JPS6038086A - Treatment of heavy metal-containing waste water - Google Patents

Abstract

PURPOSE:To efficiently remove a heavy metal from waste water in which a considerable amount of ammonia is present, by simple operation such that a trivalent chromium ion is added to waste water containing the heavy metal along with ammonia to precipitate the heavy metal along with chromium. CONSTITUTION:A trivalent chromium compound such as chromium sulfate, chromium chloride or chromium potassium alum is added to waste water having ammonia present therein and containing a heavy metal such as Ag, Au, Cd, Co, Cu, Ni, Ti, Pt or Zn to precipitate the heavy metal along with chromium. As the aforementioned trivalent chromium compound, a chromium compound obtained by reducing a hexavalent chromium salt with high toxity discharged from a chromium plating process or a chromate process may be availably utilized. The action of trivalent chromium is estimated in such a way that trivalent chromium and the heavy metal are converted to composite hydroxide and respective inherent properties thereof are lost.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the precipitation treatment of heavy metal-containing wastewater containing ammonia.

Wastewater from acid galvanizing, chemical plating, or chemical cleaning of boilers may contain large amounts of ammonia as well as heavy metals. To treat wastewater containing heavy metals,
Usually, a method is adopted in which alkali is added to wastewater and heavy metals are precipitated and separated as hydroxides. However, some heavy metals include those that form stable complexes with ammonia, e.g.
Ay + Au + Cd + Oo + Ou,
These heavy metals include Nt, Tt, Pt, Zn, etc., and when the amount of ammonia is large, it may be difficult to treat these heavy metals using a normal alkali neutralization method. As a treatment method for cases where a large amount of ammonia is contained, the ammonia may be removed by stripping, and then an alkali neutralization method may be applied. However, in this case, the ammonia concentration in the wastewater should be reduced to 100 to 200 ■/l (NH
However, it is necessary to reduce the IJ bing device to 3), but the IJ bing device has the disadvantage that maintenance is complicated and the running cost is higher than that of the alkali neutralization method. Further, as an alternative method to this treatment, there is a treatment method that exhibits a strong precipitation effect using an alkali neutralization method, such as a treatment using a sulfide method. However, the sulfide method has a hydrogen sulfide odor and a cloudy phenomenon in the treated water, and is not a very preferable method except in special cases such as the treatment of mercury-containing wastewater.

The purpose of the present invention is to solve the drawbacks of the conventional methods as described above, and even when heavy metal-containing wastewater contains a considerable amount of ammonia, heavy metals can be removed by adding trivalent chromium. This was based on the knowledge that FA can be removed from wastewater as a coprecipitate. That is, the main feature of the present invention is the treatment of heavy metal-containing wastewater, which is characterized by adding trivalent chromium ions to heavy metal-containing wastewater containing ammonia to precipitate the heavy metals together with chromium. This method has succeeded in making the treatment of heavy metal-containing wastewater much simpler than conventional methods, and in increasing the removal rate of heavy metals from wastewater more than expected. Hereinafter, the present invention will be explained with more specific examples.

The coprecipitant used in the present invention is a trivalent chromium salt, and chromium salts such as chromium sulfate, chromium chloride, and chromium potassium are suitable. As this chromium salt, highly toxic 6 is emitted from the chromium plating process and the Cronaut process.
A valent chromium salt may be reduced to a trivalent chromium salt and this may be effectively utilized. Alternatively, dehydrated chromium hydroxide sludge may be dissolved with acid and used.

Mechanism of action of trivalent chromium on ammonia complexes Heavy metals often form complexes with ammonia, similar to the dissolution change of trivalent chromium that does not form complexes with ammonia.
It is presumed that because trivalent chromium and heavy metals have become a composite hydroxide, their unique properties have been lost.

Next, the present invention will be explained using test examples and examples that do not use trivalent chromium.

Test example: pH 4 to 20 W/ containing any one of cadmium sulfate, nickel sulfate, copper sulfate, and zinc nitrate as a metal.
4. Add ammonia to the solution in step 5, Zoo.

200.400.1000 cape/l was added stepwise and adjusted to p) (10) with caustic soda.The generated hydroxide was filtered through F paper and heavy metals were measured.The results are shown in Table-1.

Table-1 Effect of ammonia Effect of ammonia consumption
It can be seen that when the content exceeds 00 mfl/, it is difficult to carry out the alkali neutralization treatment.

Example-1 (including comparative examples, the same applies hereinafter) 20 rounds using heavy metals such as sulfates or nitrates, and ammonia in N
To a solution of pi (5,0) containing 1,000 η/l as H, 20 m9/1 of chromium sulfate (as Or3+) was added, and the pH was adjusted to 10 with caustic soda.The heavy metal measurement results after filtration are shown in Table 2. show.

For comparison, ferric chloride or sulfuric acid, which is a commonly used coprecipitant, was added at 20 m/l (Fe'+ or AQ3+) as gold 4.4. Similar treatment was performed.

Table-2 Effects of Chromium From Table-2, treatment with iron salts and aluminum salts is difficult, but 3
It can be seen that Chromium Co., Ltd. is effective as a holding tool.

Example-2 Zinc nitrate 20 Wvt (as metal), ammonia y 1
．． o o ovpy/l (10 chromium sulfate as Or”+ in a pH 5.0 solution containing NH, (!:)
and 2° x β were added to examine the influence of pH.

For comparison, a solution containing only zinc sulfate (no ammonia added) as the metal at 20 my/ml was also investigated. The results are shown in Table-3.

Table 3 Influence of pH As shown in Table 3, the zinc in the treated water at pH 8 became less than 0.1 WA by simply adding 10 mW/trivalent chromium. The solubility of zinc in the case of pH 8 without the addition of ammonia is l 9.2 tnvt, and it has become clear that the properties of zinc ions change by adding a small amount of trivalent chromium.

In addition, in Example 2, the results of measuring chromium in the treated water when 20 to 30% of trivalent chromium was added were as follows, indicating that chromium was also sufficiently treated.

Claims (1)

[Claims] 1. A method for treating wastewater containing heavy metals, which is characterized by adding trivalent chromium ions to wastewater containing heavy metals, including ammonia, to precipitate the heavy metals together with chromium.