JP2005087931A - Method and device for removing heavy metal from organism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for removing heavy metals which possess excellent efficiencies in removing the heavy metals without requiring cleaning, or the like, of the electrode plates of an electrolyzer. <P>SOLUTION: The method for removing the heavy metals from an organism includes a dissolution process of dissolving the heavy metals by suspending the organism in an acid solution containing both or one of sulfuric acid and hydrochloric acid, a cleaning process of adding water to a solid content separated from the acid solution and agitating them, and an electrolysis process of removing the heavy metals by electrolyzing an aqueous solution containing the heavy metals obtained through the dissolution process and the cleaning process. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention generally relates to a method and apparatus for removing heavy metals contained in organisms such as marine products and agricultural products. More specifically, the present invention relates to a method and apparatus for removing heavy metals such as cadmium contained in the midgut gland of scallop shells and internal organs of squid that are treated as industrial waste (landfill treatment, incineration treatment, etc.).

  Conventionally, this type of technique involves immersing a living organism containing heavy metals in an acidic solution, electrolytically eluting the heavy metals into the acidic solution, and placing the eluted heavy metals on the cathode plate to which a voltage is applied. There is a method of removing heavy metals from living organisms by precipitation (see Patent Document 1). In addition, in order to improve the electrolysis efficiency in the above-described method, the biological material containing heavy metal is crushed and suspended in an acidic solution, and an electrode plate is inserted between the electrode plates. Has been disclosed (see Patent Document 2). Furthermore, in order to shorten the treatment time, a method is disclosed in which a biological material containing heavy metal is degreased, dried and then suspended in an acidic solution to elute heavy metal, and electrolytic treatment is performed (Patent Document). 3).

  In these methods, heavy metals can be quickly removed in the initial stage of heavy metal removal treatment, but as the removal treatment is repeated, a fine suspension obtained by pulverizing organisms on the cathode plate on which heavy metals are deposited. And the fat and oil contained in the living organisms adhere and the precipitation efficiency decreases, thereby increasing the time for removing heavy metals. Also, the method described in Patent Document 3 also removes fats and oils, but in order to electrolyze an acidic solution in which organisms coexist, fine solids crushed during the treatment are deposited on the cathode plate. , Heavy metal deposition efficiency decreases. In order to cope with such a situation, a method of taking out the electrode plate from the electrolytic cell and rubbing it with a high-pressure washing machine or a brush is performed every certain number of times. In addition, an electrode plate cleaning method is also performed in which the polarity of the applied voltage is reversed by changing the electrolyte (see Patent Document 4). Furthermore, an apparatus in which an oil separation tank by ultrasonic vibration is added to the electrolysis process for oil separation has been proposed (see Patent Document 5).

Japanese Patent No. 2667986 JP 2001-205224 A Japanese Patent No. 3175762 JP 2000-166517 A Japanese Patent No. 2930947

  However, the method of removing the electrode plate from the electrolytic cell and cleaning it requires a great deal of time and labor in the case of a practical plant scale. In addition, the method of reversing the polarity of the applied voltage by exchanging the electrolyte solution re-dissolves the heavy metals deposited at the same time as the suspended matter of the attached organism and the oil and fat, so that it is necessary to separate them later. The processing becomes complicated, and the expensive anode plate is severely worn, resulting in an increase in processing cost. Furthermore, the method of separating fats and oils by ultrasonic vibration does not heat the liquid, so that the separation is insufficient and the effect is small. As described above, there is a problem in the conventional technology, and there is no satisfactory method at present.

  Accordingly, the present invention overcomes the problems in the prior art, and in particular, provides a method and apparatus for removing heavy metals from a living organism that has good heavy metal removal efficiency without requiring cleaning of the electrode plate of the electrolytic cell. It is intended to provide.

  The method for removing heavy metals from an organism according to claim 1 includes an elution step of suspending the organism in an acidic solution containing sulfuric acid and / or hydrochloric acid to elute heavy metals, and the acidic solution A water washing step of adding water to the solid content separated from the mixture and stirring, and an electrolysis step of removing heavy metals by electrolytic treatment of the heavy metal-containing aqueous solution obtained through the elution step and the water washing step It is what.

  The method for removing heavy metals from an organism according to claim 2 of the present application further includes a degreasing step for removing oil and fat from the organism prior to the elution step. To do.

  The method for removing heavy metals from the organism according to claim 3 of the present invention is the method according to claim 1 or 2, wherein after the electrolysis step, a solid treatment remaining in the aqueous solution is recovered by a coagulation treatment. Further, the aqueous solution containing the solid content is reused in the elution step and / or the water washing step.

  An apparatus for removing heavy metals from an organism according to claim 4 of the present application is an elution device for suspending the organism in an acidic solution containing sulfuric acid and / or hydrochloric acid to elute heavy metal, and heavy metal In order to promote elution of water, a water washing device for adding water to the solid content separated after the elution treatment and stirring, and an electrolytic cell for electrolyzing the heavy metal-containing aqueous solution obtained by the elution device and the water washing device It is characterized by having.

  The apparatus for removing heavy metals from the organism according to claim 5 of the present invention is the apparatus for removing fats and oils in the organism before the treatment by the elution apparatus and the water washing apparatus in the apparatus of claim 4. A degreasing device, wherein the degreasing device comprises a crusher for crushing the organism, a heating stirrer for heating and stirring the crushed organism, and the heated and agitated organism And a separator for separating oil and fat.

  The apparatus for removing heavy metals from a living organism according to claim 6 of the present application is the apparatus according to claim 4 or 5, further comprising a coagulation treatment apparatus for coagulating solids remaining in the electrolytically treated aqueous solution. It is characterized by having.

  According to the method and apparatus described in claims 1 and 4 of the present invention, before the electrolytic treatment, in order to remove the fine crushed material of the organism suspended in the heavy metal-containing aqueous solution, The situation of adhering to the cathode plate is avoided, and good heavy metal removal efficiency can be maintained. Moreover, according to the method and apparatus of Claim 2 and 5 of this invention, since the fats and oils of a heavy metal organism are removed before electrolysis, the situation which the said fats and oils adhere to a cathode plate in electrolysis is avoided. Thus, it becomes possible to maintain good heavy metal removal efficiency. Furthermore, according to the method and apparatus of claims 3 and 6 of the present invention, since the solid content remaining in the aqueous solution is recovered by agglomeration treatment, the yield of the product is improved and the aqueous solution from which the solid content is recovered By reusing in the elution step and / or the water washing step, it becomes possible to reduce the wastewater treatment load. In addition, the dried material (product) obtained by this invention is less than the regulation value of heavy metal content, when using effectively as a protein protein source.

  Next, a heavy metal removing method according to a preferred embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a flowchart schematically showing a heavy metal removal method according to a preferred embodiment of the present invention.

  First, an organism containing a heavy metal is pulverized to about 1 mm using a crusher such as a meat chopper or a food processor, and then stirred while heating to solidify the protein. At this time, heating is preferably performed in a short time in order to suppress oxidation of the oil. Moreover, in order to prevent the formation of an emulsion, stirring is preferably performed using a sealed apparatus so as not to entrain air as much as possible. From the slurry-like organisms thus heat-treated, oil and fat are removed using a three-phase separator or a decanter and a centrifuge (hereinafter referred to as “degreasing step” or “pretreatment step”).

  In general, in the visceral treatment of fish and shellfish such as scallop midgut gland and squid viscera, the degreasing method by a screw press performed in the process of producing fish meal has a fine solid content. It escapes from the screen holes and is inappropriate.

  Next, the solid content is suspended in an acidic solution containing sulfuric acid and / or hydrochloric acid, and the heavy metal is eluted in the acidic solution (hereinafter referred to as “elution step”). By this elution step, the heavy metal bonded to the protein is dissociated. The acid concentration of the acidic solution has a pH of about 4 or less, preferably about 1 to about 2. Further, according to experiments conducted by the present inventors, it was found that the elution effect is substantially the same regardless of the type of acid if the pH is the same. Since the acid is practically non-volatile and inexpensive, sulfuric acid is preferred.

  Next, the acidic solution from which the heavy metal is eluted is centrifuged to separate the solid content, and about 3 to 4 times the amount of water is added to the obtained solid content and stirred for about 1 hour. This promotes the removal rate of heavy metals (hereinafter referred to as “water washing process”). This is because the heavy metal becomes a water-soluble ion after the bond between the heavy metal and the protein is dissociated by suspending in an acidic solution in the elution step, so that the elution easily proceeds even by washing with water. In addition, after adding water in a water-washing process, it is preferable to heat to about 30 degreeC-about 50 degreeC.

  In the water washing step, not only heavy metals are removed, but also excess acid remaining in the organism is removed at the same time. Therefore, when heavy metals are finally removed and neutralized by adding alkali to living organisms when used as feed / fertilizer, the amount of alkali added decreases and neutralization remains in the final product. Things are also reduced, which is very preferable from the viewpoint of cost and quality.

  The water washing process is performed 1 to 3 times depending on the heavy metal concentration in the organism. At that time, the heavy metal contained in the organism is equilibrated and distributed between the solid content and the aqueous solution in accordance with the solid-liquid ratio. Therefore, the amount of water to be added and the number of repetitions of the washing process are the initial heavy metals of the organism. It is preferable to appropriately determine the concentration and the heavy metal concentration required for the final product.

  Next, the heavy metal-containing aqueous solution obtained through the degreasing step, the elution step, and the water washing step is supplied to the electrolytic cell, and a heavy metal is deposited on the cathode plate by applying a voltage to the electrode plate of the electrolytic cell (hereinafter referred to as “electrolysis”). Process ”). In the method of the present invention, the degreasing process, the elution process, and the water washing process are performed before the electrolysis process, and the fine suspensions and fats and oils of living organisms are remarkably reduced in the electrolytic solution. The surface of the cathode plate on which heavy metals are deposited is maintained without a suspended matter or oil and fat, so that a good surface state is maintained. This shortens the electrolysis time and increases the heavy metal removal efficiency as the number of electrolytic treatments increases. The phenomenon of decline is greatly relieved.

  Next, a coagulant is added to the electrolytic solution from which heavy metals have been removed, and the remaining solid content is recovered by centrifugation (hereinafter referred to as “post-treatment process”). On the other hand, a part of the aqueous solution can be reused in the elution step and the water washing step, thereby improving the solids recovery rate and increasing the product yield. In addition, since this aqueous solution can be used repeatedly several times, it is not always necessary to carry out the aggregation treatment every time.

  The solid content recovered in the post-treatment process is dried after being neutralized together with the solid content recovered in the water washing process (hereinafter referred to as “neutralization / drying process”) and reused in feed, fertilizer, and the like. .

  The method of the present invention is a product with much less energy than the conventional method in which the solution used is evaporated each time in a concentrating tube and finally returned to the dryer to improve the product yield. The yield can be improved. In addition, the heavy metal removal method by electrolytic treatment of the present invention does not need to add an alkali or the like for adjusting pH to an aqueous solution, compared to a conventional method using an ion exchange resin or performing a precipitation treatment, Since the cadmium concentration can be reduced to about 0.01 mg / L, it can be reused as it is in the elution step and the water washing step after removing heavy metals.

  Next, a heavy metal removing apparatus according to a preferred embodiment of the present invention will be described with reference to the drawings. FIG. 2 is a schematic diagram schematically showing a heavy metal removing apparatus according to a preferred embodiment of the present invention.

  The heavy metal removal apparatus according to a preferred embodiment of the present invention, indicated as a whole by the reference numeral 10 in FIG. 2, includes a crusher 12 for crushing heavy metal-containing organisms. As the crusher 12, a meat chopper, a food processor, or the like is used. The heavy metal-containing organisms crushed by the crusher 12 are usually temporarily stored in the hopper 14.

  The heavy metal removing device 10 also includes a heating stirrer 16 for heating and stirring the pulverized heavy metal-containing organism. The heating stirrer 16 is configured to agitate a heavy metal-containing organism by an agitating blade (not shown) rotated by a motor (not shown) while heating the heavy metal-containing organism by an attached boiler (not shown). . In addition, you may use a general thing for a boiler, a motor, and a stirring blade. Moreover, since the heating stirrer 16 does not produce an emulsion, it is preferable that the heating stirrer 16 be a sealed type so that air is not involved as much as possible. The supply of heavy metal-containing organisms from the hopper 14 to the heating stirrer 16 is performed by a pump 18.

  The heavy metal removal device 10 also includes an elution device 20 for eluting heavy metals in the heavy metal-containing organism. The elution apparatus 20 has an elution tank for containing an acidic solution containing either or both of sulfuric acid and hydrochloric acid, and the heavy metal-containing organism from which the fats and oils have been removed by the three-phase separator 22 is converted into an acidic solution. The heavy metal in the heavy metal-containing organism is eluted by being suspended in the solution. In FIG. 2, reference numerals 24, 26, and 28 denote an oil / fat storage tank, an aqueous solution storage tank, and a solid content storage for storing the oil / fat, the aqueous solution, and the solid separated by the three-phase separator 22. Each tank is shown.

  The heavy metal removing device 10 is also provided with a water washing device 30 for adding water to the solid content separated after the elution treatment and stirring in order to promote elution of heavy metals. In FIG. 2, reference numeral 32 indicates a centrifuge for separating the solid content of the acidic solution from which heavy metals are eluted.

  The heavy metal removing apparatus 10 also includes an electrolytic bath 34 for performing an electrolytic treatment of the heavy metal-containing aqueous solution, and the electrolytic bath 34 includes an anode plate 34a and a cathode plate 34b.

  The heavy metal removal device 10 further includes a coagulation treatment device 36 for coagulating the electrolytic solution from which heavy metals have been removed, and a neutralization treatment tank 38 for neutralizing the coagulated solid content. As the agglomeration processing apparatus 36 and the neutralization processing tank 38, ordinary ones may be used. In FIG. 2, reference numerals 40 and 42 indicate a centrifuge and a dryer, respectively.

  An example in which the internal organs of squid are used as the heavy metal-containing organism will be described. As a raw material, 20 kg of squid internal organs (including a part of the geso) was crushed into a slurry by a meat chopper (pore diameter 3.2 mmφ). Next, the crushed material in a slurry state is supplied to a heated stirrer at a rate of about 100 liters / hour by a pump, heated at about 80 ° C. for about 8 minutes to coagulate proteins, and dissociate fats and oils. By supplying to a three-phase separator and processing the solid content discharge interval at 2 minutes 30 seconds, the solid content was 8.24 kg (water content 66.8 wt%), heavy liquid (aqueous solution) 5.9 kg (water content) Amount 90.1% by weight) and 4.5 kg of light liquid (oil and fat content). Subsequently, solid content and aqueous solution were mixed, sulfuric acid was added so that pH might be set to 2, and it stirred at about 40 degreeC for about 1 hour, and the heavy metal contained was eluted.

  The slurry thus obtained was then separated into a solid and an aqueous solution by centrifuging. And the aqueous solution was sent to the electrolysis process in order to remove heavy metals. On the other hand, in order to further remove the heavy metal remaining in the solid content, a water washing step for adding heavy water to the aqueous solution by adding 4 times the amount of water to the solid content and stirring at 40 ° C. for 1 hour. went. In this experiment, the water washing process was repeated twice, and the solid content finally obtained was neutralized with slaked lime and then dried with a dryer.

  Table 1 is a table showing the measurement results of the cadmium concentration in each step of this experiment. As can be seen from Table 1, cadmium, which was 22.4 mg / kg (per dry weight) before treatment, decreased to 1.5 mg / kg (per dry weight) after the first water washing step (this value is It has already fallen below the regulation value of 2.5 mg / kg as a feed) and decreased to 1.0 mg / kg (removal rate: 95.5% per dry weight) after the second water washing step. In addition, the fat and oil content was 42.5% (per dry weight) before treatment, but decreased to 17.0% (per dry weight) in the final dry product, resulting in a nearly satisfactory concentration. .

Table 2 shows the electrolysis conditions when the electrolytic treatment (24 hours) was performed on the heavy metal-containing aqueous solution (150 liters, pH 1.63) obtained in the elution step and the water washing step.

As a result of the electrolytic treatment, the change in cadmium concentration with time decreased to 0.01 mg / liter in 24 hours (removal rate 98.8%) as shown in Table 3. Further, no suspension or oil or fat was adhered to the cathode plate after the electrolytic treatment, and a good surface state was maintained.

  In the method according to the present invention, the cadmium concentration in the heavy metal-containing aqueous solution is almost equal to the environmental standard (0.01 mg / L) without adjusting the pH by adding alkali, unlike the conventional method using ion exchange resin or precipitation. It can be reduced to a level comparable to the above, and can be sufficiently reused in the elution process and the water washing process.

  Moreover, since fine solid content still remains in the aqueous solution from which cadmium has been removed in the electrolysis step, 5 L of 0.5 wt% chitosan solution was added to 150 L of aqueous solution, and after 5 minutes of rapid stirring and mixing, The mixture was gently stirred for 30 minutes to sufficiently form a floc, and then centrifuged to recover a solid content of 3.9 kg (water content 84.9% by weight). The cadmium concentration in the dried product of the solid content was 1.8 mg / kg, which was lower than the feed content regulation value. In this example, chitosan was used as a flocculant because chitosan is used for food addition, and when an organism from which heavy metals have been finally removed is effectively used as feed, it is not adversely affected. Because. In the present invention, a flocculant other than chitosan may be used as long as it is a flocculant used in a food processing step or the like. Furthermore, when treating an aqueous solution repeatedly used, water can be reduced by evaporating water to some extent with a concentrating tube or the like, and finally drying to recover water-soluble protein or the like.

  In this example, heating was performed at 80 ° C. to separate fats and oils from the organism, but the heating temperature was about 60 ° C. to about 100 ° C., preferably about 70 ° C. to about 80 ° C. Any range is acceptable. The reason for setting the heating temperature in this way is that if the temperature is less than 60 ° C., the protein does not coagulate much and the separation of fats and oils is poor, and if it is 100 ° C. or more, the fats and oils deteriorate. The fats and oils thus obtained contain a lot of useful substances such as docosahexaenoic acid (DHA) and can be recovered.

  In this example, the temperature of the acidic solution in the elution step and the temperature of the aqueous solution in the water washing step were set to 40 ° C., but the liquid temperature was about 10 ° C. to about 60 ° C., preferably about 30 ° C. to about 50 °. It may be in the range of C. The reason for setting the liquid temperature range in this way is that the elution rate of heavy metal is slow at less than 10 ° C, and the soluble content increases and the yield of the product decreases at 60 ° C or more.

  Using 100 kg of squid internal organs as a raw material, a degreasing step, an elution step, a water washing step, and a neutralization / drying step were performed under the same conditions as in Example 1 to obtain 14.6 kg of a dried product. Moreover, the electrolytic process, the post-processing process, and the neutralization and drying process were implemented with respect to the acidic solution containing a heavy metal, and 2.1 kg of dried products were obtained. Thereafter, a part of the aqueous solution obtained from the electrolysis step and the post-treatment step was reused in the elution step and the water washing step, and a new squid internal organ 100 kg was treated.

Table 4 shows the cadmium concentration in the dried product obtained by continuously performing the cadmium removal treatment 10 times in this manner.

  As shown in Table 4, the cadmium concentration obtained by this experiment is in the range of 0.7 mg / kg to 1.5 mg / kg (per dry weight), and the feed regulation value (2.5 mg / kg) is sufficient. Fell below. Further, in this experiment, although the cathode plate was not cleaned at all, adhesion of fine organisms and oils and fats to the cathode plate was not recognized, and a good surface state was maintained.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the invention described in the claims, and these are also included in the scope of the present invention. Needless to say, it is something.

  For example, the degreasing step and / or the post-processing step may be omitted from the respective steps in the embodiment.

It is the flowchart which showed roughly the heavy metal removal method which concerns on preferable embodiment of this invention. It is the schematic diagram which showed roughly the heavy metal removal apparatus which concerns on preferable embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Heavy metal removal apparatus 12 Crusher 14 Hopper 16 Heating stirrer 18 Pump 20 Elution apparatus 22 Three-phase separator 24 Oil storage tank 26 Aqueous solution storage tank 28 Solid content storage tank 30 Washing apparatus 32 Centrifugal separator 34 Electrolyzer 36 Coagulation treatment apparatus 38 Neutralizer 40 Centrifuge 42 Dryer

Claims (6)

A method for removing heavy metals from an organism,
An elution step of suspending the organism in an acidic solution containing sulfuric acid and / or hydrochloric acid to elute heavy metals;
A water washing step in which water is added to the solid content separated from the acidic solution and stirred;
An electrolytic process for removing heavy metals by electrolytic treatment of the heavy metal-containing aqueous solution obtained through the elution process and the water washing process;
A method comprising the steps of: The method according to claim 1, further comprising a degreasing step of removing fat and oil from the organism prior to the elution step. After the electrolysis step, further comprising a post-treatment step of recovering the solid content remaining in the aqueous solution by agglomeration treatment,
The method according to claim 1 or 2, wherein the aqueous solution from which the solid content has been collected is reused in the elution step and / or the water washing step. An apparatus for removing heavy metals from living organisms,
An elution apparatus for suspending the organism in an acidic solution containing sulfuric acid and / or hydrochloric acid to elute heavy metals;
In order to promote elution of heavy metals, a water washing device for adding water to the solid content separated after the elution treatment and stirring,
An electrolytic tank for electrolytically treating the heavy metal-containing aqueous solution obtained by the elution device and the water washing device;
A device characterized by comprising: Before the treatment by the elution device and the water washing device, the device further comprises a degreasing device for removing oil and fat in the organism, and the degreasing device is a crusher for crushing the organism, The apparatus according to claim 4, further comprising: a heating stirrer for heating and stirring the crushed organism, and a separator for separating oil and fat from the heated and stirred organism. The apparatus according to claim 4, further comprising an aggregating apparatus for aggregating the solid content remaining in the electrolytically treated aqueous solution.

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