remove a large amount of water. The dried brick peat (so-called thermal coal) still has a residual moisture content of approximately 28-30%, which is then broken down into fine granular material. When using this granule as an adsorbent, the granule is re-wetted with water before use, in which case the many fine tubes and interstices of the peat granule are filled with water. The granules are swollen. This operation is greatly facilitated by a vacuum of about 20 Torr, where air is exhausted from the tube and the gap. Other examples of black peat-containing adsorbent matrices which are also preferably used include layered matrices adhered to a net made of a material that is sufficiently durable in seawater, such as jute or nylon; is formed by depositing natural black peat on a net. In this case, the durability of the material is sufficient if it remains stable despite being moistened for a period that can be considered for use (approximately one month). be.
To produce this adsorbent matrix, natural moist black peat is placed on a screen with a mesh diameter of a few millimeters and sufficient pressure is applied from both sides to force the peat material through the screen. The subsequent drying causes the peat layers on both sides of the net to penetrate through the mesh and intermingle with each other into felt, which makes it easy to feel when freshly moistened with water or when exposed to strong water currents. Even when exposed, the peat layer will have dimensional stability.

When carrying out the method of the invention, adsorbents with substances having a large binding surface are also used as carriers, on which the humic acids are deposited.
The material used as a carrier for humic acid synthesis must be durable in seawater and allow reuse of the adsorbent matrix. As such a substance, activated carbon obtained from fuel coal or lignite in the same particle state with a particle size of 0.1 to 10 mm is preferably used. Activated carbon has a large binding surface, but the use of lignite as a humic acid carrier is preferred from a cost perspective. In addition, substances used as synthetic carriers include, for example, juute,
Also preferred are natural fiber materials such as cotton or coconut fibers, in which case the adsorbent matrix is in the form of a tangle in which the fibers are loosely bonded to each other. However, a preferred form of the matrix is one in which the natural fiber material forms a network structure, and humic acid is supported on this network structure.

Various uses can be considered depending on the type of matrix of the present invention. In order to obtain heavy metals dissolved in seawater from seawater, the matrix in the coating layer that does not permeate the matrix but is permeable to seawater can be mixed with seawater. It is preferable to make a relative movement with respect to.
This applies when the adsorbent matrix is present as granules or as a type of tangle of fibrous material. Preferably, the matrix is enclosed in a net made of, for example, nylon fibers and having a corresponding mesh diameter. For the concentration of heavy metals, a number of preferably rectangular superbodies formed in this way are arranged parallel to each other and one behind the other, and the superbodies are arranged so that a flow of seawater flows through the superbodies. It is oriented to follow the net, but placed in the ocean current so that there is sufficient exchange of seawater through the net.

In exactly the same way, if the matrix consists of a layer of adsorbent on a carrier network, except that a covering layer for the matrix is required, the matrix can be
Used to concentrate heavy metals from seawater. And in this case, the direction of flow is along a web, which is similarly arranged parallel and multiple one after the other, so that parallel different web layers are present in mutually displaced positions. ing. This allows the flow of seawater to split with the following when passing through the first layer, and good water mixing is achieved when the flow resistance is relatively low.

The distance between the mutual meshes and the number of layers are such that the flow velocity is 5 m/s.
In this case, it is determined that the desired enrichment of heavy metals in seawater is still achieved.

Since it is energetically disadvantageous to accelerate the seawater by means of pumps, it is preferred that the necessary relative motion between the matrix of the invention and the seawater be effected by means of a moving vessel suspending the net. for example,
In order to produce 1 ton of uranium per day, if 1 μg of uranium is recovered from 1 ml of seawater, approximately 10 ⁹ m ³ of seawater needs to pass through the matrix per day. When a matrix is towed through sea water at a speed of 20 km/h, its total cross-sectional area is approximately
^2000m2 is sufficient. Another advantage of using ships is that the matrix can be used in areas with low biological production. The risk of contamination of the matrix is thereby further reduced.

In order to more preferably use the granular matrix of the present invention for concentrating heavy metals from seawater, it is preferable that the matrix be swirled in a container submerged in seawater by the seawater flowing into the container. The pivoting is preferably carried out with the aid of suitable deflection devices located within the container. Particulate loss is prevented by attaching a fine mesh screen to the outlet of the container. The desired accumulation of heavy metals from seawater in the matrix is thus achieved very quickly by swirling.

After concentrating the heavy metals, the heavy metal-containing adsorbent matrix is removed from seawater. This operation is preferably carried out by replacing the part of the matrix that has adsorbed heavy metals to the desired extent as continuously as possible with a new or eluted matrix part.

When using a matrix present in the coating layer or a matrix in which the adsorbent layer is fixed on the mesh, the adsorbent matrix is very easily removed from the seawater. When the granular matrix is swirled in the adsorbent container, the granules adsorbing heavy metals suck up the particle-containing seawater from the adsorbent container at a speed of, for example, 10 m/s, e.g.
The separation is carried out by a centrifuge with a simple type of helical tube having a helical groove. The separated granules are subjected to repeated use many times, and the seawater is returned to the sea. The capacity of the centrifuge is defined such that the total matrix in the adsorbent container per adsorption period is eluted on average once.

After removing the heavy metal concentrated adsorbent from seawater, the adsorbent is treated with dilute acid (preferably hydrochloric acid or nitric acid) below PH3 to elute the adsorbed heavy metals.
It can be washed with Acids are used as heavy metal storage agents as long as their PH is kept low. The diluent used for heavy metal leaching is used for heavy metal re-leaching until the heavy metal concentration in the diluent reaches a value that is increased by an order of magnitude of 10 ³ or 10 ⁴ relative to seawater. . In this case, the pH of the acid is kept below PH2 by adding a high concentration of acid. In this way, the amount of solution fed in subsequent steps is kept small.

A particularly advantageous embodiment of the process according to the invention includes washing the heavy metal-containing adsorbent matrix with an acid salt produced by electrolysis of sodium chloride present in seawater. Electrolysis of sodium chloride is known as a type of alkaline chloride electrolysis, and has already been used on a large scale. In order to obtain the hydrochloric acid required for the method of the present invention, seawater is boiled down to a salt solution by a known method, and then hydrogen, caustic soda and chlorine are added using the following reaction formula of alkali chloride electrolysis energy + 2H ₂ O + 2NaCl → H ₂ + 2NaOH + Cl ₂ Then, according to the reaction formula H ₂ + Cl ₂ →2HCl + 43.8 kcal, chlorine and hydrogen are reacted to obtain hydrogen chloride (at the same time, energy is generated), and the obtained hydrogen chloride is introduced into water to form hydrochloric acid. What is done is done.

In this case, the heavy metal-containing hydrochloric acid is preferably added to caustic soda produced by electrolysis of sodium chloride contained in seawater. This is because caustic soda is always produced when performing alkali chloride electrolysis, so there is no way not to make effective use of it.

By adopting an alkali chloride electrolysis method to obtain the hydrochloric acid necessary for carrying out the method of the present invention from seawater, there is no need for additional costs for transporting and supplying the necessary treatment agent (hydrochloric acid); This is particularly advantageous if the method of the invention is carried out, for example, on board a ship offshore. When the hydrochloric acid and caustic soda necessary for carrying out the method of the present invention are obtained from concentrated seawater, the concentrated seawater is directly applied to the location of the heavy metal extraction device by evaporating the seawater by a known method. can get. For the evaporation of the water, the waste heat of the nuclear reactor present in the ship (or a floating body corresponding to a ship) as well as other equipment necessary for carrying out the method of the invention is used.

In a highly preferred embodiment of the present invention, in order to further concentrate heavy metals, the eluate containing heavy metals is
It can be brought into contact with an adsorbent matrix which contains biologically fresh humic acids as an adsorbent and in which up to 99% by weight of a substance used as a carrier for humic acids is present. In order to achieve the highest possible heavy metal concentration, the PH of the solution is set sufficiently high (min. 4, max. 8). The distribution coefficient of heavy metals has almost the same value even in this relatively high concentration region as in the seawater concentration region, so by inserting a matrix in the exchange column, the heavy metal concentration of the eluate can be reduced to about its initial value. It is now possible to reduce it to 1/10, and this allows
Subsequent enrichments in the matrix, for example for uranium, range from 10 3 to 10 ³ based on the dry matter of the adsorbent.
Since the value is 10 ⁴ , the uranium concentration in seawater is approximately 10 ⁷ .

Adsorbent matrices used for heavy metal concentration can also be combusted after adsorption of heavy metals. Since the ash residue in the adsorbent matrix is less than 5% of the unburned dry material, combustion further concentrates the heavy metals by about a factor of 20. This indicates that heavy metals are now present in the ash residue at a concentration approximately 10 ⁸ times greater than in seawater, and account for the main component of the ash residue by weight. As described above, heavy metals can be easily isolated by known methods.

Example 1 1 g of air-dried black peat was pulverized and then sieved to obtain granules with a particle size distribution of 70 to 10 μm in a dry state. After moistening with water, swell the granules to a particle size of 100 μm or more using natural seawater at 20°C, pH 8.3, and uranium content of 3.3 μg and vanadium content of 2 μg per unit.
10 and stirred for 4 hours. After separating particulate matter from seawater, the amount of uranium adsorbed in black peat was 18μ
g, and the amount of vanadium was confirmed to be 16 μg.

Although the uranium content in the seawater was reduced by this treatment, it was still 1.5μg/, which is equivalent to the distribution coefficient of uranium, which is 1.2× based on the dry weight of peat.
Corresponds to 10 ⁴ . Similarly, the vanadium content in seawater decreased, but was still 0.3 μg/, corresponding to a vanadium partition coefficient of 5.3×10 ⁴ .

Uranium and vanadium adsorbed in black peat are
The black peat granules are completely eluted by stirring in 200 cm ³ of 1% hydrochloric acid (PH 0.6). Approximately 4 cm ³ of hydrogen ions in hydrochloric acid are consumed per gram of black peat for elution. Concentration and subsequent elution are repeated 30 times in the manner described above using the peat described above. No decrease in the partition coefficients of uranium and vanadium is observed even after using peat as adsorbent 30 times.

Example 2 In the open sea near the island of Sylt, 54 degrees of seawater (7° C.) was pumped through a fluidized adsorbent bed at a rate of 1 per minute. This adsorbent bed consisted of a 2.7-volume tower sealed at the front with a nylon mesh with a pore size of 100 μm, in which 28 g of black peat with the same particle size distribution as described in Example 1 was constantly swirled. There is.

The seawater contained 3.3μg/uranium before the test, and the uranium contained in the seawater 54 before the test was 178μg.
Of this amount, 137 μg (corresponding to 77% of the total amount of uranium) was adsorbed by the adsorbent. At this time, the first 3 seawater pumped through the adsorbent bed with a pump has a uranium concentration of 0.1 μg /
The remaining amount of seawater had a uranium concentration of 0.4 μg/.

Example 3 Natural muddy black peat was inserted into a synthetic resin frame on both sides of a juute net (mesh diameter approximately 2 mm) and a nylon net (mesh diameter 1 mm), with the pasty peat penetrating all the meshes. Place it under pressure as shown. After then air-drying and simultaneous cross-linking, the peat layers present on both sides of the mesh are mutually stabilized by a large number of bonds running through the mesh. Peat having a collective dry weight of 3 g is thus placed on juute and nylon meshes of 1 g each. After rewetting with water, the peat layer on the mesh swells somewhat again. In stability tests, these matrices were exposed to seawater flowing along the matrices at a relative velocity of approximately 2 m/sec for a period of 4 days. The peat layer maintained its shape stability and was not leached from the net at all.

Example 4 40 g of natural black peat with a water content of about 80% obtained from the high marshes of Gros Hesepe in Emsland was stirred for about 15 hours in 120 cm ³ of 0.5N caustic soda solution and then centrifuged. 32% hydrochloric acid was added to the solution after centrifugation until the pH reached 1, and the precipitated humic acid fraction was removed by centrifugation and washed with distilled water to make it neutral. The dry weight of the humic acid thus obtained was 1.2 g. Humic acids in the amounts mentioned above were applied without pre-air drying.
20℃, PH8.3, natural seawater with uranium content of 3.3μg/
10 and stirred for 2 hours. After separating humic acid from seawater, the following results were confirmed.

(i) Uranium in seawater has decreased to 0.6μg/.

(ii) Humic acid contains 25 μg of uranium.

(iii) The partition coefficient is 3.7×10 ⁴ based on the dry weight of humic acid.

Uranium adsorbed on humic acid was completely eluted with diluted hydrochloric acid according to the method of Example 1. Concentration and elution were repeated eight times using the above matrix without deteriorating the partition coefficient.

Example 5 40 g of wet natural black peat of the same consistency as in Example 4 was dissolved in 120 cm ³ of 0.5N caustic soda solution.
Shake for 15 hours and centrifuge. First, add 3.6 g of finely divided activated carbon (average particle size 10 μm) to the solution after centrifugation.
was added, and the pH was adjusted to 1 with 32% hydrochloric acid. The humic acid fraction precipitated at this time was supported on activated carbon as a carrier, and the dry weight of the humic acid-activated carbon matrix thus obtained was 4.8
g, and the weight ratio of humic acid/activated carbon is 1/3
It was hot.

This matrix was stirred for 2 hours with natural seawater 10 as in Example 4, which reduced the uranium content of the seawater from 3.3μg/ to 0.8μg/
g/(if the matrix was air-dried before contacting with seawater) or 0.6 μg (if no pre-drying was performed). The distribution coefficient based on the dry weight of humic acid is 2.6×
10 ⁴ , 3.7×10 ⁴ .

The uranium adsorbed on the matrix was obtained in Example 1.
It was completely eluted with 1% hydrochloric acid as in .
Concentration and elution were repeated 8 times on the same matrix without deteriorating the partition coefficient.

Example 6 In the same manner as described in Example 4, 1.2 g of humic acid was isolated from 40 g of wet natural black peat. The newly precipitated humic acids are suspended in neutral conditions,
The suspension was contacted with 8 g of juute mesh for several days until it was evenly distributed over the juute and dried. The matrix was then re-wetted with seawater, which resulted in approximately 5% of the humic acids supported on the juute.
migrated back into solution, but the remaining matrix was essentially insoluble in water, with less than 1% subsequent loss of humic acid to solution even after several days in contact with flowing seawater.

Example 7 5 g of granular black peat (particle size 100-200 after moistening with water)
μm) was stirred in 50°C seawater (PH8.3, 20°C) for 3 hours. The uranium content in seawater was reduced to 1.5μg/. The separated granules were soaked in 40 cm ³ of 2% hydrochloric acid (PH
The uranium was eluted by stirring in 0.3). The eluate after centrifugation is after the peat elution process.
It had a uranium content of 2.25mg/. after that,
The second 5 g of granular black peat that had been brought into contact with seawater as described above was eluted with an eluate that had been adjusted to pH 0.3 with 32% hydrochloric acid and increased to 45 cm ³ with distilled water. The uranium content of has increased to 4mg/
The concentration was 1.2×10 ³ higher than in seawater.

The eluate was centrifuged again, adjusted to pH 7.4 by adding caustic soda solution, and diluted with distilled water.
Granular black peat 25 with the same particle size as above, increased to 50 cm ³
Stirred for 3 hours with mg. After separating the particulates from the solution, the uranium content of the eluate decreases to 220μ
g/, and that of black peat was specified at 6,760 ppm. This corresponds to the fact that the uranium distribution coefficient at pH 7.4 in this concentration range is 3×10 ⁴ based on the dry weight of the particles. This means that
It has been shown that humic acid in black peat adsorbs and concentrates uranium almost as well as in seawater, even in a concentration range that is 10 ³ higher than that in seawater.

The black peat that had adsorbed uranium was incinerated, and the ash residue contained 169 μg of uranium. The ash content of this black peat is 3% by weight, so the weight of uranium in the ash residue is approximately 22%, which corresponds to a total enrichment of 6.7×10 ⁷ .

Claims (1)

[Claims] 1 (a) Contains biologically new humic acid as an adsorbent for heavy metal concentration, and the material used as a humic acid carrier has a maximum
(b) contacting the adsorbent matrix, present at 99% by weight, with seawater for a time such that the heavy metals present in the seawater and adsorbable on the adsorbent matrix are adsorbed in as large a quantity as possible; (b) step (a); (c) After concentrating the heavy metals, the adsorbent matrix containing heavy metals is separated from seawater. (d) separating the heavy metal-containing acid obtained in step (c) from the adsorbent matrix; (e) adding an alkaline solution to the heavy metal-containing acid separated in step (d); In addition, it contains heavy metals and has a pH of 4 to 8.
(f) contacting the heavy metal-containing solution obtained in step (e) with a substance that has chemical binding or adsorption binding properties to heavy metals in order to further concentrate the heavy metals; (g) The matrix containing the heavy metal adsorbent is characterized by comprising a step of concentrating it with a chemically binding or adsorbing substance in step (f) and then post-treating it to a heavy metal salt by a method known per se. A method for recovering heavy metals dissolved in seawater by binding them to a matrix and concentrating the heavy metals in the matrix. 2. A recovery method according to claim 1, wherein the heavy metals are concentrated in a matrix formed from natural black peat. 3 The diluted acid used to elute heavy metals is
For re-elution of heavy metals, use the dilute acid until the concentration of heavy metals in the dilute acid reaches a value that is on the order of 10 ³ or 10 ⁴ higher than in seawater, when the pH of the acid is higher than that of the concentrated acid. The recovery method according to claim 1 or 2, wherein the concentration is maintained at 2 or less by addition. 4. Washing out the heavy metal-containing adsorbent matrix with hydrochloric acid obtained by electrolysis of sodium chloride contained in seawater,
Collection method described in paragraph 2 or 3. 5. The recovery method according to claim 4, wherein heavy metal-containing hydrochloric acid is added to a caustic soda solution produced by electrolysis of sodium chloride contained in seawater. 6. In order to further concentrate the heavy metals, the heavy metal-containing solution is transferred to an adsorbent matrix which contains biologically fresh humic acids as the adsorbent and in which the substance used as a carrier for the humic acids is present in an amount of up to 99% by weight in the dry state. Claim 1, which is brought into contact with
The collection method described in Section 2, Section 2, Section 3, Section 4, or Section 5.