JPS6020075B2 - Treatment method for wastewater containing toxic metals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a treatment method for removing harmful metals contained in waste water such as factory waste liquid.

The so-called "ferrite method" has been developed as a method for removing harmful metals from wastewater, and is already in practical use as an effective method for wastewater treatment. This method consists of the following steps. That is, ■ ferrous salt (mainly ferrous sulfate FeS04, 7 days 20) in an amount corresponding to the type of heavy metals contained in the ferrous salt mixing process wastewater and the amount of treated wastewater.
Pour it into the drainage water and worship it.

■ pH adjustment step Next, alkali (e.g. sodium hydroxide)
OH) and adjust the shoe of the mixed waste water to produce mixed hydroxide in the waste water. ■ Oxidation process After adjusting the pH, heat to 60-70℃ with steam or a heater,
Next, air is introduced into the wastewater to advance the ferrite reaction.

As the ferrite reaction progresses, heavy metals are incorporated into the ferrite crystal lattice and precipitate as ferrite sludge. By performing the above treatment steps, the ferrite precipitate is finally separated from the heavy metal-free water and heavy metals are removed from the waste water.

This method uses Fe20Al force addition AFe(OH)2 oxide Fe304
However, the type of compound that is ultimately produced by the oxidation of ferrous ions is determined by the reaction conditions, so ferrite must be produced under specific conditions. must be processed.

Figure 1 shows the crystal structure of the iron compound produced when an alkali is added to a ferrous salt solution and an oxidation reaction is actively carried out.
This figure shows how it changes depending on the addition ratio of alkali and the reaction temperature. As is clear from the figure, Fe304 is produced at a high reaction temperature, and Fe00 day is produced at a low temperature. Therefore, in order to generate ferrite, it is necessary to process at a high temperature of at least 60 pm or higher, and in addition,
Since ferrite formation depends on the amount of alkali added, oxidation time, etc., setting the processing conditions has been considered difficult. Separately, there have been attempts to carry out the oxidation reaction quietly at room temperature, but these had drawbacks such as requiring special equipment for the oxidation reaction and requiring a long time for the oxidation reaction.

In addition, when using the above method, the conditions for producing magnetite do not necessarily match the optimal conditions for completely incorporating a certain metal ion (for example, CD20, etc.) into the crystal lattice of magnetite. It was considered unavoidable that there were limits to the types and concentrations of

The present invention solves the above-mentioned problems at once, and is not influenced by treatment conditions, and moreover, it instantly generates a ferromagnetic oxide precipitate in wastewater that removes harmful metal ions. The present invention provides a method for removing contained heavy metal ions.

That is, the present invention can treat wastewater containing harmful metal ions.
Lepidocrosite is more than 7 times the total number of moles of harmful metal ions in the wastewater, and ferrous ions are added in a molar ratio of about 1/2 to the amount of lepidocrosite added, and the ferrous ions are combined with lepidocrosite. This method incorporates harmful metal ions into the magnetite crystal lattice produced by the reaction, making it possible to remove harmful metals contained in wastewater without any restrictions on the type or concentration of metals. That is. The present inventor has developed a pydocrocyte (yF)
When ferrous ions are added to a liquid of e00H), magnetite (Fe30
4) was found to be generated.

2yFe00H+FeOH+→Fe304 10 ratio ○ 10 days 10 It is known that Fe00 days easily dissolves in a strongly acidic region because it adsorbs ferrous ions in the form of Fe20.

When the pH of the solution is 6 or higher, especially in an alkaline region, ferrous ions are adsorbed in the form of FeOH1, so the above reaction occurs and magnetite is precipitated. In the above reaction, during the reaction, hydrogen is generated and the liquid returns to the acidic side, so it is necessary to maintain the pH of the liquid at 6 or higher at all times during the reaction by adding an alkali.

However, if the liquid is strongly alkaline, there is no need to add alkali. In addition, if the pH of the solution when adding ferrous ions is 6 or less, add an alkali and P
Adjust H to 6 or higher. In this way, the liquid fence during the reaction is
The pH of the solution when adding ferrous ions should be maintained above
area is not a problem. Furthermore, ferrous ions may be supplied in either solid or liquid form. As is clear from the above formula, the amount of ferrous ion added is 1/2 of the total amount of yFe00 days in terms of molar ratio.

If the amount of ferrous ion added is small, yFe00 days will remain in the solution, making it impossible to obtain highly pure magnetite. Further, in the above reaction, the reaction temperature does not matter at all.

This is because adsorption of ferrous ions to yFe00 day occurs in a solution with a pH of 6 or higher over the entire temperature range. In addition to these adsorption functions, the reason why the above reaction occurs instantaneously even at low temperatures is that yFe00 has a crystal structure very similar to Fe304, and the activation energy required for the structural change to Fe304 is extremely small. It is thought that this is because Note that yFe00 day can be obtained by oxidizing ferrous ions in a normal temperature solution in an acidic region. The present invention utilizes the above principle for the treatment of heavy metal-containing wastewater.

In other words, yFe is present in wastewater containing harmful metal ions.
When 00 days and ferrous ions are added and the pH is adjusted to 6 or more, conditions for magnetite production are formed in the wastewater,
yFe00 day reacts with ferrous ions to form magnetite almost instantaneously, and the harmful metal ions contained in the wastewater are incorporated into the crystal lattice of magnetite and precipitate as ferrite. Also, on day yFe00, F
Since it is generated by the oxidation of e20 ions, first, the pH of the wastewater is adjusted to 3 to 5, ferrous ions are added, and yFe00 is produced by air oxidation at room temperature. Effective processing can be performed.

According to the method of the present invention, unlike conventional methods, there is no limit to the pH range of the treatment solution, especially no upper limit, so all harmful metal ions are dissolved in the solution at high concentrations by reacting in a strongly alkaline region. In any case, all of these metal ions can be incorporated into the crystal lattice of Fe304.

Furthermore, in the present invention, it is important for the purpose of wastewater treatment to set the amount of ferrous ion added to approximately 1/2 of the total amount of yFe00 days in terms of molar ratio. Of course yFe
Ferrite is produced in an amount according to the ratio of yFe20 ions to Fe20 ions, but if the amount of ferrous ions added is extremely small, for example, if the amount of ferrous ions added is 1/under the peak of the total amount of yFe20 ions. Since yFe00 remains in the wastewater with metal ions adsorbed, the metal ions are easily re-eluted, and
Since yFe00 does not exhibit magnetism, it cannot be removed from wastewater by magnetic separation.

On the other hand, if the amount of ferrous ions added is large, the ferrous ions will remain in the wastewater and will need to be treated when it is discharged. As described above, the present invention creates conditions for producing magnetite in wastewater through the reaction between yFe00 and ferrous ions, and engages harmful metal ions in the crystal lattice of the generated magnetite to remove these harmful metals from the wastewater. In order to remove more
Wastewater treatment becomes extremely easy, and since magnetite is generated almost instantaneously, treatment time can be greatly shortened compared to conventional methods. In particular, it does not require high temperatures as reaction conditions and can be treated at room temperature, which is extremely advantageous in terms of wastewater treatment operations. Examples of the present invention are shown below. (Example) The axis of the waste water of 750 filtrate (liquid temperature 2500) containing 40 ground pm of Mzu10, Co20, C〆10, Cd20, and Zn20 was adjusted to 5.5, and FeC12 was added to the waste water. Then, at a liquid temperature of 25° C., air was blown at 1.5 times per minute to oxidize Fe20 ions and generate yFe00 in the waste water (Figure 2).

The pH of this wastewater was adjusted to 8, 9, 10, respectively.
Prepare 11 solutions, add a pH 2 solution containing 0.61% FeCe2 to each solution, add alkali, and adjust the pH of each solution to the predetermined values of 8, 9, 10, and 11, respectively. I kept it. When FeOC12 was added to all the liquids, the resulting precipitate was ferrite containing these metal ions (Figure 3). It was found that these metal ions were completely incorporated into the crystal lattice points of the ferrite, and when the pH of the solution was lowered to 3 or less, the metal ions were re-eluted only when the ferrite was slightly dissolved.
Further, the metal ion concentration in the solution when ferrite was generated was 0.01 ppm or less in all cases.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the changes in the product with respect to the alkali addition ratio and reaction temperature in the conventional method, Figure 2 is an electron micrograph of yFe added to the liquid on day 00, and Figure 3 is the product produced by the method of the present invention. This is an electron micrograph of ferrite particles. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. Lepidocrocite is added to wastewater containing harmful metal ions in an amount that is more than 7 times the total number of moles of the total harmful metal ions in the wastewater, and approximately 1/2 in molar ratio to the amount of lepidocrocite
A certain amount of ferrous ions are added, the pH is kept at 6 or higher, and harmful metal ions are worked into the crystal lattice of magnetite produced by the reaction between lepidocrocite and ferrous ions, and the harmful metals are drained away. A method for treating wastewater containing harmful metals, characterized by removing harmful metals.