GB2512814A

GB2512814A - Apparatus and method for recovery of lead

Info

Publication number: GB2512814A
Application number: GB1302445.0A
Authority: GB
Inventors: Harry Middleton; Jonathan James Quinn
Original assignee: ULTROMEX Ltd
Current assignee: ULTROMEX Ltd
Priority date: 2013-02-12
Filing date: 2013-02-12
Publication date: 2014-10-15
Also published as: GB201302445D0; WO2014125266A1

Abstract

Lead is removed from lead glass by forming a mixture of crushed lead glass, water and a base such as sodium hydroxide; agitating the mixture by ultrasound and steam sparging to form a solution comprising lead silicate and base metasilicate; removing impurities by centrifuging; adding a base sulphide to the solution to form lead sulphide; and separating the lead sulphide from the base metasilicate by centrifuging. At least part of the agitating is performed while the mixture is pressurised. Once separated, the lead sulphide can be reacted with iron chloride. Apparatus for performing the method comprises a chamber 11 for holding the mixture, means 12 for pressurising the chamber 11, ultrasonic transducers 14 arranged around the chamber 11 and from which sound waves can be directed into the chamber 11, means 15 for introducing steam into the chamber 11, a tank (106, Fig 2) in which lead sulphide can be precipitated and means (108, Fig. 2) for separating the precipitated lead sulphide.

Description

APPARATUS AND METHOD FOR RECOVERY OF LEAD

This invention relates to an apparatus and process for the recovery of lead from glass, and particularly but not exclusively to an apparatus and process for the recovery of lead from Cathode Ray Tube (CR1) scrap material.

A Cathode Ray Tube (CR1) generates images by the acceleration of electrons towards a fluorescent screen. The commercial and industrial application of CRTs is widespread, including monitors for RADAR devices and the representation of electrical waveforms in oscilloscopes. Furthermore, prior to the introduction of LCD, plasma display, and OLED technologies, Cathode Ray Tubes (CRTs) formed an integral part of all television sets and computer monitors.

A CRT generally contains lead glass, which acts to improve the optical quality of the glass and to shield the user from X-ray radiation emitted during the electron bombardment of the screen. For example, a typical CR1 is made from a lead-free screen glass and a funnel glass containing approximately 20% lead, the two being joined by a glass solder containing up to 90% lead. Whilst this lead glass performs a useful role within a CR1, it poses a substantial environmental risk when the CRT reaches the end of its life and is disposed of. Studies have shown that when CRTs are disposed of in landfill sites, lead can leach from the glass and contaminate ground water. The severity of the environmental risk is such that the disposal of CRT5 is regulated by legislation in many countries. For example, rules surrounding the disposal of CRTs are contained within the WEEE (Waste Electrical and Electronic Equipment) European Community Directive.

Currently in the UK, lead is typically separated from CR1 glass by smelting. In this process the CRT glass is melted at high temperature, which causes the lead to separate from the glass and, once separated, fall to the bottom of the furnace due to its high density. The separated lead is tapped off from the bottom of the furnace and passed into ingot moulds, whilst the glass is tapped off separately. One problem associated with this process is that it can generate submicron particles of lead.

These particles can enter the atmosphere due to the high convection currents within the furnace and therefore constitute a serious health hazard.

We have now devised an improved apparatus and process for the recovery of lead from CRT glass.

In accordance with the present invention, as seen from a first aspect, there is provided a method for at least partially dissolving a lead glass in a base, the method comprising the steps of: (a) forming a mixture comprising the lead glass and the base; and, (b) agitating said mixture by ultrasonic agitation.

The term "base" as used herein should be interpreted in accordance with the chemical definition thereof, namely a substance capable of accepting protons.

Advantageously, the step of agitating said mixture facilitates the dissolution of the lead glass in the base, forming a solution comprising lead silicate and base metasilicate.

Preferably the method is for fuDy hissokng the sad glass in the base, the step of agitating said mixture preferaby being conhnued until the sad glass has fuily dissoived in the base Preferably the base is caustic.

Said mixture preferably comprises water. Preferably the base is in the form of a 50% saturated solution.

The base may comprise sodium hydroxide (NaCH), also known as caustic soda.

Alternatively, the base may comprise potassium hydroxide (KOH), also known as caustic potash. Alternatively, the base may comprise calcium oxide (GaO), also known as caustic lime.

Preferably the step of agitating said mixture is carried out whilst said mixture is contained within a sealed container. Preferably said sealed container is pressurised for at least a portion of the step of agitating said mixture.

Preferably the step of agitating said mixture by ultrasonic agitation comprises directing sound waves towards said mixture to induce compression waves within said mixture, said sound waves being at ultrasonic frequency. The frequency of said sound waves is preferably greater than 1 MegaHertz and preferably less than 5 MegaHertz.

The step of directing sound waves towards said mixture preferably comprises directing sound waves from a plurality of locations, said plurality of locations preferably being located around the periphery of the container.

The method may further comprise the step of generating said sound waves at ultrasonic frequency. The step of generating said sound waves is preferably effected by an ultrasonic transducer and more preferably effected by a piezoelectric transducer.

The method may comprise agitating said mixture by steam sparging, said steam sparging comprising injecting steam into said mixture. Preferably said steam is pressurised. Preferably the step of agitating said mixture by steam sparging is performed concurrently with the step of agitating said mixture by ultrasonic agitation.

The step of agitating said mixture is preferably continued until the temperature of the mixture has exceeded a certain threshold, which is preferably between 5000 and 350°C. More preferably, the threshold is between 180°C and 200°C. Alternatively, or in addition thereto, the step of agitating said mixture may be continued for a certain time-period, said time-period being determined in accordance with the nature of said lead glass.

The method may further comprise the step of preparing the lead glass prior to the step of forming said mixture, said step of preparing the lead glass preferably comprising crushing said glass to form glass fragments.

The step of crushing said glass may be effected by a vertical impactor.

Preferably the step of crushing the lead glass comprises crushing said glass to form glass fragments having a diameter of between 0.1mm and 100mm. It has been found that the range of between 0.1mm and 100mm is the optimum size for treatment in order to prevent glass fragments from enteling the atmospheie. More preferably, the step of crushing the lead glass comprises crushing said glass to form glass fragments having a diameter of between 0.1mm and 12.5mm. It has been found that the range of between 0.1mm and 12.5mm piovides for maximum efficiency in the lead glass separation process described herein.

The method may comprise sorting said glass fragments in accordance with size.

Pieferably only those glass fragments having a diametei of between 0.1mm and 100mm are added to said mixture. More preferably, only those glass fragments having a diameter of between 0.1mm and 12.5mm are added to said mixture. The glass fragments having a diameter of greater than 100mm may be returned for further crushing.

In accordance with the present invention, as seen from a second aspect, there is provided an apparatus for at least partially dissolving a lead glass in a base! the apparatus comprising a container for holding a mixture comprising the lead glass and the base, and an ultrasonic transducer for generating sound waves at ultrasonic frequency, the ultrasonic tiansducei being arranged foi diiecting said sound waves towards said mixture so as to form compression waves within said mixture.

Pieferably the apparatus comprises a plurality of ultrasonic transduceis, said transduceis being preferably aiianged around a periphery of said containel.

The apparatus may comprise pressurisation means for pressuring said container.

The apparatus may comprise steam injection means for effecting steam sparging of said mixture.

In accordance with the present invention, as seen from a third aspect, theie is provided a method for recovering lead from lead glass, the method comprising the steps of: a) Foiming a mixture comprising the lead glass, watel and a base b) Agitating said mixture to form a solution comprises lead silicate and base metasilicate; c) Adding a base suiphide to said solution to form lead sulphide; d) Separating the lead sulphide from the base metasilicate; The method may further comprise the step of crushing the lead glass, this step preferably being carried out prior to the step of forming said mixture. Preferably the step of crushing the lead glass comprises crushing the lead glass comprises crushing said glass to form glass fragments having a diameter of between 0.1mm and 100mm.

More preferably, the step of crushing the lead glass comprises crushing said glass to form glass fragments having a diameter of between 0.1mm and 12.5mm.

The method may comprise sorting said glass fragments in accordance with size.

Preferably only those glass fragments having a diameter of between 0.1mm and 100mm are added to said mixture at step (a) above. More preferably, only those glass fragments having a diameter of between 0.1mm and 12.5mm are added to said mixture at step (a) above. The glass fragments having a diameter of greater than 100mm may be returned for further crushing.

Preferably the method further comprises the step of removing impurities from said solution, said step preferably being performed intermediate the step of agitating said mixture and the step of adding the base sulphide. The step of removing impurities from said solution preferably comprises removing insoluble impurities i.e. impurities that are not dissolved after completion of the step of agitating said mixture. The step of removing insoluble impurities preferably comprises centrifugation.

Preferably the step of separating the lead sulphide from the base metasilicate is effected by centrifugation.

Preferably the step of agitating said mixture comprises ultrasonic agitation.

Preferably the step of agitating said mixture by ultrasonic agitation comprises directing sound waves towards said mixture to induce compression waves within said mixture, said sound waves being at ultrasonic frequency. The frequency of said sound waves is preferably greater than 1 MegaHertz and preferably less than 5 MegaHertz. The step of directing sound waves towards said mixture preferably comprises directing sound waves from a plurality of locations, said plurality of locations preferably being located around the periphery of the container.

Alternatively, or in addition thereto, the step of agitating said mixture comprises steam sparging.

Preferably the step of agitating said mixture comprises both ultrasonic agitation and steam sparging, which are prferably performed concurrently.

The method may further comprise the step of reacting the lead sulphide with a chloride of iron, this step being carried out after the step of separating the lead sulphide. Advantageously, lead sulphide reacts with a chloride of iron to produce lead chloride, which is a highly safe compound of lead.

The method may further comprise the step of purifying the base metasilicate, said step preferably comprising passing the base metasilicate through a medium to remove any remaining metal, the concentration of this remaining metal typically being a few parts per billion. Preferably the medium comprises a ligand. Once passed through the medium, the base metasilicate is substantially pure in nature and may therefore be used for a variety of applications, for example as a geopolymer.

In accordance with the present invention, as seen from a fourth aspect, there is provided an assembly for recovering lead from lead glass, the assembly comprising: a dissolving apparatus for partially dissolving the lead glass in the base to produce a solution comprising lead silicate and base metasilicate, the apparatus being as hereinbefore described; a precipitation tank for precipitating lead suiphide, the precipitation tank being arranged to receive a base sulphide and at least some of said solution from said apparatus; and, separation means for separating the precipitated lead sulphide, the sepalation means being arranged to leceive at least some of the lead sulphide from the precipitation tank.

Preferably the separation means is arranged to receive substantially all of the lead sulphide from the piecipitation tank.

The separation means preferably comprises a centrifuge.

The assembly may comprise purification means disposed intermediate the dissolving apparatus and the precipitation tank, the purification means preferably being adapted for removing insoluble impurities from said solution. The purification means may comprise a centrifuge.

The assembly may comprise glass fragmentation means for producing lead glass fragments of prefeiably between 0.1mm and 100mm diameter, and more preferably between 0.1mm and 12.5mm diameter. The glass fragmentation means may comprise a vertical impactor.

The assembly may comprise soiting means foi sorting the glass fragments accoiding to size. The sorting means is preferably arranged to pass glass fragments having a diameter of between 0.1mm and 100mm to the dissolving apparatus and is preferably to return glass fragments having a diametei of greatel than 100mm to the glass fragmentation means. More preferably, the sorting means is arranged to pass glass fragments having a diameter of between 0.1mm and 12.5mm to the dissolving apparatus and return glass fragments having a diameter of greater than 12.5mm to the glass fragmentation means.

The assembly may comprise lead sulphide treatment means for receiving the lead sulphide fiom the sepalation means and reacting the lead sulphide with a chloride of iron to form lead chloride.

The assembly may comprise base metasilicate purification means for purifying the base metasilicate. Preferably the base metasilicate purification means is configured to pass the base metasilicate through a medium comprising a ligand.

An embodiment of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 is a schematic side view of an apparatus for dissolving a lead glass in a base in accordance with an embodiment of an aspect of present invention; Figure 2 is a schematic illustration of an assembly for recovering lead from lead glass in accordance with an embodiment of another aspect of the present invention, the assembly comprising the apparatus illustrated in figure 1; Figure 3 is a flow diagram illustrating a method for dissolving lead glass in a base in accordance with an embodiment of another aspect of the present invention; and, Figure 4 is a flow diagram illustrating a method for recovering lead from lead glass in accordance with an embodiment of another aspect of the present invention.

With reference to figure 1 of the drawings, there is illustrated an apparatus 10 for dissolving a lead glass in a base in accordance with an embodiment of the apparatus of the present invention. The apparatus 10 comprises a sealable chamber 11, which includes pressurisation means 12 for increasing the pressure within the chamber 11 relative to atmospheric pressure. A sealable inlet 13 is provided at the top of chamber 11 for introducing lead glass and a base to the chamber 11.

Various agitation means are provided for agitating the contents of the chamber 11.

Firstly, the apparatus 10 comprises a plurality of ultrasonic transducers 14 in the form of piezoelectric crystals. The ultrasonic transducers 14 are disposed about the periphery of the chamber 11 and arranged for directing ultrasound pulses into the chamber 11 to induce compression waves in the lead glass and base mixture within the chamber 11. Secondly, the apparatus 10 comprises steam sparging means in the form of a plurality of inlets 15 connected to a source of pressurised steam (not shown). In the illustrated embodiment, the steam inlets 15 are disposed at the base of the chamber 11, but it will be appreciated that the steam inlets may alternatively or additionally be disposed in other locations, such as the top of the chambei 11.

Thirdly, a paddle 16 extends downwardly from the top of the chamber 11. The paddle 16 is connected to a motor (not shown) and arranged to rotate about a substantially vertical axis. Since the lead glass and base mixtule is initially highly viscous, initial mixing will be attained though ultrasonic agitation and steam spaiging only. Once the viscosity of the mixture has reduced to a threshold level, additional agitation and mixing may be achieved through rotation of the paddle 16.

With reference to figure 3 of the drawings! in use! the lead glass is prepared by crushing to a size of between 0.1mm and 25.5mm at step 21. At step 22, the lead glass is then added to the chamber 11, along with a base such as sodium hydroxide (NaOH) prepaied to 50% saturation. The relative quantities of lead glass and sodium hydroxide are such that substantially all of the lead glass will dissolve in the sodium hydroxide solution upon agitation but no more lead glass would have dissolved if it had been added. In other words, the quantity of lead glass should be the threshold quantity that will completely dissolve in the volume of sodium hydroxide added to the chamber 11. Once the lead glass and sodium hydroxide are added, the chamber 11 is sealed by sealing of the inlet 13 and pressurised by the piessurisation means 12.

The mixture within the chamber 11, namely the lead glass and sodium hydroxide mixture, is then agitated by simultaneous steam sparging and ultrasonic agitation at step 23. The steam sparging and the ultiasonic agitation are effected by the steam inlets 15 and ultrasonic tiansduceis 14 respectively. It will be appreciated that the agitation process assists the dissolution of the lead glass in the sodium hydroxide.

Once the viscosity of the mixture has been reduced to a threshold level, the rotary paddle 16 is energised and fuithei assists with agitation of the mixture at step 24.

The process of agitation is continued until all of the lead glass has dissolved in the sodium hydroxide solution, which may be defined by a certain time period. By way of example, the time may be 3 hours but it will be appreciated that the exact time is dependent upon the nature of the lead glass being dissolved. Alternatively, the point at which all of the lead glass has dissolved may be signified by the interior of the chamber 11 reaching a certain temperature threshold. By way of example, the tempelatule thieshold may be between 5000 and 350°C, but it will be appreciated that this is again dependent upon the nature of the glass being dissolved.

With reference to figure 2 of the drawings, there is illustrated an assembly 100 for recovering lead from lead glass.

The assembly 100 comprise a caustic tank 101 for storing a base such as a 50% saturated solution of sodium hydroxide. The assembly 100 further comprises a means for storing or generating crushed lead glass 102. Both the caustic tank 101 and the means for storing or generating crushed class 102 define inputs to a pre-mixer chamber 103. In a preferred embodiment, the means for storing or generating crushed glass 102 comprises a vertical impactor (not shown) and a sorting mechanism (not shown), the impactor and the sorting mechanism being arranged to transmit only glass fragments having a diameter of between 0.1mm and 12.5mm to the pre-mixer chamber 103.

The pre-mixer chamber 103 is generally cylindrical in shape and has a volumetric capacity of approximately 10 m3. The crushed lead glass and sodium hydroxide are initially mixed together in this chamber 103, before passing to the dissolving apparatus 10 illustrated in figure 1. The agitation means 14, 15, 16 provided in the dissolving apparatus 10 causes the crushed lead glass to dissolve in the sodium hydroxide, forming a solution comprising lead silicate and sodium metasilicate.

Connected to the dissolving chamber 10 is a holding tank 104, which is in turn connected to a first centriguge 105. The first centrifuge 105 is arranged to remove the solid impurities and pass the liquid to dual precipitation tanks 106, the precipitation tanks 106 being arranged to receive a base sulphide such as sodium sulphide from a storage tank 107.

Connected to the precipitation tanks 106 is a second centrifuge 108, which is arranged to remove the precipitate, namely lead sulphide, and pass the liquid to dual product storage tanks 109.

With reference to figure 4 of the drawings, in use, the lead glass is prepared by crushing to a size of between 0.1mm and 25.5mm by the lead glass preparation means 102 at step 201. The lead glass is then passed to the pre-mixer chamber 103, along with a 50% saturated solution of sodium hydroxide at step 202. The relative quantities of lead glass and sodium hydroxide are such that substantially all of the lead glass will dissolve in the sodium hydroxide solution upon agitation but no more lead glass would have dissolved if it had been added. Once the correct quantities of lead glass and sodium hydroxide have been added to the pre-mixer chamber 103, the mixture is passed to the dissolving apparatus 11 at step 203. At step 204, the dissolving apparatus is sealed and the mixture is agitated as hereinbefore described.

Once the mixture has been sufficiently agitated to cause all of the lead glass to dissolve in the sodium hydroxide, the resulting solution comprises predominantly lead silicate and sodium metasilicate. It will be appreciated, however, that certain impurities are also present in the solution. In order to remove the solid impurities, the solution is passed from the dissolving chamber 11 to the holding tank 104 and subsequently to the first centrifuge 105 at step 205. The action of the centrifuge separates the solid impurities from the solution to leave a solution of lead silicate, base metasilicate and potentially traces of insoluble impurities. At step 206, the liquid that passes out of the first centrifuge 105 is subsequently passed to the precipitation tanks 106, whereupon sodium sulphide is added from the storage tank 107. The sodium sulphide reacts with the lead silicate to form lead sulphide, which precipitates out of the solution. The lead sulphide is separated from the solution by the second centrifuge 108 at step 207. Once separated, the lead sulphide is reacted with a chloride of iron at step 208, to form the highly safe compound lead chloride. The liquid that passes from the second centrifuge 108 is subsequently passed though a medium containing a ligand, to remove any potential soluble impurities such as metals in concentrations of a few parts per billion. Once passed through the medium, only pure sodium metasilicate remains, which may be used for a variety of applications.

Claims

Claims 1. A method for at least partially dissolving a lead glass in a base, the method comprising the steps of: (a) forming a mixture comprising the lead glass and the base; and, (b) agitating said mixture by ultrasonic agitation.
2. A method according to claim 1, wherein the step of agitating said mixture is carried out whilst said mixture is contained within a sealed container.
3. A method according to claim 2, wherein said sealed container is pressurised for at least a portion of the step of agitating said mixture.
4. A method according to any preceding claim, wherein the step of agitating said mixture by ultrasonic agitation comprises directing sound waves towards said mixture to induce compression waves within said mixture, said sound waves being at ultrasonic frequency.
5. A method according to any preceding claim, further comprising the step of agitating said mixture by steam sparging, said steam sparging comprising injecting steam into said mixture.
6. A method according to claim 5, wherein the the step of agitating said mixture by steam sparging is performed concurrently with the step of agitating said mixture by ultrasonic agitation.
7. An apparatus for at least partially dissolving a lead glass in a base, the apparatus comprising a container for holding a mixture comprising the lead glass and the base, and an ultrasonic transducer for generating sound waves at ultrasonic frequency, the ultrasonic transducer being arranged for directing said sound waves towards said mixture so as to form compression waves within said mixture.
8. An apparatus according to claim 7, wherein the apparatus comprises additional ultrasonic transducers, said transducers being arranged around a periphery of said container.
9. An apparatus according to claim 7 or claim 8, further comprising pressurisation means for pressuring said container.
10. An apparatus according to any one of claims 7 to 9, further comprising steam injection means for effecting steam sparging of said mixture.
11. A method for recovering lead from lead glass, the method comprising the steps of: (a) Forming a mixture comprising the lead glass, water and a base (b) Agitating said mixture to form a solution comprising lead silicate and base metasilicate; (c) Adding a base sulphide to said solution to form lead sulphide; (d) Separating the lead sulphide from the base metasilicate.
12.A method according to claim 11, further comprising the step of crushing the lead glass, this step being carried out prior to the step of forming said mixture.
13. A method according to claim 12, wherein the step of crushing the lead glass comprises crushing said glass to form glass fragments having a diameter of between 0.1mm and 12.5mm.
14. A method according to any one of claims 11 to 13, further comprising the step of removing impurities from said solution, said step being performed intermediate the step of agitating said mixture and the step of adding the base sulphide.
15.A method according to claim 14, wherein the step of removing impurities comprises insoluble impurities by centrifugation.
16.A method according to any one of claims 11 to 15, wherein the step of separating the lead sulphide from the base metasilicate is effected by centrifugation.
17. A method according to any one of claims 11 to 16, wherein the step of agitating said mixture is carried out whilst said mixture is contained within a sealed container.
18. A method according to claim 17, wherein said sealed container is pressurised for at least a portion of the step of agitating said mixture.
19. A method according to any one of claims 11 to 18, wherein the step of agitating said mixture comprises ultrasonic agitation.
20. A method according to one of claims 11 to 19, wherein the step of agitating the mixture comprises steam sparging.
21.A method according to any one of claims 11 to 20, wherein the step of agitating the mixture comprises concurrent ultrasonic agitation and steam spa rg in g.
22. A method according to any one of claims 11 to 21, further comprising the step of reacting the lead sulphide with a chloride of iron, this step being carried out after the step of separating the lead sulphide.
23. A method according to any one of claims 11 to 22, further comprising the step of purifying the base metasilicate by passing the base metasilicate through a medium comprising a ligand.
24. An assembly for recovering lead from lead glass, the assembly comprising: a dissolving apparatus for partially dissolving the lead glass in the base to produce a solution comprising lead silicate and base metasilicate, the apparatus being as hereinbefore described; a precipitation tank for precipitating lead sulphide, the precipitation tank being arranged to receive a base sulphide and at least some of said solution from said apparatus; and, separation means for separating the precipitated lead sulphide, the separation means being arranged to receive at least some of the lead sulphide from the precipitation tank.
25. An assembly according to claim 24, wherein the separation means comprises a centrifuge.
26. An assembly according to claim 24 or claim 25, further comprising purification means disposed intermediate the dissolving apparatus and the precipitation tank, the purification means being adapted for removing insoluble impurities from said solution.
27. An assembly according to claim 26, wherein the purification means comprises a centrifuge.
28. An assembly according to any one of claims 24 to 27, further comprising glass fragmentation means for producing lead glass fragments of between 0.1mm and 12.5mm diameter.
29. An assembly according to any one of claims 24 to 28, further comprising lead sulphide treatment means for receiving the lead sulphide from the separation means and reacting the lead sulphide with a chloride of iron to form lead chloride.
30. An assembly according to any one of claims 24 to 29, further comprising base metasilicate purification means for purifying the base metasilicate, the base metasilicate purification means being configured to pass the base metasilicate through a medium comprising a ligand.
31. An apparatus for at least partially dissolving a lead glass in a base substantially as hereinbefore described with reference to figure 1 of the accompanying drawings.
32. An assembly for recovering lead from lead glass substantially as hereinbefore described with reference to figure 2 of the accompanying drawings.
33. A method for recovering lead from lead glass substantially as hereinbefore described with reference to figure 3 of the accompanying drawings.