JPS598438B2 - Futsuso Oyobi Rinsan Iongan Yuhaisui no Renzokushiyorihohou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for continuously removing fluorine and phosphate ions from wastewater containing these ions.

Factories that produce wet phosphoric acid by decomposing phosphate rock with mineral acids, and factories that use wet phosphoric acid as a raw material to produce compound fertilizers and phosphate compounds such as sodium tripolyphosphate, produce wastewater that contains both phosphate ions and fluoride ions. Excreted in large quantities.

In recent years, environmental pollution caused by factory waste has become a problem, and the removal of fluorine and phosphate ions from the wastewater has become an important issue.

It is well known that the emission of phosphate ions has been criticized as one of the eutrophication substances, and regarding fluorine, the ``Prime Minister's Office Ordinance Setting Emission Standards'' promulgated in June 1971. Accordingly, it is set at 15 pplI1 or less, and as a special exception, it is set at 50 pplI1 or less in the phosphate fertilizer manufacturing industry.

As a means of removing these ions, a method is known in which wastewater is treated with a reactive calcium compound to generate an insoluble calcium compound and this is separated, but the present inventors have investigated various wastewater. As a result, it was found that when the wastewater contained ammonium and/or alkali metal ions, the removal of fluorine and phosphate ions, particularly fluorine ions, from the wastewater was not achieved sufficiently.

For example, P content is about 440 and F content is about 500
1) Prepare water containing p[n as well as ammonium ions and alkali metal ions (typically sodium) in various proportions as sulfates, and adjust the water to pH 7.0 with 10% slaked lime slurry. Table 1 shows the concentrations of P and F in the furnace solution after neutralization when neutralized to 5.

Although this is just one example, it is clear that the removal of P and F is hindered by the presence of ammonium and alkali metal ions.

In industries that use wet phosphoric acid, wastewater that does not contain ammonium or alkali metal ions is rarely discharged, and for this reason, the inventors had difficulty treating such wastewater, but after various studies, they found that: pH of wastewater is approximately 4
ammonium by treating with a reactive calcium compound to 5 to 5 to form a precipitated solid, then treating the precipitated solid with lime to bring the pH above about 7 and separating the precipitate. and/or regardless of the presence of alkali metal ions, fluorine and phosphate ions (p) in the treated wastewater should be reduced to 20-30 ppl 1 liter and 1 liter, respectively.
It was possible to reduce the amount to 0 to 20 ppII.

In the present invention, the neutralization reaction is carried out in at least two stages as described above, and in the first stage neutralization up to a pH of approximately 4 to 5, fluorine and phosphate ions are reacted in acidic wastewater containing fluorine and phosphate ions. Reactive calcium compounds that react to form insoluble precipitates are used, such as quicklime, slaked lime, calcium carbonate, calcium phosphate, and the like.

The lime used in the second stage neutralization is quicklime or slaked lime.

Therefore, quicklime or slaked lime may be used in both the first and second stage neutralization, but in the present invention, the first stage reaction is completed at a pH of about 4-5, and the It is absolutely necessary to carry out the second stage neutralization reaction while the precipitated solid remains present without being separated.

If the precipitated solid produced in the first stage reaction is separated in the furnace at that stage and the p liquid is neutralized in the second stage, it is not possible to reduce the concentration of phosphate ions (p) to below 40 to soppm. .

This method uses insect lime or slaked lime to adjust the pH in one step.
This is in contrast to the inability to reduce the concentration of fluoride ions below 50-100 ppIl1 when neutralizing to about 7.5.

The method of the present invention, in which the neutralization reaction of acidic wastewater is carried out in at least two stages, consists of connecting two or more reaction tanks in series, each equipped with a stirrer, and changing the neutralization stage in each tank. This is conveniently carried out by a method that involves a step of once completing the neutralization reaction.

Neutralization to pH 4 to 5 is carried out in one step or in two or more steps, and after neutralization until the final pH reaches about 7, 1 of the precipitate slurry thickened with a thickener etc.
This may be done by cyclically using parts.

Examples of the present invention are shown below.

Example I P0.09% (all concentrations below are based on weight), FO, 0
Acidic wastewater containing 5% Na20, 0.05% Na20, and 30.02% NH was introduced at a rate of 3.25 liters into two neutralization tanks equipped with a stirring device in series, with pH 40 in the first tank and pH 40 in the second tank.
pH 7. A 10% slaked lime slurry was added to each tank so that the amount was 2.

The P concentration of the treated effluent (P solution) is 16 p^, the F concentration is 25 p
It was pm.

For reference, the precipitate was collected at the outlet of the first tank, and the pH of the furnace liquid was 7. If neutralized to 5, p65ppm, F
23 pF, and if slaked lime slurry was added only to the first tank and neutralized to pH 7.5 in one stage, P 1
6pIn, F8 0pl)In.

Example 2 In Example 1, the slurry at the outlet of the second tank was led to a thickener to recover a thickened sediment slurry with a slurry concentration of 18%, and in subsequent operations, part of the thickened slurry was circulated to the first tank. and used for neutralization.

(The remainder of the thickened slurry was sent to a filter.

) The P concentration of treated wastewater is 19 ppm, the F concentration is 28 ppm.
It was pm.

Example 3 In Example 1, 10% calcium carbonate slurry was used instead of slaked lime slurry IJ in the first tank, and the pH was adjusted to 4.2.
I processed it so that

The P concentration of the treated wastewater is 18p; the F concentration is 26I1f) [
It was 11.

Example 4 P0.1%, F0.055%, Na200.04% and NH30. Acidic wastewater containing 0.15% is introduced at a rate of 3.25 liters into three neutralization tanks equipped with a stirring device in series, pH 3.6 in the first tank, pH 4.5 in the second tank, pH 4.5 in the third tank, and pH 4.5 in the second tank.
Pi-i in the tank 7. A 10% slaked lime slurry was added to each tank so that the amount was 5%.

The P concentration of the treated wastewater (P liquid) is 12 pInn, and the F concentration is 2.
It was 2ppII1.

Claims (1)

[Claims] 1. When continuously treating acidic wastewater containing fluorine and phosphate ions together with ammonium and/or alkali metal ions, the wastewater is brought to a pH of about 4 to 5 by a method selected from the group consisting of quicklime, slaked lime, calcium carbonate, and calcium phosphate. a reactive calcium compound to form a precipitated solid, and then treated with lime while the precipitated solid is present to bring the pH to about 7 or higher and to separate the precipitate. Continuous treatment method for wastewater containing phosphate ions.