JP5555950B2 - Heavy metal removing apparatus and heavy metal removing method - Google Patents

Description

  The present invention relates to a heavy metal removal apparatus and a heavy metal removal method for separating and removing heavy metals, particularly cadmium (hereinafter abbreviated as “Cd”), contained in scallop shells, shellfish, and octopus cocoons (hereinafter referred to as “uro”, etc.). .

The prior art will be described below using uro as an example, but the same applies to squid and octopus kites.
Uro contains Cd, which is a toxic substance of several tens of ppm (about 70 ppm at the maximum). Disposal of Uro, the residue after removing useful parts such as scallops, was an important issue for fishery processors.

  FIG. 11 shows the contents of a scallop, where 1 is a scallop, 2 is an ella located in the outer layer of the scallop 1, 3 is a gonad located in the outer layer of ella 2, 4 is an outermost string, and 5 is an urine is there. The scallop 1, the gill 2, and the string 4 are useful parts, and the remainder obtained by processing and removing the useful parts is a processing residue.

As a disposal method of such processing residues, disposal such as disposal of processing residues buried in the ground was performed, but there was a risk of environmental pollution due to the outflow of Cd, and it could not be said to be a fundamental disposal method. .
In some cases, only uro is disposed of, but in that case, uro is used as a processing residue.

  Therefore, as a method for treating such processing residues, after immersing the internal organs of seafood in dilute sulfuric acid and stirring to elute heavy metals in the liquid, the eluate is brought into contact with an ion exchange resin to remove heavy metals. A method for separating and removing heavy metals to be removed from an eluate is known (for example, see Patent Document 1).

  A supercritical fluid is defined as a noncondensable dense fluid above the critical temperature and pressure. When the temperature of the water in the system sealed with an autoclave or the like is increased, the density of the gas phase and the liquid phase becomes equal at the critical point (374 ° C, 22.1 MPa for water). Both phases are indistinguishable.

  Water in this state exhibits intermediate physical properties between liquid and gas and is called “supercritical water”. That is, it can be said that supercritical water has a large kinetic energy (diffusibility) equivalent to that of water vapor and a high molecular density (solving power) comparable to liquid water.

  FIG. 10 shows the water phase diagram and the temperature dependence of the dielectric constant and ion product of water. When the temperature / pressure of water is increased to 374 ° C. and 22.1 MPa (218 atm), the liquid becomes neither liquid nor gas. The temperature and pressure at this time are referred to as critical point C, water at a temperature above critical point C is referred to as supercritical water, and water at a temperature slightly lower than critical point C is referred to as subcritical water. With supercritical water and subcritical water, organic substances are much more soluble, and organic substances can be quickly decomposed into low molecules. Moreover, supercritical water treatment and subcritical water treatment are clean reactions using only water and heat, and are attracting attention as environmentally friendly technologies.

Thus, subcritical water has an excellent component extraction action and a strong hydrolysis action. Further, in subcritical water, the water ion product has a maximum value near 250 ° C., and the H ⁺ and OH ⁻ concentrations are about 30 times the normal temperature, so that the hydrolysis power is maximum near this temperature. Moreover, since the dielectric constant decreases with increasing temperature, subcritical water has the properties of an organic solvent. In this subcritical water treatment, water itself is used for the reaction, and it does not require chemicals and is unlikely to cause an environmental burden. Therefore, it is expected to be applied to waste treatment and its resource recycling process.

  Thus, research on the use of this subcritical water has also been made for the removal of heavy metals from the above-described scale 5 (see Patent Document 2).

Japanese Patent No. 3323392 Japanese Patent No. 4066259

  However, the heavy metal removing device described above requires a large amount of electric power (particularly, Patent Document 1) and has low durability despite being an expensive device such as fat attached to electrodes. There was a problem.

  Therefore, the present invention is small, energy efficient, can enable continuous processing, can process a large amount of samples, and can remove heavy metals with certainty, and heavy metal removal It aims to provide a method.

In the present invention, high-temperature and high-pressure steam is blown into a reaction vessel to which scallop, squidgoro or octopus processing residue containing cadmium (hereinafter referred to as “scallop processing residue”) is supplied, and the scallop processing residue is heated using phase change latent heat. A method for removing cadmium from a scallop processing residue in which a subcritical water treatment at 150 ° C. or higher and 200 ° C. or lower is performed for a predetermined time in the reaction vessel, and the pH before or after the subcritical water treatment in the reaction vessel Of pH 4.0 to 5. depending on the monitoring result. Adjust pH in the range of 0, cadmium from scallop processing residue cadmium from a suspension liquid in the range of pH4.0~5.0 after subcritical water treatment and separating the solid phase enriched It is a removal method.
Thereby, it is small and excellent in energy efficiency, can be continuously processed, a large amount of sample can be processed, and the heavy metal can be reliably condensed to the solid phase and removed.

It is provided with a means for monitoring the sub pH after critical water before or subcritical water treatment in the previous SL reactor.
Depending on the monitoring result, the pH can be adjusted with higher accuracy by appropriately supplying a pH adjusting agent.

According to the how, relatively subcritical water treatment under low temperature, moreover, it is possible to reliably remove heavy metals.

Also, the scallops processing residue to be supplied before Symbol reactor, pretreatment containing at least one of the salinity reduction process and grinding process may be performed.

By performing the pretreatment, it is possible to exert a synergistic effect that reduction of the durability of the improved and processing time of the apparatus main body.

Way of claim 3, the pH adjustment, characterized in that citric acid, malic acid or hydrochloric acid is used.

According to how according to claim 3, can contribute to facilitation of after-treatment.

Way of claim 4, wherein the pH adjustment is characterized in that in a range of PH4.5～5.0.

According to how according to claim 4, it is possible to reduce the Cd concentration of more reliably processed liquid phase.

  The heavy metal removing apparatus of the present invention consumes less energy, and is inexpensive and can improve durability.

It is explanatory drawing of the heavy metal removal apparatus which concerns on one Embodiment of this invention. (A) is a graph showing the cadmium concentration in the aqueous phase when subcritical water treatment is performed at 90 to 190 ° C. for 5 to 30 minutes, and (B) shows the relationship between the solid phase and the liquid phase in the test tube. It is explanatory drawing. It is a graph which shows the measurement result of cadmium concentration to a solid phase. It is a graph of a measurement result at the time of adjusting pH after performing subcritical water treatment of pH6 (non-adjustment) / 170 degreeC. It shows the separation state of the solid phase and the liquid phase and the degree of suspension of the liquid phase at each pH value as a result of observing a sample that was adjusted to pH 3.0 to pH 10 and left to stand for 24 hours or more before the subcritical water treatment It is explanatory drawing. It is a graph of an experimental result at the time of adjusting pH before and after subcritical water treatment of 180 degreeC. It is a graph of an experimental result at the time of adjusting pH before and after subcritical water treatment, and performing 200 degreeC subcritical water treatment. It is a graph of the experimental result of the subcritical water treatment to 200 degreeC in pH6 (non-adjustment). It is a graph which shows the volume reduction of a solid phase at the time of performing a subcritical water process for every process temperature with respect to pH by the weight (wt%) of the solid phase with respect to sample wet weight. It is explanatory drawing of subcritical water. It is explanatory drawing of the contents of a scallop.

  Next, a heavy metal removing apparatus according to an embodiment of the present invention will be described with reference to the drawings. In addition, although the Example shown below is a suitable specific example in the heavy metal removal apparatus of this invention, and there may be various technically preferable restrictions, the technical scope of this invention is the present invention especially. As long as there is no description which limits, it is not limited to these aspects.

  FIG. 1 is an explanatory view of a heavy metal removing apparatus according to an embodiment of the present invention.

In FIG. 1, reference numeral 10 denotes a hopper that stores scallop processing residues including the uro 5 in a state where salt content is reduced by washing with fresh water, 11 an upper heater that heats (resists) the scallop processing residues in the hopper 10, and 12 a hopper 10. The reaction tank 13 is supplied with scallop processing residue from the scallop to perform subcritical water treatment, and 13 rapidly blows high-temperature and high-pressure steam in the subcritical water region into the reaction tank 12 and uses phase change latent heat for the scallop processing residue in the reaction tank 12. A high-temperature and high-pressure steam generator for performing subcritical water treatment by heating, 14 is a buffer tank for recovering heat of scallop processing residue after subcritical water treatment, 15 is a lower heater disposed in the buffer tank 14, 16 Is a centrifugal dehydrator that performs dehydration processing by supplying scallop processing residue after heat recovery from the buffer tank 14 via a pipe 17.
It is preferable to provide means for adjusting the pH before or after the subcritical water treatment in the reaction tank 12. Through this means, the pH adjusting agent can be supplied so as to have a predetermined pH value. The position to be provided is preferably behind the hopper or the buffer tank.
Furthermore, it is preferable to provide monitoring for constantly monitoring the pH value. For example, a pH meter may be provided in the hopper.

(Preliminary experiment)
First, the effectiveness of the subcritical water treatment of the present invention, that is, the effectiveness of the subcritical water treatment for cadmium separation from the uro5 was confirmed.

  In this confirmation, when uro5 is treated with subcritical water, cadmium in uro is concentrated and immobilized in a solid fat phase (common name: Fat phase) formed between the oil phase and the aqueous phase. The effect of subcritical water treatment was confirmed with reference to the report.

  Then, the processing residue containing uro 5 was pulverized and mixed with water (scallop 1: water 3), subcritical water treatment was performed under each condition, and the sample was allowed to stand in a test tube for 24 hours or more.

  As a result, the “upper layer” is sampled from the upper part including the oil phase, and the “middle layer” is sampled from the aqueous phase. If cadmium is immobilized in the “Fat phase”, the cadmium concentration in the “upper layer” should be high, but the measurement results were rather reversed.

  When untreated, about 1 ppm of cadmium is present in the liquid phase, whereas the cadmium concentration in the liquid phase is increased by performing the treatment at 90 to 130 ° C.

  On the other hand, it was found that when the subcritical water treatment at 150 ° C. or higher was performed, the cadmium concentration in the liquid phase rapidly decreased.

  When subcritical water treatment is performed, the cadmium concentration in both the layer containing the measured oil phase and the aqueous phase decreases, so it is assumed that the cadmium in the sample is concentrated to the solid phase. The

  And from these 10 or more preliminary experimental results, it was suggested that cadmium could be separated and concentrated by subcritical water treatment of scallop processing residue.

(Subcritical water treatment temperature and reaction time)
FIG. 2 (A) shows the change in cadmium concentration in the aqueous phase when the subcritical water treatment is performed at 90 to 190 ° C. for 5 to 30 minutes.

  At this time, as shown in FIG. 2 (B), it is considered that cadmium is mainly concentrated in the solid phase 21 precipitated at the lower end of the test tube 20, so that it is higher than the solid phase 21. It is considered that the cadmium concentration can be measured and evaluated by measuring the concentration of cadmium contained in the aqueous phase 22 of the phase. Therefore, in subsequent experiments, unless otherwise specified, it is assumed that the concentration of cadmium contained in the solution sampled from the central portion of the aqueous phase 22 was measured. Here, the cadmium concentration is in a 4-fold diluted sample.

  Moreover, the sample used here adjusts the mass ratio of scallop: water at a ratio of 1: 3, and the pH of the sample is 6.2 (± 0.1) without adjustment.

  In this experiment, it is performed three times on different days, and the difference in measurement date is distinguished by the point marker type and the line type. Note that there are some differences in the cadmium concentration due to different measurement dates. Therefore, it is not possible to simply compare absolute values from this data alone.

  Here, the cadmium concentration which was 1.1 to 1.2 ppm in the untreated was as high as about 1.5 to 2 ppm when the treatment was performed at a relatively low temperature range of 90 to 110 ° C. In addition, a cadmium concentration is clearly reduced in the treatment at a temperature range of 150 ° C. or higher, and the tendency becomes more prominent as the treatment temperature becomes higher and the treatment time becomes longer. On the other hand, in the processing at 130 ° C. and 150 ° C., matching with the processing time is unclear.

  By the way, cadmium in uro5 is considered to exist in coordination with various proteins. Its main cadmium-binding substance has been found to be a substance with molecular weights of 650,000 and 100,000. As a method for dissociating cadmium from this cadmium-binding substance, dissociation due to hydrogen ion competition and dissociation due to protein degradation can be raised, but pH adjustment was not performed in the above experiment, and changes in pH value before and after treatment were also observed. I can't. Therefore, the following interpretation can be made about the result of this experiment.

  That is, in the untreated state, most of the cadmium is bound to the cadmium-binding substance, but when heated, the protein structure is broken and cadmium is eluted in the liquid. However, it is not possible to specify whether cadmium in the aqueous phase in untreated and low-temperature treatment is in an ionic state or suspended in a bound state. Further, in the subcritical water treatment at 150 ° C. or higher, it is presumed that cadmium in the liquid phase is combined with some substance and precipitated into the solid phase.

  FIG. 3 shows the results of sampling from the solid phase and measuring the cadmium concentration to confirm cadmium concentration in the solid phase. However, the sampling from the solid phase was performed by visual observation so as to be almost the same on a volume basis, and the quantitative property remains as a reference value.

  From this experimental result, it was confirmed that the cadmium concentration in the solid phase tends to increase as the processing temperature increases.

(PH dependence)
Cadmium desorption from uro5 is closely related to the concentration of hydrogen ions in the solution in addition to protein degradation. Moreover, when the uro 5 is immersed in an aqueous solution and the hydrogen ion concentration is increased, the hydrogen ions compete with the metal ions to drive out the metal ions. The hydrogen ion concentration at which 50% of cadmium is dissociated is about pH 3 to 3.5, and it is known that most cadmium is dissociated when the hydrogen ion concentration is about pH 1.

  In addition, although it is considered that some substance adsorbs cadmium and precipitates in the solid phase after the subcritical water treatment, it is assumed that this adsorbent is a kind of low molecular weight protein or amino acid. In metal ion adsorption by these organic substances, it is considered that a carboxyl group or a thiol group mainly contributes to bonding, but these bonds also compete with hydrogen ions and are strongly influenced by the pH of the solution. The hydrogen ion concentration is 100 times higher at pH 4 than at pH 6, and it is estimated that the adsorbed cadmium ions are desorbed to some extent and eluted into the aqueous phase.

  When subcritical water treatment is performed after adjusting the pH of the sample, the cadmium concentration in the aqueous phase increases as the subcritical water treatment is performed in a high pH range, and when the subcritical water treatment is performed at pH 4. However, a tendency for the cadmium concentration to be higher than when the pH was not adjusted was observed.

  Next, FIG. 4 shows the measurement results when the pH was adjusted after the subcritical water treatment at pH 6 (no adjustment) / 170 ° C.

  Since the cadmium concentration is remarkably high at pH 2, it is appropriate to consider that cadmium ions are desorbed due to competition of hydrogen ions. It can also be seen that there is almost no influence of pH adjustment at pH 8 and pH 10.

  As a result of subcritical water treatment, cadmium adsorbed on proteins and precipitated in the solid phase is considered to have no change because it does not affect cadmium adsorption even after adjustment to high pH after treatment. .

  Here, as shown in FIG. 5, in the case of pH 4, the fall of a cadmium density | concentration is recognized clearly. As a result of observing a sample that was adjusted to pH 8, pH 6 (no adjustment) and pH 4 and allowed to stand for 24 hours or more before the subcritical water treatment, the suspension of the liquid phase at pH 8 was strong, and the turbidity was slightly weak at pH 6. It was. Further, at pH 4, the liquid phase was almost transparent, and it was clearly found that suspended substances were coagulated and precipitated. This suggests that the isoelectric point of the suspended matter after the subcritical water treatment is around pH 4.

  Next, FIG. 6 shows the experimental results when pH adjustment was performed before and after the subcritical water treatment at 180 ° C. The “previous” and “rear” experimental results are in good agreement with the experimental results shown in FIG. 4, and are consistent with the sample. From this experimental result, it was found that the isoelectric point of the cadmium adsorbent is around pH 4.5.

  Among the samples described above, when the sample subjected to the subcritical water treatment after being adjusted to pH 10 is titrated to pH 4 after the treatment, the cadmium concentration in the liquid phase is reduced to 0.026 ppm. From this result, it can be seen that most of the cadmium in the suspension layer at high pH is present in an adsorbed state rather than an ionic state.

  From the above experimental results, it is assumed that the mechanism of cadmium separation from scallop samples by subcritical water treatment is as follows.

  By heating the sample, the protein is decomposed, and cadmium in the urine is eluted into the liquid phase. When the subcritical water treatment at 150 ° C. or higher is performed, a low molecular weight protein or amino acid is produced, and this substance is suspended in the solution while adsorbing cadmium. Since the isoelectric point of this substance is around pH 4.5, the suspended adsorbent is agglomerated and precipitated by adjusting the pH, and cadmium is separated and condensed into the solid phase. However, when the pH is lowered, competition between cadmium ions and hydrogen ions occurs, and coagulation precipitation and cadmium desorption may occur at the same time. Therefore, the phenomenon is complicated near pH 4, which is the branching point. It is estimated to be.

(200 ° C subcritical water treatment)
According to the prior art, when the uro 5 is subjected to a subcritical water treatment at 200 ° C., the cadmium in the uro 5 is concentrated to a solid fat phase called “Fat phase”.

However, in the above-described experiment, although it is performed in an Ar atmosphere, the fact that a solid fatty phase is generated as a result of the subcritical water treatment has not been confirmed. Further, from the experiments so far, as shown in FIG. 2, it has been found that the effect of separating cadmium becomes more prominent as the temperature is increased.
In the experiment in Patent Document 2, subcritical water treatment is performed after replacing the reaction tube with Ar gas, whereas in the present embodiment, the treatment is performed in an air atmosphere.

  FIG. 7 shows the experimental results when the pH is adjusted before and after the subcritical water treatment and the treatment at 200 ° C. is performed. For comparison, the experimental result at 180 ° C. shown in FIG. 6 is indicated by a broken line.

  The tendency that the cadmium concentration increases on the low pH side, which coincides well with the previous experimental results, was reproduced, and it was also found that at pH 4 and above, in all cases, it was below the measurement limit value.

  As a result of observing a sample corresponding to this treatment, it was found that there was a high probability that a solid phase corresponding to the “Fat phase” was not generated even when the subcritical water treatment at 200 ° C. was performed. Further, it was found that the liquid phase was clearly more transparent than the case of 180 ° C., and the suspended solids were precipitated.

  From the above experimental results, it is concluded that cadmium in the sample is more reliably concentrated to the solid phase when subcritical water treatment at 200 ° C. is performed. In addition, at least with actual operation in mind, the practical merit is greater when the treatment is performed in an air atmosphere.

(Dilution ratio)
When processing uro by subcritical water processing, energy can be saved and the running cost can be reduced as the water content during processing decreases. Therefore, when the sample was prepared, purified water was used and the water ratio was changed from 4 times by mass to no dilution, and the effect was investigated.

  The pH of the sample is unadjusted pH 6 and pH 4. In the treatment at 130 ° C., the cadmium concentration increases in proportion to the rate at which the dilution factor decreases. When the treatments at 150 ° C. and 170 ° C. are performed, a decrease in cadmium concentration is recognized as in the previous experimental results, and the above proportionality is maintained up to 2-fold dilution even if the dilution factor is reduced.

  When the sample is processed without dilution, this relationship is lost, and the processing temperature is not consistent. However, when the sample is sampled raw, the sample is often clogged at the tip of the micropipette, so that accurate quantification is difficult, and a cadmium concentration gradient also occurs depending on the portion of the sample to be sampled.

  When processing at 130 ° C. and 150 ° C. at pH 4, the concentration of cadmium by the subcritical water treatment generally increases as the dilution factor decreases. However, since the cadmium concentration is high in the case of non-dilution treatment, it can be read that the treatment can be performed at a moisture ratio of about 2-fold dilution.

  Next, FIG. 8 shows the results of the same experiment up to 200 ° C. at pH 6 (no adjustment). In this experiment, high cadmium separation effects of 0.168 ppm at 190 ° C./2 times dilution and 0.048 ppm at 200 ° C./2 times dilution were confirmed. From the above, as far as the cadmium separation effect is concerned, it is concluded that a sufficient effect can be expected even at a dilution ratio equal to or less than 1. The actual operating conditions are assumed to be determined by mechanical factors such as the durability of the valve.

(Dehydration experiment)
Thus, it was found that cadmium in uro was concentrated to a solid phase by performing subcritical water treatment of scallop processing residue. The disposal of the solid phase enriched with cadmium is handed over to a waste disposal company for a fee, but it is necessary to reduce the volume of the solid phase as much as possible in order to reduce the processing cost.

  Therefore, dehydration experiments after subcritical water treatment were conducted. Here, dehydration of solid content was attempted at pH 4.5, pH 6 (no adjustment), and pH 10.

  In addition, for dehydration, when untreated, it is a step of substituting with a coarse cloth (cotton) between 180 ° C subcritical water treatment, after removing solids with a commercially available tea strainer. Performed with the filtered one.

  In the case of untreated, when cadmium is dehydrated, most of the cadmium flows out into the liquid. Next, when the above sample was subjected to subcritical water treatment and left to stand for about 24 hours as in the previous experiments, dehydration treatment was performed. At pH 4.5 and pH 6 (unadjusted), cadmium in the liquid was used. Although the concentration was greatly reduced, at pH 10, most of the cadmium flowed out into the suspension, unchanged from the untreated case.

  In addition, the dehydration process performed this time is simple and does not perform filtration work or the like. Moreover, although dehydration is performed with a certain amount of force, the outflow of cadmium into the liquid is greatly suppressed in the low pH range.

  This is because cadmium adsorbed by some substance as a result of subcritical water treatment does not desorb by simple physical operation alone, and furthermore, this cadmium adsorbing substance does not pass through the fabric at pH 4.5-6. It shows that it is a size.

  On the other hand, since most cadmium flows out in the liquid at pH 10, it has been found that the dispersibility of the cadmium adsorbing substance is high in the high pH range, and the cloth easily passes through.

  In addition, when dehydration is performed immediately after subcritical water treatment (having been performed at pH 4.5, which has been highly effective until now), even if dehydration treatment is performed immediately after subcritical water treatment, there is sufficient cadmium separation effect. Was confirmed.

  From the above, cadmium concentrated to the solid phase by subcritical water treatment is not easily desorbed by physical operations such as dehydration, and adsorption is completed during subcritical water treatment or within a few minutes after treatment. Became clear.

  At the time of actual operation, it is considered that there is no need for a precipitation step or the like after the treatment, and it can be put into a dehydrator in a suspended state.

(Volume reduction)
In the subcritical water treatment of Uro 5, it is considered that the solid phase enriched with cadmium is delivered to a waste disposal contractor for a fee. Therefore, in order to reduce processing costs, it is important to reduce the volume of the solid phase.

  Therefore, centrifugation was performed after subcritical water treatment, and the volume reduction of the solid phase was investigated. The sample after the subcritical water treatment is put in a falcon, centrifuged at 2600 rpm / 10 minutes with a centrifuge (manufactured by Kubota Corporation, tabletop small centrifuge 2410), and the weight of the solid phase at the bottom of the falcon is measured. did. The subcritical water treatment was performed at 160 ° C., 180 ° C., and 200 ° C., and the pH was adjusted to pH 4.5, pH 6 (no adjustment), pH 8, and pH 10 before the treatment.

  FIG. 9 shows a graph in which the weight (wt%) of the solid phase with respect to the sample wet weight is plotted for each treatment temperature with respect to the pH.

  In general, the volume reduction tends to increase as the temperature increases, and the volume is reduced to 20% or less in the case of 200 ° C. treatment. However, at pH 10, the volume reduction seems to be large from this graph, but this is probably due to the fact that suspended solids are not precipitated (see FIG. 5) even after centrifugation.

  In addition, although the sample so far used what grind | pulverized the scallop processing residue containing the uro5 with the mixer, as a result of experimenting on the sample of only the unground uro5, even when the unground sample is used, it is enough It was found that there is a good cadmium separation effect. In addition, as a result of observation of the sample after the subcritical water treatment, it was found that the prototype of uro 5 was completely lost even when the unground sample was treated with the subcritical water as it was.

  Therefore, the pulverization step as a pretreatment in actual operation depends only on the durability of the sample input valve, and may be omitted in some cases.

(Summary of basic experiments)
From the experimental results so far, it has been shown that subcritical water treatment of scallop processing residue can be a useful technique in terms of both cadmium separation and volume reduction of waste containing cadmium. The processing temperature is optimally 200 ° C., which is the highest temperature condition, within the range in which the experiment was performed. Further, the processing time may be about several minutes, but in reality, it seems to vary depending on the characteristics of the processing apparatus.

  In this experimental result, when 200 ° C. treatment is performed, a sufficient cadmium separation effect is obtained without particularly adjusting the pH. However, in actual operation, the coagulation sedimentation of the liquid phase after treatment is taken into consideration. Therefore, pH adjustment or monitoring will be essential.

  In addition, it has been clarified that the isoelectric point of the cadmium adsorbing substance that appears to be generated as a result of the subcritical water treatment is around pH 4.5.

  The adsorption of cadmium generated as a result of subcritical water treatment is confirmed to be almost not desorbed by physical operations such as dehydration, and the suspension after treatment may be dehydrated and reduced in volume using a centrifuge. Was shown to be high.

  When dehydration by centrifugation was performed, it was confirmed that the volume could be reduced to 20% or less of the raw material wet weight by the 200 ° C. treatment. In actual operation, even if it is assumed that an aggregating agent or the like is administered in the dehydration step, the volume can be reduced to at least about 1/5 or less. This is directly linked to the user's cost merit. As far as the cadmium separation effect is concerned, it has been found that there is no need to worry about the dilution factor and pulverization of the sample. Thus, these are likely to be determined mainly from the mechanical properties of the processing equipment.

  It has also been confirmed that cadmium separation is not affected even when seawater (artificial seawater) is used as water during subcritical water treatment or for dilution after treatment. Use of seawater during subcritical water treatment is not preferred because corrosion of the apparatus is expected, but use of seawater is also an option for dilution after treatment.

(Processing procedure)
From the above, in the present invention, good results can be obtained by the following processing procedure. In addition, in order to suppress the corrosion of the apparatus due to salt contained in seawater, the salt content in the scallop processing residue may be reduced by immersing in fresh water or performing a cleaning process before introducing the scallop processing residue into the hopper 10.
(1) The raw material is charged into the inlet (hopper 10) of the subcritical water treatment reaction tube. At this time, if possible, the hopper 10 preheats using heat recovered from the subsequent stage (upper heater 11). If necessary, the raw material is pulverized.
(2) A subcritical water treatment (about 200 ° C./10 minutes) is performed.
(3) The sample is transferred to the buffer tank 14. At this time, heat is recovered in the buffer tank 14 (lower heater 15) and used as a heating source for the upper heater 11. The processing residue is transferred to the buffer tank 14 by removing the sample by opening the discharge valve and the like while the pressure in the reaction tank 12 remains, so that the heat of the jacket of the reaction tank is maintained. Samples for use can be sequentially added, and heat energy can be used efficiently, but it may be transferred by gravity (self-weight) or a pump.
(4) The sample is continuously transferred from the buffer tank 14 to the centrifugal dehydrator 16 for sewage treatment. At this time, a pH adjuster is administered to the centrifugal dehydrator 16.
(5) The centrifuged solid part is transported to a processing company as cadmium-containing waste, and the liquid part from which cadmium has been removed is effectively used for fertilizer, methane fermentation, or fertilization as a measure against burning.

DESCRIPTION OF SYMBOLS 10 ... Hopper 11 ... Upper stage heater 12 ... Reaction tank 13 ... High temperature / high pressure steam generator 14 ... Buffer tank 15 ... Lower stage heater 16 ... Centrifugal dehydrator 17 ... Piping

Claims (4)

High-temperature, high-pressure steam is blown into a reaction vessel supplied with processing residues of scallop, squid slag or octopus containing cadmium (hereinafter referred to as “scallop processing residue”), and the scallop processing residue is heated in the reaction vessel using phase change latent heat. A cadmium removal method from scallop processing residue for performing a subcritical water treatment at 150 ° C. or more and 200 ° C. or less for a predetermined time at
PH is monitored before or after subcritical water treatment in the reaction vessel, and pH is 4.0 to 5. depending on the monitoring result. PH adjustment in the range of 0,
Cadmium removal method from scallop processing residue cadmium from a suspension liquid in the range of pH4.0~5.0 after subcritical water treatment and separating the solid phase enriched. The method for removing cadmium from scallop processing residue according to claim 1, wherein the scallop processing residue supplied to the reaction vessel is subjected to pretreatment including at least one of salt reduction processing and pulverization processing. . The method for removing cadmium from scallop processing residues according to claim 1 or 2, wherein citric acid, malic acid or hydrochloric acid is used for the pH adjustment. The method for removing cadmium from scallop processing residues according to any one of claims 1 to 3, wherein the pH adjustment is performed in a range of pH 4.5 to 5.0 .

Images