Title of Invention	A PROCESS FOR THE RECOVERY OF METAL VALUES FROM WASTE PRINTED CIRCUIT BOARDS
Abstract	The present invention recites a simple process for the processing of waste printed circuit boards to separate metal values from non-metallic constituents. The undesirable attachments are first removed from the boards and the boards are then shredded into small pieces. These pieces are ground in a tumbling mill. A classifier is used to remove the fine particles containing very little metal values. The coarse fraction then is treated in a gravity separator to separate the heavy metallic components from the light resinous plastic material of the boards. The products of gravity separation are then treated in flotation process to further purify the heavy metal rich fraction. The products of flotation step are treated in enhanced gravity separator to remove lighter plastic particles from the product further. The valuable product is then conveniently dried up for further purification steps. The dried valuable product is treated in electrodynamic separator to obtain a further metal rich conductive fraction and a small non-conductive fraction of plastic material. Another electrostatic separation step is performed to obtain a very pure metallic conductive fraction and a small, purely non-conducting non-metallic fraction.

Title of Invention

A PROCESS FOR THE RECOVERY OF METAL VALUES FROM WASTE PRINTED CIRCUIT BOARDS

Abstract

The present invention recites a simple process for the processing of waste printed circuit boards to separate metal values from non-metallic constituents. The undesirable attachments are first removed from the boards and the boards are then shredded into small pieces. These pieces are ground in a tumbling mill. A classifier is used to remove the fine particles containing very little metal values. The coarse fraction then is treated in a gravity separator to separate the heavy metallic components from the light resinous plastic material of the boards. The products of gravity separation are then treated in flotation process to further purify the heavy metal rich fraction. The products of flotation step are treated in enhanced gravity separator to remove lighter plastic particles from the product further. The valuable product is then conveniently dried up for further purification steps. The dried valuable product is treated in electrodynamic separator to obtain a further metal rich conductive fraction and a small non-conductive fraction of plastic material. Another electrostatic separation step is performed to obtain a very pure metallic conductive fraction and a small, purely non-conducting non-metallic fraction.

Full Text	Field of Invention The present invention relates to a process for the recovery of metal values from waste printed circuit boards. The present invention particularly relates to the recovery of metals such as copper, lead, zinc, aluminum, nickel, etc. including precious metals such as gold and silver. The utility of the invention is in the field of recycling of electronic waste. The waste printed circuit boards contain significant amount of metal values. The usage of this invention lies in the recovery of aforesaid metals from non-metallic constituents of waste printed circuit boards using physical separation techniques. Background of Invention and Description of Prior Art Studies on discarded printed circuit printed boards [PCBs] reutilization have started attaining important significance and application values, which can not only achieve secondary resources recycling, but also prevent environment pollution. Physical methods show great potential and advantages on discarded PCBs reutilization as compared to chemical and biological methods. Reference may be made to US patent no. 5676318 wherein a process is claimed for grinding the printed circuit boards, separating heavier constituents from lighter filler material and then a conductive fraction from the non-conducting fraction. The process is dry, uses specialised equipment and has low throughput in continuous operation. Reference may be made to US patent no. 5887805, which claims another process that has been developed to separate the metallic constituents from the non-metallic constituents. The process involves repeated crushing and screening, separation in a cyclone and also in fluidised bed separation. However, the process requires elaborate dust collection system since it is a dry process that raises the cost and also makes the process maintenance intensive. Reference may also be made to US patent no. 5979033 that recites a device and a method to separate the copper foil from the thermosetting plastics and glass fibre of the printed circuit boards by using molten tin. Residual material floats on top of the tin bath while the copper foils sink. The process is apparently simple but requires high temperatures enhancing the cost component. Also, volatile gases need to be stabilised, which makes the process cumbersome. Reference may further be made to US patent no. 5683040 which claims a method of recycling printed circuit boards. In the said method, the printed circuit boards are cryogenically embrittled, comminuted, separated into a coarse and a fine size class, subjected to magnetic separation and then to high tension separation to obtain a conducting metal-rich fraction and a non-metallic residue. The process requires large quantities of liquid nitrogen and hence may not be very practical for commercial application. US patent no. 5788167 discloses a process that separates and isolates precious and semiprecious metals from electronic circuit boards. The process involves repeated crushing and screening, separation in a cyclone and also in fluidised bed separation. The precious metals are recovered in the high-density product of the fluidised bed separator. The process requires elaborate dust collection system since it is a dry process. Also, the maintenance is cumbersome and expensive. US patent no. 6986192 B2 claims a method for reclamation of precious metals from circuit board scrap. In this process, mild acid is used to shear away undesired metals from the precious metals plated onto the circuit boards. In order to enhance the rate of shearing away, electromagnetic field at specific frequencies need to be applied. Metals such as Cu and Ni are sheared away rapidly leaving metals such as gold which may be skimmed off or filtered. The process is essentially hydrometallurgical in nature and deals with reclamation of precious metals only. Recovery of other metals would require further treatments. The process does not address physical separation before chemical separation. Therefore, the consumption of chemicals will be high and the capacity of the process will be reduced in continuous operation. US patent nos. 5843287 and 6143139 recites a method of recovering metals from metal-containing wastes such as circuit boards, cathode ray tubes and transistors. The process requires 300-800 °C for the combustion of organic materials in the first stage. In the second, temperature needs to be raised to 1000-1550 °C in order to melt the glass formers of the waste. Low melting metals are recovered after the combustion of the organics. High melting metals are separated from the waste at their respective melting points. Requirement of such high temperatures and in stages makes the process comparatively more expensive affair. Reference may be made to US patent no 6336601 B1 wherein a method of separating metallic material from waste printed circuit boards is developed. The process requires heating up of the printed circuit boards to a temperature of 250 °C or higher. At this temperature, the joint between the solder and the copper foils become stronger and the board material becomes brittle. In the next stage, pulverisation of the circuit board is performed in which the board material disintegrates into finer particles while the solder-copper assembly is crushed into relatively coarser size. A size separation step then separates the metals from the board material. The process again require raising of the temperature to above 250 °C which means the process is likely to be more expensive than the physical, low temperature separation process. Reference may also be made to US patent no 6675454 B1 wherein a method for recycling used printed circuit boards is claimed. The process involves removal of components from the boards and joining such boards by special glue to obtain composite boards. While the energy requirements and processing cost for the method is low, it may not be possible to utilise all types of boards in this method. Also, the requirements of the circuitry would make the use of only certain type of circuit boards possible for a particular case. Reference may be made to a paper published by Wen et al. in Proceedings of the 2005 IEEE International Symposium, 16-19 May 2005. This paper treats -2+0.074 mm and -0.074 mm particles separately in electrostatic and enhanced gravity separator respectively. Dry screening at 0.074 mm in commercial scale is extremely difficult and inefficient. If wet screening is done, the large quantity of +0.074 mm fraction needs to be dried as high tension (electrostatic) separator needs a dry feed. This would not be commercially viable proposition. However, our process from the beginning is a wet process. The size classification is done in a hydrocyclone which is a commercially established operation. The said paper treats large size particles (above 1.00 mm). Liberation is not complete above 1.00 mm. Hence, misplacement of metals in the non- metallic stream and vice versa will have to be lived with in the coarser fraction. In the present invention, the material is ground to -0.5 mm and near complete liberation has been achieved. Further, high tension (electrostatic) separators are known to have very low throughput. Hence, this step without any pre-concentration is sure to be inefficient and expensive. In the present invention, the high tension separator treats materials that have been subjected to several stages of pre-concentration. Most of the non metallic materials have already been removed before it is subjected to high tension separation which is the purification stage. It may be noted that the high tension separators are meant to be used in purification (i.e. final) stage of concentration. In the cited paper, -0.074 mm particles are treated in a Falcon concentrator (enhanced gravity separator) without a preliminary removal of non-metallic constituents. The plastics at this size range have very poor settling characteristics. They also have wettability problem as the surface is hydrophobia Since the relative volume of such small plastic particles is large compared to the volume of metal in this size range, large scale processing of this size particles in Falcon concentrator is almost certain of having operational problems. The present invention utilizes a different kind of enhanced gravity separator, namely multi-gravity separator (MGS) and not a Falcon concentrator. The instant application uses flotation prior to the enhanced gravity concentration. In this manner, we have been able to remove the non-metallic particles by making use of their hydrophobic property. This is the primary novelty in our claim. This is a step that makes the entire concentration less expensive and commercially viable - a step that has not been followed by anyone before. The present process is based on inexpensive unit operations where dust pollution has been eliminated. Accordingly, keeping in view the hitherto known prior art, it may be concluded that a cost-effective process involving the use of commercially available standard equipment where all types of circuit boards can be utilized is not existing presently. Many of the processes require high temperature rendering the process energy intensive. Some of the processes use specialized equipments that are not available commercially in the market in mass scale. Some of them have low throughput and processing large tonnage of waste circuit boards may be a difficult proposition. Some of these processes use elaborate accessories that hamper the overall economy of the process. Thus, according to prior art there are a number of problems associated with the reported inventions. The present invention, therefore offers a simple solution to the problems mentioned in the prior art. In this invention all printed circuit boards are utilized regardless of their type, size or origin. The circuit boards are pulverized to a convenient size after removal of undesirable attachments such as frames, nuts, cords and switches from the boards. A series of low cost physical separation techniques are then used to separate the metal values from the non-metallic filler material. The equipments used are the same as those used in conventional mineral processing. The process is a combination of wet and dry techniques. The drying stage is required when most of the non-metals have been removed from the powdered circuit boards. Hence, it poses very little problem in terms of handling as well as cost. There is no dust problem, energy requirements are only at the pulverization stage and huge tonnage can be processed in a continuous manner. No specialized equipment is required and an existing mineral processing plant can be used for processing the waste circuit boards. Objects of the Invention The main object of the present invention is thus to provide a process for recovery of metal values from waste printed circuit boards which obviates the drawbacks of the hitherto known prior processes as detailed above. Another object of the present invention is to provide a method for processing waste printed circuit boards that does not use specialized equipment or high temperature and uses standard equipments that are used regularly in mineral processing plants. Still another object of the present invention is to provide an environment friendly method in which no toxic gas or effluent is generated for separating metallic constituents from non-metallic constituents of the printed circuit boards. Yet another object of the present invention is to provide cost-effective, high throughput process for recovering metal values from waste printed circuit boards. A further object of the present invention is to provide recovery of copper, lead, zinc, nickel, aluminum, gold and silver from the waste printed circuit boards and thereby reducing the environmental hazards caused by them. Summary of the Invention The present invention relies on a simple flowsheet for the processing of waste printed circuit boards. The undesirable attachments are first removed from the boards. They are then shredded in a mechanical shear machine into small pieces. The small pieces are ground in tumbling mill carefully to prevent generation of large quantity of ultrafines. A classifier is used to separate the fine particles containing very little or no metal value. The coarse fraction is then treated by gravity separation to separate the heavy metallic components from the light resinous plastic material of the boards. The products of gravity separation are then treated in flotation process to further purify the heavy metal rich fraction. The product of flotation step is depleted of non-metallic constituents and is then treated in enhanced gravity separator to further remove lighter plastic particles from the product. The valuable product is severely depleted of non-metallic particles and is then conveniently dried up for further purification steps. The dry product is then treated in electrodynamic separator to obtain a further metal rich conductive fraction and a small non-conductive fraction of plastic material. Another electrostatic separation step is performed on the metal rich product in a plate type separator to obtain a very pure metallic conductive fraction and a small, purely non-conducting non-metallic fraction. Accordingly, the present invention provides a process for the recovery of metal values from waste printed circuit boards which comprises of: (a) mechanically shearing the said boards into small pieces and grinding the said pieces to about 500 to 0 micron size in a tumbling mill such as ball mill, rod mill and the like; (b) removing the particles of size ranging between 50 to 0 micron from the ground material as obtained in step [a] in a standard classifier such as hydrocyclone, spiral and the like to obtain coarser particles of size 50 to 500 microns; (c) separating the coarser particles as obtained in step [b] into a heavy, a light and an intermediate product using a gravity separator such as Wilfley Table, spiral, and the like; (d) treating each of the three products as obtained in step [c] separately by flotation in mechanical, Jameson or column cells, optionally with appropriate reagents namely frothers, collectors, depressants and activators either alone or in a combination thereof to obtain metal rich products; (e) treating the metal rich products as obtained in step [d] in enhanced gravity separators such as multi-gravity separator, Knelson concentrator and the like to remove the lighter non-metallic impurities; (f) drying the metal rich product of enhanced gravity separation as obtained in step [e] and purifying it in electrodynamic separators such as high tension separator to remove remaining non-conducting non-metallic constituents; (g) treating the said metal rich product as obtained in step [f] in electrostatic separator to recover the desired metal values and obtain pure, conducting metallic fraction consisting of copper, lead, tin, iron, aluminum, cadmium, nickel, gold and silver. In an embodiment of the present invention the waste printed circuit boards may have a metallic composition of 10-13% copper, 2-3% lead, 1-2% tin, 3-4% iron, 2-3% aluminum, 0.005-0.01% cadmium, 0.1-0.5% nickel, 0.01-0.03% silver, 0.01-0.02% gold. In another embodiment of the present invention the heavy product of gravity concentration may have a specific gravity in the range of 6.0-10.0, the light product may have a specific gravity range of 1.4-3.5 and the intermediate product may have a specific gravity range of 3.5-6.0 In yet another embodiment of the present invention the flotation operation may be carried out with and without the addition of reagents as well as a combination thereof. Detailed Description of the Invention The present invention provides a process for recovery of metal values from waste printed circuit boards, which comprises of several steps. The first step is to manually remove the undesirable objects such as frames, switches, cords, nuts and big metal pieces from the waste circuit boards leaving the other electronic components attached with the boards. A mechanical shear is then used to shred the boards into small pieces. These small pieces are then ground in a tumbling mill to 500-0 micron size. The tumbling mill product, the ground waste printed circuit boards, is then subjected to a desliming operation in a classifier to remove particles in the range 50-0 micron in size. The classifier is to be operated at 10-20% solids in the feed pulp. The underflow product (coarse fraction) of the hydrocyclone is to be treated in a gravity separator with 10-15% solids in feed slurry and at 2-3 degrees inclination of the table. The concentration operation has three products, namely, concentrate, middling and tailings. The concentrate is mostly heavy metallic particles while the middling is a mixture of some misplaced heavy metallic particles and some light plastic particles. The tailings stream is mostly light, non-metallic particles. These three products are then treated separately in a flotation cell. Appropriate combination of reagents need to be used in the flotation process. While the gravity separation concentrate can be treated at 20-30% solids in feed by flotation, 15-20% solids need to be used for the middling and 8-10% solids for the tailings. The metal rich concentrates of flotation of gravity concentrate and tabling middling are combined and treated in an enhanced gravity separator (EGS) hitherto known as Stage 1. The EGS separates the lighter impurities (tailings) from the heavier metal rich fraction (concentrate) and operates at 105-115 rpm with 1-2 Ipm of wash water and 10-15% solids in feed. The tailings of this stage is mixed with the tailings of metal rich concentrate of flotation of gravity tailings and treated in EGS separately, hitherto known as Stage 2. The conditions for this stage are 110-120 rpm and 8-10% solids in feed at 1-1.2 Ipm wash water rate. Concentrates of both stages have small quantity of non-metals and are dried in a furnace at 50-60 °C. The metal rich dry concentrate of EGS Stage 1 is then treated in electrodynamic separator to remove the non-conducting non-metals (tailings). The electrodynamic separator is operated at 100-110 rpm, 15-18 KV DC and 10-12 KV AC supply in this stage, hitherto known as Stage 1. The non-conducting non-metallic tailings stream of this Stage 1 is mixed with the metal rich fraction of EGS separation Stage 2 and treated in another stage of electrodynamic separation, hitherto known as Stage 2. Electrodynamic separation of stage 2 is performed at 110-115 rpm, 20-22 KV DC and 10-12 KV AC supply. Another metal rich conductive concentrate and non-metallic non-conducting tailings stream is obtained in electrodynamic separation Stage 2. The two concentrates of electrodynamic separation (Stage 1 and 2) are further purified in plate type electrostatic separator separately to obtain purer conducting metal rich concentrates. The conditions were 30-32 KV supply for electrodynamic Stage 1 concentrate and 35-38 KV for electrodynamic Stage 2 concentrate. A last stage of electrostatic separation operation is carried out to recover additional metal value from the previous stages that would have been misplaced in the tailings stream as well as for purification of the metal rich portion. The filler materials of the printed circuit boards as well as the metals in them have poor grindability. The resinous plastic has no ductility also and hence would produce ultrafines during pulverization in a tumbling mill due to attrition grinding. The ductile metals produce very little ultrafines. Since ultrafines are difficult to process, a good control of media size prevents the generation of ultrafines in the tumbling mill. Only large size media suffice. The classifier removes the particles in the size range 50-0 micron from the ground product and enriches the starting material in terms of its metal content. This is because the ulrtafines (50-0 micron) contain very little metal values. The specific gravity of non-metallic material is in the range 2.0-1.4 while all metals have much higher specific gravity. Hence, a wet gravity separation operation to separate the heavier metallic material from the lighter non-metallic material is novel. The use of a combination of reagents for flotation in this regard is entirely novel. Enhanced gravity separator (EGS) uses a centrifugal force field to enhance the settling kinetics of the particles. Employing EGS to further separate the heavier metallic and lighter non-metallic particles is another novel feature in the present invention. Further novelty of the present invention lies in the fact that it is a combination of wet and dry processes. Initially, the wet processes eliminate the dust problem and associated environmental issues. Dispersion in liquid medium is better in obtaining a homogeneous suspension and formation of agglomerates and segregation is avoided to a great extent. This improves the separation performance by reducing the misplacement and is a novel feature in the present invention. The following examples are given by way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention. EXAMPLE-1 By way of example, 100 kg of waste printed circuit boards were procured and the undesirable attachments such as big metal pieces, frames, cords, switches, nuts etc., were removed manually. However, the smaller electronic attachments and 1C chips were left in tact. These circuit boards were then shredded in a mechanical shearing machine. The shredded circuit boards were further shredded in a manual shearing machine to about 15 to 20 mm square shape. These small pieces were then ground in a laboratory batch tumbling mill using only 50±2 mm diameter media. The mill was stopped intermittently and the material was screened at 0.5 mm to remove the 0.5 to 0.0 mm particles and the coarser material re-charged into the mill for further grinding. The grinding continued till all the materials were pulverized to 0.5 to 0.0 mm size range. The processing steps for this example are shown in Figure 1. The beneficiation process was started with 2 kg of pulverized waste printed circuit board containing 22.5% total metal by weight. It was first subjected to desliming operation in a classifier. The yield to the underflow was 84.7% and the total metal content was 25.51%. The underflow was treated in flotation to generate two products. The concentrate had a yield of 29.9% with 38.9% total metal. Yield of the tailings was 54.8% with 18.2% total metal. Metal rich product of flotation was then treated in first stage enhanced gravity separator (EGS) to obtain a concentrate at 21.91% yield and 45.7% total metal. The second stage EGS operation was carried out with the combined streams of flotation tailings and the tailings of first stage EGS. In the second stage of EGS a concentrate at 13.13% yield with 29.55% total metal was obtained. After this stage all samples were dried and the dry segment of the flowsheet was started. The dry operations started with electrodynamic separation of the first stage EGS concentrate. This stage resulted in a concentrate with 64.4% total metal at 9.1% yield. Another electrodynamic separation of the tailings of this stage and the concentrates of second stage EGS produced a concentrate at 8.4% yield with 48% total metal. Electrostatic separation of the first electrodynamic separation concentrate generated a concentrate at 5.6% yield with 74.1% total metal. This is one of the final concentrates with a composition of 48.4% copper, 4.3% lead, 4.6% tin, 11.4% iron, 3.8% aluminum, 0.008% cadmium, 1.6% nickel, 0.015% silver and 0.008% gold. Second stage electrostatic separation of the second electrodynamic separation concentrate and first electrostatic separation tailings generated a concentrate with 54.2% total metal at 9.17% yield. The concentrate of the second stage electrostatic separation was treated in a third stage of electrostatic separation. This stage produced a concentrate at 7.3% yield and with 60.3% total metal in it. Thus, according to the process route presented in this example, poor recovery of the valuable metals was obtained. EXAMPLE-2 In this case, the same previously ground material was used for beneficiation. The processing steps for this example are shown in Figure 2. The beneficiation process was started with 2 kg of pulverized waste printed circuit board containing 22.5% total metal by weight. It was first subjected to desliming operation in a classifier. The yield to the underflow was 83.6% and the total metal content was 25.5%. The underflow was treated in a gravity separator to generate three products. The heavy concentrate had a yield of 25.1% with 37.5% total metal. Yield of the light tailings was 23.0% with 12.6% total metal. The intermediate middling had 35.5% yield and 25.3% total metal. Second stage gravity separation of middling product generated a metal rich concentrate with 18.7% yield and 38.7% total metal. Third stage gravity concentration of combined first stage tailings and second stage middling and tailings produced a concentrate with 8.7% yield and 20.3% total metal. The concentrate of second stage gravity separation was treated by flotation (first stage) to generate a metal rich concentrate at 16.6% yield and 42.6% total metal. The concentrate of third stage gravity separation was treated in flotation (second stage) separately. This stage generated a concentrate at 8.0% yield with 21.1% total metal. A third stage flotation of the middling of third stage gravity separation produced a concentrate at 2.67% yield at 20.9% total metal content. The dry operations started with electrodynamic separation of the first stage gravity concentrate. The purification resulted in a concentrate with 53.7% total metal at 12.1% yield. Another electrodynamic separation of the tailings of this stage and the concentrates of first stage and second stage flotation produced a concentrate at 11.9% yield with 52.1% total metal. A third stage of electrodynamic separation of the tailings of first two stages of flotation and concentrate of third stage flotation produced a metal rich concentrate at 0.82% yield with 33.9% total metal. Electrostatic separation of the first electrodynamic separation concentrate generated a concentrate with 7.7% yield at 67.1% total metal. This is one of the final concentrates having a composition of 41.2% copper, 4.2% lead, 3.3% tin, 10.4% iron, 4.1% aluminum, 0.016% cadmium, 3.8% nickel, 0.014% silver and 0.007% gold. Electrostatic separation of the second electrodynamic separation product generated a concentrate with 56.9% total metal at 11.57% yield. The tailings of the second electrodynamic separation, the concentrate of the third stage electrodynamic separation and the tailings of second stage electrostatic separation were combined and treated in a third stage of electrostatic separation. This operation produced a concentrate at 28.4% yield and with 50.7% total metal in it. Evidently, the metal grades in the concentrates were not high enough leading to a poorer recovery of the valuable metals in this example. EXAMPLE-3 In this case also the same previously ground material was used for beneficiation. The processing steps for this example are shown in Figure 3. The beneficiation process was started with 3 kg of pulverized waste printed circuit board containing 22.5% total metal by weight. It was first subjected to desliming operation in a classifier. The yield to the underflow was 80.7% and the total metal content was 26.6%. The underflow was treated in a gravity separator to generate three products. The heavy concentrate had a yield of 38.3% with 38.4% total metal. Yield of the light tailings was 24.1% with 8.6% total metal. The intermediate middling had 18.3% yield and 25.7% total metal. Flotation of the heavy product generated a metal rich concentrate with 31.3% yield and 42.2% total metal. Similarly, flotation of middling generated a metal rich concentrate with 8.8% yield and 36.4% total metal. Flotation of tailings produced a concentrate with 5.5% yield and 18.3% total metal. The first two concentrates of flotation were combined and treated in EGS to generate a further metal rich concentrate at 31.6% yield and 47.8% total metal. The other concentrate of flotation was treated in EGS separately since these contained the finer fraction of the metal rich product. This stage generated a metal rich concentrate at 4.9% yield with 43.9% total metal. At the end of enhanced gravity separation (EGS) stages, the valuable products were dried and subjected to purification operations using dry separation techniques. The dry operations started with electrodynamic separation of the two EGS concentrates. The purification resulted in a concentrate with 68.9% total metal at 22.5% yield. Another electrodynamic separation of the tailings of this stage and the tailings of first stage of EGS produced a concentrate with 10.0% yield at 28.1% total metal. Electrostatic separation of the first electrodynamic separation product generated a concentrate with 13.3% yield at 93.1% total metal. This is one of the final concentrates that had a composition of 51.1% copper, 10.4% lead, 6.7% tin, 13.1% iron, 9.3% aluminum, 0.19% cadmium, 2.4% nickel, 0.11% silver, 0.083% gold. Electrostatic separation of the second electrodynamic separation product generated a concentrate with 44.2% total metal at 5.8% yield. The tailings of the first electrostatic separation and the concentrate of the second stage electrostatic separation were combined and treated in a third stage of electrostatic separation. This stage produced a concentrate at 6.9% yield and with 64.6% total metal in it. The composition of this concentrate was 40.1% copper, 5.1% lead, 4.4% tin, 7.7% iron, 6.5% aluminum, 0.017% cadmium, 0.69% nickel, 0.09% silver and 0.042% gold. Thus, at the end of the purification process, as presented in this example, several concentrate products were obtained with high yield and purity. Depending upon the end use they may be combined proportionately to meet the specification of downstream processing or may be recirculated in a continuous operation. The main advantages of the present invention are: 1. The process does not require specialized and sophisticated equipment for processing of waste printed circuit boards. 2. The natural hydrophobicity of non-metallic constituents is effectively exploited by wet flotation process using combination of reagents therefor. 3. All equipment and machinery required are standard and readily available worldwide. 4. An existing mineral processing plant will be able to handle the processing with only minor adjustments. 5. A continuous operation at plant level will be able to minimize/eliminate the loss of metal values to a negligible level. 6. The operation is simple and the overall processing cost is low as the operations involve only cheap, physical separation steps. 7. The techniques used are purely physical in nature and thus generate no additional harmful effluents. 8. Enables the recovery of both the metallic and non-metallic constituents separately. 9. Very little or no chemicals are used and therefore the cost effectiveness of the process is improved. We claim: 1. A process for the recovery of metal values from waste printed circuit boards which comprises of (h) mechanically shearing the said boards into small pieces and grinding the said pieces to about 500 to 0 micron size in a tumbling mill such as ball mill, rod mill and the like; (i) removing the particles of size ranging between 50 to 0 micron from the ground material as obtained in step [a] in a standard classifier such as hydrocyclone, spiral and the like to obtain coarser particles of size 50 to 500 microns; (j) separating the coarser particles as obtained in step [b] into a heavy, a light and an intermediate product using a gravity separator such as Wilfley Table, spiral, and the like; (k) treating each of the three products as obtained in step [c] separately by flotation in mechanical, Jameson or column cells, optionally with appropriate reagents namely frothers, collectors, depressants and activators either alone or in a combination thereof to obtain metal rich products; (I) treating the metal rich products as obtained in step [d] in enhanced gravity separators such as multi-gravity separator, Knelson concentrator and the like to remove the lighter non-metallic impurities; (m) drying the metal rich product of enhanced gravity separation as obtained in step [e] and purifying it in electrodynamic separators such as high tension separator to remove remaining non-conducting non-metallic constituents; (n) treating the said metal rich product as obtained in step [f] in electrostatic separator to recover the desired metal values and obtain pure, conducting metallic fraction consisting of copper, lead, tin, iron, aluminum, cadmium, nickel, gold and silver. 2. A process as claimed in claim 1, wherein the waste printed circuit boards preferably have the following metallic composition: Copper: 10 to 13% Lead: 2 to 3% Tin: 1 to 2% Iron: 3 to 4% Aluminum: 2 to 3% Cadmium: 0.005 to 0.01% Nickel: 0.1 to 0.5% Silver: 0.01 to 0.03% Gold: 0.01 to 0.02% Traces of other metals 3. A process as claimed in claim 1, wherein the heavy product of gravity concentration preferably have a specific gravity in the range of 6.0 to 12.0. 4. A process as claimed in claim 1, wherein the light product of gravity concentration preferably have a specific gravity in the range of 1.4 to 3.5. 5. A process as claimed in claim 1, wherein the intermediate product of gravity concentration preferably have a specific gravity in the range of 3.5 to 6.0. 6. A process as claimed in claim 1, wherein the flotation operation may be carried out with or without the addition of reagents either alone or in any combination. 7. A process for recovery of metal values from waste printed circuit boards substantially as herein described with reference to the examples and figures accompanying this specification.

Full Text

Field of Invention
The present invention relates to a process for the recovery of metal values from waste printed circuit boards. The present invention particularly relates to the recovery of metals such as copper, lead, zinc, aluminum, nickel, etc. including precious metals such as gold and silver. The utility of the invention is in the field of recycling of electronic waste. The waste printed circuit boards contain significant amount of metal values. The usage of this invention lies in the recovery of aforesaid metals from non-metallic constituents of waste printed circuit boards using physical separation techniques.
Background of Invention and Description of Prior Art
Studies on discarded printed circuit printed boards [PCBs] reutilization have started attaining important significance and application values, which can not only achieve secondary resources recycling, but also prevent environment pollution. Physical methods show great potential and advantages on discarded PCBs reutilization as compared to chemical and biological methods.
Reference may be made to US patent no. 5676318 wherein a process is claimed for grinding the printed circuit boards, separating heavier constituents from lighter filler material and then a conductive fraction from the non-conducting fraction. The process is dry, uses specialised equipment and has low throughput in continuous operation.
Reference may be made to US patent no. 5887805, which claims another process that has been developed to separate the metallic constituents from the non-metallic constituents. The process involves repeated crushing and screening, separation in a cyclone and also in fluidised bed separation. However, the process requires elaborate dust collection system since it is a dry process that raises the cost and also makes the process maintenance intensive.
Reference may also be made to US patent no. 5979033 that recites a device and a method to separate the copper foil from the thermosetting plastics and glass fibre of the printed circuit boards by using molten tin. Residual material floats on top of the tin bath while the copper foils sink. The process is apparently simple but requires high temperatures enhancing the cost component. Also, volatile gases need to be stabilised, which makes the process cumbersome.

Reference may further be made to US patent no. 5683040 which claims a method of recycling printed circuit boards. In the said method, the printed circuit boards are cryogenically embrittled, comminuted, separated into a coarse and a fine size class, subjected to magnetic separation and then to high tension separation to obtain a conducting metal-rich fraction and a non-metallic residue. The process requires large quantities of liquid nitrogen and hence may not be very practical for commercial application.
US patent no. 5788167 discloses a process that separates and isolates precious and semiprecious metals from electronic circuit boards. The process involves repeated crushing and screening, separation in a cyclone and also in fluidised bed separation. The precious metals are recovered in the high-density product of the fluidised bed separator. The process requires elaborate dust collection system since it is a dry process. Also, the maintenance is cumbersome and expensive.
US patent no. 6986192 B2 claims a method for reclamation of precious metals from circuit board scrap. In this process, mild acid is used to shear away undesired metals from the precious metals plated onto the circuit boards. In order to enhance the rate of shearing away, electromagnetic field at specific frequencies need to be applied. Metals such as Cu and Ni are sheared away rapidly leaving metals such as gold which may be skimmed off or filtered. The process is essentially hydrometallurgical in nature and deals with reclamation of precious metals only. Recovery of other metals would require further treatments. The process does not address physical separation before chemical separation. Therefore, the consumption of chemicals will be high and the capacity of the process will be reduced in continuous operation.
US patent nos. 5843287 and 6143139 recites a method of recovering metals from metal-containing wastes such as circuit boards, cathode ray tubes and transistors. The process requires 300-800 °C for the combustion of organic materials in the first stage. In the second, temperature needs to be raised to 1000-1550 °C in order to melt the glass formers of the waste. Low melting metals are recovered after the combustion of the organics. High melting metals are separated from the waste at their respective melting points. Requirement of such high temperatures and in stages makes the process comparatively more expensive affair.
Reference may be made to US patent no 6336601 B1 wherein a method of separating metallic material from waste printed circuit boards is developed. The process requires heating up of the printed circuit boards to a temperature of 250 °C or higher. At this temperature, the joint between the solder and the copper foils become stronger and the

board material becomes brittle. In the next stage, pulverisation of the circuit board is performed in which the board material disintegrates into finer particles while the solder-copper assembly is crushed into relatively coarser size. A size separation step then separates the metals from the board material. The process again require raising of the temperature to above 250 °C which means the process is likely to be more expensive than the physical, low temperature separation process.
Reference may also be made to US patent no 6675454 B1 wherein a method for recycling used printed circuit boards is claimed. The process involves removal of components from the boards and joining such boards by special glue to obtain composite boards. While the energy requirements and processing cost for the method is low, it may not be possible to utilise all types of boards in this method. Also, the requirements of the circuitry would make the use of only certain type of circuit boards possible for a particular case.
Reference may be made to a paper published by Wen et al. in Proceedings of the 2005 IEEE International Symposium, 16-19 May 2005. This paper treats -2+0.074 mm and -0.074 mm particles separately in electrostatic and enhanced gravity separator respectively. Dry screening at 0.074 mm in commercial scale is extremely difficult and inefficient. If wet screening is done, the large quantity of +0.074 mm fraction needs to be dried as high tension (electrostatic) separator needs a dry feed. This would not be commercially viable proposition. However, our process from the beginning is a wet process. The size classification is done in a hydrocyclone which is a commercially established operation.
The said paper treats large size particles (above 1.00 mm). Liberation is not complete above 1.00 mm. Hence, misplacement of metals in the non- metallic stream and vice versa will have to be lived with in the coarser fraction. In the present invention, the material is ground to -0.5 mm and near complete liberation has been achieved.
Further, high tension (electrostatic) separators are known to have very low throughput. Hence, this step without any pre-concentration is sure to be inefficient and expensive. In the present invention, the high tension separator treats materials that have been subjected to several stages of pre-concentration. Most of the non metallic materials have already been removed before it is subjected to high tension separation which is the purification stage. It may be noted that the high tension separators are meant to be used in purification (i.e. final) stage of concentration.
In the cited paper, -0.074 mm particles are treated in a Falcon concentrator (enhanced gravity separator) without a preliminary removal of non-metallic constituents. The plastics at

this size range have very poor settling characteristics. They also have wettability problem as the surface is hydrophobia Since the relative volume of such small plastic particles is large compared to the volume of metal in this size range, large scale processing of this size particles in Falcon concentrator is almost certain of having operational problems.
The present invention utilizes a different kind of enhanced gravity separator, namely multi-gravity separator (MGS) and not a Falcon concentrator. The instant application uses flotation prior to the enhanced gravity concentration. In this manner, we have been able to remove the non-metallic particles by making use of their hydrophobic property. This is the primary novelty in our claim. This is a step that makes the entire concentration less expensive and commercially viable - a step that has not been followed by anyone before. The present process is based on inexpensive unit operations where dust pollution has been eliminated.
Accordingly, keeping in view the hitherto known prior art, it may be concluded that a cost-effective process involving the use of commercially available standard equipment where all types of circuit boards can be utilized is not existing presently. Many of the processes require high temperature rendering the process energy intensive. Some of the processes use specialized equipments that are not available commercially in the market in mass scale. Some of them have low throughput and processing large tonnage of waste circuit boards may be a difficult proposition. Some of these processes use elaborate accessories that hamper the overall economy of the process. Thus, according to prior art there are a number of problems associated with the reported inventions.
The present invention, therefore offers a simple solution to the problems mentioned in the prior art. In this invention all printed circuit boards are utilized regardless of their type, size or origin. The circuit boards are pulverized to a convenient size after removal of undesirable attachments such as frames, nuts, cords and switches from the boards. A series of low cost physical separation techniques are then used to separate the metal values from the non-metallic filler material. The equipments used are the same as those used in conventional mineral processing. The process is a combination of wet and dry techniques. The drying stage is required when most of the non-metals have been removed from the powdered circuit boards. Hence, it poses very little problem in terms of handling as well as cost. There is no dust problem, energy requirements are only at the pulverization stage and huge tonnage can be processed in a continuous manner. No specialized equipment is required and an existing mineral processing plant can be used for processing the waste circuit boards.

Objects of the Invention
The main object of the present invention is thus to provide a process for recovery of metal values from waste printed circuit boards which obviates the drawbacks of the hitherto known prior processes as detailed above.
Another object of the present invention is to provide a method for processing waste printed circuit boards that does not use specialized equipment or high temperature and uses standard equipments that are used regularly in mineral processing plants.
Still another object of the present invention is to provide an environment friendly method in which no toxic gas or effluent is generated for separating metallic constituents from non-metallic constituents of the printed circuit boards.
Yet another object of the present invention is to provide cost-effective, high throughput process for recovering metal values from waste printed circuit boards.
A further object of the present invention is to provide recovery of copper, lead, zinc, nickel, aluminum, gold and silver from the waste printed circuit boards and thereby reducing the environmental hazards caused by them.
Summary of the Invention
The present invention relies on a simple flowsheet for the processing of waste printed circuit boards. The undesirable attachments are first removed from the boards. They are then shredded in a mechanical shear machine into small pieces. The small pieces are ground in tumbling mill carefully to prevent generation of large quantity of ultrafines. A classifier is used to separate the fine particles containing very little or no metal value. The coarse fraction is then treated by gravity separation to separate the heavy metallic components from the light resinous plastic material of the boards. The products of gravity separation are then treated in flotation process to further purify the heavy metal rich fraction. The product of flotation step is depleted of non-metallic constituents and is then treated in enhanced gravity separator to further remove lighter plastic particles from the product. The valuable product is severely depleted of non-metallic particles and is then conveniently dried up for further purification steps. The dry product is then treated in electrodynamic separator to obtain a further metal rich conductive fraction and a small non-conductive fraction of plastic material. Another electrostatic separation step is performed on the metal rich product in a plate type separator

to obtain a very pure metallic conductive fraction and a small, purely non-conducting non-metallic fraction.
Accordingly, the present invention provides a process for the recovery of metal values from waste printed circuit boards which comprises of:
(a) mechanically shearing the said boards into small pieces and grinding the said
pieces to about 500 to 0 micron size in a tumbling mill such as ball mill, rod mill
and the like;
(b) removing the particles of size ranging between 50 to 0 micron from the ground
material as obtained in step [a] in a standard classifier such as hydrocyclone,
spiral and the like to obtain coarser particles of size 50 to 500 microns;
(c) separating the coarser particles as obtained in step [b] into a heavy, a light and
an intermediate product using a gravity separator such as Wilfley Table, spiral,
and the like;
(d) treating each of the three products as obtained in step [c] separately by flotation
in mechanical, Jameson or column cells, optionally with appropriate reagents
namely frothers, collectors, depressants and activators either alone or in a
combination thereof to obtain metal rich products;
(e) treating the metal rich products as obtained in step [d] in enhanced gravity
separators such as multi-gravity separator, Knelson concentrator and the like to
remove the lighter non-metallic impurities;
(f) drying the metal rich product of enhanced gravity separation as obtained in step
[e] and purifying it in electrodynamic separators such as high tension separator
to remove remaining non-conducting non-metallic constituents;
(g) treating the said metal rich product as obtained in step [f] in electrostatic
separator to recover the desired metal values and obtain pure, conducting
metallic fraction consisting of copper, lead, tin, iron, aluminum, cadmium, nickel,
gold and silver.
In an embodiment of the present invention the waste printed circuit boards may have a metallic composition of 10-13% copper, 2-3% lead, 1-2% tin, 3-4% iron, 2-3% aluminum, 0.005-0.01% cadmium, 0.1-0.5% nickel, 0.01-0.03% silver, 0.01-0.02% gold.
In another embodiment of the present invention the heavy product of gravity concentration may have a specific gravity in the range of 6.0-10.0, the light product may have a specific gravity range of 1.4-3.5 and the intermediate product may have a specific gravity range of 3.5-6.0

In yet another embodiment of the present invention the flotation operation may be carried out with and without the addition of reagents as well as a combination thereof.
Detailed Description of the Invention
The present invention provides a process for recovery of metal values from waste printed circuit boards, which comprises of several steps. The first step is to manually remove the undesirable objects such as frames, switches, cords, nuts and big metal pieces from the waste circuit boards leaving the other electronic components attached with the boards. A mechanical shear is then used to shred the boards into small pieces. These small pieces are then ground in a tumbling mill to 500-0 micron size. The tumbling mill product, the ground waste printed circuit boards, is then subjected to a desliming operation in a classifier to remove particles in the range 50-0 micron in size. The classifier is to be operated at 10-20% solids in the feed pulp.
The underflow product (coarse fraction) of the hydrocyclone is to be treated in a gravity separator with 10-15% solids in feed slurry and at 2-3 degrees inclination of the table. The concentration operation has three products, namely, concentrate, middling and tailings. The concentrate is mostly heavy metallic particles while the middling is a mixture of some misplaced heavy metallic particles and some light plastic particles. The tailings stream is mostly light, non-metallic particles. These three products are then treated separately in a flotation cell. Appropriate combination of reagents need to be used in the flotation process. While the gravity separation concentrate can be treated at 20-30% solids in feed by flotation, 15-20% solids need to be used for the middling and 8-10% solids for the tailings.
The metal rich concentrates of flotation of gravity concentrate and tabling middling are combined and treated in an enhanced gravity separator (EGS) hitherto known as Stage 1. The EGS separates the lighter impurities (tailings) from the heavier metal rich fraction (concentrate) and operates at 105-115 rpm with 1-2 Ipm of wash water and 10-15% solids in feed. The tailings of this stage is mixed with the tailings of metal rich concentrate of flotation of gravity tailings and treated in EGS separately, hitherto known as Stage 2. The conditions for this stage are 110-120 rpm and 8-10% solids in feed at 1-1.2 Ipm wash water rate. Concentrates of both stages have small quantity of non-metals and are dried in a furnace at 50-60 °C.
The metal rich dry concentrate of EGS Stage 1 is then treated in electrodynamic separator to remove the non-conducting non-metals (tailings). The electrodynamic separator is operated

at 100-110 rpm, 15-18 KV DC and 10-12 KV AC supply in this stage, hitherto known as Stage 1. The non-conducting non-metallic tailings stream of this Stage 1 is mixed with the metal rich fraction of EGS separation Stage 2 and treated in another stage of electrodynamic separation, hitherto known as Stage 2. Electrodynamic separation of stage 2 is performed at 110-115 rpm, 20-22 KV DC and 10-12 KV AC supply. Another metal rich conductive concentrate and non-metallic non-conducting tailings stream is obtained in electrodynamic separation Stage 2. The two concentrates of electrodynamic separation (Stage 1 and 2) are further purified in plate type electrostatic separator separately to obtain purer conducting metal rich concentrates. The conditions were 30-32 KV supply for electrodynamic Stage 1 concentrate and 35-38 KV for electrodynamic Stage 2 concentrate. A last stage of electrostatic separation operation is carried out to recover additional metal value from the previous stages that would have been misplaced in the tailings stream as well as for purification of the metal rich portion.
The filler materials of the printed circuit boards as well as the metals in them have poor grindability. The resinous plastic has no ductility also and hence would produce ultrafines during pulverization in a tumbling mill due to attrition grinding. The ductile metals produce very little ultrafines. Since ultrafines are difficult to process, a good control of media size prevents the generation of ultrafines in the tumbling mill. Only large size media suffice. The classifier removes the particles in the size range 50-0 micron from the ground product and enriches the starting material in terms of its metal content. This is because the ulrtafines (50-0 micron) contain very little metal values. The specific gravity of non-metallic material is in the range 2.0-1.4 while all metals have much higher specific gravity. Hence, a wet gravity separation operation to separate the heavier metallic material from the lighter non-metallic material is novel. The use of a combination of reagents for flotation in this regard is entirely novel. Enhanced gravity separator (EGS) uses a centrifugal force field to enhance the settling kinetics of the particles. Employing EGS to further separate the heavier metallic and lighter non-metallic particles is another novel feature in the present invention.
Further novelty of the present invention lies in the fact that it is a combination of wet and dry processes. Initially, the wet processes eliminate the dust problem and associated environmental issues. Dispersion in liquid medium is better in obtaining a homogeneous suspension and formation of agglomerates and segregation is avoided to a great extent. This improves the separation performance by reducing the misplacement and is a novel feature in the present invention.

The following examples are given by way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention.
EXAMPLE-1
By way of example, 100 kg of waste printed circuit boards were procured and the undesirable attachments such as big metal pieces, frames, cords, switches, nuts etc., were removed manually. However, the smaller electronic attachments and 1C chips were left in tact. These circuit boards were then shredded in a mechanical shearing machine. The shredded circuit boards were further shredded in a manual shearing machine to about 15 to 20 mm square shape. These small pieces were then ground in a laboratory batch tumbling mill using only 50±2 mm diameter media. The mill was stopped intermittently and the material was screened at 0.5 mm to remove the 0.5 to 0.0 mm particles and the coarser material re-charged into the mill for further grinding. The grinding continued till all the materials were pulverized to 0.5 to 0.0 mm size range.
The processing steps for this example are shown in Figure 1. The beneficiation process was started with 2 kg of pulverized waste printed circuit board containing 22.5% total metal by weight. It was first subjected to desliming operation in a classifier. The yield to the underflow was 84.7% and the total metal content was 25.51%. The underflow was treated in flotation to generate two products. The concentrate had a yield of 29.9% with 38.9% total metal. Yield of the tailings was 54.8% with 18.2% total metal. Metal rich product of flotation was then treated in first stage enhanced gravity separator (EGS) to obtain a concentrate at 21.91% yield and 45.7% total metal. The second stage EGS operation was carried out with the combined streams of flotation tailings and the tailings of first stage EGS. In the second stage of EGS a concentrate at 13.13% yield with 29.55% total metal was obtained.
After this stage all samples were dried and the dry segment of the flowsheet was started. The dry operations started with electrodynamic separation of the first stage EGS concentrate. This stage resulted in a concentrate with 64.4% total metal at 9.1% yield. Another electrodynamic separation of the tailings of this stage and the concentrates of second stage EGS produced a concentrate at 8.4% yield with 48% total metal.
Electrostatic separation of the first electrodynamic separation concentrate generated a concentrate at 5.6% yield with 74.1% total metal. This is one of the final concentrates with a composition of 48.4% copper, 4.3% lead, 4.6% tin, 11.4% iron, 3.8% aluminum, 0.008% cadmium, 1.6% nickel, 0.015% silver and 0.008% gold. Second stage electrostatic separation of the second electrodynamic separation concentrate and first electrostatic

separation tailings generated a concentrate with 54.2% total metal at 9.17% yield. The concentrate of the second stage electrostatic separation was treated in a third stage of electrostatic separation. This stage produced a concentrate at 7.3% yield and with 60.3% total metal in it. Thus, according to the process route presented in this example, poor recovery of the valuable metals was obtained.
EXAMPLE-2
In this case, the same previously ground material was used for beneficiation. The processing steps for this example are shown in Figure 2. The beneficiation process was started with 2 kg of pulverized waste printed circuit board containing 22.5% total metal by weight. It was first subjected to desliming operation in a classifier. The yield to the underflow was 83.6% and the total metal content was 25.5%. The underflow was treated in a gravity separator to generate three products. The heavy concentrate had a yield of 25.1% with 37.5% total metal. Yield of the light tailings was 23.0% with 12.6% total metal. The intermediate middling had 35.5% yield and 25.3% total metal. Second stage gravity separation of middling product generated a metal rich concentrate with 18.7% yield and 38.7% total metal. Third stage gravity concentration of combined first stage tailings and second stage middling and tailings produced a concentrate with 8.7% yield and 20.3% total metal.
The concentrate of second stage gravity separation was treated by flotation (first stage) to generate a metal rich concentrate at 16.6% yield and 42.6% total metal. The concentrate of third stage gravity separation was treated in flotation (second stage) separately. This stage generated a concentrate at 8.0% yield with 21.1% total metal. A third stage flotation of the middling of third stage gravity separation produced a concentrate at 2.67% yield at 20.9% total metal content.
The dry operations started with electrodynamic separation of the first stage gravity concentrate. The purification resulted in a concentrate with 53.7% total metal at 12.1% yield. Another electrodynamic separation of the tailings of this stage and the concentrates of first stage and second stage flotation produced a concentrate at 11.9% yield with 52.1% total metal. A third stage of electrodynamic separation of the tailings of first two stages of flotation and concentrate of third stage flotation produced a metal rich concentrate at 0.82% yield with 33.9% total metal.
Electrostatic separation of the first electrodynamic separation concentrate generated a concentrate with 7.7% yield at 67.1% total metal. This is one of the final concentrates having a composition of 41.2% copper, 4.2% lead, 3.3% tin, 10.4% iron, 4.1% aluminum, 0.016%

cadmium, 3.8% nickel, 0.014% silver and 0.007% gold. Electrostatic separation of the second electrodynamic separation product generated a concentrate with 56.9% total metal at 11.57% yield. The tailings of the second electrodynamic separation, the concentrate of the third stage electrodynamic separation and the tailings of second stage electrostatic separation were combined and treated in a third stage of electrostatic separation. This operation produced a concentrate at 28.4% yield and with 50.7% total metal in it. Evidently, the metal grades in the concentrates were not high enough leading to a poorer recovery of the valuable metals in this example.
EXAMPLE-3
In this case also the same previously ground material was used for beneficiation. The processing steps for this example are shown in Figure 3. The beneficiation process was started with 3 kg of pulverized waste printed circuit board containing 22.5% total metal by weight. It was first subjected to desliming operation in a classifier. The yield to the underflow was 80.7% and the total metal content was 26.6%. The underflow was treated in a gravity separator to generate three products. The heavy concentrate had a yield of 38.3% with 38.4% total metal. Yield of the light tailings was 24.1% with 8.6% total metal. The intermediate middling had 18.3% yield and 25.7% total metal. Flotation of the heavy product generated a metal rich concentrate with 31.3% yield and 42.2% total metal. Similarly, flotation of middling generated a metal rich concentrate with 8.8% yield and 36.4% total metal. Flotation of tailings produced a concentrate with 5.5% yield and 18.3% total metal. The first two concentrates of flotation were combined and treated in EGS to generate a further metal rich concentrate at 31.6% yield and 47.8% total metal. The other concentrate of flotation was treated in EGS separately since these contained the finer fraction of the metal rich product. This stage generated a metal rich concentrate at 4.9% yield with 43.9% total metal.
At the end of enhanced gravity separation (EGS) stages, the valuable products were dried and subjected to purification operations using dry separation techniques. The dry operations started with electrodynamic separation of the two EGS concentrates. The purification resulted in a concentrate with 68.9% total metal at 22.5% yield. Another electrodynamic separation of the tailings of this stage and the tailings of first stage of EGS produced a concentrate with 10.0% yield at 28.1% total metal. Electrostatic separation of the first electrodynamic separation product generated a concentrate with 13.3% yield at 93.1% total metal. This is one of the final concentrates that had a composition of 51.1% copper, 10.4% lead, 6.7% tin, 13.1% iron, 9.3% aluminum, 0.19% cadmium, 2.4% nickel, 0.11% silver,

0.083% gold. Electrostatic separation of the second electrodynamic separation product generated a concentrate with 44.2% total metal at 5.8% yield. The tailings of the first electrostatic separation and the concentrate of the second stage electrostatic separation were combined and treated in a third stage of electrostatic separation. This stage produced a concentrate at 6.9% yield and with 64.6% total metal in it. The composition of this concentrate was 40.1% copper, 5.1% lead, 4.4% tin, 7.7% iron, 6.5% aluminum, 0.017% cadmium, 0.69% nickel, 0.09% silver and 0.042% gold. Thus, at the end of the purification process, as presented in this example, several concentrate products were obtained with high yield and purity. Depending upon the end use they may be combined proportionately to meet the specification of downstream processing or may be recirculated in a continuous operation.
The main advantages of the present invention are:
1. The process does not require specialized and sophisticated equipment for processing of
waste printed circuit boards.
2. The natural hydrophobicity of non-metallic constituents is effectively exploited by wet
flotation process using combination of reagents therefor.
3. All equipment and machinery required are standard and readily available worldwide.
4. An existing mineral processing plant will be able to handle the processing with only minor
adjustments.
5. A continuous operation at plant level will be able to minimize/eliminate the loss of metal
values to a negligible level.
6. The operation is simple and the overall processing cost is low as the operations involve
only cheap, physical separation steps.
7. The techniques used are purely physical in nature and thus generate no additional
harmful effluents.
8. Enables the recovery of both the metallic and non-metallic constituents separately.
9. Very little or no chemicals are used and therefore the cost effectiveness of the process is
improved.

We claim:
1. A process for the recovery of metal values from waste printed circuit boards which comprises of (h) mechanically shearing the said boards into small pieces and grinding the said
pieces to about 500 to 0 micron size in a tumbling mill such as ball mill, rod mill
and the like; (i) removing the particles of size ranging between 50 to 0 micron from the ground
material as obtained in step [a] in a standard classifier such as hydrocyclone,
spiral and the like to obtain coarser particles of size 50 to 500 microns; (j) separating the coarser particles as obtained in step [b] into a heavy, a light and
an intermediate product using a gravity separator such as Wilfley Table, spiral,
and the like; (k) treating each of the three products as obtained in step [c] separately by flotation
in mechanical, Jameson or column cells, optionally with appropriate reagents
namely frothers, collectors, depressants and activators either alone or in a
combination thereof to obtain metal rich products; (I) treating the metal rich products as obtained in step [d] in enhanced gravity
separators such as multi-gravity separator, Knelson concentrator and the like to
remove the lighter non-metallic impurities; (m) drying the metal rich product of enhanced gravity separation as obtained in step
[e] and purifying it in electrodynamic separators such as high tension separator
to remove remaining non-conducting non-metallic constituents; (n) treating the said metal rich product as obtained in step [f] in electrostatic
separator to recover the desired metal values and obtain pure, conducting
metallic fraction consisting of copper, lead, tin, iron, aluminum, cadmium, nickel,
gold and silver.

2. A process as claimed in claim 1, wherein the waste printed circuit boards preferably
have the following metallic composition:
Copper: 10 to 13% Lead: 2 to 3% Tin: 1 to 2% Iron: 3 to 4% Aluminum: 2 to 3% Cadmium: 0.005 to 0.01% Nickel: 0.1 to 0.5% Silver: 0.01 to 0.03% Gold: 0.01 to 0.02% Traces of other metals
3. A process as claimed in claim 1, wherein the heavy product of gravity concentration
preferably have a specific gravity in the range of 6.0 to 12.0.
4. A process as claimed in claim 1, wherein the light product of gravity concentration
preferably have a specific gravity in the range of 1.4 to 3.5.
5. A process as claimed in claim 1, wherein the intermediate product of gravity
concentration preferably have a specific gravity in the range of 3.5 to 6.0.
6. A process as claimed in claim 1, wherein the flotation operation may be carried out
with or without the addition of reagents either alone or in any combination.
7. A process for recovery of metal values from waste printed circuit boards substantially
as herein described with reference to the examples and figures accompanying this
specification.

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=4/Bd8Qir4g3Fz/9Kr1XnXA==&loc=+mN2fYxnTC4l0fUd8W4CAA==

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Patent Number

271028

Indian Patent Application Number

206/DEL/2008

PG Journal Number

06/2016

Publication Date

05-Feb-2016

Grant Date

29-Jan-2016

Date of Filing

25-Jan-2008

Name of Patentee

COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH

Applicant Address

ANUSANDHAN BHAWAN,RAFI MARG, NEW DELHI-110 001,INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	DAS AVIMANYU	NATIONAL METALLURGICAL LABORATORY P.O.BURMA MINES JAMSHEDPUR,JHARKHAND 831 007,INDIA.
2	SARKAR BISWAJIT	NATIONAL METALLURGICAL LABORATORY P.O.BURMA MINES JAMSHEDPUR, JHARKHAND 831 007, INDIA
3	MEHROTRA SURYA PRATAP	NATIONAL METALLURGICAL LABORATORY P.O.BURMA MINES JAMSHEDPUR,JHARKHAND 831 007,INDIA

PCT International Classification Number

H05K

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA