JPS5839768B2 - Rinsan Enshiyori Ritsuji no Saisei Shiorihouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for regenerating phosphate treatment sludge, and more specifically, to treating iron, zinc, and
The present invention relates to a method that allows efficient separation and recovery of phosphoric acid and heavy metal components from sludge made from phosphates of heavy metals such as nickel, and allows both to be reused.

Conventionally, methods for treating this type of sludge include: (1) adding lime or Portland cement to the sludge and kneading and hardening it (Japanese Patent Laid-Open No. 49-83692), (2) adding organic matter or powdered coke to the sludge, and 13
A method of recovering heavy metals in sludge by heat treatment at 00°C (JP-A-49-107965, hereinafter referred to as coke reduction method), and a method of dissolving sludge in sulfuric acid to separate and recover each component (hereinafter referred to as (referred to as the sulfuric acid decomposition method) is known.

However, although the method (2) above renders the sludge, which is a harmful substance, harmless, it does not take into account the components in the sludge as a method for recycling resources.

The coke reduction method (2) is effective in reusing resources, but requires a lot of equipment and requires a large amount of heat.

In addition, the sulfuric acid decomposition method (■) is an application of the normal wet phosphoric acid production method, and generally requires a large amount of sulfuric acid to be added relative to the amount of sludge, and the sulfuric acid ions (PO43-) and sulfate ions (SO4") produced by decomposition are Separation becomes difficult, and a large amount of alkali is required to recover the so4'-.

Therefore, in reality, these methods (■ to ■) are not often used, and the sludge is disposed of by methods such as burying it underground.

The present inventors conducted research on a simple, inexpensive, and efficient method for regenerating such phosphate-treated sludge. As a result, the sludge was reacted with an alkali in water to separate it into phosphoric acid and heavy metal components, and then It was discovered that by adjusting the pH of this system to a specific range or adding an appropriate amount of calcium carbonate and/or slaked lime, the precipitated heavy metals can be efficiently separated and both can be recovered separately, and the present invention was completed. I ended up doing it.

The gist of the present invention is to react phosphate-treated sludge with an alkali under heating at a pH of 11 to 12 in water to precipitate all of the heavy metal components of the sludge as their hydroxides, and to precipitate the phosphoric acid components of the sludge dissolved in the water. phosphate, and then adjusting the pH of the reaction system to 13 or higher or 8.3 to 9.3, or adding calcium carbonate and/or slaked lime to the reaction system, and then filtering off the precipitate. The invention consists in a method for regenerating treated sludge.

The sludge targeted by the method of the present invention refers to the sludge generated in the commonly practiced phosphate treatment of metals, particularly in the phosphate chemical treatment, and specifically refers to the sludge generated in the phosphate treatment of metals, specifically the sludge treated with zinc phosphate for steel, and the sludge treated with zinc phosphate for galvanized steel sheets. Included are treated sludge and iron phosphate treated sludge.

When such sludge is subjected to the process of the present invention, it is usually pulverized and dispersed in water.

The dispersion concentration is preferably 10 to 25% by weight. Note that the sludge contains heavy metal phosphates, such as iron phosphate (FePO4
), zinc phosphate (Zn3(PO4)2), nickel phosphate C
N13(PO4)2) etc.

7. By adding an alkali to the aqueous dispersion of the sludge and causing a reaction under heating, heavy metal hydroxides and alkali phosphates are formed, and the heavy metal hydroxides are precipitated.

The reaction may be carried out usually at 70 to 100°C for 1 hour or more with stirring.

The above-mentioned alkali may be any alkali as long as it can react with the sludge and remove water-insoluble heavy metal hydroxides and water-soluble alkali phosphates, such as oxides of aluminum and potassium, and water. Mention may be made of oxides and carbonates, particularly sodium hydroxide.

The amount of alkali used may be the reaction stoichiometric amount (i.e., 3 times the mole of phosphoric acid in the sludge) or a slight excess thereof, and in this case, the pH of the reaction system is in the range of 11 to 12. .

Note that it is not preferable to use a large excess amount of alkali because some of the heavy metals (for example, zinc) in the sludge will not precipitate as hydroxides.

The reaction with sludge when sodium hydroxide is used as the alkali is shown below.

Next, in order to separate the removed heavy metal hydroxide from the alkali phosphate, the heavy metal hydroxide precipitated from the reaction system may be separated by a normal sifting operation.

However, if the pH of the reaction system is in the range of 11 to 12, depending on the type of heavy metal hydroxide, the particles may be very fine, so if it is directly subjected to filtration, the particles will pass through a piece of paper. This causes undesirable phenomena such as the particles getting mixed into the r-liquid, or the particles themselves taking on a colloidal form, which slows down the filtration rate.

Therefore, the previously used alkali or acid (preferably phosphoric acid) is then added to the reaction system to adjust the pH to 13 or more or in the range of 8.3 to 9.3, and then the reaction system is subjected to one filtration. is necessary.

As a result, PO43- in the r liquid becomes a tertiary alkali phosphate (e.g. Na5PO4) or p
In the case of H8.3 to H9.3, it exists in the form of a secondary alkali phosphate salt (for example, Na2HPO4).

Although the filtration operation can be performed efficiently by adjusting the pH of the reaction system as described above, the purpose can also be sufficiently achieved by adding an appropriate amount of ordinary calcium carbonate and/or slaked lime.

In other words, the heavy metal hydroxides precipitated from the reaction system are purified in a short time.
In addition, the possibility of heavy metal hydroxides being mixed into the P liquid is greatly reduced.

The amount of such additives to be used is not particularly limited, but it is usually desirable to select the amount in the range of 1 to 30% by weight based on the solid content of the initial sludge.

If it is less than 1% by weight, sufficient effects cannot be obtained, and 3% by weight.
If it exceeds 0% by weight, PO43- of the alkali phosphate salt will be consumed unduly.

The heavy metal hydroxide taken in step 1 can be reused by washing with water and drying using the usual method.

For example, in the case of ferric hydroxide, it can be further fired to form iron oxide and reused as a pigment.

In addition, when the heavy metal hydroxides extracted are a mixed system, the solubility of various heavy metal hydroxides may vary greatly by lowering the pH, and by utilizing this solubility difference, it is possible to use dilute acids. It can be selectively dissolved and fractionated.

Dissolved heavy metal valves, such as zinc phosphate, may be used as is as a chemical conversion treatment agent, or they may be precipitated as zinc hydroxide by a conventional method, washed with water and dried by a conventional method, and used as zinc oxide. .

On the other hand, the r-liquid from which heavy metal hydroxides have been removed can be concentrated and dehydrated in a conventional manner to obtain an alkali phosphate salt, which can be reused as an agent for phosphate chemical conversion treatment.

★ ★ By employing the method of the present invention having the above-mentioned configuration, each component fraction of the phosphate-treated sludge can be extracted at a high rate in a reusable form, thereby contributing to resource conservation.

For example, 90% or more of heavy metals and 80% or more of phosphate ions can be extracted from the sludge.

Moreover, the method of the present invention does not require complicated equipment or difficult operations and can sufficiently achieve the desired purpose with a relatively small amount of heat, and also makes effective use of alkalis and acids used as processing agents. .

Note that Table 1 specifically compares the differences between the method of the present invention and the conventional method.

Next, the method of the present invention will be specifically explained with reference to Examples.

Note that examples include examples for comparison.

Example 1 The sludge used in this example was the following three types ([Yes] ~ ※※
0) and its composition (wt%) is shown in Table 2.

■ Zinc phosphate treated sludge for steel ■ Zinc phosphate treated sludge for galvanized steel sheets 0 Iron phosphate treated sludge 20 P of each of the above sludges (■ ~ 0) were collected and dispersed in 200 liters of water, and then the po contained in the sludge was dissolved. , 3 times the mole of sodium hydroxide for the number of moles of - (specifically, 6.97 in the case of [Yes], ■
9.6 in the case of 0, and 5.81 in the case of 0), and the mixture was reacted at 100° C. for 2 hours with thorough stirring.

After the reaction, the pH of the reaction system was adjusted as shown in Table 3, and then subjected to natural filtration using a piece of paper with a diameter of 24 crIL (A2).

Also, regarding sludge ■, 4 grams of calcium carbonate or 4' of slaked lime should be added to the reaction system after the reaction. After adding and thoroughly mixing, the mixture was subjected to gravity filtration in the same manner.

For each of the above systems, Table 3 shows the time required for one filtration and the analysis of the r-liquid and precipitate.

According to the results in Table 3, according to the method of the present invention, more than 80% of PO43- in the sludge can be recovered as sodium phosphate with few impurities. It is recognized that by adding an appropriate amount of slaked lime, the 1-over efficiency is improved, the 1-over time is saved, and heavy metals in the sludge can be recovered at a very high rate in the P-separated precipitate.

Claims (1)

[Claims] 1. Phosphate-treated sludge is heated in water to pH 1.
Steps 1 to 12 are reacted with an alkali to precipitate the entire heavy metal content of the sludge as its hydroxide, and the phosphoric acid content of the sludge is dissolved in water, and then this reaction system is
A method for regenerating phosphate-treated sludge, which comprises adjusting the temperature to H13 or higher or from 8.3 to 9.3, or adding calcium carbonate and/or slaked lime to the reaction system, and then filtering out the precipitate.