JPS59147611A - Preparation of filter medium for treatment of waste water containing fluorine - Google Patents

Abstract

PURPOSE:To prepare a filter medium capable of effectively removing F from waste water contg. F by molding a mixture of an insoluble Ca salt with a powdery magnetic body and treating the molded product with pressurized steam. CONSTITUTION:Powdery magnetic body of such as Fe3O4 or magnetite is mixed in 30-60% with powder of an insoluble Ca salt such as CaCO3, Ca(OH)2, CaSO4, CaF2, CaSiF6. A solidification accelerating agent such as water glass, and water, and the mixture is kneaded. The kneaded product is solidified in an autoclave by treating it with pressurized hot water. The product is prepared to 30-150 mesh grain size to obtain a filter medium 6, which is packed in a column 3. The water to be treated 1 having a pH adjusted to 8.0 is admixed with a CaCl2 soln. to obtain a mixture having Ca/F molar ratio of 5, and the mixture is fed from the bottom of the column 3. In this treatment, a magnet 4 is disposed to the top of the column to form a thin fixed layer of the filter medium 6 and to form a fluidized layer 6b below the fixed layer. F in the water to be treated is adsorbed by the filter medium 6 and removed, and the treated water is discharged through the filter 5.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a filter medium that is effective in removing fluorine contained in wastewater from factories such as the acid industry.

A conventional method for treating fluorine wastewater is to add calcium salts such as slaked lime or calcium chloride to produce calcium fluoride, which is then coagulated and precipitated. In this case, 20 to 50 PPI [l of fluorine remains in the treated water, and if the fluorine concentration in the wastewater is particularly low, not only will it take a long reaction time to produce calcium fluoride, but it will also cause the formation of fine crystals. This has the disadvantage that solid-liquid separation is difficult. Therefore, the fluorine emission regulation value (generally F1
In order to achieve the concentration below 5PPm, and in some areas 8PPI[l], post-treatment methods include adsorption using alumina, bone char, activated carbon, ion exchange resin, etc., or addition of chemicals such as soluble aluminum salts and magnesium salts. Considered. However, these post-treatment adsorption methods have a small adsorption capacity and problems with the regeneration method, and the chemical addition method has problems with the cost of chemicals and how to dispose of the generated sludge, making it impractical.

In order to solve the above problems, we have developed a method in which calcium fluoride crystal fine particles are used as seed crystals to disperse and contact with wastewater for precipitation, and a method in which fluoride fluoride fine particles are firmly supported on a solid material and brought into contact with wastewater is used. Filtration methods have been attempted to remove these. However, in all of these methods, the crystallization rate of calcium fluoride is slow and the contact between the water to be treated and the seed crystals is non-uniform, so that it is impossible to make the treatment apparatus J-shaped. Therefore, the filter medium must be replaced frequently, and this method has the disadvantage that it can only be used to treat wastewater containing low concentrations of fluorine.

In order to solve the above-mentioned problems, the present inventors have solved the above problem by forming a part of a layer of a filter medium from a powdery or granular magnetic material or a solid material containing a magnetic material on which an insoluble Cal/Rum salt removal membrane has been formed. is immobilized in a magnetic field and brought into contact with the water to be treated,
We proposed a method for removing fluorine from treated water (patent application filed in 1973).
7-92781)) The present invention has discovered an effective method for manufacturing such a filter medium, and aims to provide a filter medium that is inexpensive, easy to handle, and has excellent defluoridation ability, by adding a magnetic substance to an insoluble calcium salt. The present invention is characterized by a method for producing a filtrate for treating fluorine-containing wastewater, which comprises adding and mixing a solidification accelerator as necessary, and then molding and treating with pressurized steam.

The filtration 2 produced in this way is: (1) strong enough to be packed into a column, easy to handle, and inexpensive to remove fluorine;

(2) The crystallization rate of calcium fluoride is expressed by the following formula.

--= t< (C-C arrow)2...■L where: The crystallization rate constant (t/my·11[)K is proportional to the seed crystal surface area A and the seed crystal concentration Cd.

That is, Kcy: A, A ■ Cd, ', ■ Cdt:
Elapsed time (hr) C: 7- F concentration at 7 (mg/v) C: 7-
0047) When F temperature CmLi/l) As can be seen from the above equation 0, the crystallization rate is proportional to the seed crystal concentration and the seed crystal surface area. In other words, the larger the specific surface area of the seed crystal, that is, the smaller the particle size, the more advantageous it is, and the higher the seed crystal concentration, the more advantageous it is.

The present invention can increase the surface area specific to the seed crystal, and
Since the seed crystal concentration can be increased by 10 to 40 times compared to the conventional method, the device can be made smaller.

(3) Even if the fluorine concentration of the water to be treated is low, the crystallization rate can be increased.

(4) Even if the fluorine concentration of the water to be treated is amber, CaF2 microcrystals floating in the liquid are rarely generated.

(5) For the small amount of CaF 2 microcrystals produced, the upper part of the crystallization tank becomes a pinned layer due to the magnetic field and traps the CaF 2 microcrystals. Therefore, a stable fluorine concentration of the treated water can be obtained.

(6) CaF2 crystals (d) Unlike conventional precipitation methods, the amount of sludge generated is extremely small because it is a compact solid material.

(7) Stable treated water quality with extremely low fluorine concentration is obtained, and the p+4 of the treated water is weakly alkaline.
There is no need to readjust the pH when discharging.

A specific example of a method for manufacturing a filter medium by adding an appropriate amount of powdered magnetic material to an appropriate amount of powdered insoluble calcium salt will be described below.

Calcium carbonate (CaCO
3), slaked lime (Ca(ON)2), calcilla sulfate, t-(CaSO3) + calcium fluoride (CaF2)
, calcium fluorosilicate (CaSiF6), etc. can be used. Although suitable amounts of one or more of these can be used as a mixture, calcium fluoride is most suitable for removing fluorine from wastewater.

In addition to the above-mentioned types of industrial chemicals, as insoluble calcium salt compounds, coagulated sedimentation dried sludge or converter slag from coal-fired power plant flue gas desulfurization equipment wastewater treatment equipment contains large amounts of the above-mentioned various insoluble calcium salts. It is an extremely desirable material because it allows for the effective use of waste that was originally thought to have no choice but to be disposed of in the final stage.

α-1γ-2δ-Fe304+ as powdered magnetic material
Both Fe3O4+Feo OH and magnetite are used.
However, the amount is 10% or more, preferably 30 to 60%, based on the insoluble calcium salt.

From the perspective of removing fluoride, the older the insoluble calcium salt is, the better it is, or the less magnetic material it has, the less it will be attracted to it.

As a result of experiments, the magnetic material needs to have a force of 10 or more against insoluble lucium. However, if both the lever and the 8-IJJ plan were used, a result of 30 to 60% being H4 was obtained.

A mixture of an insoluble Cal/Rum salt and a magnetic substance (d) can be solidified by the method described below, but a solidification accelerator may be added as necessary to increase the strength of the solid.

As solidification accelerators, silicate substances such as hydraulic lath and clays such as bentonite are effective. d゛1～l
QwL%) may be added.

Combining the above mixture (a) (Tighten, add water, thoroughly knead and mold. The amount of water added is usually adjusted to about 10 to 3 QwL. Step 71 of molding is transferred and pressurized.

There are other methods such as extrusion, but any method may be used.

When the molded mixture is subjected to pressure hydrothermal treatment in an autoclave, the mixture solidifies.

The autoclave treatment conditions are usually in the presence of saturated steam at a pressure of 2 to 10 atm, and the duration of the heat treatment is about 1 to 5 hours. The higher the pressure, the shorter the processing time.

Assimilation of particles containing magnetic material occurs by pressurized heat treatment in an autoclave. Although the process is not clear,
It is presumed that with the formation of hydrates of calcium sulfate and fluoride, bonding of these particles occurs.

Next, the solidified material is adjusted to a particle size of 30 to 150 grains. The compressive strength of this solidified product is 10-20K! j
/Cηi has sufficient strength.

When the filter residue obtained in this manner is brought into contact with the water to be treated, the following reaction occurs on the surface of the particles.

(Produced crystals) Next, the CaF2 crystals act as seed crystals on the particle surfaces to promote the crystallization reaction of calcium/ium fluoride from the water to be treated, which is expressed by cause it to occur.

There is no initial reaction of the varnish (2) (3) applied to the surface of the filtration filter (when it is made of calcium fluoride), and the calcium fluoride on the surface immediately interacts with the seed crystal (7) to generate fluoride. A group of calcium chloride crystals is precipitated.Since the magnetic substance is in a passive state, it does not participate in the above reaction.

Since it is a solid substance containing a large amount of magnetic material, it responds to magnetism within the column as described in the Examples below. In other words, a magnetic force acts on the filter near the screen due to the magnetic field of the magnet and screen provided at the top of the column, and the magnetic force weakens as it moves away from the screen. As the filter medium moves downward away from the screen, the filter medium is fluidized by the water to be treated flowing upward from the downward direction.

Examples are described below.

Table 1 shows the composition of the coagulated and precipitated dried sludge from the wastewater treatment equipment of the flue gas desulfurization equipment of a coal-fired power plant.
(Fe203) 50 Wt% + diatomaceous earth 10w
[%] and mix well, further add about 2Qwt% of water and knead, make pellets with a diameter of 4 mm φ, 1 (5 cm) using an extrusion molding machine, and press in an autoclave at 10 atm and 2 qwt%.
It was subjected to pressure hydrothermal treatment for a period of time. The compressive strength of the obtained solid is 1
5K? /ctrl.

This is 50=1. The particle size was adjusted to OO mesonyu. child〕
”: Column 3 shows the solid material obtained in the drawing.
100% for the internal volume. Filter medium 6 so that F//-
Filled as. Add 9.2 to Cact 2 solution to treated water 1 containing fluorine adjusted to pH = 8.0 with Ca/F = 5 (
While adding molar ratio), water was passed from the bottom of column 3 to the top at 5v-61/1'+. The strength of the magnet 4 at the top of the column is 01~Q, 5KOe, and the filter 6 is placed at the top of the column 3.
A thin fixed layer 6a is formed, and a fluidized layer 6b is formed below it.
I tried to make it flow. In the figure, 5 indicates a screen and 7 indicates treated water.

Table 2 shows the results of the water passage treated in this manner.

As shown in Table 1 and Table 2, it can be said that the filter medium has an extremely excellent ability to remove fluorine.

[Brief explanation of drawings]

The figure shows an example of an experimental device used to confirm the effects of the present invention. 17

Claims (1)

[Claims] A method for producing a filter medium for treating fluorine-containing wastewater, which comprises adding a magnetic substance to an insoluble calcium salt, adding and mixing a solidification accelerator as necessary, and then molding the mixture and treating it with pressurized steam.