JP2008023440A - Water treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an environmentally harmonious type water treatment method inexpensive, efficient and contributing construction of a circulative society from the view point of effective resource utilization using a unutilized resource having an excellent heavy metal adsorption performance in a method of adsorbing a heavy metal in water to be treated. <P>SOLUTION: The water treatment method comprises the adsorption of the heavy metal in the water to be treated to the buckwheat hull by bringing the water to be treated containing the heavy metal into contact with a buckwheat hull. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a water treatment method. Specifically, the present invention relates to a method for adsorbing heavy metals in water to be treated using buckwheat husk, which is an unused resource.

  Heavy metals are used in various industrial fields, but heavy metals have many harmful effects on the human body and the environment, so when discharging wastewater containing them into sewers and public waters, It will be subject to the national wastewater standards, that is, the wastewater standards stipulated in the Sewerage Law or the Water Pollution Control Law, and some kind of treatment will be required. Furthermore, in recent years, regulations have been further tightened due to concerns about environmental pollution in some regions, and regulations have been imposed with additional regulations based on strict standards exceeding the national wastewater standards. In addition, although there are heavy metals that are not clearly specified as targets of regulation but have drainage standards set as items to be monitored, it is estimated that these will be regulated in the future. Thus, the situation is such that the discharge of heavy metal-containing wastewater is more strictly regulated.

  As a method for removing heavy metals from wastewater containing heavy metals, for example, an alkaline agent such as slaked lime (calcium hydroxide) or caustic soda (sodium hydroxide) is added to wastewater containing heavy metals, and precipitated as heavy metal hydroxides. There are known methods (hydride precipitation method), and a method in which a sulfide such as hydrogen sulfide is added to waste water containing heavy metals to precipitate as heavy metal sulfides (sulfide precipitation method). However, in the hydroxide precipitation method, not only the standard value cannot be cleared, but a large amount of sludge (sludge) is generated, and a new problem arises from the standpoint of environmental conservation. In addition, the sulfide precipitation method has problems such as toxicity of hydrogen sulfide, corrosiveness, odor and the like in addition to the generation of a large amount of sludge, which is not environmentally preferable. Also, it is not economical in that hydrogen sulfide is expensive. Further, these agglomeration precipitation methods have a problem that application is limited when the heavy metal concentration is dilute and precipitation hardly occurs. In addition, the coagulation precipitation method is inefficient and unsuitable for recovering and reusing heavy metals. It is desirable to collect and reuse heavy metals in wastewater from the viewpoint of not only environmental conservation but also effective utilization of mineral resources.

  As a water treatment method that can be preferably applied to water to be treated with a low concentration of heavy metals and can easily recover heavy metals, for example, waste water containing heavy metals is brought into contact with an adsorbent such as activated carbon or ion exchange resin to remove heavy metals. It is well known that chelate resins having a chelating agent residue as a functional group as an ion exchange resin are excellent in heavy metal recovery efficiency. The adsorption method does not generate pollutants like the coagulation sedimentation method, and can be said to be a method suitable for the treatment of water systems such as lakes and rivers inhabited by organisms. However, these adsorbents, in particular ion exchange resins, are very expensive themselves, and even when they are regenerated and used, the cost of the chemicals for regeneration is high.

  On the other hand, the development of a method for adsorbing and removing heavy metals in wastewater using inexpensive and abundantly available unused resources (such as biomass) is advancing. The development of an effective utilization method of unused resources is not only effective for Japan, which is scarce of resources, but also very meaningful in terms of contributing to a recycling-oriented society with less environmental impact.

Specifically, for example, as an adsorbent, a method of using an alkali solution of pretreated eggshell membrane (Patent Document 1) or feather (Patent Document 2), eggshell membrane, feather or wool (Patent Document 3), A method using a chitosan derivative (patent document 4) made from a shrimp shell or the like has been reported. Also, a method for removing various harmful pollutants dissolved in water, such as heavy metals, has been reported using activated rice husks whose surface activity has been increased by carbonizing the rice husks (Patent Document 5).
All of these use unused resources as raw materials to make effective use of resources, but on the other hand, there is a problem that the adsorbent is expensive because it requires complicated processes and a large amount of energy in the adsorbent manufacturing stage. .

  In addition, a method for adsorbing and removing heavy metals from waste water using chips, wood powder, bark and the like produced as waste from trees such as broadleaf trees and conifers has also been reported (Patent Document 6). However, trees have a very low heavy metal adsorption capacity, and a large amount of trees are required to sufficiently adsorb and remove heavy metals in wastewater. For this reason, the efficiency is poor, and the amount of waste generated is large, and has not been put into practical use.

  As described above, in a method for applying heavy metals in wastewater containing heavy metals and adsorbing heavy metals in the water to be treated, there is no known water treatment method that satisfies all of cost, efficiency, and environmental harmony. Therefore, there has been a demand for an unused resource that is easily available and excellent in heavy metal adsorption ability.

Japanese Patent Laid-Open No. 7-24207 JP-A-9-99237 JP-A-9-141033 JP-A-10-204104 JP-A-6-39277 JP-A-5-277467

  The present invention has been made in view of such circumstances, and the object of the present invention is to use an unused resource having an excellent ability to adsorb heavy metals in a method for adsorbing heavy metals in water to be treated. It is to provide an environmentally conscious water treatment method that can contribute to the establishment of a recycling society from the viewpoint of efficient use of resources.

  In order to solve the above problems, the present inventor has conducted extensive research focusing on agricultural and forestry by-products, and as a result, found that buckwheat husks discarded as unused resources have an excellent heavy metal adsorption ability. Based on this, the present invention has been completed.

That is, the present invention is a water treatment method characterized in that, firstly, water to be treated containing heavy metal is brought into contact with buckwheat husk and the heavy metal in the water to be treated is adsorbed to the buckwheat husk.
The second aspect of the present invention is that heavy metals are designated as subject of regulation stipulated in the Sewerage Law, heavy metals designated as subject of regulation stipulated in the Water Pollution Control Act, and heavy metals designated as items requiring monitoring. It is at least 1 sort (s) chosen from the group which consists of this, The said water treatment method characterized by the above-mentioned.
Third, the water treatment method according to the present invention is characterized in that the heavy metal is at least one selected from the group consisting of nickel, copper, zinc, cadmium, antimony and lead.
Fourthly, the water treatment method according to the present invention is characterized in that the water to be treated is waste water containing at least one selected from the group consisting of nickel, copper and antimony.

  In addition, as a technique for effectively utilizing buckwheat husks, those using buckwheat husks as a deodorant carrier (Patent Document 7), those using buckwheat husk itself as a deodorant (Patent Document 8), However, the use of buckwheat husk as an adsorbent for adsorbing heavy metals in the water to be treated has not been reported.

Japanese Patent Laid-Open No. 11-42278 JP 2003-305112 A JP-A-8-12311

  According to the present invention, in the method for adsorbing heavy metals in the water to be treated, by using buckwheat husks that are inexpensive and available in large quantities as adsorbents, and that are excellent in heavy metal adsorption capacity, It can be adsorbed inexpensively and efficiently. Moreover, it is possible to effectively use buckwheat husks that have been discarded as unused resources, and contribute to the establishment of a recycling society.

Hereinafter, the present invention will be described in detail.
Buckwheat is one of the most popular foods eaten for a long time in Japan, and its production reaches about 28,000 tons per year. About 70% of buckwheat flour is produced from brown buckwheat (buckwheat berries), while about 30% of buckwheat husk is discharged. Although some buckwheat husks are used as filling materials for pillows, there are also problems such as allergies, and most of them are disposed of by incineration without being effectively used. The present invention is intended to make effective use of the discarded buckwheat husk, and the buckwheat husk that can be used in the present invention is not particularly limited, such as varieties and production areas, and may be any one. . For example, native species adapted to local areas can be used, and one kind can be used alone, or two or more kinds can be used in combination.

  In the present invention, buckwheat husk can be used as an adsorbent without any pretreatment, but it may be subjected to pretreatment such as washing with water or drying. Also, the shape is not particularly limited, and can be used as it is, or pulverized into powder, granular, other arbitrary shapes, or pressed into a lump shape, depending on the use mode May be determined as appropriate. For example, buckwheat husk in an intact shape is excellent in bulkiness and air permeability, and therefore has an advantage that it is easy to dry the buckwheat husk containing water after the adsorption treatment. Buckwheat husk can be reused after heavy metal is recovered, but is finally disposed of as waste. In such a case, or even when the buckwheat husk is discarded without recovering heavy metals, it is preferable that the buckwheat husk is dried because the cost can be reduced. On the other hand, since the bulk of buckwheat husks is drastically reduced by pulverization, there is an advantage that the handling property is excellent and the space of the reaction tank (adsorption tank) can be saved.

  Buckwheat husk is rich in persistent fiber material, is physically and chemically stable and can be adapted to a wide range of pH and temperature.

  Although the details of the mechanism of heavy metal adsorption ability of buckwheat husks are unknown, physical factors due to the rough wavy structure characteristically distributed on the surface of buckwheat husks and ion exchange of polyphenols contained in buckwheat husks It is considered that the heavy metal adsorption ability is expressed by the chemical factor resulting from the ability.

The water to be treated in the present invention is not particularly limited as long as it contains at least heavy metals. For example, factory wastewater and mine wastewater discharged from establishments handling heavy metals such as plating factories, smelters, and dyeing factories. Incineration leachate, river water, lake water, sewage, etc. Moreover, the contained heavy metal is a heavy metal in a general sense, and refers to a metal having a density of 4 g / cm ³ or more. In particular, it refers to heavy metals designated as regulations subject to the Sewerage Law and Water Pollution Control Law, or heavy metals designated as items requiring monitoring. Specifically, (hexavalent) chromium, manganese, iron, nickel , Copper, zinc, molybdenum, cadmium, antimony, mercury, lead, uranium. Among them, the heavy metal to which the water treatment method of the present invention is preferably applied is at least one selected from the group consisting of nickel, copper, zinc, cadmium, antimony and lead, more preferably nickel, copper and antimony. It is at least one selected from the group. It has been confirmed that the adsorption capacity of buckwheat husks to the heavy metals is superior to that of activated carbon, which is a general adsorbent. The form of these heavy metals is not particularly limited, and may be present in any state dissolved or suspended in the water to be treated. Specifically, it is a heavy metal simple substance or an ion thereof, a heavy metal compound or an ion thereof, or an organic heavy metal compound or an ion thereof. In general, when heavy metals are complexed with organic acids such as citric acid and gluconic acid, or compounds with complexing ability such as EDTA, cyanide, amine, ammonia and polyphosphoric acid, these are stable structures, so It is difficult to treat heavy metals by oxide precipitation or sulfide precipitation. However, the buckwheat husk used in the present invention can sufficiently adsorb heavy metal even when heavy metal forms a complex.

  Although the density | concentration of the heavy metal in to-be-processed water is not specifically limited, Preferably it is 1000 mg / L or less, More preferably, it is 100 mg / L or less. If the concentration of heavy metal exceeds 1000 mg / L, the heavy metal in the water to be treated cannot be sufficiently adsorbed, and a large amount of heavy metal may remain in the treated water. Also, it requires a large amount of buckwheat husk and is not efficient. When the concentration of heavy metal exceeds 1000 mg / L, it is preferable to apply the water treatment method of the present invention after pretreatment by other general water treatment methods such as coagulation precipitation method or dilution method. It is also effective to repeatedly apply the water treatment method of the present invention.

  Although the pH of to-be-processed water is not specifically limited, Preferably it is 1-11, More preferably, it is 2-10. As mentioned above, buckwheat husk is physically and chemically stable and adaptable to a wide range of pH, but under conditions of strong acidity with a pH of less than 1 or strongly alkaline with a pH of more than 11, buckwheat husk There is a possibility that the surface of the metal may be modified and the heavy metal adsorption ability may be lowered.

  On the other hand, heavy metal adsorption occurs over a wide range of pH, but when heavy metal exists as a single ion, there is a pH range suitable for adsorption depending on the type of heavy metal, so the pH of the treated water is adjusted to that range By doing so, heavy metals can be adsorbed more efficiently. For example, in the case of nickel ions, the pH is preferably adjusted to 4-7, more preferably 5-7; in the case of copper ions, the pH is preferably adjusted to 3-6, more preferably 4-6. In the case of zinc ions, the pH is preferably adjusted to 4-7, more preferably 5-7; in the case of cadmium ions, the pH is preferably adjusted to 3-6, more preferably 4-6. In the case of antimony ions, the pH is preferably adjusted to 3-6, more preferably 4-6; in the case of lead ions, the pH is preferably adjusted to 3-6, more preferably 4-6. It is. The upper limit of each pH range described above is a limit in the case where most of the heavy metals exist as ions without generating a hydroxide precipitate, and the amount of adsorption tends to be maximized in the vicinity. In addition, the heavy metal adsorption ability of buckwheat husk is largely caused by not only chemical factors but also physical factors, and even when the pH of the water to be treated is outside the above numerical range, adsorption of heavy metals can occur.

  Although the temperature and pressure of to-be-processed water are not specifically limited, Preferably they are normal temperature and a normal pressure. The adsorption of heavy metals by buckwheat husk is considered to occur physically and chemically. The lower the temperature, the more the physical adsorption is promoted, but the higher the temperature is, the more the chemical adsorption is promoted. Be inhibited.

  The contact between the water to be treated and buckwheat husk may be carried out by either a reaction tank suspension method or a packed tower water flow method.

  In the case of a reaction tank suspension system, buckwheat husk is added to the water to be treated in a reaction tank (adsorption tank) of an appropriate volume and stirred for a certain time. The amount of buckwheat husk used is not particularly limited, and varies depending on the type, concentration, form of the heavy metal, pH of the water to be treated, presence or absence of impurities, but preferably 0.01% relative to the water to be treated. -50% by weight, more preferably 0.02-10% by weight. When the amount used is less than 0.01% by weight, the heavy metal in the water to be treated and the buckwheat hull are not sufficiently brought into contact with each other, and the heavy metal cannot be sufficiently adsorbed. When the amount used exceeds 50% by weight, in the reaction tank suspension system, stirring becomes difficult, and the contact between the heavy metal in the water to be treated and the buckwheat husk becomes uneven. The contact time is not particularly limited, but is preferably 1 hour to 1 week, more preferably 12 hours to 3 days. If the contact time is less than 1 hour, the heavy metal in the water to be treated and the buckwheat hull are not sufficiently brought into contact with each other, and the heavy metal cannot be sufficiently adsorbed. Even if the contact time exceeds one week, an increase in the amount of adsorption cannot be expected, and a large reaction tank is not practical for treating a large amount of water to be treated.

  Next, the treated water and buckwheat husk are separated into solid and liquid. The method of solid-liquid separation is not particularly limited, and any method such as precipitation, centrifugation, membrane separation and the like can be adopted, but the precipitation method or the centrifugation method is preferable. Since the specific gravity of buckwheat husk is heavier than water, it can be easily separated into solid and liquid by precipitation or centrifugation. The separated buckwheat husk can be regenerated by desorbing heavy metals by a method described later.

  In this case, the reaction tank, the solid-liquid separation means, and the desorption tank may be connected, and the buckwheat husk may be sequentially transferred by a pump and processed continuously. Alternatively, adsorption, solid-liquid separation, and desorption may be performed in one tank. A batch process in which each process is sequentially performed may be employed.

  On the other hand, in the case of the packed tower water passing method, the packed tower (adsorption tower) is filled with buckwheat husk and the treated water is passed through the packed tower to obtain treated water. The packed tower may be a fixed bed type that forms a fixed bed even when the water to be treated is passed, or a fluidized bed type in which buckwheat husks flow by passing water. Further, the water flow may be an upward flow or a downward flow. The buckwheat husk after the water to be treated is passed and subjected to the adsorption treatment can be regenerated by desorbing heavy metals by a method described later.

  In this case, adsorption and desorption may be performed alternately in a packed tower of one tower, a plurality of packed towers are arranged in parallel and adsorption treatment is performed in some towers, and desorption treatment is performed in other towers. May be performed. In the latter case, continuous water treatment can be performed by switching the packed tower through which water to be treated is passed.

  The method for desorbing heavy metals from buckwheat husks after the adsorption treatment is not particularly limited, and is a method for desorbing heavy metals by adjusting pH, a method for desorbing heavy metals using a difference in solubility, or heat. Various known methods such as a method of desorbing heavy metals using can be employed. For example, when heavy metal ions or their hydroxides are adsorbed on buckwheat husks, the lower the pH, the lower the ability of buckwheat shells to adsorb heavy metals. Can be desorbed. Further, when heavy metals in an aqueous hydrochloric acid solution are adsorbed, the heavy metals can be desorbed by using a compound having low solubility in hydrochloric acid such as sulfides and hydroxides. The heavy metal desorbed from the buckwheat husk can be recovered and reused.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these Examples.

[Example 1 and Comparative Example 1]
A nickel nitrate aqueous solution (standard solution manufactured by Nacalai Tesque, Inc.) was diluted with ion-exchanged water to a final concentration of 20 mg / L, and then adjusted to pH 4 with sodium hydroxide. 100 mL of the water to be treated thus prepared was placed in a plastic container, and the amount of buckwheat husks shown in Table 1 was added as an adsorbent, and placed in a reciprocating shaker at 25 ° C. for 48 hours. The buckwheat husk was a rectangular tetrahedron generated when normal buckwheat was peeled off by a conventional method, and was used after washing with water and air drying. Thereafter, solid-liquid separation was performed by centrifugation, and the nickel concentration of the obtained treated water was measured. From the results, the nickel adsorption rate, nickel adsorption amount, and nickel adsorption capacity (nickel adsorption amount per gram of adsorbent) were obtained. . An atomic absorption photometer (manufactured by Hitachi, Ltd., Z-8230) was used for measuring the nickel concentration.

  Next, the buckwheat husk obtained by solid-liquid separation is put into 15 mL of a desorbing solution composed of an aqueous nitric acid solution having a pH of 1, and shaken at 25 ° C. for 48 hours, and then the nickel concentration in the desorbing solution is measured. The amount of nickel desorbed and the amount of nickel remaining in the buckwheat husk (the amount of nickel remaining per gram of adsorbent) were determined.

For comparison, a commercially available activated carbon (manufactured by Wako Pure Chemical Industries, Ltd., granular) was used as an adsorbent, and the same treatment as in the case of buckwheat husk was performed.
The results are shown in Table 1.
Moreover, the relationship (nickel adsorption isotherm) between the nickel concentration in treated water and the nickel adsorption capacity is shown in FIG.

[Example 2 and Comparative Example 2]
Copper adsorption of buckwheat husk and activated carbon was carried out in the same manner as in Example 1 and Comparative Example 1 except that the water to be treated was prepared using an aqueous solution of copper (Cu) sulfate (standard solution manufactured by Nacalai Tesque). The characteristics were investigated.
The results are shown in Table 2 and FIG.

[Example 3 and Comparative Example 3]
Zinc adsorption characteristics of buckwheat husk and activated carbon were treated in the same manner as in Example 1 and Comparative Example 1 except that water to be treated was prepared using an aqueous zinc (Zn) nitrate solution (standard solution manufactured by Nacalai Tesque). I investigated.
The results are shown in Table 3 and FIG.

[Example 4 and Comparative Example 4]
The cadmium adsorption characteristics of buckwheat husk and activated carbon were treated in the same manner as in Example 1 and Comparative Example 1 except that the water to be treated was prepared using an aqueous cadmium (Cd) nitrate solution (standard solution manufactured by Nacalai Tesque). I investigated.
The results are shown in Table 4 and FIG.

[Example 5 and Comparative Example 5]
Treated in the same manner as in Example 1 and Comparative Example 1 except that the water to be treated was prepared using an aqueous chloride salt solution of antimony (Sb) (standard solution manufactured by Nacalai Tesque Co., Ltd.). The adsorption characteristics were investigated.
The results are shown in Table 5 and FIG.

[Example 6 and Comparative Example 6]
The lead adsorption properties of buckwheat husk and activated carbon were treated in the same manner as in Example 1 and Comparative Example 1 except that the water to be treated was prepared using an aqueous lead (Pb) nitrate solution (standard solution manufactured by Nacalai Tesque). I investigated.
The results are shown in Table 6 and FIG.

  The relationship between the equilibrium concentration of heavy metals in treated water at a constant temperature and the heavy metal adsorption capacity is the adsorption isotherm, which is important data for analyzing the adsorption phenomenon as basic data indicating the heavy metal adsorption capacity of the adsorbent. It is. Various formulas representing this adsorption equilibrium have been proposed. Among them, the Freundlich formula shown in formula 1 is the most famous.

Ｘ：吸着容量
Ｃ：平衡濃度
ｋ、ｎ：定数
グラフの横軸にｌｏｇＣ、縦軸にｌｏｇＸをとると、傾きｎ、切片ｌｏｇｋの一次直線になる。この傾きが大きいほど、高濃度ではよく吸着するが、低濃度ではあまり吸着しないことを意味し、傾きが小さいほど、低濃度から高濃度にわたって吸着量の変化が少ないことを意味する。ｋ（切片）が大きく、かつｎ（傾き）が小さい方が優れた吸着材であるといえる。 [Formula 1]

X: adsorption capacity C: equilibrium concentration k, n: constant When logC is taken on the horizontal axis of the graph and logX is taken on the vertical axis, it becomes a linear line of slope n and intercept logk. The larger the inclination, the better the adsorption at a high concentration, but less the adsorption at a low concentration, and the smaller the inclination, the smaller the change in the amount of adsorption from the low concentration to the high concentration. A larger k (intercept) and smaller n (gradient) can be said to be an excellent adsorbent.

  As is apparent from FIGS. 1 to 6, buckwheat husk has a higher heavy metal adsorption capacity in the water to be treated than activated carbon, which is advantageous for adsorption of heavy metals. Furthermore, when combined with the desorption tests shown in Tables 1 to 6, it can be seen that the water treatment method of the present invention is advantageous for recovery by adsorption and desorption of heavy metals. In particular, even for antimony that cannot be sufficiently adsorbed by activated carbon, buckwheat husk shows a high adsorbing ability, and the adsorbing ability is exhibited even at a low concentration.

[Example 7 and Comparative Example 7]
In the process of producing plated products by electroless nickel plating, cleaning wastewater generated when washing plated products was collected. The nickel concentration of this washing wastewater was 6.09 mg / L by atomic absorption method. The other composition was a washing wastewater for general electroless nickel plating containing small amounts of sodium hydroxide, ammonium chloride, sodium hypophosphite, ammonia and sodium citrate. The pH was 8.5.
Except that this washing wastewater was treated water, it was treated in the same manner as in Example 1 and Comparative Example 1, and the nickel adsorption characteristics of buckwheat husk and activated carbon were examined.
The results are shown in Table 7 and FIG.

  As is clear from FIG. 7, buckwheat husk has higher nickel adsorption capacity in electroless nickel plating washing wastewater than activated carbon, and also shows high adsorption ability even at low concentrations, which proves advantageous for nickel adsorption. . Furthermore, when combined with the desorption test shown in Table 7, it can be seen that the water treatment method of the present invention is advantageous for recovery by adsorption and desorption of nickel in electroless nickel plating washing wastewater. This result shows that the water treatment method of the present invention is applicable to general wastewater containing nickel.

[Example 8 and Comparative Example 8]
In the process of producing plated products by electroless copper plating, cleaning wastewater generated when washing plated products was collected. The copper concentration of this washing wastewater was 2.47 mg / L by atomic absorption method. Other compositions included formalin, sodium hydroxide, chelating agents, and general electroless copper plating cleaning wastewater. The pH was 9.3.
Except that this washing wastewater was treated water, it was treated in the same manner as in Example 1 and Comparative Example 1, and the copper adsorption characteristics of buckwheat husk and activated carbon were examined.
The results are shown in Table 8 and FIG.

  As is clear from FIG. 8, buckwheat husk has higher copper adsorption capacity in electroless copper plating washing wastewater than activated carbon, and also shows high adsorption ability even at low concentrations, which proves advantageous for copper adsorption. . Furthermore, when combined with the desorption test shown in Table 8, it can be seen that the water treatment method of the present invention is advantageous for recovery by adsorption and desorption of copper in the electroless copper plating washing wastewater. This result shows that the water treatment method of the present invention is applicable to general wastewater containing copper.

  Plating plays an important role in the industry and is used not only in the electronics industry and machine industry but also in various fields. For example, in the field of the electronics industry, in televisions, audios, and computers, the basic circuit is a printed wiring board made of copper plating, and the terminals are plated with nickel. Moreover, copper and nickel plating are also given to the electromagnetic shielding material used for the purpose of shielding the electromagnetic waves radiated | emitted from these electronic devices. In addition, precious metal plating such as chrome, gold, silver, etc. is used on the final finish surface to give aesthetics and maintain the aesthetics semi-permanently as product decoration, while copper and nickel plating are used as the base treatment. Is given abundantly.

  Thus, the demand for plating, particularly copper and nickel plating, is high, and at the same time, a large amount of heavy metal-containing wastewater is discharged from the production process of the plated product. Among them, the cleaning waste water generated when cleaning the plated product is discharged in a large amount and its concentration is low, so that the treatment is difficult. The water treatment method of the present invention can also be applied to such waste water, and its industrial utility value is extremely high.

[Example 9 and Comparative Example 9]
As waste water containing antimony, dye waste water generated when dyeing polyester fibers was collected. This dyed wastewater was filtered through a filter having a pore size of 0.45 μm to remove impurities such as fiber waste. The antimony concentration of the dyeing wastewater after filtration was 1.24 mg / L by atomic absorption method. The other composition was a dye wastewater for general polyester fibers, including dyes, leveling dispersants (isopropyl alcohol, nonionic surfactants, anionic surfactants), and acetic acid. The pH was 4.1.
The antimony adsorption characteristics of buckwheat husk and activated carbon were examined in the same manner as in Example 1 and Comparative Example 1 except that this dyeing wastewater was treated.
The results are shown in Table 9 and FIG.

  As is clear from FIG. 9, buckwheat husk has a higher antimony adsorption capacity in dyeing wastewater than activated carbon, and shows a high adsorption ability even at a low concentration, which is advantageous for adsorption of antimony. Furthermore, when combined with the desorption test shown in Table 9, it can be seen that the water treatment method of the present invention is advantageous for recovery by adsorption and desorption of antimony in dyeing wastewater. This result shows that the water treatment method of the present invention can be applied to general wastewater containing antimony.

  Antimony is used as a polymerization catalyst for polyester resins. For wastewater from factories that produce this catalyst, wastewater from factories that produce polyester resin or fibers using this catalyst, wastewater from factories that dye polyester fibers, etc. Antimony is contained. Antimony is also widely used as a raw material for electronic parts and a flame retardant, and antimony is also contained in waste water from manufacturing plants thereof. If such antimony-containing wastewater is discharged into a river or the like as it is, there is a risk of causing environmental pollution problems. While there is a strong need to solve environmental pollution problems caused by harmful substances, the concentration of antimony emissions is in the direction of becoming more severely regulated.

  As a method of removing antimony from antimony-containing wastewater, a method of removing iron salt as an insoluble precipitate by adding iron salt to the wastewater has been proposed, but the running cost is high and the amount of generated sludge is large. The complexity of the secondary processing is also a problem. In particular, an effective method for treating a large amount of wastewater with a low antimony concentration has not been proposed. The water treatment method of the present invention can also be applied to such waste water, and its industrial utility value is extremely high.

2 is a graph showing nickel adsorption isotherms obtained in Example 1 and Comparative Example 1. FIG. 4 is a graph showing copper adsorption isotherms obtained in Example 2 and Comparative Example 2. 6 is a graph showing zinc adsorption isotherms obtained in Example 3 and Comparative Example 3. 6 is a graph showing cadmium adsorption isotherms obtained in Example 4 and Comparative Example 4. 6 is a graph showing antimony adsorption isotherms obtained in Example 5 and Comparative Example 5. 6 is a graph showing lead adsorption isotherms obtained in Example 6 and Comparative Example 6. 6 is a graph showing nickel adsorption isotherms obtained in Example 7 and Comparative Example 7. 6 is a graph showing copper adsorption isotherms obtained in Example 8 and Comparative Example 8. 6 is a graph showing antimony adsorption isotherms obtained in Example 9 and Comparative Example 9.

Claims (4)

  A water treatment method characterized by contacting water to be treated containing heavy metal with buckwheat husk and adsorbing heavy metal in the water to be treated to the buckwheat husk.   The heavy metal is at least selected from the group consisting of heavy metals designated as regulated under the Sewerage Law, heavy metals designated as regulated under the Water Pollution Control Act, and heavy metals designated as monitored items It is 1 type, The water treatment method of Claim 1 characterized by the above-mentioned.   The water treatment method according to claim 2, wherein the heavy metal is at least one selected from the group consisting of nickel, copper, zinc, cadmium, antimony and lead.   The water treatment method according to claim 3, wherein the water to be treated is waste water containing at least one selected from the group consisting of nickel, copper and antimony.

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