JPH0796264A - Lead removal method from lead glass cuttings - Google Patents

Abstract

PURPOSE:To remove lead from the cut refuse of lead glass by melting and separating the cut refuse of lead glass so as not to elute a lead component in order to prevent environmental pollution. CONSTITUTION:An Na2O component is added to the cut refuse of lead glass to adjust the SiO2/Na2O wt. ratio in lead glass to 1.2-3.0 and, further, a carbon source such as coke or charcoal is mixed with the cut refuse as a reducing agent and the resulting mixture is heated and melted at 800 deg.C or higher in a two-phase or three-phase Heroult electric furnace to separate lead in the cut refuse of lead glass. This method is accepted by both of Japanese and American standards of a Pb elution test and effective for avoiding environmental pollution accompanied by the elution of lead.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for deleading lead glass cutting chips from waste such as lead glass cutting chips to prevent the elution of lead.

[0002]

2. Description of the Related Art Generally, lead glass used for optical lenses contains 20% by weight or more of PbO. In the process of processing this lead glass into an optical lens, a large amount of cutting chips are generated because of the glass cutting and polishing steps. Up to now, the cutting waste of the lead glass has been incinerated as dust, but in recent years the regulation of the elution of Pb has become stricter, and technical development for preventing the elution of these lead components has been desired. Heretofore, lead glass cuttings have been treated by a method such as incineration as waste, or coating with cement or organic matter and disposal. In the case of incineration, the Pb content scatters into the atmosphere, and in the case of coating and discarding, the Pb content elutes. Therefore, any method has been a serious problem from the viewpoint of pollution prevention.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and in order to solve the above-mentioned problem of pollution prevention, by melting lead glass cutting chips and separating lead, Pb content is reduced. It is an object of the present invention to provide a method for removing lead from cutting chips of lead glass that does not elute.

[0004]

The present invention is characterized in that lead glass is separated by mixing lead glass cuttings with a carbon source such as coke or charcoal as a reducing agent and heating and melting the mixture at 800 ° C. or higher. a lead-free process from lead glass swarf which, Na ₂ in this method, the lead glass swarf
O component is added, and the weight ratio of the contained SiO ₂ and Na ₂ O (hereinafter, the weight ratio of the contained SiO ₂ and the contained Na ₂ O is SiO ₂ /
Na ₂ O weight ratio) is adjusted to be in the range of 1.2 to 3.0, and the mixture is heated and melted. Further, in the heating and melting treatment, the melt is discharged in a molten state and rapidly cooled. Characterized by separating lead after solidification,
Further, it is a method for removing lead from cutting chips of lead glass, characterized in that the heating and melting treatment is carried out in a two-phase or three-phase ale type electric furnace.

[0005]

In the process of processing optical glass, various kinds of glass having different components are cut with a diamond cutter and then polished with an oily or water-based abrasive, so that the cutting chips contain SiO ₂ , Al ₂ other than glass components. Various inorganic and organic substances such as O ₃ and CaO are mixed as impurities. Therefore, the total amount of the inorganic components considered as the constituent components of the glass cutting waste is extremely low, around 50% by weight, as shown in Table 1 described later. Pb in lead glass is in solid solution in the state of PbO. Therefore, in order to remove PbO in the lead glass cutting wastes, a carbon source such as coke or charcoal is added as a reducing agent, and by heating and melting at 800 ° C or higher, PbO in the lead glass is reduced by the following formula. The reaction as shown in FIG. PbO + C → Pb + CO That is, PbO in the lead glass is reduced by the reducing agent C to P
b and CO, and the produced CO is volatilized. In this case, if the fluidity of the glass phase is sufficiently large, the reduced Pb will separate from the molten glass phase.

However, in the lead glass cutting chips, in addition to the glass components as described above, SiO ₂ and A
Since l ₂ O ₃ , CaO and the like and organic substances are mixed in, in the heating and melting treatment, PbO which is a glass component is reduced as shown in the above formula and separated from the glass component so that the melting point of the glass component rises and lead Separation becomes difficult. Therefore, as a result of various studies by the present inventors, when mixing a carbon source such as coke or charcoal as a reducing agent into lead glass cutting waste and heating and melting the mixture, as shown in Examples described later, SiO ₂ / N
It was found that when the a ₂ O weight ratio is adjusted to be in the range of 1.2 to 3.0 and the heating and melting treatment is performed, the separation of lead is facilitated. Therefore, in the present invention, if necessary, for example, Na ₂ CO ₃ is mixed as a Na ₂ O component into the cutting waste of lead glass so that the SiO ₂ / Na ₂ O weight ratio is in the range of 1.2 to 3.0. The melting point of the glass is lowered by the added Na ₂ O component and the fluidity is adjusted to 8
It is heated and melted at a temperature of 00 ° C. or higher to facilitate the separation of lead.

When the SiO ₂ / Na ₂ O ratio is less than 1.2 or exceeds 3.0, the separation of lead is insufficient, and the lead elution test based on the Japanese Environmental Agency Notification No. 13 and US As a result of the solute test lead based on EP method, since in many cases it leads dissolution test results do not meet the criteria SiO ₂ /
The Na ₂ O weight ratio was set in the range of 1.2 to 3.0. Furthermore,
In performing the heating and melting treatment of the lead glass cutting scraps of the present invention, an external heating type furnace can be used as a melting container, but industrially, it is a two-phase or three-phase type capable of directly energizing the material to be melted. The use of the phase ale type electric furnace is advantageous in terms of reaction efficiency and productivity. Further, the amount of the reducing agent needs to be equivalent to the amount of C shown in the above formula, but normally it is sufficient if it is about 5% by weight in the outer frame of the amount of raw glass scraps, but glass cutting scraps become a carbon source. It may contain a large amount of organic matter, and at that time, it is not necessary to add carbon. Particularly, when the ale type electric furnace is used, the ale type electric furnace is preferable because the reducing agent is supplied by the carbon lining of the hearth or the graphite electrode.

[0008]

EXAMPLES Next, examples of the present invention will be described. [Example 1] First, Table 1 below shows an example of the constituent components of cutting chips generated in the process of processing optical glass. As shown in Table 1, the total amount of cutting chips as a constituent component is 46.7%,
The remaining components are organic substances and volatile components.

[0009]

[Table 1]

5% by weight of charcoal as a reducing agent was added to 1 kg of the cutting waste material of the lead glass shown in Table 1 in the outer frame, and the mixture was heated and reduced to 1200 ° C. in a N ₂ gas stream in a silicon furnace. As a result, PbO is reduced to Pb, but remains in a state of being mixed with the glass component.
Was difficult to separate. This is PbO which is a glass component
It is considered that this is because the melting point of the glass component increased because it was reduced and separated from the glass component, making it difficult to separate lead and glass.

[Experiment 1] Then, Na ₂ O in the cutting waste material was used.
Na ₂ CO ₃ was added so that the amount of the component was about 28% by weight, and it was combined with the SiO ₂ component and vitrified to form a glass with a low melting point. Weight% was added and mixed. This compounded raw material is charged into an alumina crucible and heated up in a silicon knit electric furnace to 80
After holding at 0 ° C. for 30 minutes, the temperature was raised again, at 1200 ° C. for 1 hour, and then cooled. The sample solidified by cooling is separated into a vitreous part and metallic lead, and the residual lead in the vitreous substance is 0.2% by weight.
And almost all Pb was reduced and removed. Based on this result, 100% of the main constituents of the glass after reduction were used.
It is shown in Table 2 as%.

[0012]

[Table 2]

Next, the obtained glassy material was subjected to a lead elution test based on Japan Environmental Agency Notification No. 13 and a lead solute test based on the US EP method. As a result, as shown in Table 2, The dissolution test result was 0.2 mg / l, and the dissolution test result in the United States was 0.17 mg / l, both of which passed the standard values of 3 mg / l or less and 5 mg / l or less. In addition,
As a result of investigating the crystal structure of the vitreous portion by X-ray diffraction, it was confirmed that the vitreous portion was composed of amorphous glass. The SiO ₂ / Na ₂ O weight ratio in Experiment 1 is 6
The ratio was 6.7% by weight / 28.4% by weight = 2.3.

[Experiment 2] Next, in Experiment 2, the SiO ₂ / Na ₂ O weight ratio of the lead glass cutting waste was set to 5.6, and the reduction / heat melting treatment was performed under the same conditions as in Experiment 1 under other conditions. It was As a result, although Pb was reduced, the fluidity of the vitreous part was poor and the separation from lead was insufficient. The components after the reduction and the elution results are shown in Table 2. From the results shown in Table 2, if the SiO ₂ / Na ₂ O weight ratio in the main components of the glass is not appropriate, the flowability of the vitreous part is poor and the separation of glass and lead does not proceed sufficiently, and lead elution also increases. I was able to confirm that.

[Experiment 3] Then, appropriate SiO ₂ / Na _{2 was used.}
In order to find the O weight ratio, the lead / glass cutting chips are melted and reduced in the SiO ₂ / Na ₂ O weight ratio range of 1 to 5.75 to observe the fluidity of the glass and at the same time the dissolution test in Japan and the United States. The composition range in which the result was 5 mg / l or less was investigated. The result is shown in FIG. As shown in FIG. 1, SiO ₂ / Na ₂
When the O weight ratio is in the range of 1.2 to 3, the flowability of the melt is good, Pb and glass are sufficiently separated, and Pb in the glass is 0.1 to 0.3% by weight. It was also found that the dissolution test result was also 0.3 mg / l or less.

[Embodiment 2] Next, a specific embodiment will be described. FIG. 2 shows the 500 KVA used in the embodiment of the present invention.
It is a schematic diagram of a device configuration of a two-phase ale type electric furnace. In FIG. 2, 1 is a 500 KVA two-phase ale type electric furnace, 2 is a tilt type furnace body of the ale type electric furnace 1, 3 is carbon lining of the furnace body, 4 is a flat mold, 5 is an electrode of the ale type electric furnace 1,
6 is a transformer of 500 KVA power source, 7 is a dust collecting hood that covers the ale type electric furnace 1, and 8 is a dust collector for dust generated during the heating and melting process. Using a two-phase ale type electric furnace apparatus as shown in FIG. 2, PbO is 7.1 to 15.8 wt%.
And lead glass cutting chips containing CaO and Al ₂ O ₃ having different contents were used.

Next, the total amount of PbO, SiO ₂ , Al ₂ O ₃ and CaO, which are the main constituents of the lead glass cutting waste, and Na ₂ O, which is an additive component, is 100% by weight, and Al ₂ O ₃ is 3.
4 to 18.4 wt%, CaO 7.0 to 20.4 wt%
4 levels within the range of, and from the results of Example 1,
It was added Na ₂ CO ₃ as Na ₂ O component, SiO ₂ /
The Na ₂ O weight ratio was adjusted to approximately 1.2 to 2.8. About 20 kg of this mixed raw material was charged into an electric furnace, melted by electric current, and then held at about 1300 ° C. for 5 minutes. In both tests, the raw materials were dissolved within 5 minutes after the start of energization, and
It was confirmed that the reduction was completed promptly by holding at 00 ° C for about 5 minutes. After that, the tilted furnace body 2 was tilted, the melt was cast into the flat mold 4, and after cooling, the vitreous portion and metallic lead were separated and a lead content elution test was performed. Table 3 shows the main components of the glass after the dissolution test, the lead content in the glass, and the elution test results.

[0018]

[Table 3]

As shown in Table 3, S of lead glass cuttings
As a result of adjusting the iO ₂ / Na ₂ O weight ratio to about 1.2 to 3.0, the lead in the glass is drastically reduced, and the lead elution test results are sufficiently within the passing standards for both Japanese and US standards. The result was satisfactory. On the other hand, when a 1.2 KVA silicon knit furnace is used as a furnace for heating and melting, and a sample is placed in a crucible and externally heated, it takes several hours or more to raise the temperature to 1300 ° C., which is an industrial process. It has been found that the external heating method is undesired due to poor productivity. The lead removal method from lead glass cutting scraps of the present invention is a method of adding a reducing agent to lead glass cutting scraps to obtain SiO in the cutting scrap raw material.
_{The 2} / Na ₂ O weight ratio is adjusted to be in the range of 1.2 to 3.0. In this case,
Needless to say, if the SiO ₂ / Na ₂ O weight ratio is within the range without adding the Na ₂ O component, it becomes possible to separate lead as it is.

[0020]

EFFECTS OF THE INVENTION By separating lead from lead glass by the lead removal method from lead glass cutting waste of the present invention, the lead in the glass component becomes 1.0% by weight or less, and the treatment of the present invention was performed. After that, even if the glass scraps are discarded, the Pb elution can pass both the Japanese standard and the US standard of the elution test, and the pollution problem associated with the elution of lead can be avoided.

[Brief description of drawings]

FIG. 1 SiO ₂ / N obtained in an example of the present invention
It is a relational graph between the lead-containing and dissolution test results of a ₂ O weight ratio and in the glass.

FIG. 2 is a schematic diagram of a device configuration of a two-phase ale type electric furnace used in an example of the present invention.

[Explanation of symbols]

 1 Ale type electric furnace 2 Tilt type furnace body 3 Carbon lining 4 Flat mold 5 Electrode 6 Transformer 7 Dust collecting hood 8 Dust collector

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masanori Kato 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Hideyuki Yoshikoshi 2-3-2, Marunouchi, Chiyoda-ku, Tokyo Steel Tube Mining Co., Ltd. (72) Inventor Shinda Ikeda 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Steel Tube Mining Co., Ltd.

Claims (4)

[Claims] 1. Lead removal from lead glass cutting chips, characterized in that lead glass cutting chips are mixed with a carbon source such as coke or charcoal as a reducing agent and heated and melted at 800 ° C. or more to separate lead. Method. 2. A Na ₂ O component is added to the lead glass cutting chips, and the weight ratio of contained SiO ₂ / Na ₂ O is 1.2 to 3.
The method for removing lead from cuttings of lead glass according to claim 1, wherein the method is adjusted so as to be in the range of 0 and heat-melted. 3. The method for removing lead from cutting chips of lead glass according to claim 1, wherein in the heating and melting treatment, a molten material is discharged in a molten state, rapidly solidified, and then lead is separated. 4. The method for removing lead from cutting chips of lead glass according to claim 1, wherein the heating and melting treatment is performed in a two-phase or three-phase ale type electric furnace.