JPS6038085A - Treatment method for wastewater containing heavy metals - Google Patents

Abstract

PURPOSE:To efficiently remove a heavy metal by adding a trivalent chromium ion to waste water containing one or more of a heavy metal selected from a group comprising Zn, Ni, Cd, Pb, Fe and Mn to precipitate said heavy metal along with chromium. CONSTITUTION:A solution containing a trivalent chromium salt such as chromium (III) solfate, chromium (III) chloride or chromium potassium alum is added to waste water containing one or more of a heavy metal selected from a group comprising Zn, Ni, Cd, Pb, Fe and Mn to precipitate the heavy metal along with chromium. By this method, the sufficient removal of the heavy metal is enabled even in the vicinity of a neutral region and economical effect is extremely large. The coprecipitation effect of chromium developed by the aforementioned operation is considered in such a way that chromium and heavy metals are precipitated as composite hydroxide and the property of this composite hydroxide has property near to that of chromium.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for effectively removing heavy metals by adding trivalent chromium ions to heavy metal-containing wastewater to precipitate the heavy metals together with chromium. Provides a method that enables the treatment of heavy metal-containing wastewater, which was conventionally carried out only at pH 10 to pH II, by co-precipitation even in the near-neutral range, since most of the heavy metals do not produce poorly soluble hydroxides in neutral conditions. There is something to do.

The wastewater to be treated in the present invention is Zn and Ni.

This is wastewater in which one or more elements selected from the group consisting of Od, Pb, Fe, and Mn are dissolved.

Most of the salts of heavy metals do not produce soluble hydroxides in neutral conditions; therefore, the pH can be lowered to 10 to 11 by adding alkali.
Although the hydroxide is precipitated as a hydroxide, the pH cannot be discharged at the same pH, so the pH must be adjusted to neutral again. Therefore, the cost of drugs and equipment is significant. However, according to the present invention, heavy metals can be sufficiently removed even in the vicinity of neutrality, so the economic effect is extremely large. The shortcomings of the prior art and the effects of the present invention will become clearer by comparing the test examples and examples described below.

The mechanism of the co-precipitation effect of chromium in the present invention is not clear, but when compared with some other experimental results not specifically shown in Specification J#, it is likely that chromium and heavy metals form a composite hydroxide. It is presumed that the properties of the composite hydroxide are similar to those of chromium. .

Furthermore, the trivalent chromium ion of the present invention can be obtained by using a trivalent chromium salt solution such as chromium sulfate (1), chromium chloride (ill), or chromium chloride (ill); M)-containing wastewater, for example wastewater containing chromic acid or dichromic acid, may be reduced and used, or dehydrated sludge of chromium hydroxide after reduction treatment may be dissolved with acid and used. .

Test Example Single solutions of zinc nitrate, nickel sulfate, cadmium sulfate, chromium sulfate, and lead nitrate (as metals) (pH
Table 1 shows the solubility of 4 to 4.5) when the pH was adjusted with NaOH.

As shown in Iwa-J, at pH 7-8, Zn, Ni,
It is clear that Cd can hardly be processed.

In this example, NaOH was used to adjust p I-1, but Oa'(OH)2! Similar results were obtained using a bath solution.

Example 1 (including comparative examples; the same applies hereinafter) A mixed solution of zinc nitrate, nickel sulfate, cadmium sulfate, and lead nitrate each at 20 mf/l (as metals) (pH 4
) was adjusted to pH 7.5 with NaOH and subjected to precipitation.

The analysis results of the supernatant are shown in Table 2, AI. As shown in &1, Pb was almost detected due to the mutual coprecipitation effect of coexisting heavy metals, but Zn.

Nl and Cd remained briefly.

Next, add 100% of ferric chloride, which is commonly used as a coprecipitant.
1 rvt (as Fe) was added to the mixed solution to perform coprecipitation treatment. The results are shown in A2. Zn.

Although a coprecipitation effect is observed for Nl and Cd, Ni
, the effect on Cd was low.

Figure 3 shows the results when coprecipitation treatment was carried out by adding 100μ (as Or) of chromium sulfate instead of ferric chloride. The coprecipitation effect of chromium is significant, and Zn, Ni, Od
was also almost completely removed. However, in the table, A] and 2 are compared, and 3 corresponds to the example.

If the pH is further increased in A3, heavy metal ions will be further reduced, but as a practical matter, if heavy metals can be removed to the extent of Todoroki 3 in the table, no further treatment is necessary.

Example 2 Chromium sulfate was added stepwise to a single solution (pI-14 to 4.5) of zinc nitrate, cadmium sulfate, nickel sulfate, ferrous sulfate, and manganese sulfate (as metals) at 20 μm each. A detailed study of the effects of the addition of . The analysis results of the supernatant are shown in Table 3. All processing is pl■
7.5 = λ〉.

As shown in Tables 2 and 3, trivalent chromium has an outstanding coprecipitation effect. In normal coprecipitation treatment, it is common to add a coprecipitant in large excess to the target metal, but in the case of trivalent ROM, it is sufficient to use an amount approximately equivalent to or less than the target heavy metal.

Example 3 20 each of zinc nitrate, cadmium sulfate and nickel sulfate
W/l (as a metal) Add chromium sulfate to a single solution (pH 4-45) and then add NaOH to obtain p)(
was adjusted to 9 and coprecipitation treatment L7 was performed. The analysis results of the supernatant are shown in Table 4.

Table 4 From Table 4, it can be seen that when the pH is increased, the coprecipitation effect is excellent even if the amount of Or added is small.

Claims (1)

[Claims] 1, Zn, Ni, Cd, Pb, Fe and M
A method for treating wastewater containing heavy metals, which comprises adding trivalent chromium ions to wastewater containing one or more heavy metals selected from the group consisting of n to precipitate the heavy metals together with chromium.