JPS6133291A - Treatment of waste water containing heavy metal - Google Patents

Abstract

PURPOSE:To precipitate and treat heavy metals selectively by adding water-soluble phosphoric acid compds. and water-soluble calcium comps. to the waste water contg. heavy metals and organic acids. CONSTITUTION:Water-soluble calcium compds. such as calcium chloride plus slaked lime and water-soluble phosphoric acid compds. such as phosphoric acid plus sodium phosphate are added to the waste water contg. heavy metals such as iron, copper, cadmium plus nickel and organic acids and the mixture is suitably stirred in the state of 7-12pH and allowed to react with each other to generate the precipitate. The generated precipitate is separated by the settling separation, the filter separation and the centrifugal separation means and removed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating heavy metal-containing wastewater coexisting with organic acids.

The most common method for treating wastewater containing heavy metals such as iron, copper, cadmium, and nickel is an alkali precipitation method in which an alkali is added to the wastewater and heavy gold g is precipitated and separated as hydroxide. However, when organic acids, especially oxycarginic acid (citric acid, tartaric acid, gluconic acid, etc.) coexist in the wastewater, it is difficult to treat the wastewater using the alkaline precipitation method. For example, citric acid is said to form complexes such as tartaric acid, and since these complexes are stable, they cannot be precipitated and separated by the above method and remain in the liquid. It has been revealed that the iron ions remain as complexes because the organic acids also form stable complexes with iron ions, and that the iron complex acts as a dispersant and interferes with the precipitation of other heavy metals. The sulfide method, which is considered to be the most effective method for treating heavy metal wastewater, is difficult to apply because the iron salt added to completely precipitate the excess thorium sulfide acts as a dispersant as described above. there were.

The object of the present invention is to be able to sufficiently precipitate heavy metals in organic rn'fr and coexisting heavy metal-containing wastewater regardless of the presence or absence of iron ions. An object of the present invention is to provide a method for treating heavy metal-containing wastewater that can be applied to any of the physical methods.

The present invention involves adding a water-soluble phosphoric acid compound and a water-soluble calcium compound to wastewater containing heavy metals and organic acids, or adding a product immediately after the reaction between a water-soluble phosphoric acid compound and a water-soluble calcium compound, This is a method for treating wastewater containing heavy metals, which is characterized by adjusting the pH to 7 to 12 and performing a precipitation treatment.

Water-soluble calcium compounds and water-soluble phosphate compounds form a precipitate typified by tight OaH(PO4)30H at hydroxyl level, but if heavy metals are present in wastewater, OaH(PO4)30H is formed.
a x My (PO4) Z L (2z42y-82
) is presumed to form and precipitate.

In the formula, M is a heavy metal such as iron, copper, cadmium, nickel, etc., L is an anion such as OH""+ CI"" + 804"-, I H7+ 'L is an ion of M and L It shows an integer determined by the valence. Organic acids co-existing in the wastewater hardly contribute to the composition of the precipitate, and are only partially adsorbed or included.

Water-soluble calcium compounds used in the present invention include calcium chloride, slaked lime, calcium carbonate, etc.
Examples of water-soluble phosphoric acid compounds include phosphoric acid and various juvenile phosphates such as sodium and potassium. Wastewater containing phosphoric acid or phosphates, such as alkaline degreasing solution or plating bath wastewater containing phosphorus salt as a main ingredient, may also be used. The amount of these used is determined depending on the type of heavy metal in the wastewater, etc., but usually the ratio of calcium compounds to phosphate compounds is Oa/
The PO4 (molar ratio) is used at 1 or more, and the ratio of M/PO4 (mole ratio) between the genus Silkworm and the phosphoric acid compound is 3 or less.

The phosphoric acid compound and the calcium compound may be added to the wastewater in advance, but a hydroxyl compound prepared by reacting the phosphoric acid compound and the calcium compound may also be added. However, since hydroxyl annotite, which has been reacted in advance, loses its activity over time, it should be used within one hour after the reaction. In this case, after the phosphoric acid compound and the calcium compound are reacted in a reaction tank, suspension water containing the reaction product can be used.

After adding the phosphoric acid compound and the calcium compound to the wastewater, the pH is adjusted to pt+ 7 to 12, preferably pH 7.5 to 9, and the reaction is carried out with appropriate stirring, and the resulting precipitate is subjected to well-known sedimentation separation and filtration. Separate and remove by means of separation and centrifugation. In the precipitation treatment, the heavy metal FA can be simply made pnt' neutral or alkaline and precipitated as a hydroxide, but conventionally known iron salt coprecipitation methods and sulfide methods can also be used.

According to the present invention, by using a water-soluble phosphoric acid compound and a water-soluble calcium compound in combination, heavy metals and organic acids form an anchor structure.
heavy metals are selectively formed as precipitates. Therefore, it is possible to apply the alkaline precipitation method (pH neutral to alkaline), iron salt coprecipitation method, and sulfide method to heavy metal-containing wastewater in which organic W1t'' coexists, and heavy metals can be efficiently removed.

A reference example according to a conventional method and an embodiment according to the present invention are shown.

Reference example 1 (alkali precipitation method, iron salt co-precipitation method) Or”+ +
Organic acids (oxalic acid, tartaric acid, gluconic acid) t-iooop were added to a solution containing 04", Nk", Zn", Qu", pb"+ at 20F each. Then, ferrous sulfate or chloride was added as an iron salt. Hydroxylation with addition of ferric iron)
The fc0 reaction solution was adjusted to pH 7.5 or pflll with 17 cum and reacted for 30 minutes, and the fc0 reaction solution was filtered using filter paper Gan 50, and the filtrate was analyzed, and the results are shown in Table 1.

In either case, all the heavy metals were not sufficiently removed, and no co-precipitation effect was observed even when iron salts were added.In fact, the co-precipitation effect was worsened by the coexistence of iron salts, and the iron salts were considered to be complexes. I stayed behind and became a friend.

Example 1 A sample solution containing 1000 F citric acid and 100 Wn (as iron) of ferric chloride was added with calcium chloride, sodium phosphorus, or chloride, and then plipped with sodium hydroxide.
1 for is! ! Set it up and let it react for 30 minutes. The reaction solution was filtered using filter paper M50, the filtrate was analyzed, and the results are shown in Table 3.
Shown in the ratio.

As shown in Table 3, iron ions could be treated when calcium compounds and phosphate compounds coexisted. t7'
j It can be seen that the decrease in OOD is small and citric acid hardly precipitates.

Table-3 Example 2 06" + N1" r Zn", Ou" t P
b” + Fe”+ each for 20 Ps Quen W!
Calcium chloride and sodium phosphate'f in a solution containing 1000F! : was added and the pH was adjusted to 8K with sodium hydroxide. The reaction solution was incubated for 30 minutes, filtered using T-filter paper A50, and the filtrate was analyzed, and the results are shown in Table 4.

As shown in No. 4, treatment was difficult when calcium compounds and phosphate compounds did not coexist (&1), but heavy metals could be treated when they coexisted (A2 to A5). In particular, Ni and Ou could be treated satisfactorily when made alkaline as shown in A4 and Boil 5.

(The following is a blank space) Table 4 Example 3 A sample solution in which a calcium compound and a phosphoric acid compound coexisted was treated with sulfide by the second son method described in Reference Example 2. The heavy metal concentration and organic acid concentration were also the same as in Reference Example 2. The results are shown in Table 5.

As shown in Table 5, it has become clear that the sulfide method can be applied as long as a calcium compound and a phosphorus m compound coexist.

Example 4 Ri x 7 '7500 PS11g ferric chloride 100p
A solution containing 20F each of p (as Fe''), Zn''+ and Cd'' was hydroxylated and adjusted to pH 8 with +7 um, and this was used as the liquid to be treated.

In a separate container, 1011/It of flattened calcium (as Oa) and 41/L of sodium phosphate (as P) were mixed and reacted for 2 hours at 9 to 1 o pm to prepare calcium phosphate. Calcium phosphate f is added to the above-mentioned liquid to be treated.
s o o yp (as Oa, as P is 20 o
Furnace) and react for 30 minutes at pH 8.9.

The reaction solution was filtered using T-filter paper &50, and the filtrate was analyzed, and the results are shown in Table 6.

As shown in Table 6, it is clear that the reactivity of aged calcium phosphate is poor.

Table-゛6

Claims (1)

[Claims] 1. Add a water-soluble phosphoric acid compound and a water-soluble calcium compound to wastewater containing heavy metals and organic acids, or add a product immediately after the reaction between a water-soluble phosphoric acid compound and a water-soluble calcium compound, and adjust the pH to 7. 1. A method for treating heavy metal-containing wastewater, which comprises adjusting the concentration to 12 to 12 and subjecting it to precipitation.