JP4747326B2 - Hexavalent chromium adsorption removing agent, method for producing the same, and method for removing hexavalent chromium - Google Patents

Description

The present invention relates to a hexavalent chromium adsorption / removal agent, a method for producing the same, and a hexavalent chromium removal method, and in particular, an environmental purification agent useful for adsorption removal of hexavalent chromium, which can sufficiently expect environmental improvement and environmental conservation. In other words, the present invention relates to a hexavalent chromium adsorption / removal agent , a method of advantageously producing the same, and a method of removing hexavalent chromium using the same.

  In recent years, there are concerns about the negative effects of hexavalent chromium on the human body and the environment, and hexavalent chromium-free technology has been rapidly established, such as the development of hexavalent chromium-free trivalent chromate treatment in metal surface treatment processes. It is being done. This hexavalent chromium has a strong oxidizing power, and when it touches the human body, it may irritate the skin and respiratory organs and cause tumors and dermatitis. In Japan's environmental standards, hexavalent chromium contained in tap water is regulated to have a concentration of 0.05 ppm or less.

  In this way, although the discharge of hexavalent chromium is severely restricted, heavy metal sludge, electronic equipment, electronic circuits, metal products that have been subjected to hexavalent chromate treatment, etc. that already hold hexavalent chromium, The possibility of being dumped in nature has not disappeared, and depending on the location, they are already piled up, causing soil contamination, and rainwater, etc., can cause nearby river water, lake water, and pond water. In addition, there is a current situation that relatively high concentration of hexavalent chromium is leached into land water such as groundwater.

  As such a method for removing hexavalent chromium, a reduced hydroxide method and an ion exchange resin method are well known. Here, the former reduced hydroxide method uses a reducing agent such as ferrous sulfate, sodium sulfite, or sodium bisulfite in waste water containing hexavalent chromium under strongly acidic conditions (for example, pH is 3 or less). After reducing hexavalent chromium to trivalent chromium by acting, chromium hydroxide is generated by adding a neutralizing agent such as quick lime, and precipitated, and the precipitate is filtered, Hexavalent chromium is separated and recovered from wastewater. However, in such a method, there is a possibility that harmful gases such as SOx may be generated by using a reducing agent such as iron sulfate, and there is an inherent problem that the processing cost increases because the reducing agent is expensive. . In addition, in this reduced hydroxide method, a reducing agent tends to be used excessively in order to completely remove hexavalent chromium, and this excess reducing agent increases the COD value of wastewater. There is a risk of causing new problems.

  On the other hand, the latter ion exchange resin method uses a strongly basic anion exchange resin to adsorb and remove hexavalent chromium in the waste liquid, but the waste liquid contains a large amount of anions such as chlorine ions. In the case of coexistence, the adsorption of hexavalent chromium is hindered by such anions, and depending on the type of waste liquid, the hexavalent chromium removal effect may not be sufficiently obtained. Due to the oxidizing power, the function of the ion exchange resin is lowered, and there is a problem that stable hexavalent chromium treatment cannot be continued. Further, since the power used is large, there is a disadvantage that the running cost is high and it is not economical.

  Therefore, there is a strong demand for a method for removing hexavalent chromium that is inexpensive and has little concern for environmental impact.

  By the way, sawdust and other wood waste discharged in large quantities from the wood and wood products manufacturing industry, pulp manufacturing industry, etc. are designated as industrial waste by the Law on Waste Disposal and Cleaning, and this wood waste is an effective resource. Development of methods to be used in the future and securing of the use destination of wood chips are becoming very important. Some examples have been reported so far of application to adsorption of hexavalent chromium using wood chips from thinned and waste wood, and sawdust discharged from wood and pulp manufacturing processes.

  For example, in Patent Document 1, an organic material containing cellulose such as sawdust and pulp sludge is brought into contact with an acidic solution containing hexavalent chromium, and hexavalent chromium is reduced to trivalent chromium to remove hexavalent chromium. A method has been proposed. However, in the technique described in Patent Document 1, hexavalent chromium is reduced to trivalent chromium by a reaction that decomposes cellulose into carbon dioxide and water. The liquid to be treated and the organic material containing cellulose need to be brought into contact with each other. For purification, it is necessary to heat the liquid to be purified to a predetermined temperature (50 ° C. or higher). Therefore, it is not practical to apply such a method to the purification of a huge amount of land water. Moreover, in the future, such as around the place where the waste containing hexavalent chromium is installed, contamination with hexavalent chromium will occur. It was impossible to apply such a method to prevent pollution of river water, groundwater, etc.

  Patent Document 2 proposes an anion-adsorbing carbon material manufacturing apparatus that is inexpensive, environmentally friendly, and excellent in anion-adsorbing properties, and uses such a manufacturing apparatus to carbonize raw materials such as wood chips. The produced carbide is brought into contact with an acid solution to produce an anion-adsorbing carbon material, which is then pelletized or pulverized to obtain a product. However, when wood chips such as sawdust are carbonized, any anion-adsorbed carbon material that has been pelletized or crushed is highly likely to float in the water, and is installed and purified at the bottom of rivers and lakes and in water. It has become unsuitable to do. Further, when pelletizing an anion adsorbing carbon material, not only the process becomes complicated and the cost increases, but also depending on the binder used, there is a concern about the influence of the anion adsorbing carbon material itself on the environment.

  On the other hand, in recent years, dredging projects have been carried out as part of public works in order to remove the bottom mud accumulated at the bottom of the water system due to the deterioration of water quality in closed sea areas. There is a risk that dredging projects will not continue in the future due to problems such as securing landfill disposal sites and costs. Under such circumstances, various treatment techniques for treating dredged bottom mud have been proposed. For example, in Patent Documents 3 to 5, water glass (sodium silicate) is added to bottom mud pumped up from lakes, oceans, and the like. ) Etc. to solidify the bottom mud and make it a reusable treated soil.

  In addition, one of the applicants of the present application previously described in Japanese Patent Application Laid-Open No. H10-260260, the dredged bottom mud, which is industrial waste, is mixed with shells and / or crushed rice husks, and further used as a binder as sodium silicate. A sintered body obtained by solidifying and firing the composition obtained by adding (water glass) was proposed, and it was clarified that this was effective for purification of industrial wastewater such as factory wastewater and domestic wastewater. However, in the previously proposed sintered body for water purification, it was very effective in removing heavy metals present in the cation form, but the anion form such as hexavalent chromium as described above. It has been clarified that the removal of heavy metals present in can not effectively exhibit its effects.

JP 2001-58192 A Japanese Patent No. 3822894 Japanese Patent Laid-Open No. 11-61128 JP 11-235600 A Japanese Patent Laid-Open No. 2005-7335 Japanese Patent Laid-Open No. 2006-239583

Here, the present invention has been made in the background of such circumstances, and the problem to be solved is to generate a harmful gas such as SOx from the object to be purified contaminated with hexavalent chromium. A new environmental purification agent (hexavalent chromium adsorption / removal agent) that can be purified at a low cost without causing any concern, and a method for advantageously producing the same. And it is providing the method of removing hexavalent chromium using such an environmental purification agent.

  And, as a result of intensive studies on environmental cleaners useful for the removal of hexavalent chromium, the present inventors have formulated dredged bottom mud, sawdust and other wood chips, and sodium silicate at specific ratios, respectively. The sintered body obtained by firing the brazed composition was found to be useful in the removal of hexavalent chromium existing in the form of an anion in an aqueous solution, and the present invention was completed. .

  That is, the present invention blends dredged bottom mud, wood chips and sodium silicate obtained from the bottom of the water system in the ratio of 46 to 62%, 6 to 18% and 25 to 37%, respectively, in the solid content weight ratio. An environmental purification agent comprising a sintered body having a porous structure obtained by firing the composition thus obtained is a gist thereof.

  In addition, according to one of the desirable aspects of the environmental purifier according to the present invention, sawdust is used as the wood waste.

  And in order to produce the environmental purifier according to the present invention advantageously, in the present invention, dredged mud, wood chips and sodium silicate obtained from the bottom of the aqueous system, in a solid content weight ratio, After preparing the composition which mix | blends in the ratio of 46 to 62%, 6 to 18%, and 25 to 37%, respectively, it shape | molds to a predetermined | prescribed magnitude | size and the obtained molded object is 400 to 700 degreeC. The gist is also a method for producing an environmental purification agent characterized in that a sintered body having a porous structure is obtained by firing at a temperature of 5 ° C.

  In addition, according to one of the preferable embodiments of the method for producing an environmental purification agent according to the present invention, the sintered body obtained by firing is immersed in an acidic aqueous solution.

  Moreover, according to one of the other preferable aspects of the manufacturing method of the environmental purifier according to this invention, the said baking is performed in the state which interrupted supply of oxygen.

  In addition, the present invention provides a hexavalent chromium characterized in that the environmental purifier as described above is brought into contact with an object to be purified to remove hexavalent chromium contained in the object to be purified. The removal method is also the gist thereof.

  In one preferred embodiment of the method for removing hexavalent chromium according to the present invention, the environmental purification agent is brought into contact with the article to be purified whose pH is 2 or more and less than 5. Become.

  Thus, in the environmental purification agent according to the present invention, a composition in which dredged bottom mud obtained from the bottom of the aqueous system, wood chips and sodium silicate are blended at a predetermined ratio is used, and this composition is fired. Since the sintered body having a porous structure is obtained, the carbide of wood chips is contained or retained in the sintered body having a porous structure mainly composed of dredged bottom mud. For this reason, without using any reducing agent that generates harmful gases such as SOx, the anions in the aqueous solution can be obtained in the aqueous solution due to the carbide in the sintered body and the porous structure of the sintered body that give the environmental purifier according to the present invention. The hexavalent chromium that exists in the form can be effectively adsorbed and removed, and the raw material cost is low, and heating and energization are not required at the time of purification. It is possible to carry out the purification process.

  Moreover, in the environmental purification agent according to the present invention, since it is composed of a sintered body mainly composed of dredged mud obtained from the bottom of an aqueous system, adsorption consisting only of carbide obtained by carbonizing wood chips. Unlike materials, even if it has a porous structure, it does not float on water, and it can be purified by immersing it in the bottom of a river or lake or in water. Thus, the hexavalent chromium contained in the object to be purified can be advantageously adsorbed and removed.

  Furthermore, when the environmental purification agent according to the present invention is applied to a water area near the collection site of dredged mud, which is one of the raw materials, the environmental purification agent constitutes a substance system close to the application site. It becomes. In addition, even in the case of sodium silicate and wood chips, which are other raw materials for such sintered bodies, they are composed of naturally abundant elements. There is almost no possibility of secondary contamination due to the cleaning agent. That is, the environmental purifier according to the present invention has almost no need to worry about the influence on the environment.

  And the sintered compact which gives the environmental purification agent according to this invention has sufficient intensity | strength from the place where sodium silicate is mix | blended in a predetermined ratio as a binder, and it is easy to disintegrate in a to-be-purified material. This can be prevented, and an effective purification action can be exhibited over a long period of time.

  In addition, in the present invention, since the dredged mud and wood chips treated as industrial waste are used as effective resources, it is an industry in which securing of a landfill treatment site is a problem. It can also contribute greatly to waste reduction. In particular, for wood waste, its recycling is urgently required, so it can be said that its use as an environmental purification agent is extremely significant.

  Further, according to the method for producing an environmental purification agent according to the present invention, the composition as shown in the above is formed by molding using a composition composed of dredged mud, wood chips and sodium silicate, and firing the molded product at a predetermined temperature. A porous sintered body excellent in hexavalent chromium adsorption removal performance is advantageously obtained.

  Furthermore, according to the method for removing hexavalent chromium according to the present invention, the hexavalent chromium contained in the object to be purified is effectively obtained by bringing the environmental purifier as described above into contact with the object to be purified. Can be removed.

  By the way, in the environmental purifier according to the present invention, the dredged mud obtained from the bottom of the water system, which is the main component of the porous structure sintered body that gives it, is a river, a lake, an estuary, a closed sea area, etc. Organic matter abundantly removed from the bottom of the water system by conventional dredging work, etc. (for example, about 10-15% of the solid content in dredged bottom mud in Ago Bay, Mie Prefecture) However, the bottom mud taken out from the bottom of such an aqueous system is usually used as having a water content of about 30% to 40% after being subjected to some dehydration by an operation such as drying. It becomes. The dredged mud obtained from the bottom of this water system is not particularly limited, but when using environmental purification agents for purification of water systems (for example, rivers, lakes, estuaries, sea areas, etc.) It is desirable to be dredged mud obtained from the bottom of the water area where the environmental purification agent formed by is used, and this makes it possible to make the environmental purification agent more suitable for the on-site water area.

  In addition, the wood waste blended in the dredged bottom mud obtained from the bottom of such an aqueous system is a component for imparting a hexavalent chromium removal function to the environmental purification agent according to the present invention, and this wood waste is a predetermined ratio. By being blended and fired, wood scrap carbides are contained or retained in the sintered body, and the adsorption removal efficiency of hexavalent chromium is effectively enhanced. Note that, as the word indicates, this wood waste is not limited to any kind of wood as long as it is wood scraps or shavings. Wood chips may be mixed, and for example, wood chips discharged in wood processing industries such as a wood / wood product manufacturing industry and a pulp manufacturing industry can be used effectively. Among such wood chips, fine ones are particularly desirable. Specifically, sawdust of about 0.01 mm to 5 mm, more preferably about 0.1 mm to 1 mm is advantageously used. By using fine fine wood chips (sawdust), the compatibility with dredged mud is advantageously increased, and the carbonization degree is improved not only on the surface of the wood chips but also inside, so that even more excellent hexavalent chromium A removal effect is added.

  Furthermore, the sodium silicate compounded in the dredged mud and wood chips functions as a binder, and can provide sufficient strength to the porous sintered body obtained by firing. It is. Thereby, when the environmental purifier according to the present invention is brought into contact with an object to be purified (river water, lake water, pond water, groundwater, seawater, soil, etc.) by being immersed or buried. In addition, the environmental purification agent is prevented from collapsing and being shattered, so that an effective purification action can be exhibited over a long period of time.

  And these dredged mud, wood chips, and sodium silicate are 46-62% and 6-18% in solid content weight ratio, in obtaining the environmental purifier which consists of the sintered body of the target porous structure. And 25 to 37% of the content. In such a blending ratio, if the blending amount of wood chips is less than 6%, the removal efficiency of hexavalent chromium is extremely lowered, while if the blending amount is more than 18%, the resulting sintering is obtained. The body becomes brittle and cannot be put to practical use. Moreover, even if the blending amount of sodium silicate as a binder is less than 25%, it becomes difficult to obtain a sintered body having sufficient strength, which makes it difficult to put it to practical use. If the amount exceeds 50%, the strength of the sintered body can be increased, but the specific surface area of the sintered body is reduced, and the hexavalent chromium removal efficiency of the sintered body is reduced. In particular, in the present invention, in the present invention, the blended composition of wood chips: 10 to 15%, sodium silicate: 23 to 30%, dredged mud: the balance is advantageously employed in the solid content weight ratio. It becomes.

  As described above, in the present invention, a composition is prepared in which a specific amount of wood chips and sodium silicate are blended with the dredged bottom mud as a main component to give a sintered body having a desired porous structure. However, in addition to these three components, such a composition can be taken out from various additives, for example, the bottom of an aqueous system, if necessary, as long as the object of the present invention is not impaired. It is possible to appropriately add a chemical for agglomeration and dehydration of the bottom mud, a solidifying agent, a binding aid, a pore forming aid and the like.

  In the present invention, in order to obtain a sintered body having a porous structure that gives the target environmental purification agent, the composition obtained as described above is used. First, according to a general molding technique, By molding into a desired shape and size, unfired molded products having various shapes and sizes such as a disk shape and a granular shape are formed. Next, the obtained sintered product is fired to produce a desired sintered body.

  In the firing of such a composition, the firing temperature is generally appropriately selected at a temperature within the range of 400 to 700 ° C., and particularly preferably 600 to 700 ° C. A firing temperature within the range will be employed. This is because if the firing temperature is too low, sufficient firing cannot be performed, which makes it difficult to sufficiently increase the strength of the sintered body. This is because it causes problems such as difficulty in forming a porous structure effective for the combined body.

  In addition, it is desirable to perform the firing in a state in which the supply of oxygen is interrupted, whereby the carbonization degree of the wood chips contained in the composition can be advantageously increased, and thus higher adsorption performance can be achieved. It is applied to the sintered body.

  Then, the sintered body obtained by firing the composition is subjected to an immersion treatment in which it is immersed in an acidic aqueous solution, if necessary, in order to realize an effective porous structure on the surface more advantageously. As the acidic aqueous solution, inorganic acids such as nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid and perchloric acid, and aqueous solutions of organic acids such as oxalic acid, acetic acid and formic acid are used. In order to increase the porosity of the sintered body, an acidic aqueous solution of about 0.01 to 10M can be suitably employed. The treatment with the acidic aqueous solution is generally carried out for a period of 3 hours or more, and the upper limit thereof is about 24 hours. This is because, even if the processing time exceeds 24 hours, it is difficult to expect a large change in the processing effect.

Further, the sintered body obtained by such a firing operation and necessary treatment has a sufficient strength in the porous structure, and advantageously, the maximum load at the time of fracture of the sintered body is measured by a compressive strength tester. The uniaxial compressive strength (according to the physical test method of JIS R 5210 cement) obtained by measuring in (4) is 4.0 N / mm ² or more. In addition, the size of such a sintered body is generally formed with an outer dimension of about 0.5 mm to 10 cm in consideration of its handleability and the like.

  And in the sintered body of the porous structure obtained in this way, the carbide of wood chips is contained or retained, and by the presence of this carbide, cadmium present in the cation form and , Lead, chromium, mercury, antimony, vanadium, manganese, iron, nickel, copper, zinc, bismuth, indium, and other heavy metals, as well as heavy metals that exist in anionic form, especially hexavalent chromium, are effectively adsorbed and removed. It can be damned. Moreover, unlike the adsorption material which consists only of the carbide | carbonized_material obtained by carbonizing a wood chip from the place comprised mainly by the dredging bottom mud obtained from the bottom part of a water system, there is no possibility of floating on the water surface. Therefore, an environmental purification agent comprising such a sintered body can exhibit an effective environmental purification action, particularly a water quality purification action, and can thereby contribute effectively to environmental improvement and environmental conservation. is there.

  Here, in order to remove hexavalent chromium contained in the object to be purified, such as river water, lake water, pond water, ground water, seawater, etc., using an environmental purification agent comprising a sintered body as described above, environmental purification The agent may be poured or distributed in a target water area, such as a river, lake, estuary, or sea area, and immersed. Also, especially in rivers around places where high concentrations of hexavalent chromium are likely to flow out, such as industrial waste collection sites that contain hexavalent chromium, the environmental purifier may flow downstream due to the flow of water. It is only necessary to store the environmental purification agent in a net or a fence that can permeate water, and fix it in a river or the like.

  In addition, the environmental purification agent can be advantageously applied to soils that may be contaminated with hexavalent chromium, such as soil from which industrial waste has been discarded. For example, it can be embedded in soil. By doing so, even if hexavalent chromium is leached out by rain water or the like, hexavalent chromium contained in the soil can be adsorbed and removed advantageously by the environmental purifier embedded in the soil. It is also possible to prevent or suppress the contamination of river water and groundwater that may occur in the future.

  As described above, according to the present invention, contaminants such as hexavalent chromium contained in the object to be purified can be advantageously adsorbed and removed simply by bringing the environmental purifier as described above into contact with the object to be purified. Since no heating or the like is required at the time of purification, the purification work can be performed extremely economically.

  In the present invention, in order to maximize the adsorption / removal ability of hexavalent chromium by the environmental purifier, a pH adjuster such as hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, phthalic acid is used. It is desirable that the pH be 2 or more, but less than 5, more preferably 2 to 4.5, and even more preferably around 3. By doing so, hexavalent chromium can be removed more efficiently. . However, it is of course difficult to reduce the pH of the water area and soil directly because it places a heavy load on the environment. It is effective in removing hexavalent chromium. For example, if river water is taken out and pH is adjusted to the above range, then it is passed through a column or the like packed with the environmental purifier. It is possible to adsorb and remove hexavalent chromium continuously and more reliably, and then to neutralize the material to be purified that has passed through the column and return it to the original river, etc., adversely affecting the environment. Hexavalent chromium can be removed without any effect.

  In addition, since the sintered body that provides the environmental purification agent according to the present invention has sufficient strength due to the blending of a predetermined amount of sodium silicate, when applied to an object to be purified as described above, It will be able to exist effectively in applied water or soil without losing its shape. As a result, the environmental purification action, particularly the water quality purification action, can be advantageously exerted over a long period of time.

  Furthermore, in the environmental purification agent comprising such a sintered body, dredged bottom mud, which is the main component of the sintered body, is extracted from the bottom of the water system, and such environmental purification is performed. The environment is similar to the bottom of the water system where the agent is used. In addition, even wood chips and sodium silicates are composed of elements that are relatively abundant in nature, so the composition is close to nature. There is almost no concern about environmental pollution caused by the environmental purification agent in the water area where it is applied.

  In addition, the present invention uses both dredged mud and wood waste that are treated as industrial waste as effective resources, so that industrial waste is a problem in securing landfill disposal sites. It can also contribute greatly to the reduction of energy consumption.

  Several test examples of the present invention will be shown below, and the present invention will be clarified more specifically. However, the present invention is not limited by the description of such test examples. Needless to say. In addition to the following test examples, the present invention includes various changes and modifications based on the knowledge of those skilled in the art without departing from the spirit of the present invention, in addition to the specific description described above. It should be understood that improvements and the like can be added.

Test Example 1 (Influence of firing atmosphere)
First, as the bottom mud, the bottom mud obtained by dredging from the sea bottom of Ago Bay in Mie Prefecture was dried naturally to prepare a bottom mud with a moisture content of about 30%. And this marine bottom mud with adjusted water content, sawdust discharged from the wood processing industry (size: about 0.1 to 0.4 mm), and sodium silicate (silicate Na) are shown in Table 1 below. It mix | blended in the mixing ratio shown (solid content weight ratio), and also added water suitably, and was set as the uniform composition suitable for shaping | molding. Thereafter, the composition is formed into a disk shape, and the obtained molded product is further heated to a target temperature of 400 ° C. at a rate of temperature increase of 4 ° C./min. Thus, a disk-shaped sintered body having a diameter of about 10 mm and a thickness of about 5 mm was obtained. At this time, sample no. In No. 1, the molded product was placed in an empty can and fired in a closed state (closed) in which the supply of oxygen was cut off. In No. 2, firing was performed in a state where oxygen can be sufficiently supplied to the molded product (open). Next, by immersing the sintered body obtained above in a 1M nitric acid aqueous solution for 24 hours, the surface of the sintered body was treated to increase the porosity and improve the purification ability. It was set as the sintered compact concerning 1 and 2.

In order to evaluate the water purification capability of each of the sintered bodies thus obtained, the adsorption removal efficiency of hexavalent chromium was measured by a batch method. That is, 1 g of each sintered body was immersed in 50 mL of an aqueous K ₂ Cr ₂ O ₇ solution having a hexavalent chromium concentration of 100 ng / mL and adjusted to pH 3 with nitric acid (1N) for 2 hours. It was. Then, the concentration of hexavalent chromium remaining in the aqueous solution is measured by an electric heating atomic absorption method according to JIS K 0102, and the adsorption removal efficiency of hexavalent chromium is obtained from the obtained measurement value, and the result is obtained. The results are shown in Table 1 below.

  As is clear from the results in Table 1, sample No. It was revealed that both sintered bodies 1 and 2 have the ability to adsorb and remove hexavalent chromium. In addition, Sample No. 1 fired in a closed state (closed) in which the supply of oxygen was shut off. No. 1 sintered body was fired in an open state. It was found that the adsorption removal efficiency of hexavalent chromium was higher than that of the sintered body of No. 2.

Test Example 2 (Effect of amount of wood chips)
Sample No. 1 was prepared in the same manner as in Test Example 1 above, except that the composition with different amounts of wood chips and bottom mud was used for firing in a closed state (closed) in which the supply of oxygen was blocked. The sintered bodies according to 3 to 6 were manufactured, and the adsorption removal efficiency of hexavalent chromium was determined for each sintered body in the same manner as in Test Example 1, and the results are shown in Table 2 below.

  As is apparent from the results in Table 2, it was recognized that the adsorption removal efficiency of hexavalent chromium was improved as the amount of wood chips increased. However, it was separately confirmed that when the amount of wood chips exceeds 18% by weight, the strength of the sintered body is remarkably lowered and becomes brittle, and there is a problem in practicality. For this reason, although the adsorption removal efficiency of hexavalent chromium improves as the blending amount of wood waste increases, it is considered that the blending amount of wood waste: around 12% by weight is optimal for practical use.

  In addition, Sample No. containing no wood chips. In the sintered body according to No. 3, it was confirmed that hexavalent chromium was hardly removed.

Test Example 3 (Influence of sodium silicate content)
Sample No. in the same manner as in Test Example 1 except that firing was performed in a closed state (closed) in which supply of oxygen was shut off using a composition in which the blending amounts of sodium silicate and bottom mud were varied. . The sintered bodies according to 7 to 9 were manufactured, and the adsorption removal efficiency of hexavalent chromium was determined for each sintered body in the same manner as in Test Example 1, and the results are shown in Table 3 below.

In addition, the obtained sample No. Using the sintered bodies according to 7 to 9, their specific surface areas (m ² / g) were measured using nitrogen as an adsorbing gas in accordance with JIS B 9950, and the obtained results are shown in the following table. It was shown in 3. Furthermore, the uniaxial compressive strength was measured in accordance with the physical test method for cement according to JIS R 5210. The relative strength with respect to the uniaxial compressive strength of 7 was calculated, and the obtained calculation results are shown in Table 3 below.

かかる表３の結果から明らかなように、珪酸ナトリウム（バインダ）の配合量が増加するに従って、比表面積が小さくなり、六価クロムの吸着除去効率が低下するものの、焼結体の強度は向上することが、認められた。また、珪酸ナトリウムの配合量が２５重量％に満たない場合には、焼結体の強度が著しく低下して、脆くなり、実用に供し得ないことを、別途確認した。このため、珪酸ナトリウムの配合量は、２５重量％前後が最適であると考えられる。

As is apparent from the results in Table 3, as the amount of sodium silicate (binder) increases, the specific surface area decreases and the adsorption removal efficiency of hexavalent chromium decreases, but the strength of the sintered body improves. It was recognized. Moreover, when the compounding quantity of sodium silicate is less than 25 weight%, it confirmed separately that the intensity | strength of a sintered compact fell remarkably and became weak and cannot be used for practical use. For this reason, it is thought that about 25 weight% is the optimal compounding quantity of sodium silicate.

Test Example 4 (Influence of firing temperature)
The mixture ratio of bottom mud, wood chips and sodium silicate is a constant ratio shown in Table 4 below, while the firing temperature (sintering temperature) is changed as shown in Table 4 below to shut off the oxygen supply. Sample No. 5 was tested in the same manner as in Test Example 1 except that firing was performed in the state (closed). The sintered bodies according to Nos. 10 to 13 were manufactured, and the adsorption removal efficiency of hexavalent chromium was determined for each sintered body in the same manner as in Test Example 1, and the results are shown in Table 4 below.

  In addition, the obtained sample No. About the sintered compact concerning 10-13, the surface observation was performed with the magnification of 5000 times with the scanning electron microscope, and the result was shown in FIGS. From the result of such surface observation, it was recognized that considerable irregularities were observed on the surface of the sintered body, and a porous structure was formed.

  As is clear from the results in Table 4, it was recognized that the higher the firing temperature, the higher the adsorption removal efficiency of hexavalent chromium. 1 to 4, it can be seen that the surface area (porosity) decreases when the firing temperature reaches 700 ° C. (see FIG. 4). For this reason, it is thought that about 600-700 degreeC is the optimal firing temperature.

Test Example 5 (Effect of pH)
Except that the mixing ratio of bottom mud, wood chips and sodium silicate was the constant ratio shown in Table 5 below, and the firing was performed in a closed state (closed) where the supply of oxygen was shut off at a firing temperature of 600 ° C. In the same manner as in Test Example 1, sample no. Sintered bodies according to 14-20 were produced. Then, the adsorption removal efficiency of hexavalent chromium in each sintered body was determined in the same manner as in Test Example 1 except that the pH of the aqueous K ₂ Cr ₂ O ₇ solution was changed as shown in Table 5 below. The results are shown in Table 5 below.

As is apparent from the results of Table 5, hexavalent chromium can be removed when the pH of the aqueous solution containing hexavalent chromium (K ₂ Cr ₂ O ₇ aqueous solution) is 1 to 7. In particular, it was recognized that the adsorption removal efficiency of hexavalent chromium by the sintered body is remarkably increased when the pH is around 3.

Test Example 6 (Influence of the amount of environmental cleaner)
In the same manner as in Test Example 5, the sample No. Sintered bodies according to 21 to 24 were produced. Then, the adsorption removal efficiency of hexavalent chromium in each sintered body was changed in the same manner as in Test Example 1 except that the amount of the sintered body added to the K ₂ Cr ₂ O ₇ aqueous solution was changed as shown in Table 6 below. The results are shown in Table 6 below.

  As is apparent from the results in Table 6, it was recognized that the adsorption removal efficiency of hexavalent chromium increases as the amount of the sintered compact as the environmental purification agent increases.

Test Example 7 (Influence of treatment time)
In the same manner as in Test Example 5, the sample No. Sintered bodies according to 25 to 29 were produced. Then, the adsorption removal efficiency of hexavalent chromium in each sintered body was changed in the same manner as in Test Example 1 except that the immersion time of the sintered body in the K ₂ Cr ₂ O ₇ aqueous solution was changed as shown in Table 7 below. The results are shown in Table 7 below.

  As is apparent from the results in Table 7, it was recognized that the adsorption removal rate of hexavalent chromium improved as the immersion time (treatment time) increased. For this reason, for example, when an environmental purification agent made of a sintered body is used as a column packing material, the longer the column length (here, the amount of packing material packed in the column) is, It can be removed.

Sample No. manufactured in Test Example 4 10 is a scanning electron micrograph showing the surface of a sintered body according to FIG. Sample No. manufactured in Test Example 4 11 is a scanning electron micrograph showing the surface of the sintered body according to 11. Sample No. manufactured in Test Example 4 12 is a scanning electron micrograph showing the surface of a sintered body according to No. 12; Sample No. manufactured in Test Example 4 13 is a scanning electron micrograph showing the surface of a sintered body according to 13.

Claims (5)

A composition obtained by blending dredged bottom mud, wood chips and sodium silicate obtained from the bottom of the aqueous system at a solid content weight ratio of 46 to 62%, 6 to 18% and 25 to 37%, respectively. In the hexavalent chromium adsorption / removal agent comprising a porous sintered body obtained by firing, the composition is fired at a temperature of 400 ° C. to 700 ° C. in a state where the supply of oxygen is blocked, and the acid concentration is further reduced. A hexavalent chromium adsorption / removal agent comprising a sintered body obtained by immersion treatment in an acidic aqueous solution of 0.01M to 10M . The hexavalent chromium adsorption / removal agent according to claim 1, wherein the wood chips are sawdust. A composition obtained by blending dredged bottom mud, wood chips and sodium silicate obtained from the bottom of the aqueous system at a solid content weight ratio of 46 to 62%, 6 to 18% and 25 to 37%, respectively. In the method for producing a hexavalent chromium adsorption / removal agent comprising a sintered body having a porous structure, which is formed into a predetermined size and then fired. Sinter at a temperature of 400 ° C. to 700 ° C. in a heated state, and further immersed in an acidic aqueous solution having an acid concentration of 0.01M to 10M to obtain a sintered body. Manufacturing method. The hexavalent chromium adsorption / removal agent according to claim 1 or 2 is brought into contact with an object to be purified and the hexavalent chromium contained in the object to be purified is removed. How to remove hexavalent chromium. The method for removing hexavalent chromium according to claim 4, wherein the hexavalent chromium adsorption / removal agent is immersed in the material to be purified having a pH of 2 or more and less than 5.

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