JPS602915B2 - Treatment method for wastewater containing toxic metals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a 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. In other words, ■
Ferrous salt mixing process Ferrous salt (mainly ferrous sulfate FeS04, 7 days 20) is added to the wastewater in an amount corresponding to the type of heavy metals contained in the wastewater and the amount of treated wastewater. .

(2) Bait Adjustment Step Next, an alkali (for example, caustic soda NaOH) is added to adjust the flow of the mixed waste water to generate mixed hydroxide in the waste water.

■ After adjusting the oxidation process, heat it with steam or a heater to 60-70 p.m.
Next, air is introduced into the wastewater to advance the ferrite reaction.

As the ferrite formation 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 is Fe2 alkaline study.

This method utilizes the reaction of Fe(OH)2-Fe304, but the type of compound that is ultimately produced by the oxidation of ferrous ions is determined by the reaction conditions, so it is not possible to produce ferrite. must be processed under specific conditions. Figure 1 shows how 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 changes depending on the addition of the alkali and the reaction temperature. It is. As is clear from the figure, Fe°C4 is produced at high reaction temperatures, and Fe00 days is produced at low temperatures. Therefore, in order to generate ferrite, it is necessary to process at a high temperature of at least 600m or higher, and since ferrite formation is affected by the amount of alkali added, oxidation time, etc., it is said that setting the processing conditions is difficult. was. 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 genus ions.

However, although the above method is effective when applied to the treatment of wastewater containing a relatively large amount of harmful metal ions, there is no conventional effective method for treating a large amount of diluted liquid containing a small amount of harmful metals, so it is discharged as is. Therefore, in order to achieve so-called total volume control, there was a strong desire to develop an effective treatment method for diluted liquids.

The present invention provides an effective method for treating dilute wastewater containing small amounts of harmful metals. Lepidocrocite is added to the wastewater containing harmful metal ions in its alkaline region, and metal ions are added to the precipitated particles. ferrous ions are added in the alkaline region of the liquid containing lepidocrocite adsorbed with metal ions to create magnetite production conditions in the liquid through the reaction between lepidocrosite and ferrous ions, A small amount of metal ions contained in the wastewater can be removed by separately performing the step of incorporating metal ions into the crystal lattice of magnetite produced in the liquid by the reaction.

The principles underlying the method of the present invention will be explained below. The present inventor discovered that when ferrous ions are added to a liquid of pidochrosite (yFe00H), magnetite (4 of Fe) is generated by the following reaction under conditions where the weight of the liquid is 6 or more. Ta.

2yFe00H+FeOH-→Fe304 10 days 20 10 days 10 yFe00 days is the ferrous ion Fe2 in the strongly acidic region.
It is known that it is easily dissolved because it is adsorbed in the form of ten.

When the pH of the solution is 6 or more, particularly in an alkaline region, ferrous ions are adsorbed in the form of FeOH+, so the above reaction occurs and precipitates as magnetite. During the above reaction, H+ 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. If the liquid is strongly alkaline,
There is no need to add alkali again. Furthermore, when the pH of the solution used to add ferrous ions is 6 or less, an alkali is added to adjust the pH to 6 or more. As described above, it is sufficient to maintain the liquid barrier at 6 or more during the reaction, and the feed area of the liquid when adding ferrous ions does not matter. 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 due to the fact that yFe00 has a crystal structure similar to Fe304, and the activation energy required for the structural change to Fe℃4. This is thought to be because it is extremely small.
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-mentioned principle for the treatment of heavy metal-containing wastewater, and in particular makes it possible to effectively treat small amounts of harmful metal ions contained in the wastewater. That is, by adjusting the pH of wastewater containing harmful metal ions such as Co20, C ratio, C020, Cd20, and Zn20 to 11 to 12, and adding yFe00 to this solution, the metals in the wastewater will be reduced. Ions are adsorbed to the yFe00 day particles and precipitate. yFe0
Since metal ions are highly adsorbed on day 0, even if a small amount of metal ions are contained in a large amount of liquid, they can be adsorbed relatively easily by taking measures such as waving. However, in this state, the metal ions are simply adsorbed on the yFe00-day particles, and are relatively easily released as the pH of the solution decreases. In the present invention, metal ions are once adsorbed onto yFe00-day particles in the first step, and then in the second step, these are converted into stable ferrite particles and separated from the waste water. In the first step, heavy metal ions are
After adsorbing Fe00 and precipitating it, the supernatant solution was neutralized and discharged, and heavy metal ions were adsorbed on yFe00.
The particles are collected as a suspension. In the second step, ferrous ions are introduced into the suspension, and conditions for producing magnetite are created in the solution by introducing ferrous ions, y
Fe00 days react with ferrous ions to form magnetite almost instantaneously, and harmful metal ions are incorporated into the crystal lattice of magnetite to precipitate as ferrite. By using yFe00 day, which has excellent adsorption properties, in the first step, heavy metal ions are completely adsorbed and precipitated on yFe00 day.

In the present invention, in the next step, the yFe00 day adsorbed heavy metal ions is converted into ferrite, which has excellent sedimentation properties and can be magnetically separated, for solid-liquid separation.
It is not necessary to collect the precipitate on day yFe00 as a so-called precipitate, but it is sufficient to collect the precipitate as a suspension containing the precipitate. Generally, yFe 00 days has extremely poor sedimentation characteristics, so it is extremely difficult to collect only the precipitates.

To collect yFe00 days, use a filter press.
Moisture must be removed using a centrifuge, etc. Although yFe00 day has very good adsorption performance, it has hardly been used as an adsorbent because it is difficult to recover, but in the present invention, it is used in the first step. On yFe00, heavy metal ions are adsorbed on yFe00, and after concentrating this, in the second step, yFe is converted into ferrite, which is easy to recover.
Another major feature is that we were able to effectively utilize day 00 as an adsorbent. Ease of precipitation and recovery is the most important factor, especially when treating large amounts of water, and the present invention has made this possible through a two-step process of concentrating and recovering heavy metal ions. This is an extremely effective method for treating large amounts of water. Furthermore, according to the method of the present invention, unlike the conventional method, there is no limit, particularly no upper limit, on the range of the cape of the treated water, so by reacting in a strong alkaline region, all harmful metal ions can be dissolved. However, all of these harmful metal ions can be incorporated into the Fe°C crystal lattice. As described above, the present invention performs the harmful metal adsorption process and the ferrite formation process separately, and finally forms ferrite in which harmful metal ions are incorporated into the crystal lattice points to remove harmful metals from wastewater. At the same time, the liquid can be easily separated, making it possible to effectively utilize the characteristics of yFe00 to treat dilute metal ion-containing wastewater at room temperature, and the method of the present invention is sufficient to comply with regulations on the total amount of heavy metal waste liquid. It has the effect that it can. Examples of the present invention will be described below.

(Example) When the wastewater bait 11 was adjusted to contain 1 to 2 feet of C, C, C, and Zn20, and about 5 ta of yFe00 was added to the wastewater, the metal ion was 0.01. Completely below the legs
Fe was adsorbed on day 00 (Fig. 2).

This suspension on day yFe00 was collected, and F
Black magnetite containing eC12 was produced (Figure 3). Further, the metal ions adsorbed on yFe00 were not eluted until the magnetite dissolved. This result leads us to conclude that metal ions are incorporated into the lattice points of magnetite. Note that the liquid temperature was 25° C. during the entire treatment process.

[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 magnetite particles. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. Adding lepidocrocite to wastewater containing harmful metal ions in the alkaline region of the liquid to adsorb the metal ions to the precipitated particles of lepidocrocite, and adding the liquid containing lepidocrocite to which the metal ions have been adsorbed. By adding ferrous ions in the alkaline region of A method for treating wastewater containing toxic metals, characterized in that a step of dealing with ions is carried out separately.