JPS5813496B2 - Granulation method of calcium fluoride precipitate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for granulating calcium fluoride precipitate recovered, for example, in the abatement treatment of various waste liquids or waste gases containing fluorine.

Various abatement measures have been taken to prevent environmental pollution from fluorine ions or hydrogen fluoride in waste liquids or gases generated in smelting, chemical manufacturing, and other processes.

Among these, a treatment method in which fluorine is precipitated and separated as calcium fluoride has an excellent removal effect and is also economically advantageous, and is therefore widely used in practice.

When this method is adopted as a means for removing fluorine, the problem is how to secondaryly process the recovered calcium fluoride, but currently it is disposed of as industrial waste in most cases.

Among these, precipitates having good quality as calcium fluoride, such as those obtained in the treatment of waste liquid from the process of converting uranium hexafluoride to ammonium diuranate, waste liquid from semiconductor etching, etc., are no exception.

The inventors have conducted research on a method to reuse these high-quality calcium fluoride precipitates as a fluorine source, and found that by adding an appropriate binder and granulating them, strength can be increased. It has been found that pellets with high pulverization tendency are obtained and are useful as materials for metallurgical correction, for example.

Taking the pig iron converter treatment process as an example, this process requires limestone, lime, etc. as a solvent, as well as fluorite, but these materials are mixed into granules depending on the working conditions to prevent them from scattering during blowing. Particles are required to have a diameter of several mm to about 10-odd mm.

Therefore, when using calcium fluoride precipitate as a substitute for fluorite, it is necessary to make pellets of the same size, but if calcium fluoride precipitate is shaped and dried as it is, it is difficult to handle and use it. It easily turns into powder during the process, making it difficult to put it to practical use.

Various binders have already been proposed for granulating inorganic powder and granules, and those used in the same metallurgical field include lime, polysaccharides and other natural polymer materials, and combinations of lime and polysaccharides. Matching (JP-A-50-123082)
etc. can be given.

Although these materials are effective to some extent as binders for calcium fluoride precipitates, the pellets obtained by adding these materials, shaping, and further drying are insufficient in terms of strength and pulverization rate. It cannot be said that it is a good thing, and when it is actually used, it is not possible to obtain a constant effect.

The binder used in the method of the present invention is lime and an anionic polymer electrolyte, and by adding these two components to precipitated calcium fufluoride or its dried product, shaping it, and drying it, strength and powder can be improved. Pellets suitable for practical use can be obtained in terms of conversion rate.

The amounts of lime and anionic polymer electrolyte to be added vary depending on the precipitate formation conditions and the shaping method, but lime has an anionic content of 1 to 5 weight coefficient as Ca(OH)2 on a dry precipitation basis. Molecular electrolytes range from 0.1 to 0.5 weight factor.

In any case, if the amount added is less than this range, the effect will not be sufficient, and if the amount exceeds this range, the strength of the resulting pellets will actually decrease.

Various types of anionic polymer electrolytes can be effectively used, including polyacrylic acid or its alkali salts,
Partially amidated polyacrylic acids or their alkali salts, sodium alginate, gum arabic, etc. are particularly suitable and equally effective.

In use, such an anionic polymer electrolyte is dissolved in an appropriate amount of water and added.

Lime is used in powder or slurry form.

To granulate a calcium fufluoride precipitate according to the method of the present invention, a binder is usually added to the pre-dried precipitate and mixed well, and then molded into a predetermined size using, for example, a screw extrusion type granulator. and then dry it.

A suitable drying temperature is, for example, about 100 to 300°C; if the temperature is higher than this, the strength of the pellets may decrease.

The drying time varies depending on the drying temperature, material, equipment, etc., and can be appropriately selected by those skilled in the art depending on each condition.

If the precipitate has a high moisture content and is difficult to shape, a preliminary drying step is added.

The particle size to be granulated is usually from several tenths of a millimeter to several tens of millimeters.
If pellets with a relatively small particle size are required, preferably several mm to several tens of mm, granulation and drying may be carried out simultaneously by applying a flash drying method.

The advantages of the granulation method according to the present invention include that the binder used is easily available and that it does not contain harmful components as a solvent. It is not clear whether unexpectedly good synergistic effects can be obtained.

One reason for this is probably that lime increases the positive charge of calcium fluoride, which increases the binding effect of anionic polyelectrolytes.

The effects of the present invention will be specifically explained below using Examples.

However, the present invention is not limited to these illustrative examples.

Example 1 In this example, calcium fluoride precipitate (analytical value: Cap2
51wt%, At203 0.48wt%, Si02
0.37 wt%, remainder H20) was used.

Powdered lime and an aqueous solution of Acofloc Al10 (trade name, acrylamide/acrylic acid polymer), which is commercially available as a polymer electrolyte, are added to this precipitate and thoroughly mixed. A raw pellet with a diameter of 8 mm was made using a sieving machine, and then 200 mm in diameter was made in an electric dryer.
The pellets were dried at ℃ for 3 hours to obtain dry pellets.

Four types of pellets (Samples A, B, C, and D) were prepared by changing the amounts of lime and Acofloc A110 added, and the results of measuring the crushing strength and pulverization rate are shown in Table 1.

For comparison, the same table also lists the test results of dried pellets (comparative samples 1 and 2.3) prepared in the same manner using lime, Acofloc A110 alone, or lime and sucrose as the binder.

As is clear from this result, the pellets produced by the method of the present invention have a crushing strength of 11 to 15 k? / pellet, powdering rate 3.
While it shows a very good value of 2 to 2.3 chi,
The comparative sample had lower crushing strength and powdering rate, and was particularly inferior in powdering rate.

Example 2 In this example, small beresoto was prepared by flash drying using the same precipitate as in Example 1. That is, 2 wt of lime on a dry matter basis was added to 200 kg of calcium fluoride precipitate.
%, 0.4 wt % of sodium alginate, and 80 t of water were added to form a slurry, and dried pellets having a size of 0.5 to 2 mm were prepared using a spray dryer.

In order to measure the powderization rate of these pellets, 10 of them were
01 to 200c. As a result of shaking the sample in a glass bottle c for 30 minutes with a paint shaker, the pulverization rate (-0.4 m
The ratio of m) was 3.5.

In contrast, the pulverization rate of dry pellets obtained by adding the same amount of lime or sodium alginate alone was 75.
Section 8.1.

Claims (1)

[Claims] 1. When granulating the calcium fluoride precipitate, as a binder, lime is used in combination with Ca(OH)2 in a weight ratio of 1 to 5 and an anionic polymer electrolyte in a ratio of 0.1 to 0.5,
A method for granulating calcium fluoride precipitate, characterized in that the calcium fluoride precipitate is added.