JPS6146197B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a wastewater treatment method. More specifically, the present invention provides a method for treating blast furnace slag contact wastewater exhibiting a high COD with one or more metal oxides selected from ferric oxide, triiron tetroxide, and molybdenum trioxide under acidic conditions. This invention relates to a wastewater treatment method characterized by reducing COD. When pig iron is made in the blast furnace of a steel mill, slag is also produced as a by-product, and this is called blast furnace slag or blast furnace slag. Sand-like blast furnace slag can be used as blast furnace cement,
It has a variety of uses, including fine aggregate for fresh concrete, roads, fresh asphalt concrete, and secondary concrete products. The amount of blast furnace slag produced as a by-product reaches 318 kg per 1 ton of pig iron, which is the main product (the volume ratio of pig iron to blast furnace slag is 1:1.47 to 1.67). Blast furnace slag is often stored in piles outdoors, during which time components containing blast furnace slag are eluted by rainwater, and wastewater containing the eluted components is discharged into rivers or the sea. On the other hand, when reclaiming blast furnace slag from the sea, lakes, etc., the residual water becomes a similar leachate. However, the water eluted from blast furnace slag by rainwater and the water left over from landfilling contain various components, especially slag-containing components such as sulfur, and their chemical oxygen demand, i.e.
COD (hereinafter referred to as COD) values vary depending on the situation, but are usually over 1000 ppm, which is not desirable from a pollution standpoint. Steel factories are currently trying to solve this problem by managing and improving storage processes, but even more thorough measures are still desired. The blast furnace slag contact wastewater exhibiting high COD, which is the subject of treatment in this invention, contains sulfur,
In particular, there are sulfur polysulfide represented by Sx (x = 2, 4, 6, 8, ......), ionic S ₂ O ₃ ^-- , S ^--, etc., and more than 90% of the COD value is this. It is thought that this is caused by sulfur compounds such as Various methods can be considered for reducing the COD of such wastewater. A Method using aeration (i) Simple aeration (ii) Aeration in the presence of an oxidation catalyst near neutral pH B Methods other than aeration (i) Oxidation using an oxidizing agent (e.g. H ₂ O ₂ , NaClo, Advanced Salashco, etc.) ii) Method of precipitating as sulfide (addition of water-soluble iron salt, water-soluble zinc salt, etc.) (iii) Combination of (i) and (ii). in blast furnace slag contact wastewater to be treated.
Since the amount of COD components is too large, B
Both of these methods require large amounts of drugs and are completely unrealistic from an economic standpoint. On the other hand, among methods A, method (i) requires a long period of aeration to reduce COD and is not suitable for practical use, and method A (ii) also cannot rapidly reduce COD. This invention was made to improve the current situation as described above. In other words, the present inventors conducted various studies and determined that wastewater in contact with blast furnace slag, which exhibits high COD, was treated with ferric oxide [indicated by Fe ₂ O ₃ , iron oxide].
], triiron tetroxide [represented by Fe ₃ O ₄ , referred to as iron oxide () iron ()], and molybdenum trioxide (MoC ₃ ) under acidic conditions. This invention was achieved by discovering that the COD value can be rapidly lowered by this simple operation. The metal oxide in this invention does not need to be of high purity; it can be used even if it contains some impurities, and even if it is produced as a by-product in industry. . The shape preferably has a large surface area, and is preferably a fine powder.
Among the metal oxides used in this invention, ferric oxide is stable and inexpensive, and is a particularly recommended catalyst. In the treatment according to the present invention, it is preferable to ensure sufficient contact between the metal oxide and the COD component in the water to be treated, and for this purpose mechanical stirring or forced introduction of air (aeration) is carried out. Usually, it is preferable to forcibly introduce air bubbles while stirring mechanically. Furthermore, the treatment of this invention is carried out under acidic conditions,
PH is preferably 3 or less, most preferably PH 1.5 or less. For this PH adjustment, hydrochloric acid, sulfuric acid, nitric acid,
Mineral acids such as phosphoric acid can be used, and waste hydrochloric acid containing iron chloride etc. after surface treatment of iron plates at steel companies,
In addition, waste sulfuric acid, waste nitric acid, etc. produced in various other processes are preferably used. The amount of metal oxide used in this invention is generally about
Approx.
It is preferable to add 1000ppm;
It can be changed depending on the COD value, approximately 500
An addition amount of ~5000ppm can cover most cases. The treatment is preferably carried out at room temperature to 60°C for 2 to 5 hours. If the above conditions are met, a reduction in COD can be achieved, but by combining water-soluble iron salts such as iron chloride, it is possible to precipitate sulfur compounds in the water to be treated as iron sulfide, further reducing the COD value. It is. Since the waste hydrochloric acid after surface treatment of iron contains a large amount of iron ions, it is convenient to remove sulfur compounds while adjusting the pH. In addition, one or more of hydrogen peroxide, hypochlorite, and highly salinized salts, which are generally known as oxidizing agents, may be further added for treatment. Most of the sulfur compounds, which are thought to account for the major part of the COD components in blast furnace slag contact wastewater that exhibits high COD, are likely to precipitate as simple sulfur and adhere to the surroundings of iron oxides, forming precipitates. . The method according to the present invention is characterized in that it can rapidly reduce the COD of blast furnace slag contact wastewater from about 1000 to 1300 ppm to 200 to 300 ppm. Afterwards, it is recommended to add an oxidizing agent such as sodium hypochlorite to remove COD components. If no further treatment is performed by adding an oxidizing agent, the precipitate is separated after neutralization, diluted with water, and discharged. The treatment method of this invention can be applied to water other than blast furnace slag contact water such as Sx (X=2, 4, 6, 8......),
It can be applied to any water containing COD components such as S ₂ O ₃ ^-- and S ^-- . Next, the present invention will be explained with reference to Examples. Examples 1-1 to 1-3 Blast furnace slag contact water collected in a pit distributed in the blast furnace slag storage area of a certain steel factory was collected, and the composition and properties of this liquid (hereinafter referred to as stock solution) were investigated. The situation was as follows. COD 1520 ppm I ₂ consumption 3160 〃 PH 11.9 S 23.0ppm Na 322 〃 K 1290 〃 Ca 340 〃 Put this raw water 1 into a beaker and adjust the PH of this liquid to 1.5, 6, and 12 respectively (using a PH meter) .
Next, metal oxides (three types: Fe ₂ O ₃ , Fe ₃ O ₄ , and MoO ₃ )
Add 2 g of each powder, stir with a stirrer for 60 minutes at room temperature to prevent the powder from settling, neutralize it, leave it to stand for 30 minutes to allow the precipitate to settle out, take the supernatant liquid, and stir using a standard method. COD was measured by The results are shown in Table 1. Reference Examples 1-1 to 1-3 COD was also measured in exactly the same manner as in Example 1 for powders of three types of metal oxides, V ₂ O ₅ , MnO ₂ , and SeO ₂ . The results are also listed in Table 1.

[Table] As can be seen from Table 1, three metal oxides, Fe ₂ O ₃ or ferric oxide, Fe ₃ O ₄ or triiron tetroxide, and MoO ₃ or molybdenum trioxide, have a remarkable catalytic effect at pH 1.5. The effect of ferric oxide is particularly excellent. Example 2 Regarding ferric oxide, which has the best catalytic effect, the reduction in COD was investigated with various pH and temperature changes. COD 1050ppm of raw water (collected from different locations in the factory of Example 1), amount of ferric oxide added
The procedure was the same as in Example 1 except that the stirring time was 1000 ppm and the stirring time was 4 hours. The results are shown in Table 2.

[Table] Effects begin to appear at PH3, and become more rapid around PH1.5.
A decrease in COD is seen. The effect of processing temperature is small. Example 3 Regarding the same raw water (COD 1050 ppm) used in Example 2, the influence of the amount of ferric oxide added and pH at room temperature was investigated. Other conditions were the same as in Example 1. The results are shown in Table 3.

[Table] From Table 3, it can be seen that the catalytic effect is excellent when the amount of ferric oxide added is 1000 ppm or more and the pH is 1.5 or less. Example 4 Regarding blast furnace slag contact wastewater with a COD of 1000 ppm,
Changes in COD over time were tracked with and without the addition of 1000 ppm of ferric oxide. The pH was 1 to 1.5, and the treatment temperature was room temperature.
The results are shown in Table 4.

[Table] As shown in Table 4, when treated in the presence of ferric oxide, the rate of COD reduction (especially after 2 to 4 hours)
is very large. Example 5 (i) For blast furnace slag contact wastewater with a COD of 1110 ppm, the reduction in COD was investigated by changing the amounts of ferric oxide and molybdenum trioxide added. The pH was 1.5 and the stirring time was 4 hours. The results are shown in Table 5.

[Table] Table 5 shows that molybdenum trioxide has almost the same effect as ferric oxide, and the amount of each added is
It can be seen that 1000ppm or more is good. Next, various addition amounts of molybdenum trioxide and ferric oxide were used together, and the mixture was stirred at pH 1.5 for 4 hours, and the COD was measured. The results are shown in Table 6.

[Table] From Table 6, it can be seen that there is no synergistic effect due to the combination of both. Example 6 Weigh out one blast furnace slag contact wastewater with a COD of 1110 ppm into two containers, add ferric oxide and molybdenum trioxide to each container, and use an air pump for goldfish at a flow rate of 500 ml/min to G-2. A large number of small bubbles of air were introduced from the bottom of the container through a glass filter, and changes in COD were investigated by processing without mechanical stirring. Table 7 shows the results.
Shown below.

[Table] From Table 2, the effect of time is clear. Comparing with Table 5, almost the same effect appears in the case of stirring and the case of forcibly introducing bubbles. Example 7 Using raw water with a COD of 1016 ppm, the type of acid for PH control was changed and ferric oxide and molybdenum trioxide were added, stirring with a stirrer for 2 hours at PH 1.0 and COD was investigated. Ta. The results are shown in Table 8.

[Table] There is a tendency for products with sulfuric acid added to be slightly superior, but there is no significant difference and they can be considered to be almost the same. Example 8 After adjusting the pH of raw water with COD 1016 ppm to 1.5, ferric oxide and ferrous chloride (or ferric chloride) were added in the following combination.
Iron was added, and after stirring with a stirrer for 2 hours, the mixture was neutralized to pH 8-9, and after being left to stand, the precipitate was separated and its COD was measured. The results are shown in Table 9.

[Table] By injecting iron chloride in the same bath, we were able to lower COD by 50 to 55 ppm more than using ferric oxide alone. This is thought to be due to the formation of iron sulfide. Reference example 2 Take raw water 1 with a COD of 1000ppm and a pH of 7 in a beaker, and add various compounds at various pHs to 50ppm.
The mixture was aerated for 2 hours in the same manner as in Example 6, then neutralized, and after being left to stand, the supernatant was taken and the COD was measured. The results are shown in Table 10.

【table】

[Table] As can be seen by comparing Table 10 and Table 1, when comparing ferric oxide, triiron tetroxide, and molybdenum trioxide, there are compounds listed in Table 10 that can serve as catalysts comparable to these three. cannot be found. Reference example 3 Hydrogen peroxide, sodium hypochlorite, and highly salinized water, which are generally well-known as oxidizing agents, are added to raw water with a COD of 800 ppm under various PH conditions to obtain the necessary amounts to reduce the COD to 200 ppm. The amount of addition was investigated. The results are shown in Table 11. Furthermore, Table 11 shows
The amount required to reduce COD by 100ppm (experimental value) and the theoretical amount are also listed.

[Table] From Table 11, the reaction conditions are: H ₂ O ₂ : PH 11 or PH 1 NaclO: PH 1 NaclO: PH 1 Highly Sarashiko: PH 7 COD was achieved at an efficiency of 70 to 100% of the theoretical amount.
However, if the unit cost of its use is calculated based on this data, it becomes unrealistically high and is not suitable for practical use. Example 9 200ml of blast furnace slag contact wastewater with a COD of 1046ppm
Ferric oxide was added to each container, and N ₂ gas was fed into one container and air was fed into the other at a flow rate of 90 ml/min from the bottom of the container, and the mixture was treated under the following conditions to examine changes in COD. Ta. The results are shown in the table below. Conditions: PH 1.5 Test time 4hr. Temperature 20℃

[Table] This table shows that even if oxygen in the air dissolves into water during mechanical stirring, it does not affect the COD reduction effect in any way. Therefore, it can be said that the mechanical stirring performed in the present invention is merely for sufficient contact between the metal oxide and the COD component in the water to be treated.

Claims (1)

[Claims] 1 Blast furnace slag contact wastewater exhibiting high COD is
The wastewater is brought into contact with one or more metal oxides selected from ferric oxide, triiron tetroxide, and molybdenum trioxide under the following acidic conditions.
A wastewater treatment method characterized by reducing COD. 2. The wastewater treatment method according to claim 1, wherein the treatment is carried out under mechanical stirring. 3. Claim 1 or 2, in which the treatment is carried out by forcibly introducing air bubbles.
Wastewater treatment method described in Section. 4. The wastewater treatment method according to any one of claims 1 to 3, wherein the treatment is carried out at a pH of 1.5 or lower. 5. The wastewater treatment method according to any one of claims 1 to 4, wherein ferric oxide is a by-product produced in an industrial process. 6. The wastewater treatment method according to any one of claims 1 to 5, wherein the amount of metal oxide added is about 500 to 5000 ppm. 7. The wastewater treatment method according to any one of claims 1 to 6, wherein the treatment is performed by further adding an oxidizing agent. 8. The wastewater treatment method according to claim 7, wherein one or more of hydrogen peroxide solution, hypochlorite, and high-grade salamico is used as the oxidizing agent.