JP5541090B2 - How to recover lead from lead-containing glass - Google Patents

Description

  The present invention relates to a method for decomposing and recovering lead from lead-containing glass such as waste such as lead-containing glass used for optical lenses and cathode-ray tubes.

  Lead-containing glass used for optical lenses and cathode-ray tubes contains about 20% by weight of lead oxide. When used as a cathode ray tube glass, used cathode ray tube televisions have been dismantled, and a portion of the cathode ray tube glass has been redissolved and recycled to the cathode ray tube glass. However, in recent years, liquid crystal televisions and plasma televisions have become widespread, and the demand for cathode ray tube televisions has decreased, making it difficult to recycle them into cathode ray tube glass. In the case of discarding lead-containing glass, it has been conventionally treated by a method of solidifying cement or treating with chemicals and landfilling.

  As processing methods for lead-containing glass, methods of reduction melting, extraction with alcohol in an autoclave, extraction with EDTA, halogenation and volatile separation have been studied. As for reductive melting, as described in Patent Document 1 and Non-Patent Document 1, a method is used in which lead oxide is decomposed and recovered by a reduction reaction using a reducing agent at a high temperature at a high temperature.

In the method disclosed in Patent Document 1, sodium oxide is added to lead-containing glass cutting waste, and the ratio of SiO ₂ / Na ₂ O of the slag component is in the range of 1.2 to 3.0 at 800 ° C. or higher. It is a method of adjusting, mixing a carbon source such as coke or charcoal as a reducing agent, and subjecting it to heat melting treatment. The method disclosed in Non-Patent Document 1 is a method in which wheat flour is added as a reducing agent to a Braun tube funnel glass powder, and NaCO ₃ is added as a melting aid to perform reduction melting. In either case, the particle size of the reducing agent is not shown.

JP-A-7-96264

Inano et al., “Lead Separation from Waste CRT Glass by Reducing Melting”, Hokkaido Industrial Laboratory Report, No. 304, P71-77

  When a lead-containing glass and a reducing agent are charged into a melting furnace and reduced and melted, when a small particle size reducing agent of 10 μm or less is used, the amount of the reducing agent added exceeds 2 in the C / Pb molar ratio. Thus, it was found that the reduction reaction stagnated and the metal lead recovery rate drastically decreased. In the actual process, even if the reducing agent is added so that the C / Pb molar ratio becomes 1 to 2 as a whole, a local region having a C / Pb molar ratio larger than 2 may be generated in the melting furnace. The reaction stagnated in such a local region and the Pb concentration was not reduced, so that a high metal lead recovery rate could not be obtained.

  An object of the present invention is to provide a method for recovering lead from lead-containing glass that allows the lead oxide reduction reaction to proceed smoothly and recovers metallic lead in a high yield.

  Lead in the lead-containing glass exists in the form of lead oxide PbO. When this is reduced and melted in a reducing atmosphere, metal lead Pb is generated according to chemical formula 1 or chemical formula 2, and the generated metal lead is molten slag. Settling inside.

At this time, the melting point of the lead-containing glass itself is as low as about 1000 ° C., but when PbO is reduced and removed, SiO ₂ is the main component, and the melting point rapidly rises to near 1700 ° C. Along with this, the viscosity rises rapidly. The inventors have found that when a reducing agent having a particle size of 100 μm or more is added, the reaction proceeds without stagnation even when a local region having a C / Pb molar ratio of greater than 2 is formed.

That is, when the C / Pb molar ratio is low (about 2 or less), since there are few Pb ions contacting C per hour, the generation rate of CO and CO ₂ is slow, and the density of bubbles in the slag is low ( The number of bubbles per unit volume of slag is small). Then, since there is less contact between the bubbles, the bubbles are discharged from the slag without growing too large. The reaction between C and Pb ions is not significantly inhibited. Therefore, the formation reaction of metallic lead proceeds until C and Pb ions are almost eliminated.

  When the C / Pb molar ratio is high (about 2 or more) and the particle size of C is large (about 100 μm or more), the amount of Pb ions in contact with C per hour increases, so the generation rate of CO, etc. is fast and the slag The density of bubbles increases. Then, the contact between the bubbles increases, and the bubbles are likely to grow large. However, since the particle size of C is sufficiently larger than that of bubbles, the influence of bubbles on the contact reaction between C and Pb ions is small. Therefore, the reaction for producing metallic lead proceeds until C is reduced to some extent and is affected by bubbles.

When the C / Pb molar ratio is high (about 2 or more) and the particle size of C is small (about 100 μm or less), Pb ions become very large. The density of becomes very high. Then, there are many contacts between the bubbles, and the bubbles are very large and tend to grow. Since C has a small particle size, it adheres to or is taken in by bubbles that have grown greatly. If it becomes so, it will become easy to produce the bubble which stays in slag (because the buoyancy of a bubble falls). When the bubbles stay, the diffusion of Na ions and Ca ions in the slag becomes worse. Then, a spot mainly composed of SiO ₂ is generated, and the spot has a high melting point and viscosity and may be hardened. Thereby, the retention of bubbles, Na ions, and Ca ions is increased. When these vicious cycles occur, the slag is not in a state where C and Pb ions can contact each other, and the formation reaction of metallic lead is stagnated.

  The present invention has been made based on these findings, and is a method for reducing and melting lead-containing glass, a reducing agent and a flux, and separating and recovering lead oxide contained in the lead-containing glass as metallic lead. The reducing agent is mainly composed of a particle having a particle size of 100 μm or more, and provides a method for recovering lead from lead-containing glass.

  According to the present invention, lead can be recovered in high yield from lead-containing glass such as waste cathode ray tube glass.

It is a figure which shows an example of the apparatus which implements the method of this invention. It is a figure which shows the internal state. It is a graph which shows the relationship between the input amount of the carbonaceous reducing agent of various particle sizes, and the amount of lead recovery.

  The lead-containing glass treated in the present invention is used for an optical lens or a cathode ray tube and contains about 10 to 40% by weight, usually about 20% by weight of lead as lead oxide. This is usually crushed before being used for lead recovery.

  As the reducing agent used for reducing lead oxide in the lead-containing glass, carbonaceous materials such as graphite, granulated granule, coke, charcoal, metallic iron, aluminum, calcium, and the like can be used. The amount of the reducing agent used is about 1 to 4, and preferably about 1 to 2 in terms of molar ratio to lead oxide in the lead-containing glass.

  The present invention is characterized in that a reducing agent having a large particle size is used.

  FIG. 3 shows the results of examining the influence on the recovery rate of metallic lead by using graphite as a reducing agent and changing the particle size. In this experiment, glass with a lead oxide content of 20% by weight obtained by disassembling a cathode ray tube as a raw material was crushed to a particle size of 10 mm or less, and powdered graphite and granular graphite were sieved as reducing agents. Obtained under a sieve having an aperture of 20 μm (average particle diameter by light scattering method described in JIS Z8901: 10 μm), a sieve having an aperture of 100 μm and an aperture of 200 μm, and a sieve having an aperture of 1 mm Three types of graphite particles having an upper size and a sieve size of 2 mm were used. As the flux, sodium carbonate was used in an amount of 40 kg / h. These were put into an electric resistance melting furnace, melted for 4 hours, and the amount of metallic lead collected at the bottom was measured to determine the recovery rate of metallic lead. From these results, when the reducing agent is powder, when the reducing agent / Pb molar ratio is 2 or more, the recovery rate of metallic lead is reduced. However, if the particle size is large, the reaction can be achieved even if the amount of reducing agent is increased. Can be seen to progress. The particle size of the reducing agent is 100 μm or more, preferably 200 μm or more, more preferably 500 μm or more, and even more preferably 1 mm or more. The upper limit of the particle size is not particularly limited, but is about 200 mm, and usually about 10 mm from a practical viewpoint, except when carbonaceous material is used for the refractory or when a carbon electrode is used. In actual operation, it is possible that a reducing agent having a large particle diameter is destroyed and becomes fine particles (less than 100 μm) when it is put into a melting furnace. The proportion of the fine reducing agent in the reducing agent added is preferably 10% by weight or less, more preferably 5% by weight or less.

Although the kind of flux is not limited, a sodium-type flux, a calcium-type flux, etc. can be used. Examples of the sodium-based flux include Na ₂ CO ₃ , NaHCO ₃ , and NaOH, and examples of the calcium-based flux include CaO, CaCO ₃ , Ca (OH) ₂ , and calcium aluminate. The addition amount of the flux is SiO ₂ / Na ₂ O = 1.2 to 3 by weight ratio with Si in the glass in the case of sodium flux (CaO / SiO ₂ = 0 by weight in the case of Ca flux). 3 to 1.2 and CaO / Al ₂ O ₃ = 0.3 to 4.

  The furnace that heats the mixture containing lead-containing glass, reducing agent, and flux must be capable of heating to a temperature at which the slag can be melted, or must have a sealed structure to collect the lead vapor generated by reduction. There is. Examples of such a heating furnace include an electric resistance melting furnace, an arc furnace, an induction heating furnace, and a blast furnace.

In this heating furnace, lead-containing glass, a reducing agent, and a flux are charged to perform reduction melting. As for the charging, each may be charged from a separate charging port, or a mixture that has been mixed in advance may be charged. The inside of the furnace is reduced by the reacted CO and CO ₂ gas, but an inert gas such as nitrogen may be blown to keep the reducing atmosphere.

  If the temperature in the furnace is a temperature at which the molten state of the slag can be maintained, for example, 1200 to 1600 ° C., the lead can be separated into the bottom as metal lead in about 2 to 4 hours.

  On the other hand, the reduction of this lead oxide can be performed continuously, in which case the lead-containing glass, reducing agent, and melt are controlled while controlling the lead (including lead oxide) content in the slag to be a predetermined value or less. It is only necessary to continuously or intermittently add the agent and to continuously or intermittently extract the generated lead and slag in the molten state.

  In the method of the present invention, most of the reduced lead is shielded by the slag layer and accumulates at the bottom, but part of it is evaporated as vapor.

  When carbonaceous is used as the reducing agent, carbon monoxide generated by reducing lead oxide in the lead-containing glass can be burned with a burner, and lead vapor can be changed to lead oxide and separated and recovered. In this case, a post-combustion furnace for performing this combustion, a collecting device for collecting the generated lead oxide, and a cooling device for cooling the combustion exhaust gas as needed are provided. A bag filter, a cyclone, an electric dust collector, a wet scrubber, a venturi scrubber, a spray tower, a packed tower, or the like can be used as the collection device.

  The lead separated by the method of the present invention can be used as metallic lead as it is or after further purification.

  Slag can be used as a raw material for glass products. When a calcium-based flux is used, it can be used as a road construction material.

  Lead was recovered from the lead-containing glass with the apparatus shown in FIGS.

  As the lead-containing glass, glass obtained by disassembling the cathode ray tube was crushed to a particle size of 50 mm or less. Coke having a particle diameter of 5 mm was used as the reducing agent in such an amount that C / PbO = 1. As the flux, sodium carbonate having a particle size of 1 mm was used in an amount that would be 50% of the weight of the lead-containing glass.

  These mixtures were charged into an electric resistance melting furnace at 40 kg / h and heated to 1100-1600 ° C. to melt. As a result, a cover layer made of slag formed from the raw material charged on the surface and unreacted materials of the auxiliary material, and a molten layer of the slag layer below and the metal lead layer at the bottom were formed. The reaction occurred between the cover layer, the slag-cover layer, the electrode-cover layer and the electrode-slag layer, but mainly occurred between the electrode-slag layer. 100 kg of the slag layer was discharged every 1 to 4 hours, and 7 kg of metal lead was taken out every 1 to 4 hours.

  By burning the CO gas in the post-combustion furnace and removing the dust with the bag filter, neither CO gas nor lead and lead compounds are discharged from the chimney.

  The discharged slag was solidified by water cooling or slow cooling on a pan.

The obtained metallic lead was 98% pure, and the lead concentration in the slag was 0.1% or less. At this time, the metal lead recovery rate was 60%.
When the same test was carried out using a coke having an average particle size of 10 μm as a reducing agent, the metal lead recovery rate was 50%.

  According to the present invention, harmful lead can be recovered from lead-containing glass with high efficiency, and in particular, cathode ray tubes that are expected to be disposed of in large quantities can be treated as waste.

Claims (2)

A method of reducing and melting lead-containing glass, a reducing agent and a flux at 1100 to 1600 ° C., and separating and recovering lead oxide contained in the lead-containing glass as metallic lead, wherein the reducing agent has a particle size of 100 μm. A method for recovering lead from lead-containing glass, wherein the above-mentioned materials are mainly used and the proportion of fine particles of less than 100 μm is 10% by weight or less . The method for recovering lead from lead-containing glass according to claim 1, wherein the reducing agent is carbonaceous.

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