JPH0315517B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating various highly concentrated fluoric acid-containing liquids generated in the hydrofluoric acid production process or the surface treatment process of various instruments (for example, glass) using hydrofluoric acid. It is something.

Fluoric acid-containing waste liquids such as hydrofluoric acid generally have a high concentration, and it is difficult to neutralize them by mechanical stirring if the concentration is as it is, so it is usually diluted with wastewater from other processes or industrial water, etc. Neutralization is performed by adding a calcium-based neutralizing agent in the form of a slurry, followed by solid-liquid separation by precipitation, filtration, etc. However, the precipitation of CaF ₂ etc. that is neutralized by the calcium-based neutralizing agent is They are fine particles that are difficult to detect, and they often coexist in the waste liquid mentioned above.
Regarding the neutralization of H ₂ SO ₄ , the moisture in the dehydrated cake is also
In order to keep it below 20%, it is necessary to repeat seed crystals, extend the reaction time, and in some cases heat it.

For example, the neutralization products of hydrofluoric acid-containing liquids are mainly
It is a mixed precipitate of CaF ₂ and CaSO ₄ 2H ₂ O.
Since it is difficult to dehydrate, the actual situation is that it is passed through a pre-coat filter or an Oliver filter, and in some cases is subjected to a heating drying process to be recovered as a mixed precipitate such as CaF ₂ , CaSO ₄ .2H ₂ O, etc.

In this way, when treating a liquid containing a highly concentrated fluoric acid, conventional methods require filtration and drying steps as described above, as well as final treatment of the liquid, making the process complicated and costly. There was a drawback.

In the present invention, calcium carbonate and water are added to a liquid containing a high concentration of fluorine-based acids such as hydrofluoric acid, hydrosilicofluoric acid, borofluoric acid, zirconium hydrofluoric acid, and titanium hydrofluoric acid. This method is characterized by adding a calcium-based neutralizing agent such as calcium oxide or calcium oxide to directly solidify the liquid.

According to the method of the present invention, without diluting the waste liquid,
In addition, it is only necessary to knead the waste liquid in a cement mixer type kneader without going through processes such as filtration, dehydration, and drying, and the waste liquid can be directly recovered in a solid state without performing solid-liquid separation. .

In this case, the calcium-based neutralizer to be used is preferably added as a solid substance such as a powder, and the amount added is at least a chemical equivalent, preferably 1.1 to 1.5 equivalents, and the pH of the produced precipitate is preferably 3 or more. It is better to set it to 5 or more.

Further, as the processing method, a batch method and a continuous method can be considered, but either method may be adopted in the method of the present invention.

Example 1 Waste liquid of HF 19.7%, H ₂ SO ₄ 16.3%, H ₂ SiF ₆ 8.1%
1.26 kg and 1.1 kg (1.05 equivalent) of calcium carbonate were mixed and kneaded. When the produced precipitate was measured, the pH was
It was 1.5. Furthermore, 100 g of calcium carbonate was additionally kneaded.

The pH of the produced precipitate is 5.5 and the moisture content is 36%. After 1 day of natural drying, the moisture content is 30.5%, and after 2 days it is 27.5%.
Three days later, it was 24.5%.

The amount of calcium carbonate used in this case is 1.15 chemical equivalents, and the composition of the precipitate is CaF ₂ 55.3%,
CaSO ₄ .2H ₂ O2 was 9.6% and SiO ₂ 3.5%.

Example 2 25 kg of waste liquid same as Example 1 and 24 kg of calcium carbonate
Kg was kneaded for 60 minutes in a cement mixer type kneader.

The resulting precipitate had a pH of 6.0 and a moisture content of 31%, and the moisture content after one day of natural drying was 26.5%.

In addition, after measuring the temperature inside the kneader during the reaction,
Significant water evaporation was observed between 50 and 70°C. It is thought that the evaporation of water due to this reaction heat (neutralization heat) also contributes to the decrease in precipitate water content.

Example 3 15% HF, 9% H ₂ SO ₄ , 20% H ₂ SiF ₆ , and several % slurry of aluminum fluoride, barium fluoride, etc.
The waste liquid and calcium carbonate contained therein were continuously supplied to a kneader and kneaded. When the amount of waste liquid treated reached 4 tons and the amount of calcium carbonate fed reached 5 tons (supply time 2 hours), the supply of waste liquid and calcium carbonate was stopped, and kneading was continued for 30 minutes.

Note that the amount of calcium carbonate used in this case is 1.4 chemical equivalents.

As a result, the pH of the resulting precipitate was 6.5, and the water content was
After air drying for one day, the moisture content was 22.5%, and all were in a state where they could be immediately transported by truck.

As described above, according to the method of the present invention, fluoric acid-containing waste liquid can be directly recovered as a solid substance with extremely low water content through a neutralization reaction, so it can be immediately transported by truck, etc. It is extremely advantageous economically, as it eliminates the need for complex processes such as dilution, filtration, heat drying, and final treatment of the liquid.

Claims (1)

[Claims] 1. A method for treating a liquid containing a fluoric acid, which comprises directly solidifying the liquid by adding a calcium-based neutralizing agent to the liquid containing a highly concentrated fluoric acid.