JPS58174286A - Treatment of waste water containing heavy metal complex salt - Google Patents

Abstract

PURPOSE:To remove heavy metal complex salt in a short time with high efficiency, by adding a specific amt. of ferrous ion to org. waste water contg. a high concn. of metallic complex salt controlled to <=5pH, adding hydrogen peroxide thereto at a specific temp. and cooling the waste water then controlling the pH to 6-8. CONSTITUTION:An inorg. acid such as sulfuric acid or hydrochloric acid is added to waste water contg. heavy metal salt formed stably of heavy metal such as copper, chromium and cadmium and the org. material such as ethylene diamine tetraacetate, thiourea or the like to control the pH thereof to 5.0. Ferrous ion such as ferrous sulfate, nitrate or the like is added thereto at 0.1-2.0 times the total molar number of the above-described heavy metal ion in the waste water, whereafter the liquid temp. is controlled to 80-100 deg.C. Hydrogen peroxide is added to the waste water at 1.0-2.9 times the theoretical amt. required for oxidation of the complex salt in the waste water and after cooling, an alkali is added to the waste water to control the pH to 6-8 and the flocculated material contg. the heavy metal formed by said addition is separated.

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 Mesoki factory and laboratory wastewater, heavy metals form stable heavy metal complex salts with organic substances such as ethylenediaminetetraacetate, thiourea, ammonium citrate, and dimethylglyoxime.
Removing heavy metals is not easy.

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. There was a drawback that the value 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, oxidation treatment methods include ultraviolet treatment, chlorine, chlorine compounds, ozone, hydrogen peroxide, etc. A variety of treatment methods have been put into practical use, including treatment with an oxidizing agent alone or in appropriate combinations of these treatments. At present, no satisfactory treatment method has been found when considering reactivity, operability, and economic efficiency such as installation space.

In view of the current situation, the present invention provides organic wastewater containing a high concentration of heavy metal complex salts - After adjusting the pH to 1 PH or less, ferrous ions are added in an amount of 01 to 20 times the total number of moles of heavy metal ions in the wastewater. After complete addition, hydrogen peroxide was continuously added little by little while the liquid temperature was 80 to 100°C, cooled, and the pH was adjusted.
By adjusting f6 to f8 and separating the produced heavy metal-containing flocculated substances, organic matter in wastewater containing high concentrations of heavy metal complex salts can be decomposed, and the free heavy metal ions can be co-precipitated with iron ions to form heavy metal complex salts. The present invention has been made possible to provide a method for treating wastewater containing heavy metal complex salts that can be removed in a short time and with high efficiency, and the present invention will be described in detail below.

The wastewater in the present invention includes heavy metals such as copper, chromium, and cadmium, eterenodiaminetetraacetate, thiourea, ammonium citrate, dimethylglyoquine, oxine,
From an economical point of view, it is suitable for wastewater containing high concentrations of heavy metal complex salts stably formed with organic substances such as glycine and acetylacetone, such as wastewater with low concentrations or wastewater containing organic substances that are easily oxidized. I can't say that.

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 to adjust the pH to 5.0 or less. When the pH of the wastewater is neutral or alkaline, the oxidative decomposition of organic substances in the heavy metal complex salts described below is not sufficient.

Next, ferrous ions were added to the 5 mo/mol of heavy metal ions in the wastewater.
After adding 01 to 20 times the amount of l/number, the liquid temperature was lowered to 80
Adjust to ~100°C. The ferrous ion may be a sulfate, a nitrate, a chloride, or the like. Regarding its effect, it has already been reported that when it coexists with hydrogen peroxide, the oxidizing power of the generated hydroxyl radical (.0H)K is greater than that of hydrogen peroxide alone; In the case of the oxidation reaction at room temperature, the increase in oxidizing power due to the presence of ferrous ions is not as pronounced as in the case of room temperature, because hydrogen peroxide has sufficient oxidizing power to oxidize the oxidized substances in wastewater. . The effect of the addition of ferrous ions lies in the improvement of the removal rate of heavy metal ions due to the coprecipitation phenomenon when the coagulation and precipitation treatment is performed after the oxidation treatment, rather than the increase in the oxidizing power of hydrogen peroxide.

Hydrogen peroxide is added to the wastewater whose liquid temperature has been adjusted to 80 to 100°C as described above in an amount of 10 to 12 times the theoretical amount required to oxidize the complex salt in the wastewater.

Hydrogen peroxide is usually added to wastewater as a hydrogen peroxide solution;
Although the amount of hydrogen peroxide added is more than the theoretical amount required to oxidize and decompose oxidizable substances in wastewater, 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. Under the conditions of the present invention, the reaction efficiency of hydrogen peroxide is extremely good, so it is not necessary to add more than 12 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 suitable for 0.5 to 2 hours.

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, etc. and separating the precipitate as necessary, add Alka IJ to PH'i6-8.
Adjust to. Since some of the precipitates may be redissolved by this pH adjustment, it is desirable to separate the precipitates prior to adjusting the pH. When the above-mentioned PH adjustment is performed, if a light flocculating substance is generated in the liquid, the heavy metal ions can be sufficiently coagulated and precipitated without adding a flocculant, so if the flocculating substance is 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 order of pH adjustment before addition of hydrogen peroxide, addition of ferrous ions, and adjustment of liquid temperature may be any order, and pH adjustment after oxidation treatment with hydrogen peroxide may be carried out in any order. Alternatively, the separation of aggregated substances need not be carried out continuously, and may of course be carried out after another treatment step.

Example 1 Wastewater containing a complex salt-forming organic substance such as ethylenediaminetetraacetate in an amount of organic carbon (TOC) of 4,000 μ/l and a heavy metal of Cu ion 700 m9/lf was added to PHk2 ．． O, then ferrous sulfate i 2 f// was added, and the liquid temperature was lowered to 2
The temperatures were 0.40, 65, and 80.95°C. Next, 30 inches H
2O2113F (approximately 10 times the theoretical amount required) was continuously added in small portions over 120 minutes, left to cool, the pH was adjusted to 70, and 5 m9/l of polymer flocculant was added to coagulate and separate. , TOC removal rate and Cu removal rate of treated water were measured. The results are shown in FIGS. 1 and 2.

As is clear from FIG. 1, the TOC removal rate increases markedly at temperatures above 80°C. Further, as shown in FIG. 2, the Cu removal rate shows a significantly good value at temperatures of 80° C. or higher.

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' (i7) was varied.The TOC removal rate of the treated water was below PH5.0. Good results were shown.The TOC removal rate decreased as the pH became neutral or alkaline, but this was because hydrogen peroxide self-decomposed and released oxygen without reacting with oxidizable substances in the wastewater. This is thought to be due to the release of gas.In addition, C
The u 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 pHk was set to 3.5 and the molar ratio of ferrous sulfate to Cu ions was varied. As shown in Figure 4, the TOC removal rate showed good values regardless of the presence of ferrous ions, indicating that ferrous ions hardly contributed to the increase in the oxidizing power of hydrogen peroxide. It means. 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 combine with Cu. It can be seen that CuO plays an important role in the formation and co-precipitation of CuO.

Example 4 Waste water 11 discharged from a plating process containing complex salt-forming organic substances such as ethylenediaminetetraacetate and thiodeurea as TOC amount of 5 ml, IC 10 m9/, and heavy metal as Cu 620 m·n/l'fc (PH: 9
5) Sample k, add HC1' to make P H'e 3.0, then add 400 m9 of ferrous sulfate as Fe,
The liquid temperature was 80°C. Next, 30 liters of H2O2 were continuously added in small portions over 100 minutes, and after cooling, the PH
When the water quality of the supernatant liquid was analyzed, the TOC was 19.
! IA//l, Cu was 6m9/l.

For comparison, 30% H
When 2O2 was added all at once and the reaction time was 1100 minutes, the wastewater was treated, and the TOC of the supernatant was 4.
84mg/1XCu was 67m9/l. In this case, the TOC removal rate and Cu removal rate are significantly lower than when H2O2'kl O is added for 0 minutes. The reason for this is that in the case of bulk addition, rapid gas generation is observed immediately after addition, so it is thought that 02 gas due to decomposition of H2O2 escapes together with the CO2 gas generated by the reaction, and that much is wasted. It's fine.

Example 5 Wastewater was treated in the same manner as in Example 4, except that the amount of 30% H2O2 added was 'i12'5f and the addition time was 120 minutes.The water quality of the supernatant after flocculation treatment was TOC
was 80'''9/l, and Cu was 1 m9/l.

[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 with the removal rate of copper ions, Figure 3 shows the PH and T of wastewater when treated in Example 2.
A graph showing the relationship between the OC removal rate and FIG. 4. A graph showing the relationship between the molar ratio of ferrous sulfate to heavy metal ions and the TOC removal rate when the treatment of Example 3 was applied. FIG. 3 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 is performed.

Claims (1)

[Claims] The total pH of organic wastewater containing high concentration of heavy metal complex salts is adjusted to 5 or less, and the pH is adjusted to 0 with respect to the total number of moles of heavy metal ions in the wastewater.
Add 1 to 20 times the amount of ferrous ions and lower the liquid temperature to 80 to 1
Treatment of wastewater containing heavy metal complex salts, characterized by continuously adding hydrogen peroxide little by little at a temperature of 00°C, cooling, adjusting pH to 6 to 8, and separating generated heavy metal-containing aggregated substances. Law.