JP4734643B2 - Method for removing heavy metals from scallop visceral waste - Google Patents

Description

  The present invention relates to a technique for effectively utilizing heavy metals and scallop visceral waste by removing heavy metals such as cadmium from scallop visceral waste.

  Currently, scallops (scallops) are cultivated in industries such as Hokkaido and Aomori Prefecture, but the disposal of waste from soft parts such as shells and midgut glands generated during processing is a major issue ( Such scallop visceral waste is commonly referred to as uro, and scallop visceral waste is simply referred to as uro in the specification, claims, drawings and abstract of the present application. There).

Previously, these uros were dumped into the ocean, but with the ratification of the London Convention, ocean dumping was banned, requiring costly land treatment. Our waste, on the other hand, is rich in high-quality proteins, amino acids, fats, high-functional fatty acids such as EPA and DHA, and minerals such as phosphorus and calcium. Use value can be expected. However, urine contains relatively high concentrations of heavy metals such as cadmium derived from seawater due to bioconcentration, which hinders the effective use of urine waste.
Uro is incinerated on the coast of the Sea of Okhotsk in Aomori Prefecture and Hokkaido, but this method raises the cost of incineration and creates new problems such as the disposal of incineration residues containing heavy metals. On the other hand, in Hokkaido, a technology for removing cadmium by sulfuric acid leaching and electrowinning has been developed over 8 years since 1991 by a research institution centered on the Provincial Industrial Research Institute (Non-patent Document 1: Sakuta). Shinichi, Kagenobu Shimakage: Development of marine waste (scallopuro) recycling technology by hydrometallurgical process, resources and materials, Vol. 120, No. 2, pp. 71-77 (2004)).

  A processing facility based on this technology is currently operating in Sunahara-cho, Hokkaido (currently Mori-machi after the merger in 2005). Here, the cadmium was leached by immersing the boiled urine in a 3% dilute sulfuric acid aqueous solution (pH = 0.7), and this was electrolyzed and then dissolved again in a 5% aqueous sulfuric acid solution. In particular, it is recovered as a cadmium hydroxide precipitate by the addition of sodium hydroxide.

  High concentrations of protein and fat are dissolved in the immersion liquid of uro, which significantly deteriorates the efficiency of electrowinning. In order to efficiently remove cadmium by electrowinning, it is desirable to remove such high-concentration proteins and fats (lipids) prior to electrowinning. Moreover, in the electrowinning, the concentration of cadmium in the leachate is a few ppm, so there is a problem that a great amount of power is required. In order to perform electrowinning efficiently, it is desirable to concentrate cadmium at a low concentration to an appropriate concentration for electrowinning by adsorption and elution using an ion exchange resin or a chelate resin. However, in the case of porous ion exchange resins and chelate resins, a fatal problem is that poisoning occurs due to the high concentration of protein or fat in the immersion liquid of uro blocking the pores of the resin and the function of the resin is significantly reduced. There is.

  In the previous study, the present inventors proposed a process for adsorbing and concentrating cadmium using mandarin orange juice residue instead of these synthetic porous resins (Patent Document 1: Japanese Patent Application Laid-Open No. 2005-058951 “Scallop visceral soaking). Separation / removal / concentration / recovery method of heavy metals and fats and proteins in liquid ”(published on March 10, 2005)). However, this process also has the following problems. That is, in adsorbents of citrus juice residue, cations such as lead and ferric ions are adsorbed at a pH as low as about pH = 2, but the pH at which cadmium is adsorbed is relatively high and causes sufficient adsorption. In order to achieve this, it is necessary to raise the pH to about 6. In order to raise the pH of the immersion liquid obtained using sulfuric acid to 1 or less to about 6, it is necessary to add a large amount of alkali such as sodium hydroxide, which requires a large cost.

  In order to remove heavy metals in urine, as described above, heavy metals are leached by immersing them in an acid aqueous solution such as dilute sulfuric acid, and the heavy metals leached in the aqueous solution in this way are economically separated. -It must be fixed for recovery or to prevent leakage into the environment. There are two methods for separating and recovering heavy metals: (1) ion exchange, adsorption method or precipitation method, or (2) electrowinning method. The method cannot be used effectively.

In the separation of heavy metals by ion exchange, adsorption or precipitation, it is necessary to set the pH of the aqueous solution to a pH suitable for them. A low pH aqueous acid solution is effective for leaching heavy metals from urine, whereas a high pH solution is preferred for separating leached heavy metals. For this reason, in order to raise the pH of a liquid, addition of alkalis, such as caustic soda and calcium hydroxide, is required, but this involves a great deal of cost. Furthermore, when urine is immersed in an acid aqueous solution, a large amount of protein, fat, and the like are eluted. However, since these significantly inhibit the separation of heavy metals, it is not easy to separate heavy metals from the aqueous solution.
In addition, even when heavy metals are removed by the current electrolytic collection method, as described above, it is possible to efficiently perform electrolytic collection, such as removing a large amount of proteins and lipids from a low pH immersion liquid in advance. This means is not yet well established.
Sakuta Junichi, Shimakage Kazunobu: Development of marine waste (scallops) recycling technology by hydrometallurgical process, resources and materials, Vol. 120, No. 2, pp. 71-77 (2004) Japanese Patent Application Laid-Open No. 2005-058951 “Method for Separation / Removal / Concentration / Recovery of Heavy Metals and Fats and Proteins in Scallop Dipping Solution”

  An object of the present invention is to provide a new technique capable of efficiently and economically removing heavy metals such as cadmium from uro and effectively utilizing those heavy metals and components in uro.

As a result of repeated research, the present inventors have found an aggregating agent capable of efficiently aggregating proteins and lipids in uro from the sulfuric acid leachate of uro, and have derived the present invention.
Thus, the present invention includes a step of immersing scallop visceral waste (uro) in a sulfuric acid aqueous solution, leaching heavy metals in uro into the sulfuric acid aqueous solution, and adding a flocculant to the exudate after the immersion step. The present invention provides a method for removing heavy metals from uro, comprising the step of aggregating and removing proteins and lipids in uro. According to a particularly preferred embodiment of the present invention, the flocculant is a flocculant produced from amber astringent.

  If the technique provided by the present invention is used, heavy metal is removed from the scale, so that the scale-resistant waste scale can be effectively used as a high-quality fertilizer and feed. In addition, proteins and fats eluted at high concentrations in the leachate are separated and recovered by a flocculant represented by those derived from persimmon astringents, and can be used effectively as high-quality fertilizers and feeds, just like uro itself. Furthermore, the recovered heavy metals can be sold as intermediate raw materials to non-ferrous metal smelters.

  The heavy metal in uro is considered to exist as a metal chelate in which the carboxyl group at the end of the protein contained in uro and the nitrogen and sulfur atoms of the same protein are coordinated. In order to release such heavy metals from uroproteins, it is necessary to make contact with an aqueous acid solution by utilizing a cation exchange reaction of a carboxyl group. Examples of the acid aqueous solution include inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid, and organic acids such as citric acid and malic acid. Among these, organic acids such as citric acid and malic acid act as a strong leaching agent for heavy metals, but hinder the separation of metals from the later leachate. Furthermore, hydrochloric acid corrodes the equipment, and nitric acid and phosphoric acid cause environmental pollution. On the other hand, sulfuric acid is inexpensive and has a low environmental impact, so it is optimal as a leachate.

  Thus, a low pH, that is, a higher concentration aqueous acid solution (sulfuric acid aqueous solution) is preferable for leaching of metal from uro. When leaching is performed with an aqueous sulfuric acid solution, a large amount of proteins and lipids are simultaneously eluted from the urine into the aqueous solution, and the immersion liquid is colloidal. In the present invention, proteins and lipids in uro are aggregated and removed using an aggregating agent that has the ability to aggregate proteins and lipids in a colloidal and low pH solution. As the aggregating agent, various aggregating agents used for the purpose of aggregating proteins and lipids in the field of biochemistry and the like can be used. However, a synthetic flocculant widely used in water treatment generally does not exhibit an aggregating function with respect to the colloidal low pH liquid as described above, and the eluted protein or lipid is later used as a fertilizer. It is also not preferable from the viewpoint of use as feed.

  The present inventors have found that an aggregating agent manufactured from Kashiwabu is particularly suitable as the aggregating agent used in the present invention. The flocculant composed of persimmon is a natural flocculant that has been used since ancient times to separate and remove rice-derived proteins in sake, and its safety has been established. As is well known, persimmon astringent consists of water, sugar, persimmon tannin, and the like. Persimmon tannin, which is the main component, is one of condensed tannins that are condensed by the action of water to become a high molecular weight substance. It is convenient to use a commercially available product as it is as a flocculant derived from persimmon to be applied to the present invention (for example, those sold under the name of Ginjo Tama Shibu aseptic from Tomiyama Co., Ltd.), It can also be prepared if necessary. The production of the astringent flocculant generally comprises a step of squeezing the persimmon astringent manually or using a machine, and a subsequent aging step. The use concentration of the persimmon flocculant, the ratio of addition to the leachate, and the like can be easily determined by experiments depending on the persimmon agglutinating agent to be applied. For example, the astringent flocculant manufactured by Tomiyama Co., Ltd. is generally used as a 10% aqueous solution (see Examples described later).

  Thus, according to the present invention, by using a flocculant, especially a flocculant produced from astringent shiitake, a conventional heavy metal separation and recovery method, namely (1) ion exchange, adsorption method or precipitation method, and (2) The above-described problems in the electrolytic collection method can be solved, and heavy metals and uro can be effectively used. Hereinafter, the present invention will be described in detail according to the preferred embodiments of the present invention when combined with these existing methods.

(I) Removal of heavy metals by ion exchange, adsorption method or precipitation method As described above, a liquid having a pH as low as possible is preferable for leaching of heavy metals. On the other hand, it is necessary to increase the pH in order to remove heavy metals by ion exchange, adsorption or precipitation. In order to increase the pH, it is usually necessary to add an alkaline substance such as caustic soda. However, this is accompanied by an increase in cost. According to the present invention, the initial pH of the leachate and the solid-liquid ratio between uro and leachate are maintained at appropriate values, thereby achieving a pH suitable for natural separation without the addition of an alkaline substance from the outside.

FIG. 1 shows an example of a flow sheet of a method suitable for removing heavy metals by ion exchange, adsorption method or precipitation method.
As shown in FIG. 1, according to a preferred embodiment of the present invention, the dipping process is performed using two tanks. That is, in the first tank, heavy metal in uro is leached using a dilute sulfuric acid aqueous solution having a pH of 1-2, and further, the leachate obtained in the first tank is transferred to the second tank. A larger amount of uro is immersed in the leachate than in the first tank, and dipping is performed until the pH of the leachate is 2.5-5. Thus, the first tank is for leaching heavy metals, and the second tank is for raising the pH.

  A low pH acid aqueous solution, that is, a higher concentration aqueous acid solution is preferred for metal leaching from uro. However, when the leached heavy metal is later separated by an adsorption method or the like, a high concentration of acid gives an obstacle. For this reason, it is important to find an optimum acid concentration or optimum pH range that does not impede the separation of heavy metals by adsorption or the like and can effectively leach heavy metals from uro. The inventor has found that the pH range is 1-2, preferably 1.3-1.9. In the example shown in FIG. 1, heavy metal is leached using a dilute sulfuric acid aqueous solution having a pH of 1.5.

The leaching time in the first tank is, for example, 24 hours when operating at 30 ° C., but the time can be shortened by raising the temperature. The solid-liquid ratio in the first tank is, for example, 1:20 to 1: 8, preferably 1:12 to 1: 9. By performing such a leaching operation, the concentration of heavy metals such as cadmium in the urine placed in the first tank can be reduced below the environmental standard value. After the leaching in the first tank is completed, all of the leaching liquid in the first tank is transferred to the second tank, and then a new leaching liquid is added. In this case, the concentration of sulfuric acid in the new leachate is, for example, 40 to 60 mol / m ³ , preferably 45 to 55 mol / m ³ . During the leaching in the first tank, as will be described later in connection with the second tank, an increase in pH occurs due to protein, but the increase in pH in the first tank is an obstacle to the complete removal of heavy metals such as cadmium. Therefore, it is preferable to keep the pH at an appropriate value, for example, pH 1.5 by adding a small amount of sulfuric acid.

  After the leaching in the first tank is completed, all the leachate obtained in the first tank is transferred to the second layer. That is, the liquid volume of the 1st tank and the 2nd tank is the same. In the second tank, a larger amount of uro is immersed in the leachate obtained in the first tank as described above than in the first tank. FIG. 1 shows an example in which a double amount of urine in the first tank is immersed in the second tank. Thus, the solid-liquid ratio in the second tank is, for example, 1:10 to 1: 3, preferably 1: 6 to 1: 4. The immersion time is generally 5 to 6 hours.

  When such an operation is performed in the second tank, the pH of the leachate gradually increases. This is understood to be due to the hydrolysis reaction of the protein in uro. Here, when the protein or fat is aggregated / removed later using an aggregating agent, particularly an astringent agglutinating agent, if the pH of the liquid is too high, heavy metals are contained in the floc produced as a result of the aggregation. In order to effectively separate and remove heavy metals, it is important to separate proteins, fats and heavy metals separately. The inclusion of heavy metals in the floc complicates the separation operation and leads to an increase in cost. . The present inventors have found that the pH for preventing heavy metals from being contained in the floc is about 5 or less, preferably about 4.5 or less.

Thus, the operation for increasing the pH in the second tank is carried out until the pH of the leachate is generally 2.5 to 5, preferably 3 to 4.5, particularly preferably 3 to 4. Do.
In a more preferred embodiment of the immersion process of the present invention as described above, a part of the uro after immersion in the second tank is transferred to the first tank, and new uro of an amount corresponding to the uro transferred to the first tank is added to the first tank. Refill 2 tanks. In the case shown in FIG. 1, as a preferred example, half of the urine immersed in the second tank is transferred to the first tub and replenished with new uro corresponding thereto. Thus, the immersion process can be carried out by continuous operation by repeatedly moving the leaching solution of uro and dilute sulfuric acid in opposite directions.
As described above, the urine obtained by removing heavy metals such as cadmium obtained from the first tank is used for fertilizer and feed.

On the other hand, when a flocculant composed of persimmon is added to the leachate from the second tank, most of the dissolved protein and fat in the liquid become floc and can be easily removed by filtration. The concentration and amount of the astringent flocculant added in this case are, for example, 50 to 20 L, preferably 35 to 30 L with respect to 1 m ³ of the leachate as a 10% aqueous solution. The floc removed by filtration does not contain heavy metals and can be used as fertilizer or feed because it is all natural astringent, protein and fat.
The heavy metal in the filtrate after filtering and separating the floc can be easily removed by a conventional precipitation method or ion exchange / adsorption method (see FIG. 1).

(II) Removal of heavy metals by electrowinning As described above, 3% dilute sulfuric acid aqueous solution (pH = 0.7) is used as the immersion liquid in the current electrowinning. According to the present invention, when a flocculant composed of persimmon is added to such a liquid having a very low pH, most of the protein and fat dissolved in the liquid become floc and can be easily removed by filtration. Also in this case, the concentration and amount of the astringent flocculant added is, for example, 50 to 20 L, preferably 35 to 30 L as a 10% aqueous solution with respect to 1 m ³ of the leachate. The floc removed by filtration does not contain heavy metals and can be used as fertilizer or feed because it is all natural astringent, protein and fat. On the other hand, the leachate after aggregation and filtration treatment does not contain proteins or lipids, thus enabling efficient electrowinning to remove heavy metals such as cadmium.
Hereinafter, the embodiments of the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

Change in pH of uro leachate over time This example illustrates the fact that the pH of uro dilute sulfuric acid leachate is increased by uro. FIG. 2 shows the relationship between pH and time of a 100 g urine sample immersed in 1 L of dilute sulfuric acid leachate having an initial pH of 1.6 and 1.9. It can be seen that the pH increases with time. The reason why the pH rapidly increased after 15 hours when the initial pH was 1.9 was that a 50 g sample of uro was newly added at this point.

Time required for leaching and removing the entire amount of cadmium from uro This example illustrates the time required for leaching and removing cadmium from uro using an aqueous sulfuric acid solution. FIG. 3 shows the relationship between the leaching / removal percentage of cadmium from uro (100 g: about 30 samples) and the soaking time when a dilute sulfuric acid leaching solution having a pH = 1.5 at 30 ° C. is used. It can be seen that an immersion time of 24 hours or more is required to achieve 100% leaching / removal.

1. Processing of scale by the process shown in FIG. 1 This embodiment shows an example in which the scale is processed by the process shown in FIG. In a beaker (first beaker: first tank) containing 1 liter of dilute sulfuric acid aqueous solution (pH = 1.5) having a concentration of 50 mM (M = mol / L) with 100 g of urine placed on a plate. The aqueous solution was stirred with a magnetic stirrer. In this case, the temperature of the liquid was kept at 30 ° C. by heating the aqueous solution. After 24 hours, the scale was taken out and the leachate was transferred to the second beaker (second tank). The extracted uro was completely dissolved in aqua regia, and the concentration of cadmium in the liquid was measured using an ICPS-8100 type ICP atomic emission spectrometer manufactured by Shimadzu. In the second beaker, 200 g of uro was put in the same manner as the first beaker and stirred in the same manner. The pH of the solution after 5 hours was 4.0, and the concentration of cadmium was 3.16 ppm.
After the uro was taken out, 33 mL of Tomiyama Co., Ltd. Toshiyama Co., Ltd. Ginjo Tama Shibu Aseptic, diluted to 10% with water was added to the solution after leaching and stirred. The produced floc was removed by filtration, and the concentration of cadmium in the filtrate was analyzed by the same method and found to be 3.05 ppm. The cadmium concentration decreased from 3.16 to 3.05 ppm before and after the agglomeration operation because of the addition of 33 mL of persimmon juice. Therefore, the leached cadmium does not go to floc, and it is recognized that the entire amount has been transferred to the filtrate.
By adding a small amount of calcium hydroxide to the filtrate, all metal components including cadmium were precipitated as hydroxides, which were separated by filtration. Cadmium was not detected in the filtrate.
As described above, when the flow sheet is processed according to the process shown in FIG. 1, all of the cadmium in the uro is removed and the removed cadmium can be recovered at a low cost as a hydroxide precipitate. It was.

Removal of protein and fat from dilute sulfuric acid soaking solution for electrowinning This example removes protein and fat from low pH dilute sulfuric acid soaking solution that is actually operated to remove cadmium etc. by electrowinning However, it shows that the present invention can be applied.
Ginjo Tamashibu, an agaric flocculant made by Tomiyama Co., Ltd. diluted to 10% in 15 mL of an actual dilute sulfuric acid immersion solution with a pH of 0.7 collected at a processing facility for Uro in Sunahara on February 3, 2006 When 0.5 mL of sterilization was added, good aggregation / separation was achieved. The concentration of zinc and cadmium in the liquid after removing the first immersion liquid and floc by filtration was measured with an ICPS-8100 type atomic absorption emission spectrometer manufactured by Shimadzu. The results are shown in Table 1. It can be seen that the concentrations of both metals hardly change before and after the aggregation and do not shift to floc. That is, it was confirmed that a floc that can be used as fertilizer or feed without containing heavy metals such as cadmium can be obtained, and that a leachate suitable for electrowinning can be obtained without containing protein or lipid.

The catch of scallops in Hokkaido in 2000 was about 400,000 tons. In Aomori Prefecture, the catch of scallops in 2002 was 95,000 tons. Occupies an important industrial position in the region. Of the scallops, the main part of the market is the scallops, and the shells and internal organs become waste. Of these, the midgut gland contains heavy metals such as cadmium at a very high concentration, making it a difficult-to-process hazardous waste. On the other hand, the internal organs are rich in high-quality proteins and fats, and if heavy metals can be removed, they become raw materials for high-quality fertilizers and feeds.
The present invention provides a technology that contributes to the recycling of visceral waste from scallops and the effective use of heavy metals, and greatly contributes to local industries such as Hokkaido and Aomori Prefecture.

The flow sheet of the method which can remove heavy metal from the internal organs waste (uro) of scallop shells according to this invention and can aim at effective utilization of heavy metal and uro is illustrated. The time change of pH of the urine leachate when dilute sulfuric acid leachate is used in practicing the present invention is illustrated. The relationship between the leaching / removal percentage of cadmium and the dipping time when using a dilute sulfuric acid leachate when practicing the present invention is illustrated.

Claims (3)

Simmering visceral waste (uro) of scallops in sulfuric acid aqueous solution, leaching heavy metals in uro into sulfuric acid aqueous solution, and adding flocculant to leachate after said immersing step to add protein and lipid in uro A method of removing heavy metals from the urine including the step of agglomerating and removing, wherein the immersing step leaches heavy metals in the urine using a dilute sulfuric acid aqueous solution having a pH of 1 to 2 in the first tank, in the second tank, by immersing the large amount of uronium than in the first tank to the leaching solution obtained in the first tank, from performing the immersion until the pH of the leaching solution is 2.5 to 5 And the flocculant is a flocculant produced from amber astringent. Some of uronium after immersion in a second tank was transferred to the first tank, and characterized in that recruit new uronium in an amount corresponding to Paulo transfer to the first tank to the second tank The method of claim 1. The method according to claim 1 or 2, wherein the heavy metal-containing liquid after the flocculant addition step is subjected to heavy metal separation / recovery by ion exchange, adsorption, or precipitation.

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