JPS582165B2 - Processing method for chromic acid waste liquid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is an aging waste solution discharged from a chromium plating factory containing hexavalent chromium and its aqueous solution, or a chromium-containing etching waste solution for plastic plating and its washing solution. Heavy metals such as iron and copper are contained in mixed waste liquid containing more than 20% of waste per liter.
The chromic acid-containing waste liquid, which contains more than 3.0 g of chromic acid and is of no use in leather tanning or other industries, can be easily and economically treated, and can be used as a chromic acid solution for leather tanning. The present invention relates to a method for treating chromic acid-containing waste liquid suitable for use.

As is well known, the current situation is that there are no chromium resources produced in Japan, and the entire amount is imported.

Therefore, in each industry that uses chromium raw materials, from an economic standpoint that favors the use of resources, wasteful abandonment is not only unacceptable;
Furthermore, it is a well-known fact that the abandonment of chromium-containing waste is unacceptable from a pollution control standpoint.

Therefore, for example, efforts are being made to effectively utilize aging waste liquid from chromium plating, waste liquid from chromium-containing etching of plastics, and their washing liquids.

However, these waste liquids always contain heavy metals such as iron and copper, and when the content of these heavy metals is less than log of 1 liter, it can be used as a leather tanning agent, for example. Its use is considered to be acceptable in practice.

However, in the actual situation of a plating factory or an etching factory, chromium-containing waste liquid is aged and used continuously until it becomes so-called aged waste liquid due to economical work management and handling of valuable chromium. In reality, the heavy metal content in waste liquid, which has no use as it is, is 2 in 1 liter.
At present, the content has reached 0g or more.

Therefore, even if these waste liquids were to be used, for example, for leather tanning, those in the industry are well aware that they cannot be used as they are because chromium ions and heavy metal ions form complex complexes. It is a fact.

Therefore, the actual situation is that these chromic acid waste liquids with a high content of heavy metals, which cannot be used at all, are appropriately diluted with water and reduced, and then discarded as chromium hydroxide sludge.

Recently, methods for using chromic acid-containing waste liquid for leather tanning have been devised, such as the chromic acid crystallization method by heating the waste liquid and the cation exchange resin flow method, but the former method However, there are problems in the processing, etc., and there are problems in implementing it industrially.

In addition, the latter method causes severe deterioration of the resin,
In addition, it requires steps such as resin activation with sulfuric acid, and the actual situation is that it cannot be easily implemented due to troublesome work management and rising operating costs.

In the present invention, the heavy metal content is 2 in 1 liter of aged waste liquid containing chromic acid generated from a chrome plating factory or a plastic plating etching factory, or a single liquid from each washing waste water, or a mixed waste liquid of any kind.
The present invention relates to a method for treating chromic acid waste liquid, which is related to a method for recovering a chromium sulfate liquid suitable for leather tanning using a simpler work process than containing 0 g or more of liquid.

Next, the gist of the present invention will be explained in detail.

As mentioned above, in the acidic waste liquid containing hexavalent chromium generated from a chrome plating factory or an etching factory for plastic plating, heavy metals such as iron and copper are particularly
Waste liquid containing 0g or more (this waste liquid may also contain washed water of any amount left over).

), first add soda ash or caustic soda solution as an alkali to the treatment solution at room temperature or in a slightly heated state, and adjust the pH of the solution to a range of 4 to 7.
Heavy metals such as iron and copper that accompany the liquid form gel-like precipitates as basic carbonates and hydroxides.
It can be easily filtered out from chromic acid-containing liquids.

Next, sulfuric acid is added to the hexavalent chromium-containing clear filtrate from which heavy metals have been separated, and the pH of the liquid is adjusted to a range of 0.5 to 1.0. Reduction is performed by introducing sulfur dioxide gas.

The chromium sulfate solution thus reduced and then pH-adjusted can be used for leather tanning.

In other words, in chrome tanning, it is trivalent chromium that exhibits the tanning effect, while hexavalent chromium is worthless, and when heavy metals such as iron and copper are present in the tanning solution,
It reacts with chromium to form complex complexes, making it impossible to perform a satisfactory tanning operation.

In the present invention, it is possible to industrially use waste liquids containing 20 g or more of heavy metals per liter of waste liquids, such as aging waste liquid from chrome plating or etching waste liquid from plastic plating, for which no effective treatment or use has been found in the past. It is possible to obtain a chromium sulfate-containing liquid suitable for chrome leather tanning by a simple method, and the invention is of great benefit to the leather tanning industry.

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

Example 1 The chrome plating waste aging liquid discharged from a chrome plating factory is strongly acidic, and the free acid content is 80% in terms of H2SO4.
g/l, and when the liquid was analyzed, it showed the following values.

Cr6+Fe T-SO4 Zn Cu Specific gravity g/l1
08 14 3.5 1.2 1.5 1.19 When 160 g of powdered soda ash was added to 1 liter of the above waste liquid at a liquid temperature of 25°C under stirring, a gel was formed at a pH of 4. A precipitate of 50% was formed.

Next, this precipitate-containing liquid was filtered to obtain a transparent chromium-containing liquid.

Next, in order to reduce the hexavalent chromium present in this chromium-containing liquid, SO2 gas was passed through the solution for about 40 minutes in a hot melt at 50 to 60 DEG C. for reduction.

Completion of the reduction reaction was confirmed by the iodine method. Next, excess SO2 gas was removed by heating for about 1 hour.

When the obtained reduced chromium solution was analyzed, the following results were obtained.

(Remarks) SO2 gas reduction method Also, in the same manner, 180 g of soda carbonate powder was added to 1 liter of waste aging liquid with the same composition as above, and the pH of the liquid was adjusted.
=6.5, the addition of alkali was stopped and the heavy metal precipitate formed was filtered as before.

Next, sulfuric acid with a concentration of 15% was added to the obtained transparent chromic acid solution to adjust the pH of the solution to 0.6 to 0.8.
5 g was added to reduce the chromium content, and the reduced solution was analyzed.

Its composition is as shown below.

The above-mentioned reduced solution can be adjusted to pH 2 to 3 and used for leather tanning.

Example 2 Etching waste liquid discharged from a plastic plating etching factory and showing the following analytical values was treated in the same manner as in Example 1 by the heavy metal removal and glucose reduction method.

That is, 195 g of soda carbonate powder was added to 1 liter of the above waste liquid, the pH of the liquid was adjusted to 6.5, and the resulting heavy metal precipitate was filtered off. To the transparent chromic acid solution, 15% sulfuric acid was added. After adjusting the pH of the liquid to 0.6 to 0.8,
Hexavalent chromium was reduced by adding 80 g of glucose.

This reduced chromium sulfate solution showed the following analytical values.

The above chromium sulfate solution can be adjusted to pH 2 to 3 and used for leather tanning.

Claims (1)

[Claims] 1 A single liquid or two or more types of chromium plating aging liquid discharged from a chrome plating factory and its aqueous solution, and chromium-containing etching waste liquid discharged from a plastic plating etching factory and its washing liquid. First, caustic soda or soda ash is added to the waste liquid containing 20 g or more of chromic acid-containing waste liquid components, especially heavy metals such as iron and copper, out of 1 liter of the waste liquid at room temperature or slightly added. It is added in a warm state, the pH of the solution is adjusted to a range of 4 to 7, the dissolved heavy metals are precipitated from the chromic acid-containing waste solution, and this is separated and removed from the transparent P solution. In order to reduce hexavalent chromium, a reduction treatment using a conventional reducing agent, that is, sulfur dioxide gas, or by first adding sulfuric acid, adjusting the pH of the solution to a range of 0.5 to 1.0, and then adding glucose. After performing the reduction treatment, adjust the pH to 2 to 3,
A chromium sulfate solution suitable for leather tanning that does not contain heavy metals harmful to leather tanning and hexavalent chromium is easily obtained from the waste liquid through a simple processing process. Middle, 20
A chromic acid waste solution, which is characterized in that a chromium sulfate solution suitable for leather surface tanning is obtained from a chromic acid-containing waste solution consisting of a chromium plating aging solution or a plastic plating etching waste solution containing more than Processing method.