JPS643552B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a method for treating wastewater containing a high concentration of heavy metal complex salts, in which heavy metals form stable complex salts together with organic substances.

In general, in various industrial wastewater such as the Metsuki factory and laboratory wastewater, heavy metals form stable heavy metal complex salts with organic substances such as ethylenediaminetetraacetate, thiourea, ammonium citrate, and dimethylglyoxime. is not easy to remove.

Conventional methods for removing free heavy metal ions include coagulation-sedimentation treatment, which involves generating hydroxides by adjusting the pH and adding an inorganic flocculant such as aluminum sulfate or polyaluminum chloride, or a polymer flocculant such as polyacrylamide. Generally, methods such as sulfide method using sodium sulfide, adsorption method, and ion exchange resin method are adopted, but these methods have limited removal efficiency in the case of heavy metals that form stable metal complexes. The drawback was that it was extremely low. Therefore,
In order to increase the removal efficiency, it is necessary to oxidize and decompose stable heavy metal complex salts into free heavy metal ions. For this reason, oxidizing treatment methods include ultraviolet treatment and oxidizing agents such as chlorine, chlorine compounds, ozone, and hydrogen peroxide. Various treatment methods have been put into practical use, either alone or in appropriate combinations of these treatments. However, when considering reactivity, operability, and economic efficiency such as reaction rate, reaction efficiency, equipment cost, operating cost, post-treatment of unreacted oxidant, complexity of operation, and installation space, no satisfactory treatment method has been found. The current situation is that there is no such thing.

In view of the current situation, the present invention aims to adjust organic wastewater containing a high concentration of heavy metal complex salts to PH5 or less, and then
Add 0.1 to 2.0 times the amount of ferrous ions and raise the liquid temperature to 80
By continuously adding hydrogen peroxide little by little at 100℃, cooling, adjusting the pH to 6 to 8, and separating the generated heavy metal-containing aggregates, wastewater containing high concentrations of heavy metal complex salts can be removed. The present invention has made it possible to provide a method for treating wastewater containing heavy metal complex salts, which can remove heavy metal complex salts in a short period of time and with high efficiency by decomposing organic matter and co-precipitating free heavy metal ions with iron iron. The present invention will now be described in detail.

The wastewater in the present invention contains heavy metal complex salts stably formed with heavy metals such as copper, chromium, and cadmium and organic substances such as ethylenediaminetetraacetate, thiourea, ammonium citrate, dimethylglyoxime, oxine, glycine, and acetylacetone. From an economic standpoint, this is not suitable for wastewater containing low concentrations of organic matter or for wastewater containing organic matter that is easily oxidized.

In the present invention, first, an inorganic acid such as sulfuric acid or hydrochloric acid is added to wastewater containing a high concentration of heavy metal complex salts, and the pH is adjusted.
Adjust to below 5.0. When the pH of the wastewater is neutral or alkaline, the oxidative decomposition of organic matter in the heavy metal complex salts described below is not sufficient.

Next, after adding ferrous ions in an amount of 0.1 to 2.0 times the total number of moles of heavy metal ions in the wastewater, the liquid temperature is adjusted to 80 to 100°C. Ferrous ion is sulfate,
Any of nitrates, chlorides, etc. may be used. Regarding its effect, it has already been reported that when it coexists with hydrogen peroxide, the oxidizing power of the generated hydroxyl radical (・OH) is greater than that of hydrogen peroxide alone, but as in the present invention, In the case of oxidation reactions, hydrogen peroxide has sufficient oxidizing power to oxidize substances in wastewater;
The increase in oxidizing power due to the presence of ferrous ions is not as pronounced as at room temperature. The effect of the addition of ferrous ions lies in an improvement in the removal rate of heavy metal ions due to a coexistence phenomenon when a coagulation and precipitation treatment is performed after oxidation treatment, rather than an increase in the oxidizing power of hydrogen peroxide.

Hydrogen peroxide is added in an amount 1.0 to 1.2 times the theoretical amount required to oxidize the complex salt in the wastewater to the wastewater whose liquid temperature has been adjusted to 80 to 100°C as described above. Hydrogen peroxide is usually added to wastewater as a hydrogen peroxide solution;
The amount of hydrogen peroxide added is more than the theoretical amount required to oxidize and decompose oxidizable substances in wastewater, but adding too much hydrogen peroxide will not only waste hydrogen peroxide, but also cause it to remain in the treated water and cause secondary There is a risk of causing pollution. Since the reaction efficiency of hydrogen peroxide is extremely good under the conditions of the present invention, it is not necessary to add an amount exceeding 1.2 times the theoretical amount required. The shorter the time for adding hydrogen peroxide, the better in order to speed up the process, but if the time is too short, the reaction will proceed too rapidly, which is dangerous, and the reaction efficiency will also decrease. Therefore, it is not desirable. Hydrogen peroxide is added continuously in small amounts, and the addition time is 0.5~
2 hours is appropriate.

Through the above treatment, the organic matter in the heavy metal complex salts in the wastewater is oxidized and decomposed, and some of the generated free heavy metal ions are co-precipitated with iron ions, and some remain in the liquid, so that the wastewater can be further processed. After cooling by standing to cool or separating the precipitate as necessary, alkali is added to adjust the pH to 6 to 8. Since some of the precipitates may be redissolved by this pH adjustment, it is desirable to separate the precipitates prior to adjusting the pH. By adjusting the PH as described above, if enough flocculating substances are generated in the liquid, heavy metal ions can be sufficiently flocculated and precipitated without adding a flocculant, so if the flocculating substances are separated,
Heavy metal complex salts can be immediately removed with high efficiency. If the above pH adjustment alone is insufficient to produce flocculants, it is desirable to further add an inorganic flocculant such as aluminum sulfate or polyaluminum chloride, or a polymer flocculant such as polyacrylamide. In the above pH adjustment, it is necessary to appropriately select the pH value depending on the type of heavy metal to be removed.

In the present invention, the PH adjustment before addition of hydrogen peroxide, the addition of ferrous ions, and the adjustment of liquid temperature may be carried out in any order, and the PH adjustment after oxidation treatment with hydrogen peroxide may be carried out in any order. Alternatively, the separation of aggregated substances need not be performed continuously, and may of course be performed after another treatment step.

Example 1 HCl was added to wastewater 1 containing 4000 mg of organic carbon (TOC) and 700 mg of Cu ions as heavy metals, and the pH was set to 2.0. ,
Next, 2g/of ferrous sulfate was added, and the liquid temperature was lowered to 20%.
The temperatures were 40, 65, 80, and 95°C. Next, _113g of 30% _H2O2
(approximately 1.0 times the required theoretical amount) in small amounts continuously at 120
Add over a few minutes, let it cool, then adjust the pH to 7.0.
After flocculating and separating by adding mg/mg of polymer flocculant, the TOC removal rate and Cu removal rate of the treated water were measured. The results are shown in FIGS. 1 and 2.

As is clear from Figure 1, TOC at temperatures above 80℃
The removal rate increases significantly. Furthermore, as shown in Figure 2, the Cu removal rate shows extremely good values at temperatures above 80°C.

Example 2 Wastewater was treated in the same manner as in Example 1, except that the liquid temperature for hydrogen peroxide addition was 80°C and the pH was varied. The TOC removal rate of treated water showed good results when the pH was below 5.0. The TOC removal rate decreases as the pH becomes neutral or alkaline, but this is because hydrogen peroxide self-decomposes and releases oxygen gas without reacting with oxidizable substances in wastewater. it is conceivable that. Note that the Cu removal rate also shows the same tendency as the TOC removal rate.

Example 3 Wastewater was treated in the same manner as in Example 1, except that the pH was 3.5 and the molar ratio of ferrous sulfate to Cu ions was varied. As shown in Figure 4, the TOC removal rate shows a good value regardless of the presence of ferrous ions, which means that ferrous ions hardly contribute to the increase in the oxidizing power of hydrogen peroxide. are doing. On the other hand, as shown in Figure 5, the Cu removal rate clearly increases when ferrous ions are present at 0.1 mole or more (relative to the number of moles of Cu), and ferrous ions form compounds with Cu. At the same time, it can be seen that it plays an important role in the coagulation and precipitation of Cu, such as exhibiting a coprecipitation effect.

Example 4 Contains 5000 mg of complex organic substances such as ethylenediaminetetraacetate and thiourea as TOC amount,
Wastewater 1 (PH: 9.5) discharged from the plating process containing 620 mg of Cu as a heavy metal was collected, HCl was added to adjust the pH to 3.0, then 400 mg of ferrous sulfate was added as Fe, and the liquid temperature was lowered to 80 ℃.
Next, 113 g of 30% H ₂ O ₂ was continuously added in small portions over 100 minutes, and after cooling, the pH was adjusted to 7.0, and 5 mg of a polymer flocculant (polyacrylamide) was added to coagulate and precipitate. Water quality analysis of the supernatant after treatment revealed that TOC was 195 mg/, and Cu was 6.
mg/.

For comparison, 30
%H ₂ O ₂ was added all at once and the reaction time was 100 minutes to treat wastewater.
TOC was 484 mg/, and Cu was 67 mg/. In this case, the TOC removal rate and Cu removal rate are significantly lower than when H ₂ O ₂ is added over 100 minutes. The reason for this is that in the case of bulk addition, rapid gas generation is observed immediately after addition, and together with the CO ₂ gas generated by the reaction,
This is because O ₂ gas from the decomposition of H ₂ O ₂ escapes, and it can be considered that that amount is wasted.

Example 5 The amount of 30% H ₂ O ₂ added was 125 g, and the addition time was
When the wastewater was treated in the same manner as in Example 4 except that the time was 120 minutes, the water quality of the supernatant after the flocculation treatment was as follows.
TOC was 80 mg/, and Cu was 1 mg/.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the treatment temperature and the removal rate of organic carbon (TOC) when the treatment of Example 1 is applied, and Figure 2 is a graph showing the relationship between the treatment temperature and the removal rate of organic carbon (TOC) when the treatment of Example 1 is applied. A graph showing the relationship between the copper ion removal rate and Figure 3 is a graph showing the relationship between wastewater PH and TOC removal rate when the treatment of Example 2 is applied. Figure 4 is a graph showing the relationship between the TOC removal rate and the treatment of Example 3. A graph showing the relationship between the molar ratio of ferrous sulfate to heavy metal ions and TOC removal rate when applying
FIG. 5 is a graph showing the relationship between the molar ratio of ferrous sulfate to heavy metal ions and the removal rate of heavy metal ions when the treatment of Example 3 was performed.

Claims (1)

[Claims] 1 Organic wastewater containing high concentrations of heavy metal complex salts
Adjust the pH to below 5, add 0.1 to 2.0 times the amount of ferrous ions to the total number of moles of heavy metal ions in the wastewater, and continuously add hydrogen peroxide in small amounts at a temperature of 80 to 100℃. 1. A method for treating wastewater containing heavy metal complex salts, which comprises: adding water to the wastewater, cooling it, adjusting the pH to 6 to 8, and separating the generated heavy metal-containing aggregated substances.