JPS5842127B2 - Method for recovering hydrofluoric acid from fluorine-containing mud - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering fluorine in fluorine-containing mud as hydrofluorosilicic acid, which is produced when waste acid produced when producing sulfuric acid from copper smelting exhaust gas is defluorinated.

The term "fluorine-containing mud" here refers to muddy waste whose main component is calcium gold gypsum fluoride, which has no utility and is currently piled up in the open.

As a result of investigating the recovery of fluorine from the above-mentioned fluorine-containing mud, the inventors succeeded in recovering the fluorine as hydrosilicofluoric acid, and further purified this hydrosilicic acid. It was found that a product comparable in quality to liquid hydrofluoric acid can be obtained.

Therefore, an object of the present invention is to provide a method by which hydrosilicofluoric acid can be advantageously recovered from the fluorine-containing mud.

The present invention will be explained in detail below.

The chemical composition of the fluorine-containing mud used as a starting material in the present invention varies depending on its source, but an average analysis example thereof is shown in Table 1 below.

In the present invention, sulfuric acid is first added to fluorine-containing mud and roasted in a roasting furnace (electric furnace).

Due to this sulfation roasting, fluorine in the fluorine-containing mud becomes HF and volatilizes.

The reaction equation in this case is that all the components of the fluorine-containing mud are CaF2
Considering this, it becomes as follows.

CaF2+H2SO4→2HF+Ca5O4 Therefore, the amount of sulfuric acid used in the roasting is preferably determined to be 1 equivalent or more based on the above reaction formula.

Furthermore, as the temperature during roasting increases, the recovery rate of fluorine in the fluorine-containing mud increases, but on the other hand, impurities such as As and AI tend to accompany the mud, so the recovery rate of fluorine slightly decreases. However, it is preferable to roast at a relatively low temperature.

The roasting time is usually 4 to 6 hours, although the roasting time is continued until white smoke generated by roasting is no longer observed.

According to the inventor's experimental results, it is preferable to roast at a temperature of about 200°C.

The table below shows an example of the relationship between roasting conditions and volatility rate. 2.

As seen in the table above, the volatilization rate of components in fluorine-containing mud is slightly influenced by the roasting temperature and the amount of sulfuric acid used.
Fluorine volatilization rate is high under all conditions.

However, since CI and As also volatilize together with fluorine, CI and As are mixed in as impurities when fluorine is recovered, as will be described later.

The gas (volatile matter) generated by roasting as described above is mixed with silicic anhydride (Si02) and water (preferably distilled water).
Hydrosilicic acid (H2S 1Fa) is produced by absorbing the gas into an aqueous solution suspended in the gas and reacting with HF in the gas.

This absorption is preferably carried out in two stages; in the first stage, for example, an aqueous solution in which Sio2 is suspended in 8 times the volume of water is used, and in the second stage, an aqueous solution in which SiO2 is suspended in 155 times the volume of water is used. Use.

In the actual operation of this absorption, the gas generated from the furnace is passed through a condenser to condense and collect the sulfuric acid content in the gas, and after the sulfuric acid content has been separated, the gas is absorbed as described above. HF in the gas is collected in the absorption liquid.

After the HF has been separated, the gas is dissipated by washing through, for example, a 5φ NaOH solution.

The absorption liquid containing H2SiF6 produced by the reaction of HF in the above gas with SiO□ and H2O in the absorption liquid contains unreacted silicic anhydride and hydrolyzate, so these are separated by Then, an aqueous solution of H2S t Fe is obtained.

The impurities in the H2 Si Fe aqueous solution obtained in this way, especially when the contents of CI and As are extremely small, can be used as is as an electrolyte for electrolytic refining of crude lead, but as mentioned above, fluorine-containing mud Since the CI and As in it will volatilize together with fluorine during roasting, when using mud containing not a small amount of these impurities as a raw material, the above H2
CI in S1Fa aqueous solution.

Contamination with As, etc. is unavoidable.

When using an H,+5iFe aqueous solution containing extremely small amounts of CI and As as the electrolytic solution, the Pb will react with CI and PB during the electrolytic refining of crude lead.
C1□ is formed and precipitates are generated, and the conductivity of the electrolytic solution is lowered, thereby deteriorating the state of electrodeposition.

On the other hand, As has the adverse effect of contaminating the electrolytic lead formed at the cathode.

Therefore, in the present invention, Hj obtained as described above
If the amount of CI and As mixed in the 3tFa aqueous solution is not small, a purification treatment as described below is further performed.

Lead oxide (Resurge) is added to an aqueous H2SiF6 solution to precipitate CI in the aqueous solution as PbCl2.

At this time, if SO4 ions are mixed in the above aqueous solution, Pb
Since it precipitates as SO4, if this is separated by f, CI and S
An aqueous solution substantially free of O4 is obtained.

In the present invention, H2S i Fe obtained in this way
The aqueous solution is purified by electrolytic treatment.

This electrolytic treatment is usually carried out using a lead anode and a ship type plate.

This electrolytic treatment yields extremely high purity hydrofluorosilicic acid.

As described above, according to the present invention, it becomes possible to advantageously recover hydrosilicofluoric acid of high purity, which can be applied to the electrolytic refining of crude lead, from fluorine-containing mud that has conventionally been discarded.

The present invention will be specifically explained below by way of examples.

Example Fluorine-containing mud 555 5' was used as a starting material.

Its composition is shown in Table 3 below.

The above fluorine-containing mud was placed in a roasting furnace, and sulfuric acid 380
Kf was added and roasted at 200°C, and roasting was continued until no white smoke was observed.

0.2 m3'min of volatile gas produced by this roasting is introduced into an absorption tower containing a suspension of silica powder 53 and 1 suspended in water. (concentration approximately 1.3%) to generate H2SiF6.

The composition of 0.215 m3 of the obtained silica hydrofluoric acid solution is shown in Table 4 below.

Next, in order to increase the purity of the hydrosilicofluoric acid obtained as described above, it was further purified by the following procedure.

The above-mentioned hydrofluoric acid solution was placed in a displacement reaction tank, and 3.2 KP of type lead slag consisting of 060 weight parts of Pb and 40 weight parts of Pb was added thereto as litharge, and the resulting precipitate was separated.

Obtained sap 0.215m3 and P residue 1.65K
The composition of p is as shown in Tables 5 and 6 below.

The sap liquid 115.61 obtained as described above was electrolytically treated using a lead anode 11 and a seed plate l Kp,
Purified hydrofluoric acid having the composition shown in Table 7 below: 0.215
m3 was obtained.

As is clear from the above table, highly purified hydrofluoric acid with extremely low impurity content was obtained, and this product can be used as an electrolytic solution for electrolytic refining of crude lead.

Claims (1)

[Claims] 1. A process characterized by roasting fluorine-containing mud in the presence of sulfuric acid, absorbing the generated volatile gas into an aqueous liquid containing silicic anhydride, and separating the generated hydrosilicofluoric acid. A method for recovering hydrosilicofluoric acid from fluorine-containing mud. 2. Precipitation produced by roasting fluorine-containing mud in the presence of sulfuric acid, absorbing the resulting roasted gas into an aqueous solution containing silicic anhydride, and reacting the resulting aqueous solution containing hydrosilicofluoric acid with lead oxide. A method for recovering purified hydrofluoric acid from fluorine-containing mud, which comprises separating the materials and electrolytically treating the resulting aqueous liquid.