JPS6227874B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for treating wastewater containing heavy metals. Conventionally, the most well-known method for treating wastewater containing heavy metals is to add alkali to the wastewater to generate and remove heavy metal hydroxides in the wastewater. These materials easily dissolve in water, and the risk of secondary pollution associated with their dumping was extremely high. In order to solve this problem, a method of separating and removing heavy metals from wastewater by incorporating them into the crystal lattice of ferrite, which is a ferromagnetic oxide, has been proposed in Japanese Patent Application No. 127816/1984 (Japanese Patent Publication No. 22307/1983). ), and this method has now been put into practical use. In this method, a predetermined amount of ferrous salt is added to a waste liquid containing heavy metals, the liquid is kept alkaline, and an oxidizing gas such as air is blown in to oxidize the ferrous salt, so that heavy metals are added to the crystal structure. It produces ferrite that incorporates The heavy metal hydroxides produced by this method are difficult to dissolve in water, and this is a highly preferred treatment method with little risk of secondary pollution associated with dumping. However, in order to carry out such a method efficiently, it is preferable to carry out the oxidation reaction while the liquid is heated, and therefore, the number of steps and costs for this heating are required. Note that when the reaction temperature is lower, it becomes difficult to produce ferrite, and the particle size of the ferrite produced becomes smaller, making solid-liquid separation difficult and oxidation time becoming longer, resulting in many practical problems. An object of the present invention is to improve these disadvantages and provide a method for treating heavy metals in wastewater at a low temperature, that is, at almost the same temperature as the wastewater. That is, the present invention provides wastewater containing hazardous heavy metals with at least
Add 0.002 mol or more of ferrous salt, and further add about 1 equivalent of alkali to the acid radical in the solution to adjust the pH of the waste solution to 8 to 12, and store the solution in an atmosphere with an oxygen partial pressure of 0.1 atmosphere or less. It is characterized by producing large ferrite precipitates in a short time at room temperature without heating the reaction solution. Here, in the present invention, it is preferable to carry out the above-mentioned stirring at a high speed, for example, it is effective to use a stirring speed of 100 rpm or more. Also, the normal temperature mentioned above refers to the temperature near the earth's surface, but the temperature is approximately 40°C.
℃ or lower and 0℃ or higher (solidification occurs below this temperature). It is thought that the precipitate normally produced by the room-temperature ferrite reaction in air is a mixture of ferrite and goethite, and its particle size is extremely small. In other words, a decrease in the reaction temperature means a decrease in the ferrite production rate, and since the oxidation rate is considered to be the rate-determining condition for the ferrite production reaction, it is important to reduce the oxidation rate in response to a decrease in the reaction temperature for ferrite production. considered preferable. In other words, in the method of the present invention in which the oxidation reaction is carried out by stirring at room temperature at a speed of 100 rpm (revolutions per minute) or more, it is necessary to maintain the oxygen partial pressure at 0.1 atmosphere or less. When the oxygen partial pressure exceeds 0.1 atm, the amount of goethite produced increases significantly. Furthermore, even if ferrite is produced, its particle size will be significantly smaller than 300 Å, making solid-liquid separation difficult. The present invention will be explained in more detail below with reference to Examples. Example 1 0.05 mole of ferrous sulfate was dissolved in 500 ml of a heavy metal solution containing about 100 ppm each of Cu ²⁺ , Cd ²⁺ , and Pb ²⁺ with a total concentration of about 300 ppm, and the solution was heated to 20°C and an oxygen partial pressure of 0.02 atm. Place it in a nitrogen-oxygen mixed gas (1 atm) and add caustic soda to maintain the pH at 10 while using a homogenizer (Nippon Seiki Seisakusho Model AM-8).
The mixture was stirred at a speed of 10,000 rpm. After stirring for 1 hour, the precipitate was black and ferromagnetic, and magnetized barium ferrite was added to the solution to separate the precipitate. A portion of the liquid after separation was sampled and the remaining metal concentration was examined by atomic absorption spectrophotometry, and the results shown in Table 1 were obtained.

[Table] These are far below the drainage standards. Example 2 Cu ²⁺ 50ppm, Ni ²⁺ and Zn ²⁺ 250ppm each
A heavy metal solution with a total concentration of approximately 550 ppm containing 500
Dissolve 0.05 mol of ferrous sulfate in 1 ml and stir the solution at 20°C.
Place it in reduced pressure air at 0.05 atm, add caustic soda to maintain the pH at 10, and use a homogenizer (Nippon Seiki Seisakusho Model AM-8) to heat it at 10,000 r.p.
The mixture was stirred at a speed of m. The precipitate after 1 hour of stirring was black and ferromagnetic, and magnetized barium ferrite was added to the solution to separate the precipitate. A portion of the liquid after separation was sampled and the remaining metal concentration was examined by atomic absorption spectrophotometry, and the results shown in Table 2 were obtained.

[Table] These are far below the drainage standards. Note that an oxygen partial pressure of 0.1 atmosphere or less can be easily obtained by diluting air with an inert gas such as nitrogen or reducing the pressure as shown in the examples. The effect of the present invention does not change even if a ferrous salt other than ferrous sulfate shown in the examples is used as the ferrous salt used in the present invention, the effect of the present invention does not change, and it can be used as a by-product during pickling of iron plates, titanium oxide production, etc. It is considered desirable to use ferrous chloride and ferrous sulfate, which are generated in large quantities, economically and from the standpoint of industrial waste and effective use of materials. Note that the present invention is not limited to the above-mentioned embodiments, but is applicable to the treatment of wastewater containing any concentration of heavy metals and at any temperature.

Claims (1)

[Claims] 1 In a method for removing harmful heavy metal ions contained in wastewater by binding them to ferrite in the presence of ferrous ions, the above harmful metals are removed by oxidizing ferrous salts in an atmosphere with an oxygen partial pressure of 0.1 atmosphere or less. A method for treating wastewater containing heavy metals, the method comprising: combining ferrite with ferrite.