JPH0215252B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heavy metal adsorbent made by treating activated carbon with polyethyleneimine and carbon disulfide, and a method for producing the same. Chelating ion-exchange resins are highly regarded as effective for adsorption and removal of heavy metals in wastewater, as environmental pollution caused by heavy metal ions contained in industrial wastewater has become a social issue. In particular, chelating ion exchange resins based on phenol aldehyde resins or styrene resins and having chelate functional groups such as iminodiacetic acid, thiourea, and dithiocarbamic acid have been put into practical use as effective processing agents. However, when adsorbing and removing mercury, which is particularly harmful to the human body, these resins have a low adsorption rate, so if they are packed in a column and passed through the column, high-speed processing will significantly reduce the adsorption capacity life. Not suitable for processing in large quantities. Also,
These chelating ion exchange resins are
It is easily affected by pH and cannot adsorb and remove organic mercury and colloidal mercury at all, so it is not satisfactory as a treatment for industrial wastewater, research, and laboratory wastewater that contains mercury in various forms. There is still room for further improvement. On the other hand, granular activated carbon is used to treat heavy metals and organic matter in wastewater to compensate for the above drawbacks, but it generally has poor selectivity for heavy metal ions, especially mercury ions, and has a low adsorption capacity at low concentrations. , and is susceptible to the effects of pH and coexisting salts, which poses a practical problem. To solve this problem, Japanese Patent Publication No. 53-22554 and Japanese Patent Publication No. 54-8474 disclose adsorbents in which sulfur-containing amino compounds such as thiourea, thiosemicarbazide, and thioacetamide are supported on activated carbon. An adsorbent in which a sulfur amino acid and a hydrohalic acid are supported on activated carbon has been proposed. However, since thiosemicarbazides are generally easily soluble in water, when used to remove heavy metal ions from an aqueous solution, there are problems such as part of the thiosemicarbazides being eluted, and this problem has not necessarily been solved. Furthermore, when actually filling a column etc. and passing water containing heavy metal ions through it, there are many points to consider, such as the contact area of the adsorbent with water, adsorption capacity, mechanical strength, etc., making it economical and practical. At present, a certain adsorbent has not yet been obtained. As a result of intensive research to solve this problem, the present applicant found that treating activated carbon with a water-soluble amine and carbon disulfide provides an extremely simple and economical method for adsorption after water treatment (after washing with large amounts of water). It was discovered that a heavy metal ion adsorbent with almost no decrease in performance could be obtained, and that the obtained adsorbent could absorb heavy metal ions,
It was discovered that the adsorbent has excellent selectivity and adsorption capacity, especially for mercury ions, and has an excellent adsorbent life, and has previously applied for a patent (Japanese Patent Laid-Open Publication No. 159835/1983). However, the adsorbent described in JP-A-55-159835 was not fully satisfactory in terms of exchange capacity for heavy metals, especially mercury, that is, total exchange capacity and flow-through point exchange capacity. Therefore, the present inventors conducted further intensive research to improve this point, and found that when activated carbon is treated with polyethyleneimine and carbon disulfide by adjusting the impregnation rate to activated carbon within a specific range, heavy metals, especially It has been discovered that the total exchange capacity and flow-through point exchange capacity for mercury are significantly improved, and the present invention has been achieved. That is, the present invention provides a heavy metal adsorbent which is prepared by treating activated carbon with polyethyleneimine and carbon disulfide in the presence of water to impregnate the activated carbon with a reaction product of polyethyleneimine and carbon disulfide, in which the amount of impregnation is smaller than that of the activated carbon. A heavy metal adsorbent characterized by a concentration of about 9 to 30% by weight and activated carbon are treated with polyethyleneimine and carbon disulfide in the presence of water to impregnate the activated carbon with a reaction product of polyethyleneimine and carbon disulfide. When producing a heavy metal adsorbent, first, polyethyleneimine is impregnated onto activated carbon in an amount of about 8.5 to 20% by weight based on the activated carbon, and then the impregnated amount is adjusted to a total amount of about 9 to 30% by weight based on the activated carbon. This is a method for producing a heavy metal adsorbent characterized by treatment with carbon disulfide. The adsorbent of the present invention has excellent total exchange capacity and flow-through point exchange capacity for heavy metals, especially mercury;
If the amount of the reaction product of polyethyleneimine and carbon disulfide impregnated is less than about 9% by weight based on activated carbon,
The adsorption effect by the ligand is not sufficient, the activated carbon is only surface modified, and the total exchange capacity for heavy metals, especially mercury, is small. Moreover, if it exceeds about 30% by weight, the pore volume and specific surface area of the activated carbon become small, and the adsorption effect by the micropores of the activated carbon is significantly reduced, making it impossible to obtain a sufficient adsorption capacity. In particular, among the adsorbents of the present invention, those impregnated with activated carbon in an amount of about 10 to 25% by weight are preferred. The adsorbent of the present invention has a reaction product of polyethyleneimine and carbon disulfide attached thereto, but unreacted polyethyleneimine or carbon disulfide may also be attached thereto. In order to obtain the adsorbent of the present invention, it is desirable to maintain the molecular weight and concentration of polyethyleneimine, the charging ratio (bath ratio) of activated carbon and polyethyleneimine, and the reaction temperature within predetermined ranges. As a method, polyethyleneimine is impregnated with activated carbon in an amount of about 8.5 to 20% by weight based on the activated carbon. At that time, if the amount of polyethyleneimine impregnated is less than about 8.5% by weight based on the activated carbon, the adsorption effect by the ligand will not be sufficient, and the activated carbon will only be surface-modified, and the total exchange capacity for heavy metals, especially mercury, will be small. You can only get things. Moreover, if it exceeds about 20% by weight, the pore volume and specific surface area of the activated carbon become small, and the adsorption effect by the micropores of the activated carbon is significantly reduced, making it impossible to obtain a sufficient adsorption capacity. The molecular weight of the polyethyleneimine used in the present invention is preferably 600 to 6000, and the molecular weight is preferably 600 to 6000.
If it is smaller, impregnation is easier, but it is not preferable because it tends to elute into water during adsorption treatment. Furthermore, if the molecular weight exceeds 6,000, it tends to be difficult to control the impregnation rate to about 8.5 to 20% by weight, which is not preferable. The aqueous solution of polyethyleneimine is 2
~20% by weight is preferred, and 3-15% by weight is particularly preferred. If the concentration of polyethyleneimine is less than 2%, it tends to be difficult to impregnate approximately 8.5 to 20% by weight, which is undesirable. If it exceeds 20% by weight, the viscosity of the aqueous solution increases, making separation and washing difficult. Not only does this tend to become difficult, but the amount of polyethyleneimine recovered increases, which is not economically desirable. In addition, the charging ratio of activated carbon and polyethyleneimine aqueous solution also affects the impregnation rate, with a weight ratio of 1:3.
It is preferable to set the ratio to 1:10. If the bath ratio is less than 1:3, it will tend to be difficult to obtain the desired impregnation rate, and if it exceeds 1:10, it will not be possible to carry out impregnation treatment in large quantities, which is not economically preferable. Furthermore, the temperature at which polyethyleneimine is impregnated onto activated carbon is preferably 10°C to 90°C. Even if the temperature is lower than 10°C or higher than 90°C, it is not preferable because it tends to make it difficult to obtain the desired impregnation rate. The polyethyleneimine-impregnated carbon obtained in this way has a ratio of about 8.5% polyethyleneimine to activated carbon.
It is preferable that the unadsorbed polyethyleneimine aqueous solution is separated by solid-liquid separation, and then thoroughly washed with water to remove the polyethyleneimine attached to the surface. Furthermore, the solid-liquid separated polyethyleneimine aqueous solution can be used repeatedly as many times as the concentration is adjusted. Next, in the second stage, the polyethyleneimine-impregnated carbon obtained above and carbon disulfide are treated at 40°C to 100°C using water as a solvent.
It is preferable to treat with If the temperature is lower than 40°C, the cross-linking three-dimensional reaction will not proceed sufficiently, so not only will it not be possible to form a thiocarbohydrazide structure, but
This is not preferable since it also tends to elute into water. In addition, the amount of carbon disulfide added is as follows:
It is preferable to use 0.2 to 1.1 equivalents per equivalent of primary and secondary amino groups of polyethyleneimine impregnated on activated carbon. If it is less than 0.2 equivalent,
Not only does the cross-linking three-dimensional reaction not proceed sufficiently and elution into water tends to increase, but also the adsorption capacity for mercury tends to decrease, and if the amount of carbon disulfide added exceeds 1.1 equivalent, excessive Carbon disulfide is adsorbed on activated carbon and not only produces a bad odor, but also
This is not preferred because it tends to lower the pH. The activated carbon used in the present invention may be of any type, but it is particularly preferable to use coconut shell charcoal activated with steam. In addition, the particle size of activated carbon is
It is an important factor that controls the liquid flow rate and adsorption amount.
80 mesh, preferably 20 to 60 mesh is used. The adsorbent thus obtained has high selective adsorption properties for heavy metals such as mercury (organic mercury, colloidal mercury), copper, cadmium, silver, and gold, especially mercury, and has excellent total exchange capacity and flow-through point exchange capacity. Since there is a chelating ion exchange resin,
This can be removed by contacting with a hydrated silver solution. The contact method includes a batch method in which the adsorbent is simply mixed with a solution and shaken, and a column method in which the adsorbent is packed in a column and the liquid is passed through it, but the column method is generally used. At this time, the temperature of the heavy metal-containing solution is suitably 15 to 50°C, and the contact time is suitably 3 minutes to 1 hour. According to the present invention, it is possible to obtain a heavy metal adsorbent in which the adsorption capacity hardly decreases after water treatment (after washing with large amounts of water) using an extremely simple and economical method. It has high selectivity and adsorption capacity (total exchange capacity and flow-through point exchange capacity) for heavy metals such as cadmium, silver and gold, especially mercury, and has an excellent adsorbent life. Next, the present invention will be explained in more detail with reference to Examples. Example 1 Polyethyleneimine (Epomine) with a molecular weight of 1200
SP-012, manufactured by Nippon Shokubai Chemical) 10g with ion-exchanged water
To this was added 20.0 g of coconut shell activated carbon (20-50 mesh, manufactured by Daiichi Carbon Industries), stirred at 30°C for 2 hours, filtered, and thoroughly washed with ion-exchanged water. . Based on the weight increase after drying, the impregnation rate of polyethyleneimine was 15% by weight. Next, 23.0g of polyethyleneimine-impregnated carbon was obtained.
was slowly stirred with 2.6 g of carbon disulfide and 100 g of ion-exchanged water, heated and stirred at 40°C for 1 hour and then at 75°C for 4 hours, filtered, and thoroughly washed with ion-exchanged water. An adsorbent was obtained. The total impregnation rate (determined from weight increase) of the adsorbent thus obtained was 23% by weight. Example 2 Polyethyleneimine (Epomine) with a molecular weight of 1800
SP-018, manufactured by Nippon Shokubai Chemical) 5g with ion-exchanged water
To this was added 20.0 g of coconut shell activated carbon (30 to 60 mesh, manufactured by Daiichi Carbon Industries), stirred at 43°C for 2 hours, filtered, and thoroughly washed with ion-exchanged water. . Based on the weight increase after drying, the impregnation rate of polyethyleneimine was 10% by weight. Next, 22.0g of polyethyleneimine-impregnated carbon was obtained.
was slowly stirred with 2.5 g of carbon disulfide and 100 g of ion-exchanged water, heated at 4.0℃ for 1 hour, and then heated to 85℃.
After heating and stirring for 3 hours, the mixture was filtered and thoroughly washed with ion-exchanged water to obtain an adsorbent. The total impregnation rate of the adsorbent thus obtained was 15% by weight. Comparative Example 1 10 g of a polyethyleneimine aqueous solution (Epomin P-1000, manufactured by Nippon Shokubai Chemical) with a molecular weight of 70,000 and a concentration of 30% by weight was dissolved in 90 g of ion exchange water, and 20.0 g of coconut shell activated carbon (20 to 50 mesh) was added to this. hand,
After stirring at 30°C for 2 hours, the mixture was filtered and thoroughly washed with ion-exchanged water. Based on the weight increase after drying, the impregnation rate of polyethyleneimine was 3.0% by weight. Next, 20.6 g of polyethyleneimine-impregnated carbon was obtained.
was slowly stirred with 1.0 g of carbon disulfide and 100 g of ion-exchanged water, heated and stirred at 40°C for 1 hour and then at 90°C for 4 hours, filtered, and thoroughly washed with ion-exchanged water. An adsorbent was obtained. The total impregnation rate of the adsorbent thus obtained was 4.5% by weight. Comparative example 2 Polyethyleneimine with a molecular weight of 300 (Epomin SP
−003, manufactured by Nippon Shokubai Chemical) 30g with 70% ion-exchanged water
To this, 20.0 g of coconut shell activated carbon (30 to 60 mesh, manufactured by Daiichi Carbon Industries) was added, and the mixture was heated at 30℃ for 3 hours.
After stirring for an hour, the mixture was filtered and thoroughly washed with ion-exchanged water. Based on the weight increase after drying, the impregnation rate of polyethyleneimine was 27% by weight. Next, 25.4 g of polyethyleneimine impregnated carbon was obtained.
was slowly stirred with 9.5 g of carbon disulfide and 100 g of ion-exchanged water, heated and stirred at 50°C for 1 hour and then at 75°C for 4 hours, filtered, and thoroughly washed with ion-exchanged water. An adsorbent was obtained. The total impregnation rate of the adsorbent thus obtained was 40% by weight. Reference Examples 1-2 The adsorbents obtained in Examples 1-2 and Comparative Examples 1-2 and the raw material coconut shell activated carbon were each dried in a dry state.
A sample of 0.10 g was immersed in 50 ml of a low-concentration mercury-containing aqueous solution, and the residual mercury concentration after immersion at 30° C. for 12 hours was measured by low-temperature vaporization reduction atomic absorption spectrometry. The results are shown in Table 1. The composition of the mercury-containing aqueous solution is as follows. (Hg ²⁺ ; 10 mg/, NaCl; 5 g/, PH=
6)

[Table] Reference Examples 3 to 4 0.10 g of each adsorbent obtained in Examples 1 to 2 and Comparative Example 1 was collected in a dry state, immersed in 50 ml of a highly concentrated mercury-containing aqueous solution, and immersed at 30°C for 24 hours. The residual mercury concentration after boiling was measured by chelate titration to determine the total exchange capacity. The results are shown in Table 2. The composition of the mercury-containing aqueous solution is as follows. (Hg ²⁺ ; 1000mg/, NaCl; 5g/, PH
=6)

[Table] Reference Example 5 The adsorbent obtained in Example 1 and Comparative Example 1 was
As a wet resin for each glass column in mmφ
The chamber was filled with 60 ml, and the mercury-containing liquid was passed through the chamber in a downward flow at a space velocity of 5. The flow rate until the mercury concentration in the flow-through exceeds 5 ppb was determined, and the flow-through point exchange capacity is shown in Table 3. The composition of the mercury-containing liquid is as follows.
(Hg ²⁺ ; 200mg/, NaCl; 5g, PH6)

【table】

Claims (1)

[Scope of Claims] 1. A heavy metal adsorbent prepared by treating activated carbon with polyethyleneimine and carbon disulfide in the presence of water to impregnate the activated carbon with a reaction product of polyethyleneimine and carbon disulfide, the amount of which is impregnated with activated carbon. A heavy metal adsorbent characterized in that the amount is about 9 to 30% by weight. 2. The adsorbent according to claim 1, wherein the amount of impregnation is about 10 to 25% by weight based on the activated carbon. 3. When manufacturing a heavy metal adsorbent by treating activated carbon with polyethyleneimine and carbon disulfide in the presence of water to impregnate the activated carbon with a reaction product of polyethyleneimine and carbon disulfide, first, polyethyleneimine is added to the activated carbon, Approximately 8.5-20 for the activated carbon
1. A method for producing a heavy metal adsorbent, which comprises impregnating the activated carbon in an amount of 9% to 30% by weight, and then treating the adsorbent with carbon disulfide so that the total amount of impregnated carbon is about 9 to 30% by weight. 4. The manufacturing method according to claim 3, wherein the polyethyleneimine has a molecular weight of 600 to 6,000.