WRAP MDD018/23 WEEE separation techniques. Holman Wilfley wet shaking table trial report

Transcription

1 WRAP MDD018/23 WEEE separation techniques Holman Wilfley wet shaking table trial report Abstract This report describes trials conducted with SGS Mineral Services on a Holman Wilfley Wet Shaking table for WRAP project MDD018/23. The aim of the project was to trial innovative techniques to tackle some of the more difficult separations encountered by primary and secondary WEEE processors. Recovering copper from mixed WEEE is a notoriously difficult separation and several techniques have been tested during this project to attempt to find a solution to the problem. The wet shaking table is a technique which originates from the mineral processing industries and has been in use for many years. Its use in the recycling industry is a recent development. The aim of this specific trial was to test the technique s ability to recover fine copper from a copper plastic mixture. Fine copper is often found in the WEEE plastic stream and the recovery of it from plastic is currently a problem for which there are no suitable solutions. The copper-rich plastic mixture was pre-treated in two ways in order to size reduce the sample material. This allowed for an investigation into the effect of particle size on the success of the separation to be carried out. One sample of the copper-rich plastic was granulated to a <2.36mm fraction and a 2.36 to 5mm fraction. Another sample was hammer milled, producing three fractions with size ranges 0-3mm, 3 to 5mm and >5mm. Some of the copper-rich plastic material was left in its original condition at 8-12mm. Each of the samples was processed on the wet shaking table, with the following conclusions. The <2.36mm and 0-3mm fractions performed best and significant amounts of copper were recovered from both. The other four fractions performed poorly, but it should be noted that in the cases where the material had been size reduced and screened, most of the copper from the feed material appeared in the smallest particle size fraction and hence there was actually very little copper to recover from the larger fractions. If a wet shaking table is selected as a technique to recover a copper fraction from WEEE, the copper-rich plastic should be size reduced to below 3mm.

2 A wet shaking table capable of processing 1 tonne per hour of size reduced copper-rich plastic from WEEE processing has an installed capital cost of 110,000 and a payback time of nine months. Therefore this technique has good potential for use in the WEEE recycling sector. Table of contents Abstract Information from Trial Photograph of Trial Equipment Description of Trial Equipment Trial Objectives Sample Material Trial Methodology Trial 1 - less than 2.36mm granulated copper rich plastic Feed Material Results Photographs of product samples Analysis of product samples Discussion of results Conclusions from trial Trial to 5mm granulated copper rich plastic Feed Material Results Photographs of product samples Analysis of results samples Discussion of results Conclusions from trial Trial 3 - Copper-rich plastic without pre-treatment Feed Material Results Photographs of product samples Analysis of product samples Discussion of results Conclusions from trial

3 5.0 Trial mm milled copper rich plastic Feed Material Results Photographs of product samples Analysis of results samples Discussion of results Conclusions from trial Trial 5-3mm to 5mm hammer milled copper rich plastic Feed Material Results Photographs of product samples Analysis of product samples Discussion of results Conclusions from trial Trial 6-0mm to 3mm milled copper rich plastic Feed Material Results Photographs of product samples Analysis of product samples Discussion of results Conclusions from trial Economic calculation Overall final conclusions of the trial

4 List of figures Figure 1: Photograph of the trial equipment... 6 Figure 2: Close up of wet shaking table deck... 7 Figure 3: Schematic indicating where each of the product fractions is collected in relation to the table... 9 Figure 4: Photograph of the -2.36mm granulated copper-rich plastic feed material Figure 5: Photograph of the -2.36mm material on the wet shaking table Figure 6: Photograph of trial 1 concentrate Figure 7: Photograph of trial 1 concentrate Figure 8: Photograph of trial 1 concentrate Figure 9: Photograph of trial 1 middlings Figure 10: Photograph of trial 1 tailings Figure 11: Photograph of concentrate 1 from scavenge trial Figure 12: Photograph of the mm granulated copper rich plastic material Figure 13: Photograph of trial 2 concentrate Figure 14: Photograph of trial 2 concentrate Figure 15: Photograph of trial 2 concentrate Figure 16: Photograph of trial 2 middlings Figure 17: Photograph of trial 2 tailings Figure 18: Photograph of the copper-rich plastic material as it is Figure 19: Wet shaking table in operation on the copper-rich plastic without size reduction Figure 20: Photograph of trial 3 concentrate Figure 21: Photograph of trial 3 concentrate Figure 22: Photograph of trial 3 concentrate Figure 23: Photograph of trial 3 middlings Figure 24: Photograph of trial 3 tailings Figure 25: +5mm milled copper-rich plastic feed material Figure 26: Trial 4 concentrate Figure 27: Trial 4 concentrate Figure 28: Trial 4 concentrate Figure 29: Trial 4 middlings Figure 30: Trial 4 tailings Figure 31: 3-5mm milled copper rich plastic feed material Figure 32: Trial 5 concentrate Figure 33: Trial 5 concentrate Figure 34: Trial 5 concentrate Figure 35: Trial 5 middlings Figure 36: Trial 5 tailings Figure 37: 0-3mm hammer milled copper rich plastic material Figure 38: Wet shaking table in operation on the 0-3mm hammer milled material Figure 39: Trial 6 concentrate Figure 40: Trial 6 concentrate

5 Figure 41: Trial 6 concentrate Figure 42: Trial 6 middlings Figure 43: Trial 6 tailings List of tables Table 1: Throughput information for trial Table 2: Mass balance results for trial Table 3: Analysis of feed, middling and tails fractions from trial Table 4: Analysis of concentrate 1, 2 and 3 from trial Table 5: Results of copper anaylsis including product sepaartion efficiency, Q Table 6: Throughput information for trial Table 7 : Mass balance results for trial Table 8: Throughput information for trial Table 9: Mass balance results for trial Table 10: Throughput information for trial Table 11: Mass balance results for trial Table 13: Throughput information for trial Table 14: Mass balance results for trial Table 15: Throughput information for trial Table 16: Mass balance results for trial Table 17: Results of analysis on feed, middling and tails from trial Table 18: Analysis of concentrates 1, 2 and Table 19: Results of copper analysis for trial 6 including product separation efficiency, Q.. 41 Table 20: Payback calculation for a wet shaking table

6 1.0 Information from trial Trial host: SGS Mineral Services, the trial was conducted at a facility in Cornwall, UK. Trial equipment: Holman Wilfley wet shaking table Trial date: 10 th February Photograph of trial equipment Figure 1 is an annotated photograph of the wet shaking table used in the trial. Deck with riffles Water supply to table Feed trough Feed hopper Product collection trough Additional water can be added to the feed here Tailings product outlet in buckets Head motion Figure 1: Photograph of the trial equipment 6

7 Copper collects off this edge of the table Water flows over the table in this direction Top edge Bottom edge Figure 2: Close up of wet shaking table deck The table moves backwards and forwards in the direction of the arrow in Figure 2. The riffles shallow longitudinal ridges - can clearly be seen in the photograph. The riffles decrease in height from the bottom edge to the top edge of the table. Water flows over the table from the top edge to the bottom edge. 1.2 Description of trial equipment The wet shaking table at SGS mineral services in Cornwall is a half sized Holman Wilfley table. This means it has a quarter of the area of a full sized unit but operates in the same way as a full table. Figure 1 shows the feed point in the corner of the table where the feed material is added. Water flows out of holes in a pipe which runs along the top of the table. There is also a separate supply of water into the feed trough. In operation, the table moves forward and backward, this motion is called the stroke. The table is made with shallow longitudinal ridges running from one side to the other called riffles. The movement of the stroke is in the direction of the riffles. The table is pushed forward with a slow stroke, tensioning a spring as it does so. When the table reaches the specified stroke length the spring then releases its tension and pulls the table back quickly, hitting the retaining stops. As the table moves forwards the particles rise and are momentarily suspended. As the table moves backwards the dense particles settle back down and the motion gradually causes the particles to move along the riffles in the direction of the table s forward stroke. The light material stays in the upper layer and flows down 7

8 over the riffles with the flow of water. An analogy for the movement would be to compare it to a magician pulling a table cloth from under the table contents. In the context of WEEE separation, copper (coarse, dense material) will settle against the riffles and travel upwards to the far side of the table. Plastic will settle in the upper layer and will travel down over the riffles with the water to the bottom edge of the table. The height of the riffles decreases along the length of the table from the feed to the product end. The riffles are higher near the feed and tailings edge of the table, approximately 7-8mm high. The riffles decrease in height to only a few millimetres near the concentration end and top edge of the table. The riffles are approximately 5cm apart. The plastic particles jump over the high riffles whilst the copper travels up the riffles. The height of the riffle is connected to the material being processed on the table and different riffle patterns can be used depending on the material being processed. For coarser particles, common within the recycling industry, the height of the riffles can be as much as 20-25mm. Depending on the type of material, the size of table used in this trial would be expected to process kg/hr. A full size table, dimensions 5.8m long x 1.75m wide x 1.2m high with a nominal deck area of 8.0m 2, can handle around tonnes per hour. If the material is coarse and has a close size distribution then the throughput can be as high as tonnes per hour. Finer material or material with a wide size distribution will have a lower throughput. There are four process variables for a wet shaking table: Stroke length (maximum stroke length of 19mm); Deck angle; Wash water flow rate; and Position of splitter plate. The first three variables have an effect on whether a separation is achieved. The last one has an effect on the products collected both in terms of quantity and quality. The stroke length is the distance the table moves forwards and backwards. For all the trials it remained constant at 15mm. The stroke can be increased to a maximum of 19mm for coarse material or decreased to 5mm for very fine material. If the particle size is large and the feed material has a low density then a longer stroke is required to separate the particles. The deck angle can be adjusted from 0 to a maximum of 9. During the trials the deck angle was set at 7. Typically for fine material a flatter deck angle is used but the actual settings need to be fined tuned during start up and are relative to the density of the material. The feed rate should be kept constant and the solids feed density should be around 25%. This is to ensure that a steady state on the deck is maintained, as fluctuations in the flow of 8

9 material will affect the separation. The wash water flow rate range is 18 to 38 litres per minute. The table produces five product fractions, illustrated in Figure 3. There are three concentrate fractions produced at the end of the table which consist of the dense material. Concentrate 1 is from the top corner, concentrate 2 is from the upper middle part of the table and concentrate 3 is from the lower middle part of the table. Beneath these three fractions, at the bottom corner of the table, is a fraction known as the middlings. This fraction will often contain a mixture of the concentrate material and the tailings material and may need reprocessing. At the centre bottom edge of the table is the tailings fraction which is the light material. The table can also be tuned for a three way split, one product in the concentrate, one product in the middlings and one product in the tailings. The copper material will be found in concentrates 1, 2 and 3. Glass may be found in concentrate 3 whilst the middling and tailings are mainly plastic. Concentrate 1 Concentrate 2 Direction of table movement Concentrate 3 Riffles Middlings Tailings Figure 3: Schematic indicating where each of the product fractions is collected in relation to the table A moveable splitter plate determines what material is collected as concentrate 3 and what material is rejected in the middlings. During operation the bed of material on the table is observed in order to determine if the splitter plate position needs to be adjusted. It should be positioned just at the point where the two materials being separated form a distinct line. Once correctly set, the table will operate in steady state with constant flows of materials, so the plate should not require further adjustment. If the splitter plate is positioned incorrectly, valuable product (i.e. copper) could be rejected to the middlings fraction, which would then need reworking in order to recover the copper. Conversely, the splitter plate could be positioned so that the concentrate contains less valuable materials (i.e. plastic/glass), which is also undesirable. If concentrate 3 contained very little copper and more plastic/glass then it should be directed into the middlings fraction. 9

10 1.3 Trial objectives The overall objective of the trial was to separate valuable metals from glass, stone and plastic. The specific aim was to produce a high purity copper stream which has a saleable potential. The key to achieving an effective separation is likely to be the particle size and shape. Market research indicates that the combustible component of the copper fraction must be reduced to below 5% by weight to make it attractive to the majority of copper smelters in Europe. A higher content of stone and glass can be tolerated as they are inert in the smelter. However separating copper from stone and glass increases the value of both fractions. The stone and glass has no value when mixed and sold with copper but may be saleable as a useful aggregate substitute if it can be separated with a low copper content. 1.4 Sample material The samples used for these trials were copper-rich plastic fraction sourced from Axion s WEEE processing plant in Salford, UK. The copper-rich plastic was size reduced in two different ways: granulation and hammer milling. This produced five different fractions, along with the original material itself for testing. The different samples were chosen to allow the effects of particle size on the separation to be investigated. The six samples were: 1. <2.36mm granulated copper-rich plastic; mm granulated copper-rich plastic; 3. Copper-rich plastic as it is ; mm hammer milled copper-rich plastic; mm hammer milled copper-rich plastic; and 6. +5mm hammer milled copper-rich plastic. 1.5 Trial methodology The objective for each sample of material was the same, so the trial methodology used for each sample was also the same. Prior to processing the material the feed rate was measured by timing a fixed amount of material though the feed system. The results for each of the throughputs are shown in the relevant trial sections. After each of the samples was tested on the table the samples were dried by SGS Services and returned to Axion s facility at Salford. A scavenge of the tailings for trial 1 was conducted. This involved passing the tailings material over the table again to see if there was any copper which had not been recovered by the first pass. Two techniques were used to determine the composition of the fractions in order to analyse the sample material. 10

11 In order to identify any losses of copper in the middlings and tailings fractions a sodium polytungstate solution was used as a sink-float medium. This method was chosen as any residual copper would be very small and difficult to hand sort. The same procedure was applied to the feed material to allow the analysed feed composition and the back calculated feed composition to be compared. The same method was used for samples of feed, middlings and tailings. A small sample spear was used to take a representative sample from each bag. The sample was then weighed and added to a container of sodium tungstate solution with a density of 1.7g/cm 3. Ideally the copper would sink and everything else would float. The two fractions were removed from the container and dried. Where the material was large enough the fractions were hand sorted. An estimation of the copper content was made for those fractions where a hand sort was not possible due to very small particle size. Once the physical analysis of the samples was completed, product and reject separation efficiencies, Q and R, were calculated. For this trial the product separation efficiency, Q, is the probability of correctly recovering copper to the desired product stream. The reject separation efficiency, R, is the probability that everything else is correctly sorted to the secondary product stream. In this case the secondary product stream is of no use and only the copper is a useful product. The three concentrate fractions from the table are classed as the product stream and the middling and tailing fractions is the secondary product. 11

12 2.0 Trial 1 - less than 2.36mm granulated copper rich plastic 2.1 Feed material The feed material for trial 1 was the <2.36mm granulated copper-rich plastic. At this particle size there are no plate like particles, which are present in the copper-rich plastic that is normally produced by Axion at Salford. The particles after granulation are cuboid in shape. The reason for this is that most injection moulded plastic used in WEEE is 3 to 5 mm thick, so when granulated to less than 5mm the cuboid shape arises. It is thought that evenly shaped particles like the cuboids perform better on a wet shaking table than the flat plate like particles, so it was expected that the size reduced material with a cuboid shape would perform well during the trial. Figure 4: Photograph of the -2.36mm granulated copper-rich plastic feed material 12

13 2.2 Results Figure 5: Photograph of the -2.36mm material on the wet shaking table Figure 5 shows the wet shaking table in operation. The clear boundary between the copper and plastic is shown by the line. The feeding system blocked during the trial and required manual intervention to ensure the table received a consistent flow of material. The throughput was determined by measuring the time taken for a known quantity of feed material to pass though the feed system. The results are shown in Table 1. The throughput was quite low but was limited by the capacity of the feeding system, which may need to be changed for this type of material. Trial Material Quantity Times Feed rate g s kg/hr Table 1: Throughput information for trial 1 A sample of the tailings from the trial was reprocessed to see if there was any copper present. This showed that there was no copper so the first pass of the material had achieved as good a separation as was possible and reworking of the tailings was not required. 13

14 2.3 Photographs of product samples Figure 6: Photograph of trial 1 concentrate 1 Figure 7: Photograph of trial 1 concentrate 2 14

15 Figure 8: Photograph of trial 1 concentrate 3 Figure 9: Photograph of trial 1 middlings 15

16 Figure 10: Photograph of trial 1 tailings 2.4 Analysis of product samples Table 2 shows the mass balance for trial 1. It should be noted that the feed amount was not weighed It has been back-calculated from the product fractions so the loss/gain is zero. For all other trials the feed amount was correctly weighed and the loss determined. Feed Total Trial Con 1 Con 2 Con 3 Middlings Tailings Loss/Gain Amount Output g g % g % g % g % g % g g % % % % % Table 2: Mass balance results for trial 1 The results of the sink float analysis are shown in Table 3. Trial 1 Sample Weight of dry sample Dry copper weight % of copper Feed % Middlings % Tails % Table 3: Analysis of feed, middling and tails fractions from trial 1 16

17 The hand sorting results are shown in Table 4. Copper Glass Plastic Fraction weight Trial 1 g % g % g % Concentrate % 5 3% 2 1% 194 Concentrate % 32 10% 0 0% 323 Concentrate % % 0 0% 387 Table 4: Analysis of concentrate 1, 2 and 3 from trial 1 Fraction Fraction Copper % Copper % Copper weight weight purity recovered Feed % Concentration % 26% Concentration % 41% Concentration % 28% Middlings % 2% Tails % 0% Product totals % 97% Q 94% Table 5: Results of copper anaylsis including product sepaartion efficiency, Q 2.5 Discussion of results Table 3 and 4 show the results of the analysis for each of the product fractions from the trial 1. Fraction Fraction Copper % Copper % Copper weight weight purity recovered Feed % Concentration % 26% Concentration % 41% Concentration % 28% Middlings % 2% Tails % 0% Product totals % 97% Q 94% Table 5 shows just the copper analysis as this is the main area of focus. It can be seen that the copper concentration in concentrate 1 is 96% and in concentrate 2 is 90%. Both of these are high purities for copper fractions recovered from WEEE and should meet the copper smelter s requirements. 67% of the copper in the feed was recovered in 17

18 concentrates 1 and 2. Over a quarter of the copper was recovered to concentrate only at a 50% purity level. 3 but The back calculated copper content of the feed, 16%, is very close to the actual analysed copper content of the feed, 17%, which shows that the analysis is consistent. The product separation efficiency, Q value (which is the probability that the copper is correctly sorted into one of the three product fractions) is 94% for concentrates 1, 2 and 3. This is a high separation efficiency and means that the majority of the copper is recovered. The results of a scavenge on the trial 1 tailings is illustrated in Figure 11 below, concluding that no copper had been lost in the tailings fraction in the first trial. Figure 11: Photograph of concentrate 1 from scavenge tria l 2.6 Conclusions from trial The technique is very good for the separation of copper from plastic with this feed material. A copper fraction with 26% recovery at 96% purity was produced. Taking into account all three concentrate fractions the copper recovery is 95%, at a purity of 75%. The probability that the copper is correctly sorted into one of the concentrate fractions is 94%. Therefore the trial objective of recovering the copper into a saleable fraction has been achieved. With further system adjustments and fine tuning even better results may be obtained. 18

19 3.0 Trial to 5mm granulated copper rich plastic 3.1 Feed material The feed material for trial 2 was the 2.36 to 5mm fraction of the granulated copper-rich plastic material. Figure 12: Photograph of the mm granulated copper rich plastic material 3.2 Results Th ere was much less copper in the feed material for trial 2, compared to trial 1, which indicates that most of the copper went into the less than 2.36mm fraction when the material was granulated and sieved. There was a clear layer of glass which occurred at the transition zone between the copper and plastic. It may be possible to fine tune the machine to produce only glass in the middling fraction. The throughput results are shown in Table 6. 19

20 Trial Material Quantity Times Feed rate g s kg/hr Table 6: Throughput information for trial Photographs of product samples Figure 13: Photograph of trial 2 concentrate 1 20

21 Figure 14: Photograph of trial 2 concentrate 2 Figure 15: Photograph of trial 2 concentrate 3 21

22 Figure 16: Photograph of trial 2 middlings 3.4 Analysis of results samples Table 7 shows the mass balance for trial 2. Figure 17: Photograph of trial 2 tailings 22

23 Feed Total Trial Con 1 Con 2 Con 3 Middlings Tailings Loss/Gain Amount Output g g % g % g % g % g % g g % 272 3% % % % Table 7 : Mass balance results for trial 2 The losses in the mass balance are due to the collection technique used for the material. Buckets were used to collect the product fractions. Losses occurred when these were swapped over and also when the buckets were emptied. Because it was clear during the trial that there was very little copper present in the sample the decision was made not to analyse each product fraction quantitatively. 3.5 Discussion of results Visual inspection of the samples showed there was very little copper in the concentrate 1 fraction; however there were other metals present. There was more copper in concentrate 2 whilst concentrate 3 contained glass, plate-like plastic particles and copper. Most of the copper in concentrate 3 was in the form of polyvinylchloride (PVC) coated wires: if the material was granulated to a smaller size it would liberate the copper from the PVC and the level of copper recovery would improve. 3.6 Conclusions from trial The technique did not work very well with this feed material, but this is not thought to be due to the particle size, but more due to the fact that the copper content of the material was very low. This is a characteristic of the feed material, with the copper tending to appear in the smallest particle size fraction during the granulation process. 4.0 Trial 3 - Copper-rich plastic without pre-treatment 4.1 Feed material The feed material for trial 3 was the copper-rich plastic with no size reduction. 23

24 Figure 18: Photograph of the copper-rich plastic material as it is 4.2 Results During the trial it was observed that the material tended to flow over the table and the riffles did not catch the copper. Figure 19 shows the material on the table and it can be seen that it has lumped together on the table and not spread out correctly. This is probably due to the shape of the plastic particles; the plate-like shape means they flow with the water over the riffles. The separate throughput timings are shown in Table 8. Trial Material Quantity Times Feed rate g s kg/hr 3 Test Test Average 128 Table 8: Throughput information for trial 3 24

25 Figure 19: Wet shaking table in operation on the copper-rich plastic without size reduction 4.3 Photographs of product samples Figure 20: Photograph of trial 3 concentrate 1 25

26 Figure 21: Photograph of trial 3 concentrate 2 Figure 22: Photograph of trial 3 concentrate 3 26

27 Figure 23: Photograph of trial 3 middlings 4.4 Figure 24: Photograph of trial 3 tailings 27

28 Analysis of product samples Table 9 shows the mass balance details for trial 3. Feed Total Trial Con 1 Con 2 Con 3 Middlings Tailings Loss/Gain Amount Output g g % g % g % g % g % g g % % % % % Table 9: Mass balance results for trial 3 Again there was clearly very little copper in this material, in comparison to trial 1, so quantitative analysis was not conducted on each of the product fractions. 4.5 Discussion of results The separation of this material was not very good as the particles were too big. The plastic particles tend to be in the range 8-12mm but the copper can vary from very small pieces, only 2-3mm long and 0.5mm in diameter, up to larger pieces of 10-15mm in length. Higher riffles and an increased flow of water may possibly improve the separation but this would require further work to be undertaken in order to confirm this. There was very little copper material in concentrate 1, only 1% of the feed, and was 4% of the feed in concentrate 2. Both fractions consisted of a mixture of copper and plastic. Concentrate 3 contained 9% of the feed but again this was both copper and plastic. The largest amount of material was in the middlings fraction. During the trial the plastic often formed a mass on the table which did not allow the copper to separate out correctly. At the boundary between the copper and plastic, as seen in Figure 19, the plastic particles did not spread out evenly and formed lumps of material which prevented the separation from occurring. 4.6 Conclusions from trial Processing the material as it is does not yield satisfactory results and the trial objective was not achieved. This means that in order to recover the copper using a wet shaking table, the feed material must be size reduced before processing. 28

29 5.0 Trial mm milled copper rich plastic 5.1 Feed material The feed material for trial 4 was the +5mm fraction of the hammer milled copper-rich plastic. Figure 25: +5mm milled copper-rich plastic feed material 5.2 Results At the start of this trial it appeared that there was no separation occurring but it became apparent that there was very little copper in the sample. The table tilt was increased to 9 to see if this helped achieve a separation, but it had no effect. The water pressure dropped during this trial, which had an effect on the wetting of the material, which was very dry. Even taking this into account the separation would still have been poor due to the small amount of copper in the feed. Table 10 shows the throughput information for trial 4, which is in the same range as the other trials. Trial Material Quantity Times Feed rate g s kg/hr

30 Table 10: Throughput information for trial Photographs of product samples Figure 26: Trial 4 concentrate 1 Figure 27: Trial 4 concentrate 2 30

31 Figure 28: Trial 4 concentrate 3 Figure 29: Trial 4 middlings 31

32 5.4 Analysis of results samples Figure 30: Trial 4 tailings Feed Total Trial Con 1 Con 2 Con 3 Middlings Tailings Amount Output Loss/Gain g g % g % g % g % g % g g % % % % % Table 11 shows the mass balance for trial 4. Feed Total Trial Con 1 Con 2 Con 3 Middlings Tailings Loss/Gain Amount Output g g % g % g % g % g % g g % % % % % Table 11: Mass balance results for trial 4 As no separation was observed, further analysis was not conducted on any of the product fractions. 5.5 Discussion of results There was very little copper in this sample. The copper was concentrated in the smaller size fractions produced by hammer milling. The material also appeared to be too dry. Wetting the feed prior to feeding onto the table may have improved the separation slightly. 5.6 Conclusions from trial There was very little copper present in this fraction so no significant separation occurred. 32

33 6.0 Trial 5-3mm to 5mm hammer milled copper rich plastic 6.1 Feed material The feed material for trial 5 was the 3 to 5mm fraction of hammer milled copper-rich plastic. Figure 31: 3-5mm milled copper rich plastic feed material 6.2 Results Again there was very little copper in this sample of material so no significant separation occurred. There was a small amount of copper and plastic present in the middling and tailings fractions and some balled up copper was observed in concentrate 1 and 2. Table 12 shows the throughput information for trial 5. Trial Material Quantity Times Feed rate g s kg/hr Table 12: Throughput information for trial 5 33

34 6.3 Photographs of product samples Figure 32: Trial 5 concentrate 1 Figure 33: Trial 5 concentrate 2 34

35 Figure 34: Trial 5 concentrate 3 Figure 35: Trial 5 middlings 35

36 Figure 36: Trial 5 tailings 6.4 Analysis of product samples Table 13 shows the mass balance for trial 5. Feed Total Trial Con 1 Con 2 Con 3 Middlings Tailings Loss/Gain Amount Output g g % g % g % g % g % g g % 271 3% 292 3% % % Table 13: Mass balance results for trial 5 As the observed levels of copper in the feed material were low, no further analysis was conducted on any of the product fractions. 6.5 Discussion of results It appears that during the size reduction process the copper has concentrated into the smallest particle size fraction and hence there was very little copper present in this fraction. 6.6 Conclusions from trial The results from trial 5 are inconclusive because of the small amount of copper in the feed. 36

37 7.0 Trial 6-0mm to 3mm milled copper rich plastic 7.1 Feed material The feed material for trial 6 was the 0-3mm fraction of the hammer milled copper-rich plastic. Figure 37: 0-3mm hammer milled copper rich plastic material 7.2 Results It was noted during the trial that the feed material contained a significant proportion of plastic particles greater than 3mm. This means that the material was not screened correctly, perhaps due to a hole in the screen. The throughput measurement for this trial is shown in Table 14. Trial Material Quantity Times Feed rate g s kg/hr Table 14: Throughput information for trial 6 37

38 Figure 38: Wet shaking table in operation on the 0-3mm hammer milled material Figure 38 shows a photograph of the wet shaking table in operation during the trial. At the top edge of the table a clear copper stream can be seen flowing up and along the riffles. In the lower section of the photograph there is a darker material, mainly plastic and dust which is flowing down over the riffles. 7.3 Photographs of product samples Figure 39: Trial 6 concentrate 1 38

39 Figure 40: Trial 6 concentrate 2 Figure 41: Trial 6 concentrate 3 39

40 Figure 42: Trial 6 middlings Figure 43: Trial 6 tailings

41 Analysis of product samples Table 15 shows the mass balance for trial 6. Table 16 and 18 are the results of the analysis on each of the product fractions. Table 18 shows the results for the copper component only. Feed Total Trial Con 1 Con 2 Con 3 Middlings Tailings Loss/Gain Amount Output g g % g % g % g % g % g g % % % % % Table 15: Mass balance results for trial 6 Trial 6 Sample Weight of dry sample Dry copper weight % of copper Feed % Middlings % Tails % Table 16: Results of analysis on feed, middling and tails from trial 6 Sample Copper Glass Plastic weight Trial 6 g % g % g % g Concentrate % 0 0% 15 58% 26 Concentrate % 0 0% 42 11% 389 Concentrate % 5 2% 7 2% 325 Table 17: Analysis of concentrates 1, 2 and 3 Fraction Fraction Copper % Copper % Copper weight weight purity recovered Feed material % Concentration % 1% Concentration % 29% Concentration % 26% Middlings % 9% Tails % 7% Total feed material back calculated from product weights and compositions % Mass balance error % Product separation efficiency Q 56% Table 18: Results of copper analysis for trial 6 including product separation efficiency, Q 41

42 7.5 Discussion of results The concentrate fractions contained a significant number of large pieces of plastic (>3mm), which should not have been present in a 0-3mm sieved fraction. This was probably due to a fault with the screen used to prepare the trial samples. This did have some effect on the separation. If the material had been sieved correctly then a better separation would probably have been achieved because the oversize plastic particles tended to follow the copper into the concentrate fraction. The content of copper measured in the feed material was 12%. However back calculating the feed composition from the measured product compositions gave an estimate of 9% copper in the feed. This discrepancy is significant and may be due to loss of materials through spillages during the trial. The product separation efficiency, Q, was rather low at 56%. This is the probability that copper was correctly sorted into the concentrate fractions. 10% of the copper was lost to the middling and tailings fractions. This reduces the Q value. Therefore the machine settings should possibly be adjusted, recover more copper into the concentrate fraction, for example by repositioning of the splitter plate between concentrate 3 and the middlings fractions. A small amount of copper was collected in the tailings fraction. It was likely that this was due to poor wetting of the material which caused some of the copper to be swept over the riffles with the plastic. The product photographs show that concentrate 1 contained a small amount of copper and some large plastic chips, concentrate 2 contained more copper along with some large plastic chips and concentrate 3 contained both copper and plastic. If the feed material had been screened correctly and the larger pieces of plastic removed then the results would have been better as less oversize plastic would have been carried into the concentrate fractions. 7.6 Conclusions from trial This trial showed that copper in the 0-3mm fraction from the hammer milled product could be recovered by the wet shaking table. The separation efficiency was rather low at 56% but the overall copper content of the three concentrate fractions was high at 90%. The concentrate fractions contained a total of 8.7% combustible plastic. If oversize plastic material had not leaked through the screen then the concentrates would have contained less than 5% plastic. This would make the material acceptable for processing by conventional copper smelters. 42

43 8.0 Economic calculation A simple payback calculation was completed in order to determine the economic potential of the wet shaking table for recovery of copper from WEEE plastic mixtures. 43

44 Trial Host Trial Holman Wilfley Equipment Equipment Wet Shaking Table Capacity te/hr 1 Cost of unit including feed system and installation Basis of operation hr/yr 3000 Overall Equipment Effectiveness OEE % 70% Plant Input te/yr 2100 Operating Costs Water Quantity kg/hr 100 Cost (assuming 2/te) /hr 0.20 Power Quantity kw 50 Cost (assuming 10p/kW hr) /hr 5 Water and Power costs /te of feed 5.20 Water and Power costs /yr Wear costs for granulator /te feed 6 /yr Labour costs (assuming 15/hr) Annual process licence costs 0 Total Operating Costs Revenue Assume 10% of feed is separated as product Product extracted te/yr 210 Value of product /te 1000 /yr Margin /yr Payback time months 15 Table 19: Payback calculation for a wet shaking table 44

45 The calculation assumes a capacity of 1 tonne per hour for a full size Holman Wilfley separation table and an installed cost for the unit, including feed granulator, of 180,000. The plant is assumed to operate 12 hours per day, 5 days a week, 50 weeks a year, giving 3,000 hours of operation per year. The payback calculation assumes a overall equipment effectiveness (OEE) of 70%, where the OEE is defined as follows: OEE capacity rate x quality rate x availability actual throughput capacity rate rated throughput quality rate % of on specification product actual run hours availability available run hours Therefore the overall plant throughput will be 2,100 tonnes per year, Operational costs: The feed material is currently sent to landfill and once the copper has been recovered the residue material will still be sent to landfill so there is no net cost or benefit from disposal of the residue fraction. It is assumed that 10% fresh water is lost per tonne of material sent to landfill with a water cost of 2/te. A total power consumption of 50 kw is assumed for operation of the granulator, separation table and associated pumps and sieves. The power cost is assumed to be 10p/kW hr. Wear costs for the granulator are estimated to be 6 per tonne of feed. The calculation assumes that the system will require one operator at a total job cost of 45,000 per year. The revenue estimate assumes that 10% copper is extracted the feed. This means that the plant will recover about 210 tonnes of copper concentrate. The value of this material will fluctuate but is assumed to be approximately 1,000 per tonne. Therefore the margin is 141,480 and so the payback time is nine months. The economic assessment shows that a unit processing 1 tonne per hour of size reduced copper-rich plastic from WEEE processing should generate an operating margin of about 140,000/year. This should pay back the 180,000 installed cost for the system in around 15 months. 45

46 9.0 Overall final conclusions of the trial Fine copper can be successfully recovered from the following feed materials using a wet shaking table: -2.4mm granulated copper-rich plastic from secondary WEEE processing; and 0-3mm hammer milled copper-rich plastic. For the -2.36mm granulated material 95% of the copper was recovered, at a concentration of 75% copper. For the 0-3mm hammer milled material 56% of the copper was recovered at 90% purity. The wet shaking table was partially successful when trying to recover copper from the +2.4mm size fraction of the granulated copper rich plastic material. The wet shaking table, could not recover copper efficiently from copper-rich plastic mixtures which had not been size reduced. The copper content of the 3-5mm and +5mm fractions from hammer-milled copper-rich plastic was very low so there was no benefit in trying to separate these fractions. The trial showed that when copper-rich plastic is size reduced, the majority copper tends to end up in the smallest fraction; copper-rich plastic should therefore be milled or granulated to less than 5mm, ideally less than 3mm, prior to using a wet shaking table for copper recovery. The feed material should be fully wetted before processing in order to assist with separation. The wet shaking table can potentially be tuned to produce a glass fraction in the middlings. However the presence of glass in the copper fraction is not a problem for copper smelters because it ends up in the furnace slag fraction and does not interfere with furnace operation. The throughput of the quarter size table used for the trial varied from 80 kg/hr to 150 kg/hr depending on the material being processed. This means that the throughput of a full size table should be in the range 320 to 600 kg/hr. Axion believes that a modified feed mechanism should allow a single full size table to achieve 1te/hr with a -3mm feed material. 46