JPH0432716B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating waste liquid containing heavy metals.

Conventionally, heavy metal-containing waste liquids have generally been treated by a neutralization coagulation sedimentation method. The neutralization coagulation precipitation method is a treatment method that adjusts the pH of waste liquid to convert heavy metals into insoluble hydroxides or oxide precipitates, and performs solid-liquid separation. Although this method is easy to operate, it has the disadvantage that it cannot efficiently remove all the various types of heavy metals that coexist in a single treatment because the optimal pH range for precipitation differs depending on the type of heavy metal. ing. Additionally, when the produced sludge is solidified and dumped, it has the disadvantage that there is a great concern that it will re-elute. On the other hand, add ferrous salt to heavy metal waste liquid and add alkali to raise the pH to 8 or higher.
12 or less and oxidizes some of the ferrous ions by contacting with oxygen-containing gas or adding an oxidizing agent to form spinel-type ferrite precipitates, and heavy metal ions are incorporated into the precipitated particles. The treatment method of solid-liquid separation after adsorption is a recently developed method that has many advantages, including the ability to treat most heavy metals all at once, produce stable sludge, and enable magnetic solid-liquid separation. This is called the ferrite method.

However, this ferrite method is basically suitable for removing heavy metal ions that tend to form cations, but is not suitable for removing some metalloids that easily form anions or some harmful anions. There is a drawback that there is no

The present invention eliminates the above-mentioned drawbacks and provides a method for treating waste liquid that can remove some metalloids that tend to form anions and some harmful anions even if they contain heavy metals. .

In the present invention, ferrous salt is added to the waste liquid containing heavy metals, an alkali is added to maintain the pH at 8 or more and 12 or less, and ferrous iron is added to the waste liquid containing heavy metals by contacting it with a gas containing oxygen or adding an oxidizing agent. oxidizes some of the ions,
In a waste liquid treatment method in which a spinel-type ferrite precipitate is generated, heavy metal ions are incorporated or adsorbed into the precipitated particles, and then solid-liquid separation is performed, a soluble alkaline earth metal salt is added to the ferrous ion before the oxidation of the ferrous ion. It is characterized in that it is added to the waste liquid up to the point in time.

In this invention, typical ferrous salts used are ferrous chloride, ferrous sulfate, and mixtures thereof. A typical alkali is caustic soda, which is most commonly used, but milk of lime can also be used. If the waste liquid is originally strongly alkaline and its pH exceeds 12 even after adding ferrous salt, it is necessary to add acid in advance.
The invention can thus also be applied to alkaline waste liquids. The reason why the adjusted pH was limited to 8 or more and 12 or less was because
If the pH is lower than 8, not only will it be difficult to obtain a spinel-type ferrite precipitate by oxidation, but the time required for oxidation will be too long;
If the temperature is higher, ferrite precipitate will be formed, but a different phase will be more likely to occur. Oxidation conditions should be optimally determined depending on the amount and concentration of waste liquid. In general, heating and air oxidation are appropriate for a small amount of high concentration waste liquid, while oxidation at room temperature is considered to be economical for a large amount of low concentration waste liquid. Also, certain oxidizing agents such as hypochlorites, chromates, nitrates, etc. can be used.
When oxidizing at room temperature using these oxidizing agents, the particles of the ferrite precipitate produced are generally fine, so it may be necessary to select oxidation conditions. Since the ferrite in the generated precipitate is a ferromagnetic substance, magnetic separation is possible, and of course solid-liquid separation can be easily performed by methods such as sedimentation separation and vacuum filtration. The most important requirement is to add a soluble alkaline earth metal salt during these treatment steps. As a result, an insoluble salt of the metal to be removed and the alkaline earth metal is formed, which can be co-precipitated with the spinel ferrite produced in a later step, making it possible to effectively treat the waste liquid. Soluble alkaline earth metal salts include halides such as calcium chloride, strontium chloride, and barium chloride, nitrates, and calcium sulfate, which has a relatively high solubility, may also be used.

According to the method of the present invention described above, metals and semimetals such as selenium, tellurium, tungsten, and molybdenum, which have been insufficiently treated by conventional methods, can be removed at the same time. These metals and metalloid metals are not currently included in the wastewater standards based on the Water Pollution Control Act, but they correspond to metals that are being considered as subject to future regulations. It is clear that the effectiveness of inventions will become increasingly important not only now, but in the near future. This method also makes it possible to remove fluorine and phosphoric acid.

Next, examples of the present invention will be described.

Example 1 Heavy metal waste liquid 1 containing copper, hexavalent chromium, and zinc at a concentration of approximately 100 mg/, and tungsten, tellurium, and molybdenum at a concentration of 100 mg/ each
After adding 0.1 mole of ferrous chloride to the solution, 2 g of barium chloride was added, and 10 N caustic soda was added, and while maintaining the pH at 10, the mixture was heated to 65°C and heated at 2 g/min.
Blow in air to generate ferrite precipitate,
Analysis of the liquid revealed copper, total chromium, and zinc.
0.03mg/or less, tungsten, tellurium,
The concentration of molybdenum is 0.4mg/or less, 4
mg/or less, and 2 mg/or less. In addition, in the water quality of the treated solution when barium chloride was not added, copper, total chromium, and zinc were below 0.03 mg/, but the concentrations of tungsten, tellurium, and molybdenum were 70 to 80 mg/. . Comparing this with the residual amount of 0.4 mg/ml when barium chloride was added, it can be seen how great the effect of barium chloride addition is.

Example 2 Manganese, cadmium, nickel 200mg/,
Ferrous chloride was added to waste liquid containing 50 mg/each of fluorine and phosphate ions and 200 mg/molybdenum.
Add 0.2 mol of calcium chloride, add caustic soda, stir while keeping the pH at 10, oxidize by bringing it into contact with air at the liquid surface, and after about 10 hours, add 2 g of calcium chloride to remove the ferrite particles that had already formed. At the same time, analysis of separated water from which precipitates were removed using a permanent magnet revealed that manganese, cadmium, and nickel were less than 0.05 mg/day, fluorine was 0.5 mg/day, phosphoric acid was about 0.1 mg/day, and molybdenum was below 4 mg/day. Ta. For comparison, a waste liquid with the same composition as above was treated in the same manner as above except that calcium chloride was not added, and approximately 150 mg/molybdenum remained in the separated water after treatment. When compared with the residual amount of 4 mg/ml when calcium chloride is added, it can be seen how great the effect of calcium chloride is.

As explained in detail above, the present invention provides tellurium,
This method has the effect of effectively removing metals such as molybdenum and tungsten from waste liquids that have been difficult to remove in the past.

Claims (1)

[Claims] 1 Adding ferrous salt to waste liquid containing heavy metals,
By adding an alkali to maintain the pH at 8 or more and 12 or less, some of the ferrous ions are oxidized by contacting with oxygen-containing gas or by adding an oxidizing agent, producing a spinel-type ferrite precipitate, and heavy metal ions. A method for treating waste liquid in which solid-liquid separation is performed after incorporating or adsorbing iron into the precipitated particles, characterized in that a soluble alkaline earth metal salt is added to the waste liquid before oxidizing the ferrous ions. How to treat waste liquid.