JP4000346B1 - Method for removing heavy metal from organic substance containing heavy metal, and method for producing food obtained thereby - Google Patents

Abstract

[PROBLEMS] Some marine products contain heavy metals harmful to internal organs, and some agricultural products such as vegetables, beans, and grains contain heavy metals absorbed from the soil. Since inevitably contains heavy metals, it provides a technology for economically removing heavy metals from these agricultural and marine products while maintaining freshness and quality.
By mixing and stirring an organic substance containing heavy metal together with a heavy metal adsorbent in a weakly acidic aqueous solution, the heavy metal is simultaneously adsorbed and removed from the organic substance and the liquid phase in a short time.
[Selection] Figure 1

Description

The present invention relates to a method for removing heavy metals from organic materials containing heavy metals while maintaining freshness and quality, and further relates to a technique for using organic materials from which heavy metals have been removed as food.

In the case where low freshness and low quality organic substances that are not suitable for food are processed, they can be used as feed or fertilizer after removing heavy metals.

Methods for removing heavy metals from organic materials containing heavy metals include methods in which organic materials are immersed in a strongly acidic aqueous solution (pH 1) such as sulfuric acid to dissociate the heavy metals and then deposited on the electrode (Patent Document 1). A method of adsorbing and removing heavy metal in the liquid phase after dissociating the heavy metal into the liquid phase (Patent Document 2), and adsorbing the heavy metal in the liquid phase after dissociating the heavy metal into the liquid phase using microorganisms such as lactic acid bacteria and yeast There is a method of removing (Patent Document 3).

However, the method of precipitating an organic substance in a strongly acidic aqueous solution (pH 1) such as sulfuric acid to dissociate heavy metals and then depositing it on the electrode uses a denatured useful component (protein, lipid, etc.) in the organic substance and uses an alkali such as lime. Neutralization does not return to denaturation, and it is difficult to use organic matter in which a large amount of lime added to neutralize strongly acidic aqueous solution remains in the form of gypsum as food. There were problems such as high cost and long processing days.

In addition, with regard to the method of adsorbing and removing heavy metal in the liquid phase after dissociating heavy metal into the liquid phase using self-digesting enzymes, it is difficult to suppress contamination by bacteria because the heavy metal is adsorbed in the neutral range, and organic matter is likely to decay. In addition, the generation of a wide variety of degradation products due to other enzymes is a major problem when used as food.

Furthermore, for the method of adsorbing and removing heavy metal in the liquid phase after dissociating heavy metal into the liquid phase using microorganisms such as lactic acid bacteria and yeast, dissociation of heavy metal into the liquid phase, solid-liquid separation of organic and liquid phases, and liquid A series of steps for removing heavy metal from the phase takes a long time, and the quality such as taste and odor is lowered. Therefore, it can be used as feed and fertilizer, but it is difficult to use as food.

On the other hand, the inventor announced a method of adsorbing and removing cadmium by determining the number of cadmium binding sites and binding constants of scallopuro and mixing and stirring with scallopuro in nitric acid solution using insolubilized humic acid as an adsorbent. (Non-Patent Document 1). However, according to the above method, the insolubilized humic acid adsorbed by cadmium remains in the treated scallop and is difficult to use as a food.
JP 07-203036 A JP 06-106155 A Japanese Patent No. 3174825 Hideki S.H. , Akira S. (1997) A new method for the removal of toxic metal ions from acid-sensitive biomaterial. Journal of colloid and interface science 190, pp. 206-211.

This invention makes it a subject to isolate | separate a heavy metal economically in a short time, and to utilize as a foodstuff, maintaining the freshness and quality from the organic substance containing a heavy metal.

The heavy metal removal method of the present invention is characterized in that heavy metals can be simultaneously removed from an organic substance and a liquid phase by stirring and mixing the heavy metal adsorbent in an acidic aqueous solution without heating the organic substance containing the heavy metal. By carrying out at a low temperature, the action of self-digesting enzymes and the growth of microorganisms can be suppressed, and heavy metals can be removed in a short time while maintaining the freshness and quality of organic matter.

Further, the heavy metal removal method of the present invention uses a competitive adsorption equilibrium of the organic matter and the adsorbent with heavy metal ions, and the heavy metal adsorption capacity of the adsorbent is excessive with respect to the heavy metal adsorption capacity of the organic matter under weakly acidic conditions. The adsorbent may be added so that the heavy metal can be more efficiently adsorbed and removed simultaneously from the organic substance and the liquid phase.

Moreover, it is preferable to perform the heavy metal removal method of this invention on low-temperature conditions of 2 degreeC-7 degreeC.

Furthermore, the organic substance obtained by the heavy metal removal method of the present invention is free from cadmium of 90.0% and can be used as food.

According to the present invention, since heavy metals can be removed from organic substances containing heavy metals in a short period of time under weak acidity, it is possible to economically separate heavy metals from agricultural and marine products containing heavy metals such as cadmium without impairing freshness and quality, feed, It can be used not only as a fertilizer but also as a food.

The “heavy metal” in the present invention refers to cadmium, lead, arsenic, mercury and the like, and means at least containing cadmium and existing in an ionic form.

In the present invention, organic substances containing heavy metals are targeted. The “organic matter” in the present invention refers to marine products such as seafood, livestock products such as livestock meat and chicken eggs, and agricultural products such as vegetables, beans, and grains, and not only natural products but also genetically modified products and processed products. included. Therefore, it is obvious to those skilled in the art that squid viscera, soybeans, and the like are included in the organic matter. The “squid internal organs” generally refers to the viscera of a bandit, and sometimes only the liver.

The “heavy metal adsorbent” in the present invention refers to a resin, fiber or natural material having a chelating action or an ion exchange action, and includes those inexpensive natural materials such as corrosive substances, algae and clay minerals for those skilled in the art. It is self-explanatory.

In the present invention, “acid” refers to organic acids such as formic acid, lactic acid, acetic acid and citric acid, or inorganic acids such as hydrochloric acid, sulfuric acid and phosphoric acid, and “acidic” generally refers to a pH of less than 7.0. The “acidic aqueous solution” refers to a liquid in which an acid is dissolved in water and is acidic.

“Mixing and stirring” in the present invention refers to mixing and stirring the organic substance containing heavy metal and the heavy metal adsorbent, and may be stirred after combining the organic substance containing heavy metal and the heavy metal adsorbent. The other may be added while stirring one.

“Adsorption” in the present invention means that a heavy metal is attracted to a heavy metal adsorbent or that a heavy metal is captured by the heavy metal adsorbent, and includes not only positive adsorption but also negative adsorption. Further, “adsorption removal” means removal of a heavy metal adsorbent on which heavy metals have been adsorbed, and removal of only heavy metals from a heavy metal adsorbent on which heavy metals have been adsorbed.

Competitive adsorption equilibrium in the present invention means that when a heavy metal adsorbent is added to a solution containing an organic substance containing heavy metal, a phenomenon in which cadmium heavy metal is competing competitively between the organic substance and the adsorbent occurs. By adding the adsorbent so that the adsorption capacity of the material is excessive with respect to the adsorption capacity of the organic matter, it means that the previous phenomenon reaches an equilibrium state, that is, the mutual adsorption action reaches an equilibrium state, In the state of competitive adsorption equilibrium, the adsorbent adsorbs more heavy metals than the organic matter.

“Weakly acidic” in the present invention preferably means pH 3.0 to 5.0, more preferably pH 4.0 to 4.5.

In general, heavy metals are bound to specific proteins (metallothionein) in organic matter. In order to completely dissociate heavy metals bound to metallothionein (99.5% or more) by acid treatment, a strong acid at pH 1.0 is used. (Patent Document 1). According to the heavy metal (adsorption) removal method of the present invention, heavy metals can be separated from organic substances under weakly acidic conditions by mixing and stirring an organic substance containing heavy metals and a heavy metal adsorbent.

In the heavy metal removal method of the present invention, it is preferably performed under conditions of pH 4.5 or less, more preferably performed under conditions of pH 4.0 to 4.5, from the viewpoint of suppression of quality degradation due to self-digestion and propagation of various bacteria. preferable.

The heavy metal removal method of the present invention is carried out by adding an adsorbent so that the heavy metal adsorption capacity is about 40 times that of organic substances (10.0 to 20.0% of organic substances on a dry weight basis) under weakly acidic conditions. Thus, it is possible to simultaneously separate heavy metals from the organic substance and the liquid phase in a short time.

Moreover, it is preferable to perform the heavy metal removal method of this invention on low temperature conditions, Preferably it is 1 to 12 degreeC, More preferably, it is 2 to 7 degreeC, More preferably, it is performed on low temperature conditions of 4 to 6 degreeC.

In conventional acid treatment methods, heavy metals are dissociated using substitution reactions between heavy metals in organic substances and liquid phase hydrogen ions, and strong acidic aqueous solutions are used because the hydrogen ion concentration in the liquid phase is the driving force for substitution reactions. There was a need. In the heavy metal removal method of the present invention, the heavy metal concentration in the liquid phase is always kept at a low concentration by immediately removing a small amount of heavy metal dissociated from the organic material into the liquid phase with the adsorbent, and the concentration difference between the organic material and the heavy metal in the liquid phase As a driving force, the heavy metals are dissociated from the organic matter, so that 99.0% or more of the heavy metals in the organic matter can be removed even under weakly acidic conditions.

In the conventional method, it took 4 to 7 days to reduce the heavy metal (Patent Document 3). However, according to the heavy metal removal method of the present invention, it takes a short time of about 24 hours under mildly acidic and low temperature conditions. Can remove more than 99.0% of heavy metals, so that it can suppress acid denaturation of proteins and lipids, self-digestion by enzymes, and proliferation of various bacteria that cause deterioration of freshness and quality. It can be used as food.

Moreover, in order to use the organic substance from which heavy metals have been removed as food, it is necessary to adjust the neutrality with a neutralizing agent. However, the hydrogen ion concentration of the acidic aqueous solution used in the present invention is used in the existing technology. It is about 1 / 10,000 of a strongly acidic aqueous solution (pH 1.0), and the amount of neutralizing agent can be greatly reduced, so it hardly affects the quality.

According to the present invention, the heavy metal contained in the organic substance can be removed until it becomes 0.1 mg / kg or less in a water-containing state. Further, since heavy metals can be removed in a short time under weak acidity, the work safety is high and the processing cost is low.

According to the method of the present invention, the processing time and the amount of chemicals used can be significantly reduced compared to the existing technology, which is inherently low cost, but cheap natural materials such as corrosive substances, algae and clay minerals are used as the adsorbent. By doing so, the cost of the heavy metal adsorbent can be further greatly reduced, so it is suitable for the production of feed and fertilizer from low freshness and low quality organic matter that cannot be used as food.

EXAMPLES Hereinafter, although an Example demonstrates this invention more concretely, this invention is not limited at all by these Examples.

In this example, squid internal organs were used.

What homogenized 200 g of internal organs of fresh squid (Uragawa-cho, Hokkaido) containing cadmium as the organic substance to be treated was used.

The squid viscera was added to 190 g of dilute citric acid (manufactured by Wako Pure Chemical Industries), adjusted to pH 3.0, and stirred for 2 hours. Since the pH increased when squid viscera was added, dilute aqueous citric acid solution was added to adjust the pH to 4.0.

Next, 20% of chelate resin (Eporus MX-8C made by Miyoshi Oil & Fats) is added to the squid viscera, and a stirring blade is attached to a stirrer (Tokyo Rika Histarr HI-15) to prepare an aqueous solution, squid viscera and chelate resin. The mixture was stirred for 24 hours.

The stirring speed was such that the chelate resin diffused throughout, and the treatment temperature was maintained at 5 ° C. in an incubator (LTI601SD manufactured by EYELA).

As a result, cadmium in the squid viscera, whose initial concentration was 23 mg / kg in the water-containing state, decreased to 0.6 mg / kg or less in the above state after 12 hours, and 0.1 mg / kg in the state after 24 hours. It became the following. Then, when neutralizing with sodium bicarbonate and comparing the flavor and taste with raw, the flavor was almost the same, and the taste was slightly inferior to that of raw, but not inferior.

FIG. 1 shows the transition of the cadmium concentration in the liquid phase, the solid phase, and only the liquid phase in order to show the state where cadmium was separated from the squid viscera by the method according to the present invention. In this example, immediately after the stirring, the cadmium dissociation rate from the solid phase, that is, the organic substance exceeds the cadmium adsorption rate in the heavy metal adsorbent, so the cadmium concentration in the liquid phase is relatively high. Since the dissociation rate and the dissociation adsorption rate are equal, the cadmium concentration in the liquid phase is lowered.

On the other hand, FIG. 2 shows a state in which cadmium is separated from the squid viscera by passing only liquid through a column filled with the heavy metal adsorbent and circulating it without stirring the organic substance and the heavy metal adsorbent simultaneously. According to this example, since cadmium cannot be quickly removed from the liquid phase, it takes time to separate cadmium from the solid phase. It can be seen that the separation of cadmium takes at least four times longer than the method according to the invention.

In addition, when no heavy metal adsorbent is added, the cadmium concentration in the liquid phase increases with the dissociation of cadmium from the organic matter, so when washed with an acid having a pH of 4.0 to 4.5, the cadmium in the organic matter is 80.0% to Dissociates about 50.0%.

Table 1 shows the correlation between the elapsed time, the residual concentration of cadmium, and the cadmium removal rate. In the method according to the present invention, since the heavy metal adsorbent and the organic substance are mixed and stirred simultaneously, it is clear from Table 1 that the heavy metal dissociated from the organic substance is quickly captured by the adsorbent.

FIG. 3 shows the results of a cadmium elution experiment with citric acid. The same weight citric acid aqueous solution was added to the squid viscera (water-containing product), and the pH was adjusted by changing the citric acid concentration. It can be seen that the cadmium elution rate increases rapidly with decreasing pH in the range of about pH 4.0 to 5.0. It can also be seen that in order to elute 99.0% or more of cadmium, the pH must be at least 3.0 or less.

FIG. 4 shows the relationship between the amount of citric acid added and the pH when the same amount of citric acid aqueous solution was added to the squid viscera (water-containing product) (same conditions as in FIG. 3). When adjusting to pH 4.5, about 1.0% citric acid may be added to the squid viscera, and about 2.0% at pH 4.0, but when adjusting to pH 3.0, about 10% is added. 0.0% citric acid must be added. From this figure, it can be seen that by performing the cadmium treatment in the strongly acidic region, not only the quality of the organic matter to be treated is impaired, but also the treatment cost is greatly increased.

FIG. 5 shows the results of a cadmium adsorption experiment using a weak acid cation exchange chelate resin (A) and a strong acid cation exchange resin (A). The experiment was conducted with an initial cadmium concentration of 10 ppm and a resin addition amount of 200 g / L. The adsorption rate (▲) of the chelate resin increases rapidly from about pH 3.0 as the pH rises, but the adsorption rate (Δ) of the strongly acidic resin hardly changes at pH 3.0 or higher. From the figure, it seems that the strongly acidic cation exchange resin whose cadmium adsorption rate is not affected by pH seems to be more suitable for the cadmium removal operation according to the present invention, but the regeneration of the resin having such adsorption characteristics. Requires a cadmium desorption treatment with a strongly acidic aqueous solution having a pH of 1.0 or less. Therefore, when considering the cost and safety of the process including regeneration of the adsorbent after use, an adsorbent having an adsorption characteristic such as a chelate resin that can be regenerated with a weakly acidic aqueous solution is suitable.

FIG. 6 compares the pH dependence of cadmium elution from the squid viscera (FIG. 3) and cadmium adsorption to the chelate resin (FIG. 5). At pH 3.0 where the cadmium elution rate from the squid viscera is high, the cadmium adsorption rate to the chelate resin is extremely low, and at pH 6.0 where the cadmium adsorption rate to the chelate resin is high, the cadmium desorption rate from the squid viscera is extremely low. From this, it can be seen that the optimum operating condition for efficiently transferring cadmium in the squid viscera to the chelate resin is around pH 4.5 where both the desorption rate and the adsorption rate are about 50%. As described above, operation at about pH 4.5 is advantageous in terms of cost.

The change in pH of the squid viscera with the treatment temperature is shown in FIG. From this figure, it can be seen that at 30 ° C., the pH decreases due to the increase in fatty acids due to lipid degradation.

In this example, the experiment was conducted on soybeans containing cadmium.

As the organic substance to be treated, 50 g of soybean containing cadmium (in this company, soybean grown on soil containing cadmium) crushed with a mill (Minister blender manufactured by Oster) was used.

The pulverized soybean was immersed in 50 g of dilute citric acid aqueous solution adjusted to pH 3.0 and stirred. Since the pH increased when the soybean ground material was added, an aqueous citric acid solution was added to adjust the pH to 4.0.

A stirring blade was attached to the stirrer, and the aqueous solution and soybean were mixed and stirred. The stirring speed was such that the chelate resin diffused throughout, and the treatment temperature was maintained at 5 ° C. in an incubator.

It took about 12 hours for the soybean to absorb water and swell, and then cadmium dissociation occurred. Therefore, after 12 hours, the resin was added to the chelate and stirring was continued for about 36 hours.

As a result, cadmium in soybean, which had an initial concentration of 1.77 mg / kg in a water-containing state, decreased to 0.6 mg / kg or less in the above state after 36 hours, and 0.07 mg in the above state after 48 hours. / kg or less. After that, it was neutralized with baking soda and compared with raw soybeans in flavor and taste.

When the treatment is carried out at about pH 3, the adsorption efficiency of the chelate resin is low and the resin needs to be frequently exchanged. Therefore, the treatment takes 3 to 4 days, and the amount of the organic acid used is also about 5 to 10 times. Further, when treated at about pH 5.0, the dissociation rate of cadmium from the organic matter is low, and the treatment takes a long time. Therefore, the taste is significantly lowered due to the effects of self-digestion by the enzyme and the propagation of various bacteria.

FIG. 1 is a graph showing changes in cadmium concentration in a liquid phase and a solid phase and only in the liquid phase when an organic substance containing cadmium and a heavy metal adsorbent are mixed and stirred. In FIG. 1, the horizontal axis indicates time (h), and the vertical axis indicates cadmium concentration (mg / kg). Fig. 2 shows the liquid phase, solid phase, and liquid phase only cadmium when the organic substance containing cadmium and the heavy metal adsorbent are not stirred at the same time, but only the liquid is passed through the column packed with the heavy metal adsorbent and circulated. It is a graph which shows transition of a density | concentration. In FIG. 2, the horizontal axis indicates time (h), and the vertical axis indicates cadmium concentration (mg / kg). FIG. 3 is a graph showing the pH dependence of the cadmium elution rate from the squid viscera. The horizontal axis of FIG. 3 indicates pH (pH), and the vertical axis indicates cadmium elution rate (%) from the squid viscera. FIG. 4 is a graph showing changes in pH due to addition of citric acid. The horizontal axis of FIG. 4 shows the amount of citric acid added (%) with respect to the squid viscera in a water-containing state, and the vertical axis shows pH (pH). FIG. 5 is a graph showing the pH dependence of Cd adsorption by a weakly acidic cation exchange chelate resin and a strongly acidic cation exchange resin that are heavy metal adsorbents. The horizontal axis in FIG. 5 indicates pH (pH), and the vertical axis indicates cadmium adsorption rate (%). FIG. 6 is a graph comparing the pH dependence of the cadmium elution rate from the squid viscera (FIG. 3) and the cadmium adsorption rate to the chelate resin as the heavy metal adsorbent (FIG. 5). The horizontal axis of FIG. 6 indicates pH (pH), and the vertical axis indicates cadmium adsorption rate (%) or elution rate (%). FIG. 7 is a graph showing the change in pH of the squid viscera with the treatment temperature. The horizontal axis in FIG. 7 indicates time (h), and the vertical axis indicates pH (pH).

Claims (3)

Prepare an acidic aqueous solution with a pH of 3.0 to pH 5.0 containing the organic substance without heating the organic substance containing the heavy metal, and have a chelating action and an ion exchange action for adsorbing the heavy metal in this weakly acidic region. A method for removing heavy metals, comprising adding resin or fiber to the acidic aqueous solution and mixing and stirring under low temperature conditions of 2 ° C to 7 ° C to simultaneously adsorb and remove heavy metals from the organic substance and the liquid phase. Utilizing the competitive adsorption equilibrium of the organic matter and the adsorbent with heavy metal ions, the adsorption capacity of the heavy metal of the adsorbent becomes excessive with respect to the heavy metal adsorption capacity of the organic matter under the condition of pH 3.0 to pH 5.0. The heavy metal removal method according to claim 1, wherein the adsorbent is added. Prepare an acidic aqueous solution with a pH of 3.0 to pH 5.0 containing the food without heating the food containing heavy metal, and have chelating action and ion exchange action to adsorb heavy metal in this weakly acidic region. The heavy metal is removed by adding a resin or fiber to the acidic aqueous solution and mixing and stirring under a low temperature condition of 2 ° C. to 7 ° C., thereby simultaneously adsorbing and removing the heavy metal from the food and liquid phase. A method for producing food.

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