WO2013104895A1

WO2013104895A1 - Recovery of metals

Info

Publication number: WO2013104895A1
Application number: PCT/GB2013/050018
Authority: WO
Inventors: Jeremy Pearce; Harry Middleton
Original assignee: Itri Innovation Ltd.; Ultromex Ltd.
Priority date: 2012-01-09
Filing date: 2013-01-07
Publication date: 2013-07-18
Also published as: GB201200261D0

Abstract

A method for recovering metal from electronic waste, the method comprising; contacting electronic waste with a recovery solution to dissolve metals from the electronic waste into the recovery solution, wherein the recovery solution comprises nitric acid and ferric chloride; and raising the p H of the recovery solution to precipitate at least some of said metals therefrom.

Description

Recovery of Metals

The present invention relates to the recovery of valuable metals from waste electronics. In particular, the present invention relates to the recovery of metals such as copper and tin from printed circuit boards.

In recent years, there has been concern about the growing volume of end-of-life electronics. A large amount of electronic waste is consigned to landfill without any attempt being made to recycle the constituent materials. This represents both a source of pollution and a waste of valuable resources. With growing pressure to avoid land-filling this electronic waste material, there is a need to develop a method for recycling the material and to enable recovery of the valuable metals therein.

During the manufacture of printed circuit boards, there is commonly a step of stripping a solder mask from the board. US 5,244,539 discloses such a method for manufacturing a printed circuit board. The method relies upon the use of a metal-dissolving liquid to perform the stripping. The metal dissolving liquid is used to solubilise the tin and to provide a bright finish to the copper on the board. Nitric acid is commonly used in the metal dissolving liquid. The use of various additives to control the extent and quality of the process are well known (see, for example, US 5,505,872). In these prior art documents the intention is to strip a solder layer from the surface of the board; the methods are not conducted for sufficient time to dissolve metals forming part of the board. Nor are these methods carried out when components are present on the board, due to the risk of component damage.

EP 0 023 729 discloses a method for de-tinning tin plate. The method is applied to old cans, tin plate, lacquered tin sheet waste and the like. The method uses an oxidising solution and a source of ferric ions. The method exploits a low temperature exchange reaction between iron and tin. There is no teaching to use this method to recover metals from electronic waste, nor of precipitating out dissolved metals from the de-tinning solution.

Accordingly, there is a desire for a recycling process to prevent the present loss of valuable metals from electronic waste into landfill. Moreover, there is a desire for a process that will overcome, or at least mitigate, some or all of the problems associated with the methods of the prior art or at least provide a useful or optimised alternative.

According to a first aspect, the present invention provides a method for recovering metal from electronic waste, the method comprising:

contacting electronic waste with a recovery solution to dissolve metals from the electronic waste into the recovery solution, wherein the recovery solution comprises nitric acid and ferric chloride; and

raising the pH of the recovery solution to precipitate at least some of said metals therefrom.

The present disclosure will now be further described. In the following passages different aspects of the disclosure are defined in more detail. Each aspect so defined may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.

The method of the present invention is for the recovery of metals from electronic waste. Electronic waste, or e-waste, is a term in the art used to describe any discarded electrical or electronic devices. Electronic waste will contain useful metals from the electronic connections and wiring required for the device to have functioned. Associated with this waste there will also be waste in the form of casing or wiring supports.

Electronic waste can take many forms including, by way of example, computers, mobile phones and other household electrical devices. Electronic waste will contain a wide variety of different materials. For example, cathode ray tube monitors and televisions may contain solder, lead, cadmium and beryllium.

Preferably, the electronic waste comprises or consists of circuit board waste. That is, preferably the waste includes circuit boards and/or printed circuit boards, or broken fragments thereof. Such circuit board waste preferably comprises the electronic components originally soldered to a printed circuit board, since these can be readily recovered using the method of the present invention. A printed circuit board will necessarily contain metal, in particular in the form of wiring and contacts, and may further include solder applied to the contacts. The present inventors have discovered that the use of the recovery solution disclosed herein allows for the treatment of bulk electronic waste. Advantageously, the use of the recovery solution comprising nitric acid and ferric chloride allows for the dissolution of the metals commonly used in the electronic waste. Moreover, increasing the pH allows for the precipitation of at least some of the dissolved metals from the recovery solution. These metals can then be separated, refined and reused.

The inventors have further discovered that the recovery solution can be applied without needing to pre-grind the electronic waste. Indeed, preferably there is no grinding step and the electronic waste is not in a powder form. It will be appreciated that the electronic waste may be damaged or fragmented, for example, if recovered from a skip or landfill. However, the present method allows for the treatment of such waste and even the separation and recovery of electronic components therefrom. In one embodiment it may be advantageous to homogenise the electronic waste with a first fragmentation step. This fragmentation step preferably is conducted to ensure a uniform waste for treatment, without completely destroying the electronic components that may be present. For example, when the waste is primarily circuit board waste, the waste is preferably fragmented to have a longest diameter of from 1 to 10 cm, more preferably from 2 to 8 cm and most preferably from 3 to 7 cm.

The present inventors have discovered that the method of the present invention allows for the recovery of metals from electronic components and also for the recovery of discreet electronic components. These components may be separated from the waste by the dissolution of their metal contacts or the solder holding them to the waste, or by shearing. Moreover, because there is no need to grind the waste, it is easy to coarsely filter and separate the treatment mixture. Due to the different relative sizes, without a pre-ground board it is possible to separately recover (1 ) any non-metal waste, such as the plastic from printing circuit boards; (2) discrete electronic components, such as transistors or resistors; (3) any metal precipitated from the solution; and (4) the recovery solution with dissolved metals therein. Additionally, since the residue from the above (1 ) is not a fine powder, it may be more readily handled and processed. Preferably the above materials (1 ) and/or (2) are recycled as appropriate using known recycling techniques. In one embodiment electronic components are separated from the waste by using a standard shearing technique. One advantage of removing electronic components in this way rather than by dissolution of their metal contacts or solder is that damage may be less likely to occur to the components. For example, metals such as, for example, gold, are not lost from the components when the components are contacted with the recovery solution. Another advantage of the use of shearing is that it may avoid an increase in the metals content (including undesirable metals) of the recovery solution, which can lower throughput and use up nitric acid. Since the undesirable metals content is reduced, a higher value metal cake may be obtained on precipitation. Furthermore, reducing the metals content may serve to reduce the occurrence of a run-away exothermic reaction that may occur at excessive metals content. In an alternative embodiment, the occurrence of such a run-away exothermic reaction may be reduced by employing automated temperature control and/or cooling. The recovery solution comprises nitric acid and ferric chloride. The recovery solution preferably comprises from 10 to 60% v/v nitric acid solution, preferably from 20 to 30 % v/v, more preferably about 20% v/v. This concentration of the solution is sufficient to dissolve the metals commonly present in electronic waste. In particular, the nitric acid function to dissolve metals, notably silver and tin from solder as well as copper, lead, iron and other minor metals. Any exposed gold is liberated by undermining but not dissolved. The recovery solution preferably comprises from 1 to 40% w/v ferric chloride, preferably from 1 to 15% w/v, more preferably from 5 to 10% w/v, even more preferably about 5% w/v. The ferric ions function to accelerate dissolution of tin and copper alloys. The halide ions function to solubilise tin and to prevent sludge formation. In addition, when the electronic waste comprises silver, the presence of the halide ions may result in the formation of insoluble AgCI from which silver may be recovered. Accordingly, use of ferric chloride over other ferric ion sources, such as ferric nitrate, is particularly advantageous. In the second step of the method the pH of the recovery solution is increased. Before the pH is increased, there may be some metal precipitated from the solution, for example any gold, for example from edge connectors, and silver as an insoluble salt i.e. AgCI. Therefore, preferably the above materials (1 ) and (2) are first removed from the recovery solution. This facilitates the removal of the desired metal precipitates. The first metal precipitate can then be recovered, if desired, before the pH is increased. Since different metals can precipitate out at different pH's, this can provide a cost effective method of separating out the different metals recovered. The pH of the recovery solution comprising nitric acid and ferric chloride before use will preferably be less than 1. More preferably, the pH of the solution will be from -1 to 1 and most preferably about 0. The use of these harsh conditions allows for the full dissolution of metals from the electronic waste into the recovery solution. In addition, below pH 1 precipitation of AgCI may occur, allowing recovery of silver contained in the electronic waste.

The pH of the recovery solution is increased to precipitate at least some of the metals therefrom. Preferably the metals are recovered as a filter cake following the filtration of the recovery solution. Preferably the pH is ultimately increased to from 6 to 14 and more preferably to about 7. The pH of about 7 allows more efficient precipitation of metals from the recovery solution, without requiring the use of excess base. Furthermore, the neutral pH allows for safer handling of the recovery solution.

In one embodiment the method comprises the step-wise increase in the pH. As a consequence, a coarse separation of the metals dissolved from the electronic waste may be performed. Indeed, it has been discovered that some gold, silver and tin precipitates may form during the initial dissolution step. Lead then precipitates up to a pH of about 1 . Finally, metals such as copper and tin may be recovered around a pH of 7. The method may further comprise recovering precipitated metal from the recovery solution, preferably by filtration or centrifuge.

In one embodiment the electronic waste comprises tin and at least one other metal, and the step of raising the pH comprises:

raising the pH to at least 12 to precipitate the at least one other metal; and recovering tin dissolved in the recovery solution.

The at least one other metal may comprise, for example, iron, copper and/or lead. In this embodiment the pH is raised to at least 12, preferably to at least 13. At such pH values tin remains in solution, typically in the form of a sodium hydroxystannate solution. Most other metals in the recovery solution, such as iron, copper and lead, precipitate at such pH values. Since the number of different types of metal remaining in solution will be small, the recovery of tin from the recovery solution may occur more easily and at higher purity. In this embodiment the pH is raised straight to at least 12. In other words, the pH is raised from the initial pH of the recovery solution to at least 12 without stopping at intermediate pH values for any significant periods of time. For example, the pH may be raised from the initial pH of the recovery solution to at least 12 within a period of 24 hours, preferably 12 hours, more preferably 5 hours, even more preferably 3 hours, still even more preferably 2.5 hours, still even more preferably 2 hours. This reduces undesirable precipitation of tin at the same time as precipitation of the at least one other metal. In other words, the amount of tin remaining in solution, and therefore being in a form suitable for efficient recovery, is increased. To avoid undesirable precipitation of tin, the pH should be increased as fast as possible. However, increasing the pH may also increase the temperature of the system, which may be undesirable. To avoid significant increases in the temperature, the pH is preferably increased over a period of at least 10 minutes, more preferably at least 30 minutes, even more preferably at least 60 minutes, still even more preferably at least 80 minutes. In a preferred embodiment the pH is increased over a period of from 60 to 150 minutes, preferably from 90 to 120 minutes. The pH may be increased at the desired rate by, for example, alternating steps of: (i) adding batches of hydroxide to the recovery solution, and (ii) waiting for the recovery solution to cool, until the desired pH is reached.

The tin may then be recovered in a number of ways. In one embodiment, the pH is reduced to a pH of from 3 to 7, preferably from 3.5 to 5, more preferably about 4. At such pH values a Sn(OH)₄ precipitate typically forms. The Sn(OH)₄ may be separated from the recovery solution using known techniques such as, for example, filtration. Process parameters such as pH, aging time and electrolyte concentration may be controlled in order to avoid the precipitation of a gelatinous Sn(OH)₄ precipitate. For example, aging the Sn(OH)₄ precipitate for at least 5 hours, preferably at least 15 hours, more preferably at least 24 hours results in the Sn(OH)₄ precipitate being more easily separable from the recovery solution. Tin may be recovered from the Sn(OH)₄ precipitate by known techniques such as, for example, a standard smelting technique. In an alternative embodiment, the tin may be recovered by electrowinning without the need to reduce the pH. This reduces the amount of acid used in the process. In a further alternative embodiment the tin may be recovered by the use of a complexing and/or stabilising agent. Suitable stabilising agents include, for example, tartaric acid and boric acid, which stabilise tin oxide colloids. To aid the recovery of tin the precipitate of the at least one other metal is preferably removed from the recovery solution prior to recovering the tin, preferably by filtration or centrifuge.

raising the pH to 8 or less to cause precipitation of tin and the at least one other metal;

separating the precipitate from the recovery solution;

re-suspending the precipitate in a hydroxide solution; and

recovering tin from the hydroxide solution.

The at least one other metal may comprise, for example, iron, copper and/or lead. In this embodiment the pH is raised to 8 or less, preferably from 3 to 7.5, more preferably from 4 to 7. At such pH values a precipitate forms and may be separated from the recovery solution. Re-suspension of this separated precipitate in a hydroxide solution, such as a sodium hydroxide solution, may provide a tin hydroxystannate solution from which tin may be recovered using, for example, the methods described above. The amount of tin recovered in this embodiment is particularly high in comparison to the embodiment in which the pH is raised to at least 12. When the pH is decreased from at least 12 to from 3 to 8, typically at least a third of the tin remains in solution. This is presumably due to the production of NaN0₃ upon neutralisation of NaOH with nitric acid, which acts as a concentrated electrolyte.

In one embodiment the electronic waste comprises copper and at least one other metal, and the step of raising the pH comprises:

raising the pH to from 3 to 5 to precipitate the at least one other metal; and recovering copper dissolved in the recovery solution.

The at least one other metal may comprise, for example, iron, tin and/or lead. In this embodiment the pH is raised to from 3 to 5, preferably from 3.5 to 4.5, more preferably to about 4. At such pH values copper remains in solution while metals such as tin and iron precipitate. Copper may then be recovered from the recovery solution in a number of ways. In one embodiment the pH is raised to a pH of from 8 to 10, preferably from 8.5 to

9.5, more preferably to about 9. At such pH values a copper precipitate forms, which may be recovered from the recovery solution, for example by filtration. To aid recovery of the copper precipitate, the precipitate of the at least one other metal is preferably removed from the recovery solution prior to raising the pH to from 8 to 10. In an alternative embodiment copper may be recovered by the use of a complexing agent, such as, for example, ammonia or EDTA. In a further alternative embodiment, the copper may be recovered by electrowinning.

Any suitable alkali or base may be used in order to increase the pH of the solution. The use of a metal hydroxide is preferred, in particular sodium hydroxide is preferred due to its ready availability and low cost. Any suitable acid may be used in order to increase the pH of the solution. The use of nitric acid is preferred due to is ready availability and low cost.

In some embodiments suppression agents may be added to the recovery solution in order to avoid dissolution of particular metals. By adding particular suppression agents it is possible to control which metals dissolve into the recovery solution and, therefore, which metals are to be recovered. For example, resorcinol may be used as a

suppression agent to inhibit the dissolution of copper from the electronic waste. By limiting the types of metals dissolved into the recovery solution, the purity and recovery rates of the selected metals may be increased, and their recovery from the recovery solution may be simplified. Suitable suppression agents are known in the art and include, for example, sulfamic acid; benzotriaole, benzoimidazole, imidazole, and derivatives thereof; propylene glycol, ethylenediamine, diethylene glycol, bisphenol A, and an ethylene oxide adduct or ethylene oxide-propylene oxide adduct thereof (preferably, ethylene oxide-propylene oxide adduct with an propylene oxide terminal); ethylene oxide-propylene oxide copolymers, and the like; pyrrole and pyrrole derivatives; pyrazole and pyrazole derivatives; imidazole and imidazole derivatives; and triazole and triazole derivatives.

In some embodiments metal complexing agents, such as ammonia and EDTA, may be used in order to recover metals from the recovery solution.

Preferably the step of contacting the electronic waste with a recovery solution comprises immersing the electronic waste in the recovery solution. In this way, the metals present in the electronic waste will be fully contacted by the recovery solution and the maximum recovery yield will be obtained. Preferably the electronic waste remains immersed in the recovery solution for at least 30 seconds, more preferably at least 1 minute, more preferably at least 5 minutes and most preferably from 10 minutes to 1 hour. Longer treatments may be suitable, but process efficiency favours a faster processing time. The optimum immersion duration is from 30 to 40 minutes. Preferably the treatment is conducted in a batch-wise manner.

Preferably the immersed circuit board waste and the recovery solution are agitated during the processing. While the agitation may comprise mechanical stirring or the like, preferably the agitation comprises ultrasonic agitation. The use of ultrasonic agitation helps to encourage the dissolution of the metals from the electronic waste into the recovery solution. Accordingly, processing times can be decreased and the efficiency of the process is improved. Moreover, the agitation encourages the separation of components attached to circuit boards. Preferably mechanical agitation is avoided to reduce fragmentation of the electronic waste and the consequential loss of handle-ability.

Preferably the electronic waste is immersed until substantially all of the metal in the waste is dissolved. In this way the highest recovery yields can be achieved.

The present inventors have discovered that the method is suitable for the recovery of one or more of lead, gold, silver, copper, zinc and tin from electronic waste. Obviously, the metals that can be recovered will depend upon the electronic waste and the metals contained therein. Preferably the method is used for at least the recovery of tin from electronic waste. Tin is a common component in solders and will commonly be present in electronic waste. Preferably the method is used for recovery of metals from electronic waste containing lead-free solders. The method is particularly suitable for the recovery of tin, copper and silver, which are typical components of lead free solders. Preferably the method further comprises a step of subjecting the precipitated metals to a conventional recovery treatment to obtain one or more substantially pure metals therefrom.

The process of the present invention may be carried out by a standalone unit.

Alternatively, the process may be carried out by an "add-on" unit to a standard waste PCB processing unit. According to a further aspect the present invention provides a method for recovering silver and/or gold from electronic waste, the method comprising;

contacting electronic waste comprising gold and/or silver to be recovered with a recovery solution comprising nitric acid and ferric chloride at a pH of at most 1 ; and

recovering precipitated gold and/or AgCI from the recovery solution, preferably by filtration and/or centrifuge.

Gold may be separated from a precipitate of gold and AgCI by adding water to dissolve AgCI and then filtering the resulting solution. Other metals which may be contained in the electronic waste, such as, for example, tin, iron, lead and/or copper, may dissolve in the recovery solution, and may be recovered therefrom, for example by the use of electrowinning, by the use of one or more complexing agents, or by increasing the pH of the recovery solution to precipitate at least some of said other metals therefrom. The invention will now be discussed further with reference to the figures, provided purely by way of example, in which:

Figure 1 shows a flow chart of the method steps of the present invention. Examples

The invention will be described with reference to the following examples which are provided by way of example and are not limiting. Example 1

A source of electronic waste comprising waste circuit boards was obtained. The waste circuit boards were in the form of fragments, but had not been intentionally ground. 481 g of fragments were immersed sequentially into a solution of 5 %w/v ferric chloride and 20 %v/v concentrated nitric acid (69%). The solution was held in a beaker suspended in an ultrasonic bath for 40 minutes.

The electronic components originally attached to the waste circuit boards remained intact and were separated from the boards. Some copper dissolved from the waste boards, but was found to have primarily re-plated onto steel components in the waste. A small amount of precipitate was observed in the beaker and this was filtered from the solution. When the metals in the precipitate were characterised by X-ray fluorescence, they were found to be 97 wt% lead. In a next step the pH of the solution was adjusted to pH 7 using sodium hydroxide. A brown precipitate was formed, separated and dried. When metals in the precipitate were characterised by X-ray fluorescence, they were found to be 31 wt% tin, 33 wt% copper, 8 wt% lead, 25 wt% iron and 3 wt% zinc. The supernatant contained no metals. Example 2

707 g of fragments from waste circuit boards were immersed sequentially into a solution of 5 %w/v ferric chloride and 20 %v/v concentrated nitric acid (69%) in a beaker suspended in an ultrasonic bath for 40 minutes.

The components originally attached to the waste circuit boards remained intact and were separated from the boards by the treatment. These were then separated, sorted and removed for further recycling. A small amount of precipitate was obtained from the initial dissolution step. The metals content was characterised by X-ray fluorescence as containing 22 wt% tin and 47 wt% silver.

The pH of the solution was adjusted to pH 7 in a second step using sodium hydroxide. At a pH of less than 1 a white precipitate was observed. At a pH of 7 a brown precipitate was formed, washed, filtered, dried and metals content analysed by X-ray fluorescence. This proved to be 48 wt% tin, 1 wt% copper, 12 wt% lead and 20 wt% iron. The supernatant contained no significant quantities of metals. Example 3

401 g of fragments from waste lead-free soldered circuit boards were immersed sequentially into a solution of 5 %w/v ferric chloride and 20 %v/v concentrated nitric acid (69 %) in a beaker suspended in an ultrasonic bath for 40 minutes. The components originally attached to the waste circuit boards remained intact and were separated from the boards by the treatment. These were then separated, sorted and removed for further recycling. 0.15 g of precipitate was recovered from the initial dissolution step. The metals content was characterised by X-ray fluorescence as containing 74 wt% silver, 5 wt% gold and 20 wt% iron.

The pH of the solution was adjusted to pH 13 in a second step using sodium hydroxide. The precipitate was separated by centrifuge and the metals content characterised by X- ray fluorescence as containing 30 wt% iron, 4 wt% copper, 1 wt% lead and other minor metal impurities.

The pH of the solution was adjusted to pH 4 using nitric acid. 23 g of white precipitate was recovered using a centrifuge. The metals content was characterised as 100 wt% tin.

As demonstrated by the foregoing examples, the method of the present invention is suitable for the recovery of metals from electronic waste. Moreover, the present invention has a number of advantages. There is no need for pre-processing of the electronic waste before treatment. The method results in the detachment of electronic components from the waste which can be recovered and treated separately.

Additionally, high yields of the metal recovery are obtained.

The foregoing detailed description has been provided by way of explanation and illustration, and is not intended to limit the scope of the appended claims. Many variations in the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art and remain within the scope of the appended claims and their equivalents.

Claims

Claims:

1. A method for recovering metal from electronic waste, the method comprising; contacting electronic waste with a recovery solution to dissolve metals from the electronic waste into the recovery solution, wherein the recovery solution comprises nitric acid and ferric chloride; and

2. The method according to claim 1 , wherein the step of contacting the electronic waste with a recovery solution comprises immersing the electronic waste in the recovery solution.

3. The method according to claim 2, wherein the method further comprises agitating the recovery solution and the immersed circuit-board waste.

4. The method according to claim 3, wherein the agitation comprises ultrasonic agitation.

5. The method according to any of claims 2 to 4, wherein the electronic waste is immersed until substantially all of the metal in the waste is dissolved.

6. The method according to any of the preceding claims, wherein the electronic waste comprises circuit-board waste.

7. The method according to any of the preceding claims, wherein the electronic waste is contacted with a recovery solution having a pH of less than 1 , and/or wherein the pH is raised to from 6 to 14, and preferably to about 7.

8. The method according to any of the preceding claims, wherein the pH is raised by the addition of NaOH.

9. The method according to any of the preceding claims, wherein the recovery solution comprises:

(i) from 10 to 60% v/v nitric acid solution, preferably from 20 to 30% v/v; and/or (ii) from 1 to 40% w/v ferric chloride, preferably from 1 to 15% w/v.

10. The method according to any of the preceding claims, the method further comprising removing any electronic waste residue from the recovery solution before raising the pH.

1 1 . The method according to any of the preceding claims, wherein the electronic waste is not provided in the form of a powder.

12. The method according to any of the preceding claims, wherein the electronic waste is circuit-board waste and comprises whole circuit-boards or sections thereof.

13. The method according to any of the preceding claims, wherein the step of raising the pH is conducted stepwise to allow for the separate precipitation and recovery of different metals.

14. The method according to any of the preceding claims, wherein the metals recovered comprise one or more of lead, silver, iron, copper, gold, zinc and tin.

15. The method according to any of the preceding claims, wherein the method comprises additionally recovering and sorting electronic components separated from the electronic waste by the dissolution of metal from the electronic waste.

16. The method according to any of the preceding claims, the method further comprising subjecting the precipitated metals to further treatment to recover one or more substantially pure metals.

17. The method according to any of the preceding claims, wherein the electronic waste is immersed for at least 30 minutes in the recovery solution before the pH is raised.

18. The method according to any of the preceding claims further comprising recovering precipitated metal from the recovery solution, preferably by filtration and/or centrifuge.

19. The method according to any of the preceding claims, wherein the electronic waste comprises tin and at least one other metal, and the step of raising the pH comprises:

20. The method according to claim 19, wherein the tin is recovered by:

electrowinning; and/or

reducing the pH of the recovery solution to from 3 to 7, preferably from 3.5 to 5, to precipitate tin; and/or

the use of a complexing agent.

21 . The method according to any of claims 1-18, wherein the electronic waste comprises copper and at least one other metal, and the step of raising the pH comprises: raising the pH to from 3 to 5 to precipitate the at least one other metal; and recovering copper dissolved in the recovery solution.

22. The method according to claim 21 , wherein the copper is recovered by:

electrowinning; and/or

increasing the pH of the recovery solution to from 8 to 10, preferably about 9; and/or

the use of a complexing agent, such as ammonia.

23. The method according to any of claims 19-22, wherein the precipitated at least on other metal is separated from the recovery solution prior to the recovery of the tin or copper.

24. The method according to any of claims 1-18, wherein the electronic waste comprises tin and at least one other metal, and wherein the step of raising the pH comprises:

separating the precipitate from the recovery solution;

re-suspending the precipitate in a hydroxide solution; and

recovering tin from the hydroxide solution.