JPH0147217B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel method for adsorption and removal of arsenic compounds in exhaust gas, which has excellent heat resistance and chemical resistance, is easy to handle, and can be used repeatedly.

Conventional methods for treating mixed gases containing arsenic include passing the mixed gas into liquid copper sulfate to precipitate it as copper arsenide, or passing the mixed gas through a quartz tube heated to high temperatures, then cooling it and solidifying it as metallic arsenic. Additionally, methods are known in which a gas mixture is introduced onto heated copper, iron, nickel, or cobalt to cause arsenic to react with these metals and to diffuse the reaction products into the interior of the metal. However, all of these methods are incomplete as methods for removing arsenic, and in order to sufficiently reduce the arsenic concentration in the processing gas, they not only require complicated and large equipment, but also require heating at hundreds of degrees Celsius. The reaction is carried out under high heat, and the process is dangerous and consumes a large amount of energy. Furthermore, since it is difficult to re-separate arsenic from the reaction product with arsenic, the reaction product must be removed from the treatment system and disposed of, and needless to say, it cannot be reused.

The present inventors have worked diligently to develop a new method for adsorption and removal of arsenic compounds in exhaust gas that has excellent heat resistance and chemical resistance, is easy to handle, and can be used repeatedly, which was not possible using conventional methods. As a result of the study, the mixture obtained by adding water and sulfuric acid to powdered titanic acid (titanium dioxide hydrate) is granulated into fine particles, molded, and fired. It has been discovered that when impregnated, adsorbed and retained, it has properties suitable for adsorbing and removing gaseous arsenic compounds. The present invention is a method for removing arsenic components in a gas, which comprises bringing titanic acid particles adsorbed and retained an oxidizing agent aqueous solution into contact with an arsenic component/containing gas.

The removal method of the present invention will be explained in detail below.

The chemical formula of titanic acid used in the present invention is
Any titanium dioxide hydrate represented by TiO ₂ .nH ₂ O (n = 0.5 to 2.0) may be used, but titanyl sulfate (TiOSO ₄ ), titanium tetraisopropoxide (Ti
[OCH (CH ₃ ) ₂ ] ₄ ), titanium tetrachloride (TiCl ₄ ), etc. manufactured by hydrolysis have a large specific surface area and are convenient for the purpose of obtaining an adsorbent with a large retention capacity. It is.

Powdered titanic acid can be granulated and molded by adding water and sulfuric acid, kneading, extruding, granulating, and firing according to the method disclosed in JP-A-55-8844, which has sufficient strength and specific surface area as an adsorbent. (approx. 200m ² /g)
However, if this is further crushed and sieved, any grain size of less than ten millimeters can be obtained. Further, if the kneaded product is formed into a spherical shape by compression granulation, which is commonly used as a method for forming the kneaded product, any particle size up to several centimeters can be obtained without causing a decrease in the specific surface area.

If you want a high level of arsenic adsorption treatment effect, you can obtain it by sieving small particles, but usually
A suitable range is 0.1 mm to 1 cm, more preferably 0.5 to 5 mm. In order to avoid an increase in ventilation resistance due to adsorbent filling, an adsorbent with a large particle size may be used.

The titanic acid of the present invention has sufficient granulation strength as a titanic acid alone system as a packed adsorbent, but it also has sufficient granulation strength when it is granulated and calcined from a mixture containing alumina or silica, or a total of 30% by weight of both. Maintain sufficient strength. When the content is further increased, the strength decreases. If priority is given to strength, the content of these inorganic substances may be reduced. If priority is given to changes in the properties of the filler due to the inclusion of these substances, the adsorbent may be prepared as a molded body containing these two or other inorganic or organic substances. In addition, granulation and molding are carried out separately.
It is also possible to mix sieved titanic acid, alumina or silica filler and use it as a mixed packing type adsorbent.

Further, in the present invention, the oxidizing agent used for adsorption and retention on the titanic acid granules is a common oxidizing agent such as permanganic acid or its salts, chromic acid and its salts, nitric acid and its hydrochloric acid, peroxide, sulfuric acid, etc. Any water-soluble material may be used. It is effective if the concentration of the oxidizing agent in the aqueous solution is about 0.1% or more, but preferably 3% is sufficient. The required amount of oxidizing agent aqueous solution is the amount required for the purpose of moistening the adsorbent surface, and is 0.1 to 2.0 ml per 1 g of adsorbent.
It may be any amount, but preferably 0.5 to 1.0 ml. If 2.0ml or more of an oxidizing agent aqueous solution is adsorbed and retained, the small spaces between the adsorbent particles will be filled with the small solution, making it difficult for gaseous substances to enter and causing an increase in ventilation resistance, so low ventilation resistance is desired. This is inconvenient in some cases. When the titanic acid granules carrying the oxidizing agent aqueous solution thus obtained are brought into contact with a gas containing a gaseous arsenic compound, the arsenic compound is efficiently adsorbed onto the granules and removed. Arsenic components targeted for removal include arsenic alone (AS ₄ ,
Examples include arsenic compounds such as AS ₂ ), arsine (AsH ₃ ), arsenic pentafluoride (AsF ₅ ), and organic compound derivatives thereof. Furthermore, in the present invention, in addition to the arsenic component, substances that are oxidized by the oxidizing agent to produce oxidized acid anions are also adsorbed and removed, so the mixture containing phosphine (PH ₃ ), stibine (SbH ₃ ), etc. When applied to gases, these are removed at the same time as arsenic components, which is extremely convenient. The contact between the granules and the gas can be carried out in a packed column of any shape, either vertically or horizontally. Adsorption and removal is possible at the contact temperature of the gas, and no special cooling or heating is required, but the gas may be pretreated if necessary.

To recover arsenic from granular titanic acid that has adsorbed arsenic gas, the granular titanic acid is taken out of the packed tower and put into an alkaline aqueous solution, stirred as a slurry, and the titanic acid is transferred and dissolved into the aqueous solution by filtration. It can be recovered. The liquid property should be alkaline, but if the speed of dissolution is important, strong alkalinity (PH10 or higher) is advantageous, and in this case, 1
More than 90% of adsorbed arsenic can be recovered within hours. As long as the type of alkali is a common alkali such as sodium hydroxide or potassium hydroxide, there will be no problem, so it is advantageous to use sodium hydroxide from the viewpoint of effectiveness and economy. Since the required amount of alkaline aqueous solution is sufficient to maintain a slurry state with titanic acid, arsenic can be recovered as a small amount of extremely concentrated arsenic solution.

Further, the dearsenated titanic acid granules can be used repeatedly.

Furthermore, this titanic acid granule has excellent heat resistance, so it can be used in high-temperature mixed gases up to 300℃ without losing its shape, but the oxidant aqueous solution will evaporate, resulting in poor performance. It decreases slightly.

Next, the present invention will be explained using Examples, but the present invention is not limited to the following Examples unless the gist of the invention is exceeded.

Example: Granulation and
Molded titanic acid granules (0.5mmφ×7mmL)
1.6 ml of oxidizing agent aqueous solution is adsorbed and retained on the surface of 2.0 g. Oxidizing agent aqueous solution is potassium permanganate 0.3g
3.0 ml of concentrated nitric acid was added to the solution, and water was added to make a total of 100 ml. This oxidant adsorbed titanic acid is
It was filled into a conduit in the As analysis method shown in K0101-1979, and both ends were sealed with glass wool as shown in FIG. The glass wool on the gas introduction side was impregnated with lead acetate. According to the JIS analysis method, potassium iodide, tin chloride () and zinc are added to arsenic acid to generate arsine, and the gas is passed through a conduit filled with oxidizing agent-adsorbing titanic acid particles, followed by diethyldithiocarbamic acid. The amount of arsenic that was not adsorbed and removed was determined by absorbing it into a silver solution and measuring the absorbance of the reddish-purple color produced. When the amount of unadsorbed arsenic was measured by varying the amount of arsine generated, it was found that arsenic was completely adsorbed and removed up to the amount of 100 μg generated in terms of arsenic atoms (As).

It is found that arsine is effectively removed by the combination of a minimal amount of oxidizing agent and particulate titanic acid.

Comparative Example As shown in Figure 2, one end of a glass conduit in which granular titanic acid was not sealed was connected to the same arsine generating liquid as in the example, and the other end was connected to the same oxidizing agent as in the example.
The arsine that had passed through the oxidizing agent was further introduced into an arsine absorption tube through a glass tube.
Arsine was emitted under the same conditions as in the example, and the amount of unadsorbed arsenic was measured under the same analytical conditions. When the amount of unadsorbed arsenic was measured by varying the amount of arsine generated, 0.45 μg was already unadsorbed for 10 μg of generated arsenic in terms of arsenic atoms, and 4.55 μg was unadsorbed for 100 μg of generated arsenic. Ta. The adsorption effect hardly improved even when the amount of oxidizing agent was increased or the oxidizing agent concentration was increased. It is found that even if a significantly larger amount of oxidizing agent is used than in the examples, the effect of adsorbing and retaining the oxidizing agent is not far superior to that of titanic acid.

[Brief explanation of drawings]

FIG. 1 shows an example of a gaseous arsenic removal apparatus used to carry out the method of the present invention. FIG. 2 is an example of a removal device for comparison. 1...Arsine generating liquid, 2...Glass wool,
3... Oxidizing agent adsorbed titanic acid granules, 4... Glass conduit, 5... Arsine absorption liquid, 6... Oxidizing agent aqueous solution.

Claims (1)

[Claims] 1. A method for removing arsenic components in a gas, which comprises bringing a gas containing an arsenic component into contact with titanic acid particles that have adsorbed and retained an oxidizing agent aqueous solution.