JP2548096B2 - Method of treating wastewater containing cadmium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is applicable to iron, copper, mining wastewater and industrial wastewater.
The present invention relates to a rational and economical treatment method for wastewater containing lead, aluminum, and especially zinc and cadmium.

[Conventional technology and its problems]

Conventionally, various methods have been used as a means for treating wastewater containing cadmium, but among them, caustic soda, slaked lime, or sodium carbonate is added to the wastewater in a considerable amount, and heavy metals in the wastewater are precipitated and separated as hydroxides. The most common method was to

However, in this case, in order to keep the cadmium at 0.1 mg / l or less of the drainage standard, it was necessary to set the pH to 10.5 or higher, so the cost of the chemicals such as caustic soda, slaked lime or sodium carbonate becomes high, and the pH was set to 10.5. The treated water is treated as a drainage standard pH
Reverse neutralization was necessary in order to achieve 8.6 or less, and the construction of reverse neutralization equipment and the consumption of neutralizing agents such as sulfuric acid were unavoidable for that purpose.

Furthermore, according to this treatment method, aluminum etc. redissolved at pH 10.5 precipitates when it is reverse-neutralized to pH 8.6, and the treatment etc. is required, and the stable volume of the precipitated hydroxide is It was extremely large (40%), and various problems such as high dehydration cost were observed.

[Means for solving problems]

In view of such circumstances, the present inventors have earnestly conducted experimental research, and as a result, have analyzed heavy metal-dissolved wastewater containing cadmium,
First, by neutralizing with calcium carbonate, almost all of iron, copper, lead, and aluminum dissolved in the waste liquid and most of zinc are precipitated and removed from the liquid, and at the same time, the generated precipitate is It was clarified that the stable volume was only a fraction of the stable volume of the starch when a chemical such as caustic soda was used, and the dehydratability was extremely good.

However, since zinc and cadmium still remain in the neutralizing solution, caustic soda is added to the solution to adjust the pH to 8
By adjusting the pH to 8.6, the total amount of zinc and most of the cadmium was precipitated, and in order to remove a small amount of cadmium remaining in the solution, the precipitate produced by the pH adjustment was subjected to solid-liquid separation. In addition, a small amount of chelating resin or chelating agent is added to the supernatant water to promote this, and the treated water in which the pH of the wastewater and all dissolved heavy metals are kept below the wastewater standard is economical. It has succeeded in getting it.

In this case, since the amount of cadmium in the supernatant water separated by solid-liquid separation after pH adjustment is extremely small, the consumption of the chelating agent is extremely small.

In short, the treatment method of the present invention is to neutralize the wastewater containing cadmium with calcium carbonate to a pH of about 6,
Next, the neutralized solution is adjusted to pH 8 to 8.6 with caustic soda.

This is a method for treating wastewater containing cadmium, characterized in that after solid-liquid separation of the precipitate generated by this, cadmium slightly remaining in the supernatant water is promoted by a chelating agent or the like.

[Action]

According to the above treatment method, iron, copper,
By compounding acids such as lead and aluminum, replace most of the consumed alkaline amount with inexpensive calcium carbonate,
By using an alkaline agent such as caustic soda for the removal of zinc and cadmium precipitates, it is possible to achieve a remarkable effect mainly in reducing the drug price and the stable volume of the formed precipitate.

〔Example〕

Hereinafter, the method of the present invention will be described more specifically according to one embodiment.The test apparatus used was a normal aeration type neutralization apparatus consisting of a neutralization tank having a capacity of 16 l, and the stock solution for treatment was iron 20 mg / l. , Copper 250mg / l, aluminum 230mg / l, zinc 350m
An artificial wastewater of pH 3.5 containing g / l and 10 mg / l of cadmium was used.

This treatment stock solution 10l was charged into the aeration-type neutralization tank, and firstly, calcium carbonate powder 2460mg / l was added and aerated and stirred at an air amount of 12.6l / min for 60 minutes to pH 6.3 (neutralization step), Most of the iron, copper, aluminum and zinc dissolved in the stock solution are precipitated.

Then, the above precipitate is left as it is in a caustic soda 40
The pH was adjusted to 8.44 by adding 0 mg / l and stirring for 10 minutes (pH adjusting step). In this case, not only iron, copper, and aluminum but also a large amount of zinc, which remained in a relatively large amount in the neutralization step, and most of cadmium were precipitated. Here, the solid-liquid in the neutralization tank is separated, and the precipitate is taken out, dehydrated and discarded. In this case, the stable volume of the precipitate (24
(After time) is 8%, which is one fifth of the stable volume of the final precipitate obtained by the conventional general treatment method described above, which is 40%, which is expected to greatly improve the dehydration property. is there.

On the other hand, in the supernatant water obtained by the solid-liquid separation, a chelating agent (for example, trade name "Aron chelate S-1") is added.
(Toagosei Kagaku Kogyo Co., Ltd.) was added at 5 mg / l and stirred for 5 minutes (chelation process), and this was rapidly filtered through a sand filtration tank (filtration process).
mg / l, copper 0.01 mg / l, aluminum 0.3 mg / l, zinc 0.11 mg / l
l, cadmium was 0.006 mg / l, and in particular, treated water was obtained that was well below the cadmium drainage standard of 0.1 mg / l (see Table-1).

Table-1 The test results in the above examples are shown in Table 1 above in comparison with the test results by the conventional method performed using the same artificial undiluted solution.

〔The invention's effect〕

As described above, according to the method of the present invention, the stable volume of the neutralized precipitate is extremely small, which is a fraction of that of the conventional method, and as a result, a precipitate having good dehydration property can be obtained. Can be significantly reduced.

Furthermore, most of the neutralization is done by low pH neutralization with inexpensive calcium carbonate, and reverse neutralization is not required. The rationality and economic effects are extremely remarkable, for example, the treatment of the produced aluminum precipitate is not required and the overall treatment cost of the precipitate and the cost of the neutralizing agent can be remarkably reduced.

Claims (1)

(57) [Claims] 1. Aeration of wastewater containing cadmium,
A neutralization step of adjusting the pH to about 6 with calcium carbonate, a solid-liquid separation step of precipitating hydroxide produced through a pH adjusting step of adjusting the neutralized water to pH 8 to 8.6 with caustic soda, and the step obtained A method for treating wastewater containing cadmium, comprising a chelation treatment step of adsorbing supernatant water to a chelating agent and a filtration step of filtering the liquid.