WO2019217059A1

WO2019217059A1 - Precious metal recovery apparatus and related processes

Info

Publication number: WO2019217059A1
Application number: PCT/US2019/028305
Authority: WO
Inventors: Jakub PEDZIWIATR; Ronald Todd GRAVES
Original assignee: Jabil Inc.
Priority date: 2018-05-11
Filing date: 2019-04-19
Publication date: 2019-11-14

Abstract

Systems, processes, apparatuses and materials disclosed relate to the recovery of precious metals from a substrate into solution, such as, for example, using a leaching solution. In addition, systems and processes are disclosed for recovering precious metal from the leaching solutions. Processes disclosed herein also relate to methods for regenerating leaching solutions.

Description

PRECIOUS METAL RECOVERY APPARATUS AND

RELATED PROCESSES

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to and the benefit of U.S. Patent Application Serial No. 16/152,672, filed October 5, 2018, which clai s priority to and the benefit of U.S. Provisional Application Patent Serial No. 62/670,290, filed May 11, 2018, the entire disclosures of which are hereby incorporated by reference.

TECHNICAL FIELD

[0002] This disclosure relates to an apparatus for precious metal recovery and a related process for precious metal recovery, more specifically to a tank and material movement system combined with an electrowinning unit that are used in the process of shredding, milling, leaching and harvesting precious metals.

BACKGROUND

[0003] Processes to extract metals, such as precious metals, from waste products are known in the existing art. For example, Patent Cooperation Treaty Application No. W02013090517, entitled,“Apparatus and Method for Stripping Solder Metals During the Recycling of Waste Electrical and Electronic Equipment”; United States Patent Application Publication No. 2013/0276284, entitled“Method for Recycling of Obsolete Printed Circuit Boards”, and United States Patent Application Publication No. 2017/0369967, entitled “Methods, Materials and Techniques for Precious Metal Recovery”, are directed to largely manual or otherwise less efficient methods of extracting precious metals from waste electrical and electronics equipment, such as from the printed circuit boards associated with such waste electronics equipment.

[0004] As detailed in the foregoing and like known references, waste products, such as waste electrical equipment, may include aspects, such as the printed circuit boards, that include precious metals in, for example, pins, connectors, contacts, and the like. Those aspects of the waste products which include precious metals may be subjected to extraction of the precious metals therefrom. To date, these extractions are understood to be complex chemical processes that have often been unsuitable for large-scale extractions, at least because they require sophisticated custom-built extraction tools.

SUMMARY

[0005] Disclosed herein are implementations of systems, processes, apparatuses and materials which relate to the recovery of precious metals from a substrate into solution, such as, for example, using a leaching solution. In addition, systems and processes are disclosed for recovering precious metal from the leaching solutions. Processes disclosed herein also relate to methods for regenerating leaching solutions.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The disclosure is best understood from the following detailed description when read in conjunction with the accompanying drawings and are incorporated into and thus constitute a part of this specification. It is emphasized that, according to common practice, the various features of the drawings are not to-scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity.

[0007] FIG. 1 is a flow diagram of a process with apparatus for precious metal recovery according to an embodiment of the invention.

[0008] FIG. 1A is a flow diagram of an alternate dry end process with apparatus for precious metal recovery according to an embodiment of the invention.

[0009] FIG. 2 is a perspective view of an apparatus for precious metal recovery according to an embodiment of the invention.

[0010] FIG. 3 is a cross-sectional view of the apparatus for precious metal recovery according to an embodiment of the invention.

[0011] FIG. 4 is a perspective view of an apparatus for precious metal recovery according to an embodiment of the invention.

[0012] FIG. 5 is an elevation view of an apparatus for precious metal recovery according to an embodiment of the invention.

[0013] FIG. 6 is another elevation view of an apparatus for precious metal recovery according to an embodiment of the invention.

[0014] FIG. 7A and 7B are photographs of oversize material comprising the copper core of PCBs and undersize material comprising the majority of the precious metals of the PCBs, respectively, illustrating the results of two stages of the dry end process according to an embodiment of the invention.

[0015] FIG. 8 is a perspective view of an electrowinning unit according to an embodiment of the invention.

[0016] FIG. 9 is an elevational view of an electrowinning unit according to an embodiment of the invention.

[0017] FIG. 10 is a view of an electrowinning unit according to an embodiment of the invention.

[0018] FIG. 11 is a photograph showing an electrowinning unit according to an embodiment of the invention.

[0019] FIG. 12 is a photograph showing two sides of an electrowinning anode plate according to an embodiment of the invention.

[0020] FIG. 13 is an illustrative diagram of an electrowinning unit shown with electrowinning anode plate removed according to an embodiment of the invention.

DETAILED DESCRIPTION

[0021] The figures and descriptions provided herein may be simplified to illustrate aspects of the described embodiments that are relevant for a clear understanding of the herein disclosed processes, machines, manufactures, and/or compositions of matter, while eliminating for the purpose of clarity other aspects that may be found in typical similar devices, systems, compositions and methods. Those of ordinary skill may thus recognize that other elements and/or steps may be desirable or necessary to implement the devices, systems, compositions and methods described herein. However, because such elements and steps are well known in the art, and because they do not facilitate a better understanding of the disclosed embodiments, a discussion of such elements and steps may not be provided herein. However, the present disclosure is deemed to inherently include all such elements, variations, and modifications to the described aspects that would be known to those of ordinary skill in the pertinent art in light of the discussion herein.

[0022] Embodiments are provided throughout so that this disclosure is sufficiently thorough and fully conveys the scope of the disclosed embodiments to those who are skilled in the art. Numerous specific details are set forth, such as examples of specific aspects, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. Nevertheless, it will be apparent to those skilled in the art that certain specific disclosed details need not be employed, and that embodiments may be embodied in different forms. As such, the exemplary embodiments set forth should not be construed to limit the scope of the disclosure.

[0023] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. For example, as used herein, the singular forms "a", "an" and "the" may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises," "comprising," "including," and "having," are inclusive and therefore specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof.

[0024] The steps, processes, and operations described herein are thus not to be construed as necessarily requiring their respective performance in the particular order discussed or illustrated, unless specifically identified as a preferred or required order of performance. It is also to be understood that additional or alternative steps may be employed, in place of or in conjunction with the disclosed aspects.

[0025] Yet further, although the terms first, second, third, etc. may be used herein to describe various elements, steps or aspects, these elements, steps or aspects should not be limited by these terms. These terms may be only used to distinguish one element or aspect from another. Thus, terms such as "first," "second," and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, step, component, region, layer or section discussed below could be termed a second element, step, component, region, layer or section without departing from the teachings of the disclosure.

[0026] FIG. 1 illustrates a process 100 for precious metal recovery in accordance with an implementation, where precious metal includes for example, but is not limited to, gold, silver and palladium. Process 100 includes multiple operations, such as for example, dry end 105, leach 125 and harvest 150. Each operation automatically feeds a next operation to recover the precious metal and recycle the precious metal-free liquid. In general, in dry end 105, waste feed or feedstock, which may include but is not limited to, electronic waste, printed circuit board(s) (PCB), precious metal plated connectors, precious metal pins, industrial precious metal scrap, and bulk jewelry scarp, are reduced in size, e.g. by grinding or like processing. For purposes of illustration, PCBs are used herein as an example. An exemplary system may take in 1000 lbs. of PCBs at a time, for example. PCB powder from dry end 105 is automatically fed or conveyed to leach 125, where precious metals are recovered from the PCB powder using a system of tanks, filters, and liquids. Precious metal- rich liquid from leach 125 is automatically passed to harvest 150 to recover precious metal(s).

[0027] In an implementation shown in FIG. 1, dry end 105 can include a shredder 110 connected to a rod mill 115, which in turn can be connected to additional rod mill(s) 120 as described herein. The last rod mill 115 or 120 can then connected to a leach tank 230 in leach 125 as described herein. In this description, connected to can refer to mechanical connections, conveyer systems, and other like apparatus for moving material from one unit to another.

[0028] Size reduction is accomplished, for example, by shredder 110, which may be a conventional shredder. Shredder 110 may be capable of shredding PCBs into 0.75-inch pieces or smaller. If 1000 lbs. of PCBs went into shredder 110, approximately, 1000 lbs. of shredded PCBs should exit shredder 110. Shredded PCBs can then be fed or automatically conveyed into rod mill 115, which will further reduce the size of the PCBs. Oversize materials and undersize materials are output from rod mill 115. Oversize materials from the PCBs that, for example, have a particle size of greater than 4mm and contain mainly copper and should be free of precious metal are extracted from system 100. As an illustrative example, for 1000 lbs. of original PCBs, about 800 lbs. of oversize material will be extracted.

[0029] FIG. 7A shows a photo of example oversize material comprising the copper core of PCBs. The pieces of the PCBs have been stripped of the boards through friction between the milling rods of, for example, rod mill 115. Aqua Regia assays have shown that there may be no precious metal, e.g., gold, left in the oversize material. The oversize material makes up the bulk of the mass initially input into dry end 105.

[0030] Undersize material, may be, for example, PCB powder, having high precious metal content. For 1000 lbs. of original PCB’s, there may be about 200 lbs. of PCB powder. The PCB powder may contain, on a proportional basis, approximately 200 grams of precious metal per ton of PCB powder, for example. It is noted that the percentage of precious metal is dependent upon on the type of input waste feedstock. For example, low grade waste feedstock will yield a lower precious metal content than high grade waste feedstock. In an implementation, the PCB powder may be fed to rod mill 120, which can be used to further reduce the particle size of the PCB powder. The output material is, for example, at least 35 US mesh and smaller.

[0031] FIG. 7B shows a photo of example undersize material. Undersize material may comprise ground components that have been attached to the base of the PCBs. The components may have been removed from the board through friction in between the milling rods of, for example, rod mill 115. The components have also been ground into a fine powder through the friction between the milling rods. The undersize material accounts for a fraction of the initial mass but carries the majority of the value. [0032] FIG. 1A is a flow diagram of an alternate dry end 105A for precious metal recovery according to an implementation. Dry end 105A can include a shredder 110 having a demagnetizer 112 situated proximate to shredder 110. Shredder 110 is connected to a rod mill 115 via a conveyer such as a screw conveyor, for example. The screw conveyor, for example, moves material from shredder 110 to rod mill 115 at a constant rate. Rod mill 115 is further connected to a hammer mill 118, as described herein, via a separator 116, such as for example, a vibrating screen separator. Hammer mill 118 can be connected to additional rod mill(s) 120 as described herein. Last rod mill 115 or 120 can then connected to leach tank 230 in leach 125 as described and shown with respect to FIG. 1A.

[0033] Operationally, waste feedstock is input to shredder 110 and demagnetizer 112, which shreds and demagnetizes the waste feedback. Demagnitized shredded waste feedstock can then be automatically fed or conveyed into rod mill 115, which will further reduce the size of the waste feedback. Oversize materials and undersize materials are output from rod mill 115 via separator 116. Undersize materials can be automatically fed or conveyed to hammer mill 118 if additional grinding is needed for the undersize materials. The finer ground undersize materials can be then automatically fed or conveyed to rod mill 120 for further processing. Output of rod mill 120 is then automatically fed or conveyed to leach tank 230, as shown in FIG. 1A.

[0034] The undersize material, such as for example, the PCB powder are fed from dry end 105 or dry end 105A to leach 125, where precious metals are recovered from the PCB powder using a system of tanks, filters, and liquids. Leach 125 may be carried out by exemplary tank system 200 shown and described with reference to FIGS. 1-6, for example.

[0035] As shown in FIG. 1, tank system 200, includes for example, a leach tank 230 which receives and mixes the PCB powder with a leaching solution. A settling tank 235 equipped with a solid-liquid separation system 240 which processes the wet mixture and feeds wet solids into a rinse/conveying system column 243. The solids are conveyed into a collection bin 245 and the precious metal-rich liquid is transferred to harvest 150 for further processing.

[0036] FIGs. 2 and 4 are perspective views of tank system 200, FIG. 3 is a cross- sectional view of tank system 200, and FIGs. 5 and 6 are elevation views of tank system 200. The figures show leach tank 230 positioned in a fixture 205 with settling tank 235 positioned below. Settling tank 235 is equipped with solid-liquid separation system 240, which feeds or conveys to rinse/conveying system column 243 via filter media 244. Settling tank 235 is further equipped with filters 236, through which leaching fluid is pumped out of settling tank 235. Filters 236 can be for example, but are not limited to, bag filters.

[0037] Operationally, in leach tank 230, undersize material or PCB powder, is stirred in leaching fluid for about 10 to 60 minutes (depending on the composition of the feed material) in order to leach out precious metal from the PCB powder. The leaching fluid, for example, is a chemical fluid that has an oxidation strength to oxidize and dissolve the precious metal. The leaching fluid can be, for example, but is not limited to, an acid, cyanide or halide based and the like. In an implementation, the leaching fluid used herein is described in U.S. Provisional Application No. 62/641,863, filed March 12, 2018, the entire disclosure of which is hereby incorporated by reference.

[0038] Leach tank 230 may constantly stir the PCB powder in the leaching fluid. As noted, settling tank 235 equipped with solid-liquid separation system 240 is underneath leach tank 230. The wet mixture settles into settling tank 235 and the solids from the PCB powder settle out in settling tank 235 and the leaching fluid is pumped through filters 236. Separation system 240 in settling tank 235 removes some or all of the solids from the PCB powder, which may still be wet, and conveys them towards and through filter media 244, which may be, for example a candle filter, and then to rinse/conveying system column 243. In rinse/conveying system column 243, the solids are rinsed with a liquid, such as water, to remove valuable leaching fluid and precious metals that are still trapped in the wet solids and a vertical conveyance/solid-liquid separation system, such as a vertical sand screw located within column 243 (as best shown in FIG. 6) moves and assists in further separating precious metals from the other solids. The solids are conveyed into collection bin 245 (shown in FIG. 1) and the precious metal -rich liquid is transferred to electro winning unit 155 for further processing. The solids may be rinsed with liquid, such as water, while they are moved to collection bin 245 to recover any residual precious metal-rich liquid. Such precious metal -rich liquid may also be transferred to electrowinning unit 155 for further processing.

[0039] Referring back to FIG. 1, in harvest 150, the precious metal-rich liquid is processed by removing precious metal (e.g. gold) and returning precious metal-free (e.g. gold- free) liquid to the prior operation, leach 125. Harvest 150 may be carried out by electro winning unit 155 shown and described with reference to FIGS. 8-13. FIG. 8 is a perspective view of an electrowinning unit, FIG. 9 is an elevational view of an electrowinning, FIG. 10 is a view of an electrowinning unit, FIG. 11 is a photograph showing an electrowinning, FIG. 12 is a photograph showing two sides of an electro winning anode plate and FIG. 13 is an illustrative diagram of an electrowinning unit shown with an electrowinning anode plate. In an implementation, electrowinning unit 155 is located on top of leach tank 230.

[0040] In general, electrowinning unit 155 comprises two electrodes. In particular, electrowinning unit 155 comprises rotating electrowinning cathode disk 320 (a first electrode), which is attached to bearing 315, both of which rotate about a central axis indicated by line A-A. Electrowinning cathode disk 320 also rotates about a shaft (not shown) located along a portion of the central axis. Electrowinning cathode disk 320 may be stainless steel and operates as the cathode in electrowinning unit 155. Electrowinning unit 155 further includes an electrowinning anode plate 325 (a second electrode), which may be made, for example, of stainless steel and has two electrowinning anode plate sides 325a (also shown as anode a) and 325b (also shown as anode b) located on either side of electrowinning cathode disk 320. Electrowinning anode plate sides 325a and 325b are held together with fixtures 305a and 305b. Electrowinning anode plate 325 has the same axis and is parallel to electrowinning cathode disk 320. Electrowinning anode plate 325 operates as the anode in electrowinning unit 155. Electro winning unit 155 further includes a scrapper 310, which is attached to fixture 305a and 305b. Scrapper 310 includes a slit in which electrowinning cathode disk 320 rotates through. Scrapper 310 harvests plated material from the electrowinning cathode disk 320 as it rotates. Electrowinning unit 155 may have one or more scrappers 310. Electrowinning anode plate 325 is stationary while electrowinning cathode disk 320 rotates on the central axis. The electrowinning anode plate 325 can vary in shape. In FIGS. 9 and 10 it is shown as a l35-degree angle, for example. In an implementation, electrowinning anode plate 325 can be a half circle as shown in the example photographs shown in FIG. 11-12, for example

[0041] Operationally, as the precious metal-rich liquid is received from rinse/conveying system column 243 by electrowinning unit 155, the precious metal (e.g. gold) is attracted to electrowinning cathode disk 320. Scrapper 310 scrapes the precious metal as electrowinning cathode disk 320 rotates and separates precious metal and precious metal-free liquid.

[0042] FIG. 13 is a view of electrowinning unit 155 with electrowinning anode plate 325 and scrapper 310 removed to show other elements. As shown, electrowinning unit 155 comprises rotating electrowinning cathode disk 320 that rotates axis A-A. Electrowinning cathode disk 320 also rotates about rotating shaft 345 located along axis A-A. Contact plate 330 is in electrical and mechanical communication with electrowinning cathode disk 320 and shaft 345, which allows for current transfer between electrowinning cathode disk 320 and shaft 345. Shaft coupling 335 is in electrical and mechanical communication with contact plate 330 and bearing 315. Rotating contactor 340 is in electrical communication with shaft 345 and rotates about shaft 345 and also transfers current from shaft 345 to a stationary shaft (not shown).

[0043] In general, a precious metal recovery process includes shredding waste feedstock to create shredded waste feedstock and grinding the shredded waste feedstock to create oversize material and undersize material. The undersize material is stirred in a leaching fluid for a predetermined period of time to create a solid- liquid material. The solid-liquid material settles in a settling tank and solids are separated from the solid-liquid material. The separated solids are rinsed with a liquid to obtain a precious metal-rich liquid. Precious metals and precious metal-free liquid are recovered from the precious metal-rich liquid using an electrowinning unit. In an implementation, the precious metal-free liquid is used at least a portion of the leaching solution. In an implementation, the solid- liquid material is conveyed to the settling tank to allow the solids to settle in the settling tank. In an implementation, the separated solids are filtered through a filter media prior to rinsing. In an implementation, the rinsed solids are conveyed to a collection bin. In an implementation, the step of grinding includes multiple grinding steps. In an implementation, the oversize material and the undersize material are separated via a separator. In an implementation, the precious metals in the precious metal-rich liquid are attracted to an electrode and the precious metals are then scraped from the electrode and the precious metal-free liquid is conveyed to a leach tank. In an implementation, the electrode is a cathode disk and the cathode disk is rotated relative to at least one scraper to scrape the precious metals.

In general, a precious metal recovery apparatus includes a leach tank intaking ground waste feedstock and mixing the ground waste feedstock with a leaching fluid to create solid-liquid material. The apparatus includes a settling tank in fluid communication with the leach tank, where the solid-liquid material is allowed to settle. The apparatus includes a separation system in mechanical communication with the settling tank, where solids are separated from the solid-liquid material. The apparatus includes a rinse and conveying system column in fluid communication with the separation system, where separated solids are rinsed to create a precious metal-rich fluid. The apparatus includes an electrowinning unit in mechanical communication with the rinse and conveying system column, where the electrowinning unit recovers precious metals and precious metal- free liquid from the precious metal-rich liquid. In an implementation, the separation system is a sand screw. In an implementation, the rinse and conveying system column is vertical. In an implementation, the apparatus includes a collection bin in mechanical communication with the rinse and conveying system column, where the collection bin intakes rinsed solids from the rinse and conveying system column. In an implementation, the electrowinning unit is in mechanical communication with the leach tank, where the electrowinning unit conveys the precious metal-free liquid to the leach tank. In an implementation, the apparatus includes at least one grinding mill in mechanical communication with the leach tank, the at least one grinding mill grinding shredded waste feedstock to create undersize material and oversize material. In an implementation, the apparatus includes a shredder in mechanical communication with the least one grinding mill, the shredder shredding waste feedstock. In an implementation, the apparatus includes a separator in mechanical communication with at least the leach tank, the separator separating the undersize material and oversize material to feed the undersize material to the leach tank. In an implementation, the electrowinning unit further includes an electrode, the electrode attracting the precious metals in the precious metal-rich liquid; and a scraper positioned proximate to the electrode, the scraper scraping the precious metals from the electrode. In an implementation, the electrode is a cathode disk which rotates relative to the scraper. In an implementation, the at least one grinding mill includes at least one rod mill and a hammer mill.

[0044] While the disclosure has been described in connection with certain embodiments, it is to be understood that the disclosure is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.

Claims

What is claimed is:

1. A precious metal recovery process comprising:

shredding waste feedstock to create shredded waste feedstock;

grinding the shredded waste feedstock to create oversize material and undersize material;

stirring the undersize material in a leaching fluid for a predetermined period of time to create a solid-liquid material;

separating solids from the solid-liquid material that has settled in a settling tank; rinsing the separated solids with a liquid to obtain a precious metal-rich liquid; and recovering precious metals and precious metal-free liquid from the precious metal- rich liquid using an electrowinning unit.

2. The precious metal recovery process of claim 1, further comprising:

using the precious metal-free liquid as at least a portion of the leaching solution.

3. The precious metal recovery process of claim 2, further comprising:

conveying the solid-liquid material to the settling tank to allow the solids to settle in the settling tank.

4. The precious metal recovery process of claim 3, further comprising:

filtering the separated solids through a filter media prior to rinsing.

5. The precious metal recovery process of claim 4, further comprising:

conveying rinsed solids to a collection bin.

6. The precious metal recovery process of claim 5, wherein the step of grinding includes multiple grinding steps.

7. The precious metal recovery process of claim 6, further comprising:

separating the oversize material and the undersize material via a separator.

8. The precious metal recovery process of claim 5, further comprising:

attracting the precious metals in the precious metal-rich liquid to an electrode; scraping the precious metals from the electrode; and

conveying the precious metal-free liquid to a leach tank.

9. The precious metal recovery process of claim 8, wherein the electrode is a cathode disk and further comprising:

rotating the cathode disk relative to at least one scraper to scrape the precious metals.

10. A precious metal recovery apparatus comprising:

a leach tank intaking ground waste feedstock and mixing the ground waste feedstock with a leaching fluid to create solid-liquid material;

a settling tank in fluid communication with the leach tank, wherein the solid-liquid material is allowed to settle;

a separation system in mechanical communication with the settling tank, wherein solids are separated from the solid-liquid material;

a rinse and conveying system column in fluid communication with the separation system, wherein separated solids are rinsed to create a precious metal-rich fluid; and

an electrowinning unit in mechanical communication with the rinse and conveying system column, wherein the electrowinning unit recovers precious metals and precious metal-free liquid from the precious metal-rich liquid.

11. The precious metal recovery apparatus of claim 10, wherein the separation system is a sand screw.

12. The precious metal recovery apparatus of claim 10, wherein the rinse and conveying system column is vertical.

13. The precious metal recovery apparatus of claim 10, further comprising:

a collection bin in mechanical communication with the rinse and conveying system column, wherein the collection bin intakes rinsed solids from the rinse and conveying system column.

14. The precious metal recovery apparatus of claim 13, further comprising:

the electrowinning unit being in mechanical communication with the leach tank,

42 wherein the electrowinning unit conveys the precious metal-free liquid to the leach tank.

15. The precious metal recovery apparatus of claim 14, further comprising:

at least one grinding mill in mechanical communication with the leach tank, the at least one grinding mill grinding shredded waste feedstock to create undersize material and oversize material.

16. The precious metal recovery apparatus of claim 15, further comprising:

a shredder in mechanical communication with the least one grinding mill, the shredder shredding waste feedstock.

17. The precious metal recovery apparatus of claim 16, further comprising:

a separator in mechanical communication with at least the leach tank, the separator separating the undersize material and oversize material to feed the undersize material to the leach tank.

18. The precious metal recovery apparatus of claim 17, wherein the electrowinning unit further comprises:

an electrode, the electrode attracting the precious metals in the precious metal-rich liquid; and

a scraper positioned proximate to the electrode, the scraper scraping the precious metals from the electrode.

19. The precious metal recovery apparatus of claim 18, wherein the electrode is a cathode disk which rotates relative to the scraper.

20. The precious metal recovery apparatus of claim 15, wherein the at least one grinding mill includes at least one rod mill and a hammer mill.