JPH0334995B2 - - Google Patents

Description

[Detailed description of the invention]

[Background of the Invention] Technical Field The present invention relates to a method for separating and removing arsenic from arsenic-containing waste liquid. BACKGROUND OF THE INVENTION Arsenic is a useful element that is currently widely used in herbicides, agricultural chemicals, insecticides, preservatives, feed additives, catalysts in various manufacturing processes, and in the medical field. On the other hand, arsenic, which is present as a compound in waste liquids from chemical factories, metal smelters, etc., is extremely toxic, and environmental pollution due to arsenic content in waste liquids has become a social problem today. Conventionally, the most commonly used method for removing arsenic from arsenic-containing waste liquid is a coprecipitation method using a metal hydroxide, particularly ferric hydroxide. However, this method requires the addition of a large amount of chemicals, and the resulting precipitate has poor sedimentation and permeability, requiring a large investment in solid-liquid separation equipment.
Furthermore, the dehydration of the precipitate after solid-liquid separation is poor, and a large amount of sludge is generated after treatment. As other methods, adsorption removal methods using activated carbon, activated alumina, metal-impregnated activated carbon, or chelate resin, and ferric hydroxide precipitation flotation methods are being considered, but these methods have problems in terms of processing arsenic-adsorbing sludge and high costs. However, there are problems in the following points, and a fully satisfactory method has not yet been obtained. [Summary of the Invention] In the process of conducting intensive studies on a method for removing arsenic that does not have the above-mentioned problems, the present inventors discovered that
It was discovered that a specific porous limestone such as coral limestone has an unexpected ability to adsorb arsenic, and as a result of repeated research on an efficient arsenic removal method using such limestone, the present invention was achieved. That is, in the method for removing arsenic according to the present invention, a waste liquid containing arsenic is brought into contact with porous limestone having a porosity of 10 to 50 cm ³ /g, and arsenic in the waste liquid is removed from the surface and inside the pores of the porous limestone. It is characterized by being adsorbed to. In a preferred embodiment, the present invention includes a method for removing arsenic in which the arsenic removal efficiency is further improved by subjecting the porous limestone to a specific treatment. According to the arsenic removal method of the present invention, it is easy to separate (filter) porous limestone that has adsorbed arsenic from waste liquid, and such porous limestone exists in large quantities in Japan and is inexpensive. Therefore, it is extremely advantageous in terms of cost. [Specific description of the invention] Porous limestone The limestone used as an arsenic adsorbent in the present invention is
It is a porous limestone having a porosity of 10 to 50 cm ³ /g, preferably 15 to 35 cm ³ /g. Here, a mercury intrusion porosimeter is used to measure the void ratio. Typical examples of such porous limestone are:
It is coral limestone (hereinafter referred to as coral). Taking coral from Tokunoshima, Kagoshima Prefecture as an example, its composition is as follows.

〔Example〕

Hereinafter, the effects of the present invention will be specifically explained using examples. Example 1 Tokunoshima coral limestone (coral) was crushed with a dior crusher and then classified with a sieve, and the particle size was adjusted to 5 to 6 meshes, 6 to 20 meshes, 20 to 150 meshes, and 150 meshes. Thereafter, it was washed with water until the water was no longer cloudy, and finally washed twice with ion-exchanged water and dried in a dryer (100°C). Put 50 ml of an arsenic disodium arsenate aqueous solution adjusted to arsenic concentration of 2 ppm or 8 ppm and 40 g each of Coral whose particle size was adjusted above into a 100 ml Erlenmeyer flask, seal the Erlenmeyer flask with parafilm, and store at room temperature for 10 days. 20-25°C). Thereafter, it was filtered, and the arsenic concentration in the filtrate was determined by the diethyldithiocarbamate silver method. Table 1 shows the experimental results when the initial arsenic concentration was 8 ppm.

[Table] As the particle size becomes smaller, the arsenic concentration in the aqueous phase decreases more greatly. This is thought to be because the surface area of corals up to 150 meshes increased as the particle size decreased. When the coral particle size is 150 mesh or less, the arsenic concentration in the aqueous phase is higher than when it is between 20 and 150 mesh.
It is also thought to be related to the pore diameter of coral. Example 2 Various treated corals were prepared from the 5 to 6 mesh size coral obtained in Example 1 as follows. FeCl ₃ treated coral Coral was immersed in a 40% FeCl ₃ 6H ₂ O aqueous solution for 30 minutes, then thoroughly washed with water and dried at 100°C.
This dried coral was designated as FeCl ₃ -treated coral. _MgNO3 -treated corals were immersed in a 50% _MgNO3 aqueous solution for 30 minutes, then thoroughly washed with water, and dried at 100°C. Glutaraldehyde-treated coral Soaked in 2.5% glutaraldehyde for 30 minutes, then thoroughly washed with water and dried at 100°C. MgNO ₃ +Fe(OH) ₃ -treated coral The above MgNO ₃ -treated coral was immersed in a solution in which Fe(OH) ₃ was generated for 30 minutes, then thoroughly washed with water, and dried at 100°C. Wet treated coral Boiled in distilled water for 30 minutes to expel the air in the pores. After that, I washed it thoroughly with water and did not dry it. Nostok-immobilized coral Coral was placed in a Nostok algae suspension and subjected to an ultrasonic cleaner while cooling on ice for 30 minutes. Thereafter, only the corals were taken out, thoroughly washed with water, and then cultured. Nostok was immobilized on the coral by culturing, and this was designated as Nostok-immobilized coral. Using each treated coral prepared above,
An arsenic adsorption experiment was conducted in the same manner as in Example 1. The results are shown in Table 2. As a control, the results obtained in Example 1 for untreated coral (5 to 6 meshes) are also shown.

[Table] From the results in Table 2, it can be seen that all treated corals are more effective in removing arsenic than when untreated coral is used. In particular, in the case of coral treated with FeCl ₃ , 8.0 ppm of arsenic could be completely removed. In addition, in the case of wet treatment, although the air in the pores of the coral was simply expelled, the arsenic removal ability was improved. This is thought to be due to the increased effective surface area of coral. Example 3 40 g each of untreated coral of 5 to 8 mesh size and 8 to 120 mesh size prepared in the same manner as in Example 1 was placed in a 200 ml triangular frust containing 50 ml of an aqueous solution of disodium hydrogen arsenate, and placed in a shaker. The arsenic solution concentration was measured after each time shown in Table 3. The measurement was carried out by flameless atomic absorption spectrophotometry using an atomic absorption flame spectrometer (AA-855, manufactured by Japan Journal Atsushi Co., Ltd.). The results are shown in Table 3 and FIG.

【table】

[Table] From Table 3 and FIG. 1, it can be seen that the adsorption rate is higher for coral with smaller particle size. This seems to be due to the difference in the surface area of coral. 72
There is also a difference in the amount of arsenic adsorbed after hours: 480 μg for 5 to 8 meshes and 550 μg for 8 to 120 meshes. Example 4 The 5 to 8 mesh size coral obtained in Example 3 was heat treated at 650° C. for 2 hours in an electric furnace to obtain calcined coral. An aqueous solution of disodium hydrogen arsenate having a concentration of 8.07 ppm was brought into contact with the heat-treated coral in the same manner as in Example 3, and changes in the concentration of the arsenic solution over time were examined. In addition, as a control experiment, an arsenic adsorption experiment using untreated coral was conducted at the same time. The results are shown in Table 4 and FIG.

【table】

[Table] Comparing the difference in adsorption speed between calcined coral and untreated coral, it can be seen that the calcined coral is much larger. After one hour, the concentration of arsenic in the solution had decreased to about 1/10 in the fired one, but it had not even reached 1/2 in the untreated one. This is thought to be because the pores on the surface of the coral extend into the interior as continuous pores due to firing, thereby increasing the surface area. Examples 5 and 6 FeCl ₃ treatment obtained by treating the 5-8 mesh size coral obtained in Example 3 with ferric chloride aqueous solutions of concentrations 1%, 2% and 4% in the same manner as in Example 2. Example 4 for coral (Example 5) and Al ₂ (SO ₄ ) ₃ treated coral (Example 6) obtained by treatment in the same manner with aluminum sulfate aqueous solutions at concentrations of 1%, 2% and 4%. An arsenic adsorption experiment was conducted in the same manner as (however, the initial concentration of the arsenic solution was 18.0 ppm).
As a control, an arsenic adsorption experiment using untreated coral was conducted at the same time. The results are shown in Tables 5 and 6.

[Table] Comparing the adsorption rates of FeCl ₃ -treated coral and untreated coral, the untreated one is on the order of ppm, while the FeCl _3- treated one is already on the order of ppb after 10 minutes. . This is thought to be due to the extremely high rate of chemical adsorption of arsenic by the Fe content on the coral surface. Also, after 12, 24, and 72 hours, the concentration of arsenic in the solution increased, but this is thought to be due to the long period of shaking, which caused the coral to become fine and float instead of settling.

[Table] Regarding the Al ₂ (SO ₄ ) ₃ treated coral, the above
It can be seen that the adsorption rate is much higher than that of FeCl ₃ -treated coral as well as untreated coral. Example 7 Using an apparatus as shown in FIG. 3, an arsenic adsorption experiment was conducted using a column method. First, 50 g of untreated coral of 5-8 mesh size obtained in Example 3 and 30 ml of ion-exchanged water were placed in a column, and disodium hydrogen arsenate solution (concentration 4900 ppb) was added dropwise at a speed of 8.
It was added dropwise at a rate of ml/6 min. 8.4 ml of each test tube was collected using a fraction collector, and the arsenic content of the collected liquid was determined by flameless atomic absorption spectrophotometry. Here, the adsorbent-filled column has an inner diameter of
A glass tube with a diameter of 20 mm and a height of 30 mm was used, and a Microfractionator (FC-80K) manufactured by GILSON was used to collect each 8.4 ml. The results are shown in Table 7 and FIG.

[Table] Example 8 The calcined coral of Example 4 was used in place of the untreated coral of Example 7, and an arsenic adsorption experiment was conducted using the column method in the same manner as in Example 7. However, the concentration of the dropped arsenic aqueous solution was 5670 ppb, and the dropping speed was
It was 8.20ml/min. The results are shown in Table 8 and FIG.

【table】

[Table] Example 9 In place of the untreated coral of Example 7, Example 5
Using the 2% FeCl ₃ treated coral obtained in Example 7, an arsenic adsorption experiment was conducted using the column method in the same manner as in Example 7. However, the concentration of the dropped arsenic aqueous solution was 4780 ppb, and the dropping speed was 8.30 ml/6 min. The results are shown in Table 9 and FIG.

【table】

[Table] Example 10 Disodium hydrogen arsenate solution with arsenic concentration of 12.7 ppm
100 ml was treated with 80 g of the 4% FeCl ₃ -treated coral obtained in Example 5, resulting in almost 100% adsorption of arsenic in the solution. This arsenic-adsorbing coral has a pH of 1, 2,
10 g of each was added to 20 ml of water adjusted to 3, 4, and 5, and the desorption of arsenic was examined after 1 day, 15 days, and 30 days. The results are shown in Table 10.

[Table] The desorption of arsenic adsorbed on coral treated with 4% FeCl ₃ due to differences in pH was investigated, and even after 30 days, not even 1% desorption occurred. It can be seen that once adsorbed, it is difficult to desorb.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the results of Example 3, FIG. 2 is Example 4, FIG. 4 is Example 7, FIG. 5 is Example 8, and FIG. 6 is a graph showing the results of Example 9. FIG. 3 is an explanatory diagram showing the apparatus used in the arsenic adsorption experiments by the column method in Examples 7 to 9.

Claims (1)

[Claims] 1. Bringing arsenic-containing waste liquid into contact with porous limestone having a porosity of 10 to 50 ^{cm 3} /g, and adsorbing arsenic in the waste liquid onto the surface and pores of the porous limestone. A method for removing arsenic from arsenic-containing waste liquid, characterized by: 2. The method for removing arsenic according to claim 1, wherein the porous limestone is coral limestone. 3. Claim 1, wherein the porous limestone has been previously treated with one or more of ferric chloride, aluminum sulfate, magnesium nitrate, ferric hydroxide, and glutaraldehyde, or The method for removing arsenic according to item 2. 4. The arsenic removal method according to claim 1 or 2, wherein the porous limestone is calcined, wetted, or immobilized with Nostok algae.