Method for recovering palladium from a rinsing composition

Abstract

The present invention relates to a method for recovering palladium from a rinsing composition, the method comprising the steps (a) providing an acidic rinsing composition derived from a spray rinsing of a palladium-activated substrate with an aqueous solution, wherein the acidic rinsing composition comprises metallic palladium, metallic tin and tin ions; (b) treating the acidic rinsing composition with an acidifier agent to obtain a stabilized acidic rinsing composition having a pH of ≤ 0.9; (C) treating the stabilized acidic rinsing composition with an oxidizing agent to obtain an oxidized rinsing composition comprising dissolved palladium ions, and dissolved Sn4+ ions, (d) contacting the oxidized rinsing composition with an ion exchange resin to adsorb palladium ions on said resin to obtain a treated rinsing composition comprising the dissolved Sn4+ ions, and a loaded ion exchange resin comprising palladium ions.

Description

[0001]

[0002] Method for recovering palladium from a rinsing composition

[0003] Field of the Invention

[0004] The present invention relates to a method for recovering palladium from a rinsing composition comprising palladium-tin colloids. The method is in particular suited to recover palladium from a rinsing composition which is obtained during a process for activating a non-conductive substrate for subsequent metallization.

[0005] Background of the Invention

[0006] The metallization of non-conductive substrates such as plastic substrates has a long tradition in modern technology. Typical applications can be found in the automotive industry, the household appliance and sanitary industry to produce metallized decorative surfaces and in the electronics industry for the production of metallized, conductive surfaces on non-conductive substrates.

[0007] However, making such substrates receptive for a metal layer is demanding and usually involves several different steps. Typically, a respective method starts with a surface modification of the substrate’s surface, typically known as etching, followed by an activation step.

[0008] In the activation step, very often precious metals are utilized as activators, most commonly palladium, of which colloidal palladium-tin is the most prominent one. Palladiumtin colloids are structurally composed of metallic palladium and metallic tin in the core covered by a shell of tin(ll) ions and chloride ions, maintaining the metallic state of palladium. Typically, a respective activation composition comprises up to 100 mg / L metallic palladium.

[0009] Upon activation by contacting the non-conductive substrate with such an activator in an activation composition, palladium adsorbs on the surface of the substrate and serves as starting point for a subsequent metallization. This metallization starts normally with an electroless metallization such as electroless copper or nickel plating to deposit a thin copper layer, followed by electrolytic metallization with electrical current, e.g. electrolytic deposition of a copper layer, to strengthen the electroless plated metal layer.Typically, after the activation step the activated substrate is rinsed with water to avoid contamination of the subsequent bath for electroless metallization with palladium. This, however, means that a significant amount of palladium is lost through the rinse water. Since palladium is comparatively expensive it is desired to avoid an unnecessary loss of such a precious resource during the activation process. Therefore, methods are known in the art for recovering palladium from the used activator solutions which still contain high amounts of palladium which makes the process cost efficient.

[0010] EP 2865769 B1 refers to an activated carbon for adsorbing a noble metal as palladiumtin colloids from an aqueous solution containing the noble metal, a noble metal adsorption filter containing the activated carbon, and a method for recovering a noble metal using the activated carbon.

[0011] DE 10024239 C1 refers to a method for recovering colloidal palladium from the palla-dium-tin colloid-containing activator solution through by means of membrane filters. Comparatively high pressure is needed, e.g. about 10 bar, in order to provide the required pressure for filtration. However, own observations have shown that a filter with raising amounts of colloidal palladium can be quickly blocked and result in an undesired over-pressure. Furthermore, recovering particles includes typical significant amounts of tin accompanied by the metallic palladium.

[0012] US 4435258 A refers to a method for recovering palladium from spent catalytic colloidal palladium bath by dissolving the palladium to form a true solution followed by electrodeposition employing a nickel anode and a nickel or copper cathode. However, such an electrowinning requires additional energy and equipment which cannot easily accommodated in each and every production site.

[0013] US 2002 / 119085 A1 describes a method for selectively separating and recovering palladium from an aqueous palladium / tin catalyst solution. The method includes the steps of adjusting the pH of the aqueous solution to a specified pH range thereby precipitating the tin, and producing a soluble form a palladium. The solution can be either pre-filtered or settled and subsequently processed through ion exchange resin in a conventional manner, or processed in an upflow direction through an at least partially fluidized bed of ion exchange resin to remove and concentrate the palladium for recovery.

[0014] Some problems arise with precipitation, for example, because the precipitated tin species must be carefully removed, otherwise the precipitates will clog the ion exchange resin column. In addition, the precipitates may also contain palladium compounds, whichultimately further reduces the palladium yield, especially if rinsing solutions with low palladium concentrations are also to be processed.

[0015] Due to the increasing prices of precious metal catalyst, there is a growing demand to also recover precious metals not only from the used activator solutions but also from rinsing solutions. One of the problems with recovering palladium from rinsing solutions is the low concentration of the precious metals which leads to low cost efficiency. Another problem is the instability of the rinsing solution, which leads to precipitation or turbidity and thus causes problems in the recovery process.

[0016] Thus, there is an ongoing demand to recover palladium from a colloidal palladium activator, in particular from a rinsing composition comprising such colloids.

[0017] Objective of the Invention

[0018] It is the objective of the present invention to provide a method for recovering palladium from a rinsing composition comprising palladium colloids, wherein the method is efficient, safe to handle, requires only low costs and a minimum of equipment, and as far as possible recovers palladium only with a minimum amount of tin contamination.

[0019] Summary of the Invention

[0020] These objectives are solved by a method for recovering palladium from a rinsing composition, the method comprising the steps

[0021] (a) providing an acidic rinsing composition derived from a spray rinsing of a palladium-activated substrate with an aqueous solution, wherein the acidic rinsing composition comprises metallic palladium, metallic tin and tin ions; preferably having a palladium concentration of at least 2.0 mg / L, and preferably having a total tin concentration comprising metallic tin, Sn2+ions and Sn4+ions of at least 0.25 g / L;

[0022] (b) treating the acidic rinsing composition with an acidifier agent to obtain a stabilized acidic rinsing composition having a pH of < 0.9;

[0023] (c) treating the stabilized acidic rinsing composition with an oxidizing agent to obtain an oxidized rinsing composition comprising

[0024] dissolved palladium ions, and

[0025] dissolved Sn4+ions (derived from metallic tin and Sn2+ions),(d) contacting the oxidized rinsing composition with an ion exchange resin to adsorb palladium ions on said resin to obtain a treated rinsing composition comprising the dissolved Sn4+ions, and a loaded ion exchange resin comprising palladium ions.

[0026] In the context of the present invention, it is understood that the metallic palladium, the metallic tin and tin ions (Sn2+ions and Sn4+ions) are derived from palladium-tin colloids which are used in activation composition to provide a palladium-activated substrate. In the context of the present invention, spray rinsing is understood as spraying the aqueous solution over the palladium-activated substrate to rinse away excess palladium-tin colloids which are not adsorbed or adhered at the surface of the palladium-activated substrate, whereby an acidic rinsing composition is obtained to be provided in step (a). In the context of the present invention, all compositions are considered as aqueous compositions if not mentioned otherwise and having more than 51 w.-% (weight-%) water regarding the total weight of the composition.

[0027] The present invention avoids, in fact does not use a precipitation step to precipitate tin species and remove these precipitated tin species before using the ion exchange resin to adsorb palladium ions in step (d). This leads to higher palladium recovery, the danger of clogged separation column, and further reduced method steps.

[0028] The present invention does not use active carbon at any step.

[0029] Own experiments have shown that over time atmospheric oxygen and dissolved oxygen in the rinsing solution will partially or completely oxidize the Sn2+ions to Sn4+ions (also mentioned here as tin(ll) or Sn(ll) ions, and tin(IV) or Sn(IV) ions). This is even more true if an immersion rinsing (also called submersible sink) is used for rinsing which is often used for days within the activation process. The oxidation finally results in the formation of poorly soluble Sn(OH)4(s), which leads to precipitation and turbidity in the acidic rinsing composition. By reaction with atmospheric oxygen, further oxides are formed, especially SnC>2 (tin stone), which further accelerate the precipitation in the acidic rinsing composition. These reactions expose the metallic palladium-tin (Pd-Sn) core because the SnCh ligand shell is degraded. The naked metallic Pd-Sn cores partially agglomerate into particles, which leads to further precipitation. The particles of these precipitations (agglomerates of the Pd-Sn core and the Sn(OH)4precipitations) are very small (< 1 pm) and can only be separated with extreme difficulty or only by processes such as microfiltration using high pressure application. Even if separation is successful, a mixture of tinand palladium compounds is obtained, which must be further separated. Therefore, a cloudy solution is obtained, which preferably consists of Sn species [Sn(OH)4; SnCh] and contain the metallic colloid core Pd-Sn as agglomerated precipitations.

[0030] The present invention therefore significantly avoids turbidity and precipitation in each step of the whole method which otherwise would complicate the recovery of the palladium and would reduce the palladium recovery yield.

[0031] Within step (a) a highly palladium concentrated acidic rinsing composition is provided by using spray rinsing step to rinse the palladium-activated substrates. The spray rinsing with the aqueous solution generates the acidic rinsing composition comprising palla-dium-tin colloids of consistent quality. Own experiments have shown that in contrast to prior art methods (e.g. immersion rinse wherein the substrates are immersed in one or more rinsing baths), the obtained acidic rinsing composition containing palladium is a clear composition because it is continuously removed from the overall metallization process (i.e. not carried over further or collected with other compositions obtain from further rinsing steps) and preferably directly provided for step (a) without timely delay or further steps. That means, the obtained acidic rinsing composition from a spray rinsing step shall be quickly further processed within the palladium recovery method according to the invention. The acidic pH of the provided acidic rinsing composition is preferably derived only from spray rinsing of the palladium-activated substrate which comes directly from the activation step wherein the activation composition is applied having a pH below 1. It was found that the stability of the acidic rinsing composition obtained from the spray rinsing treatment is low without stabilization. This solution is preferably stable without precipitations and turbidity for time period of less than 3 to 6 hours, preferably less than 1 to 2 hours, having a pH preferably from 1.0 to 1.8.

[0032] Within step (b), the acidic rinsing composition of step (a) is preferably directly processed without intermediate steps and time delays, wherein the acidic rinsing composition of step (a) is treated with an acidifier agent to lower the pH value to obtain the stabilized acidic rinsing composition. Step (b) therefore seems to temporarily stabilize the tin(ll) ions in the stabilized acidic rinsing composition until a subsequent process step is conducted. It was found, that during step (b) the palladium-tin colloids will be mainly maintained in its structure. However, in case dissolved oxygen would generate Sn4+ions from Sn2+ions, the precipitation of poorly soluble tin species as Sn(OH)4 can be avoided. As a result, this stabilized acidic rinsing composition does not show any precipitation or turbidity for a long period of time, preferably up to 48, more preferred up to 28 hours, mostpreferred up to 24 hours.

[0033] As a further advantage, the spray rinsing and immediately draining the obtained acidic rinse composition from the entire metallization process into the recovery process reduces the carryover of palladium after activation into the subsequent metallization steps, as it occurs in prior art processes using immersion rinsing. As a result, a high coating quality is always achieved in the subsequent metallization processes.

[0034] Within step (c), the stabilized acidic rinsing composition of step (b) is preferably directly processed without intermediate steps and time delays, wherein the stabilized acidic rinsing composition of step (b) is treated with an added oxidizing agent. Here, the palladiumtin colloids will be dissolved, wherein palladium (Pd(0)) and tin (Sn(0)) as well as the Sn2+ions are oxidized, so that an oxidized rinsing composition comprising dissolved (iono-genic) Pd ions and Sn4+ions is obtained. Palladium ions can be Pd2+ions and / or Pd4+ions. Here, the oxidizing agent is preferably dosed very precisely so that a minimal excess of oxidizing agent is introduced into the solution. As a result, this oxidized acidic rinsing composition does not show any precipitation or turbidity for a certain period of time, preferably up to 28 hours, more preferred up to 24 hours.

[0035] Within step (d) the oxidized acidic rinsing composition of step (c) is loaded onto an ion exchange resin which occupies a certain volume in an ion exchange resin separation column of a separation unit. Such a unit is known to the skilled person. Preferably, the contact time of the oxidized acidic rinsing composition with the ion exchange resin is minimized. This can be achieved by high loading and comparable low resin volume. This largely reduces precipitation of the oxidized acidic rinsing composition during loading and therefore avoids possible blockage of the resin in the column. Further, the damage to the functional groups of the resin by oxidizing agent surplus is also avoided or reduced. Thus, it is possible to achieve a very high palladium (palladium ions) uptake at the ion exchange resin (preferably up to 20 g Pd / I ion exchange resin). Furthermore, the Sn4+ions are almost completely separated, which remain dissolved in the treated rinsing composition (eluate). Therefore, with the inventive method, a selective separation of palladium from rinsing composition is achieved.

[0036] Detailed Description of the Invention

[0037] The present invention is further illustrated in the following examples without limiting the scope of the invention as herein defined in the claims.

[0038] As described for step (a) above, the palladium-activated substrate is spray rinsed withthe aqueous solution. Preferably, the used aqueous solution comprises or is tap water (fresh water) or DI water (de-ionized water). Preferably, the aqueous solution does not contain any further compounds, in particular does not contain organic compounds. Preferably, the obtained acidic rinsing composition has a pH of the obtained acidic rinsing composition is preferably from 1.0 to 1.8, more preferably from 1.0 to 1.4, whereby at this point the pH value is only derived from the acidic pH of a palladium activation composition. No acidifier agent was added at this point.

[0039] The obtained acidic rinsing composition preferably has a palladium concentration of at least 2.0 mg / L, more preferred from 2.0 to 8.0 mg / L, or most preferred from 3.0 to 6.0 mg / L. Such concentrations make the method most efficient.

[0040] While the palladium concentration in the obtained acidic rinsing composition is quite constant, the tin(ll) ion concentration can vary in a broader range and having a total tin concentration, comprising metallic tin, Sn2+ions and Sn4+ions, of at least 0.25 g / L, or from 0.5 g / L to 1.5 g / L, or from 1.0 to 1.8 g / L. Sn2+ions and Sn4+ions are representing the majority of the total tin concentration.

[0041] In one embodiment of the present invention, the provided acidic rinsing composition has a palladium concentration of at least 2.0 mg / L and a total tin concentration comprising metallic tin, Sn2+ions and Sn4+ions of at least 0.25 g / L.

[0042] In another embodiment of the present invention, the palladium concentration in the provided acidic rinsing composition can be from 2.0 to 8.0 mg / L, and the total tin concentration, comprising metallic tin, Sn2+ions and Sn4+ions, can be from 0.25 g / L to 1.8 g / L. The reason is, that during the use of the activation composition additional Sn(ll) ions, preferably as dissolved SnCh, have to be added. This addition is needed because the Sn(ll) ions of the shell of the colloids are oxidized to Sn(IV) ions by atmospheric oxygen. However, Sn(ll) ions are required to stabilize the ligand shell around the colloids. Therefore, Sn(ll) ions must be constantly added to keep e.g. a concentration of about 5 g / L in the activation composition. In consequence, the total tin concentrations of up to 18 g / l can occur in an used (older) activation composition (e.g. mainly up to 5 g / L Sn(ll), up to 13 g / L Sn(IV) ions and smaller amounts of metallic tin), which then also leads to correspondingly higher total tin concentrations in the obtained acidic rinsing composition. The concentration of palladium, tin and tin ions can be adjusted by controlling the flow speed and spraying time of the spray rinsing to obtain the acidic rinsing composition. The acidifier agent in step (b) is preferably a mineral acid, more preferred a chloride-containing mineral acid, more preferred hydrochloric acid, which is used to lower the pH value and to complex and stabilize the tin ions from the acidic rinsing composition of step (a) in order to slow down the precipitation of Sn(OH)4 in the further course. In a most preferred embodiment, the acidifier agent is concentrated hydrochloric acid (37 w.-% (w -weight) means an aqueous solution with 37 w.-% hydrochloric acid).

[0043] The pH value of the stabilized acidic rinsing composition is preferably adjusted to < 0.8 or the pH can preferably be adjusted from 0.4 to 0.9. Own experiments showed that a low pH in the stabilized acidic rinsing composition shifted the Sn(OH)4(s) species concentration to a lower concentration compared to the higher pH of the acidic rinsing composition. This can prolong the time after step (b) before step (c) is conducted. If needed, the stabilized acidic rinsing composition could be stored for up to 48 hours, preferred 24 to 48 hours, most preferred less than 24 hours, before step (c) is applied. If needed, e.g. if the acidic rinsing composition carries high tin ion concentrations, e.g. containing 1.5 g / L Sn(IV) ions, the pH can be adjusted from 0.4 to 0.6.

[0044] In step (b) continuously fresh obtained acidic rinsing composition of step (a) is used which means in the context of the present invention, that the obtained acidic rinsing composition is directly processed with step (b) without time-delay, preferably less than 3 to 6 hours, more preferably less than 1 to 2 hours. The stabilization and strict time management prevents precipitation or clouding of the solutions throughout the entire process. This is different to prior art methods, wherein rinsing compositions are used and collected over several days and then are fed into a palladium recovery unit.

[0045] In step (c), the added oxidizing agent, capable to oxidize palladium to palladium ions and tin and Sn2+ions to Sn4+ions, is preferably provided in an equimolar concentration or in an excess over the overall concentration of palladium, tin and tin(ll) ions, wherein the excess is preferably less than 10 percent, more preferred less than 5 percent. As small the excess is, this will avoid damaging the ion exchange resin in step (d).

[0046] The used oxidizing agent is added to obtain a concentration from 0.1 g / L to 2 g / L in the oxidized rinsing composition.

[0047] The used oxidizing agent can be selected from the group consisting of persulfate, permanganate and peroxides. Preferably, the oxidizing agent is selected from the group consisting of permanganate, peroxyacetic acid, hypochlorite or hydrogen peroxide. More preferably, the used oxidizing agent is an environmentally friendly oxidizing agent. Most preferably the oxidizing agent comprises H2O2, more preferred is H2O2, (35 w.-%in water), and is added to obtain a concentration from 0.2 to 0.8 g / L in the oxidized rinsing composition. This further avoids the introduction of any further salt load, which could cause wastewater problems and trigger precipitation.

[0048] After step (d) the oxidized rinsing composition is preferably a solution being free of colloids, in particular free of palladium-tin colloids. The oxidized rinsing composition is also free of precipitates, in particular free of precipitates of tin species.

[0049] In a preferred embodiment, the method comprises between step (c) and step (d) an additional step (pre-d) rendering the oxidizing agent inactive preferably by adding an aqueous solution of iron (II) salts and / or permanganate. In a preferred embodiment, step (pre-d) does not comprise a boron-containing agent. Step (pre-d) can help to reduce possible damaging of the ion exchange resin in step (d). Also after this additional step, the oxidized rinsing composition is free of colloids, in particular free of palladium-tin colloids2, and also free of precipitates, in particular free of precipitates of tin species.

[0050] Preferably, the ion exchange resin in step (d) is a cation exchange resin highly capable to adsorb palladium ions while tin ions are passing through without being adsorbed. More preferred the cation exchange resin comprises functional groups selected from the group consisting of urea-groups, thiol-groups, thioronium-groups, and thiourea-groups. A usable resin is Resin PRU (can be purchased e.g. from Atotech Deutschland GmbH & Co. KG).

[0051] Preferably step (d) is conducted directly or not later 5 to 10 hours after step (c) or after step (pre-d) to avoid precipitation or turbidity of the oxidized rinsing composition. Although step (b) allows to take more time, in one embodiment of the inventive method all steps (a) to (c) (including optional step (pre-d) are conducted within 5 to 10 hours and is then processed with step (d).

[0052] In one embodiment of the present invention, the ion exchange resin is filled in an ion exchange column wherein the ion exchange resin is preferably loaded with a high loading speed of 50 - 100 BV / h, in contrast to the prior art, where a loading speed of 5-10 BV / h is normally used. Preferably, the volume of the ion exchange resin within the column is from 2 I - 5 I. (BV stands for bed volume and represents the amount / volume of the resin per column and h stands for hour.)

[0053] The oxidized rinsing composition is preferably not filtered before loaded onto the ion exchange resin and step (d) preferably is applied without additional pressure (atmospheric pressure) or a slight over-pressure of up to 0.5 bar, preferred 0.2 to 0.4 bar.The method of the present invention may comprise an additional step to finally obtain the palladium, wherein (e) combusting the loaded ion exchange resin is conducted. No so-called electrowinning is used.

[0054] Preferably, the inventive method for recovering palladium from a rinsing composition comprises additional steps

[0055] (pre-a1) contacting a non-conductive substrate with an activation composition comprising

[0056] Palladium-tin colloids and tin ions,

[0057] to obtain a palladium-activated substrate; and

[0058] (pre-a2) spray rinsing the palladium-activated substrate with an aqueous solution to obtain a rinsed palladium-activated substrate and an acidic rinsing composition comprising palladium-tin colloids and tin ions.

[0059] The method for recovering palladium is preferably used wherein the activation composition according to step (pre-a1) has a pH of below 1.

[0060] The activation composition preferably comprises palladium in a total concentration ranging from 20 mg / L to 100 mg / L, based on the total volume of the activation composition. Preferred is a method of the present invention, wherein the non-conductive substrate comprises, preferably is selected from the group consisting of plastics, resin-containing laminates, glasses, ceramics, semi-conductors, and mixtures thereof. Such substrates can be used in the electronic industry for the production of electronic articles as IC ships, printed circuit boards, connectors, lead frames etc. and also in the automotive and white goods industry for the production of metallized surface on shower heads, door handles, car body parts such as bumpers, trim panels, etc.

[0061] Preferred plastics comprise, preferably are selected from the group consisting of thermoplastics, more preferably comprise, preferably are selected from the group consisting of polyacrylates, polyamides, polyimides, polyesters, polycarbonates, polyalkylenes, polyphenylenes, polystyrenes, polyvinyls, or mixtures thereof.

[0062] Preferred resin-containing laminates comprise, preferably are selected from the group consisting of fiber-enforced resin-containing laminates, most preferably glass-fiber-en-forced laminates. Very preferably, the resin-containing laminates are selected from the group consisting of resin one or more than one polymer of epoxys, polyvinylesters,polyesters, amides, imides, phenols, alkylenes, sulfones, or mixtures thereof, most preferably epoxy, imides, or mixtures thereof.

[0063] Preferred glasses comprise, preferably are selected from the group consisting of silica glass, soda-lime glass, float glass, fluoride glass, aluminosilicate glass, phosphate glass, borate glass, borosilicate glass, chalcogenide glass, aluminum oxide glass, or mixtures thereof.

[0064] Preferred ceramics comprise, preferably are selected from the group consisting of glassceramics, aluminum oxide ceramics, or mixtures thereof.

[0065] Preferred semi-conductors comprise, preferably are selected from the group consisting of silicon-based semi-conductors, more preferably silicon-based semi-conductors comprising silicon dioxide and / or silicon.

[0066] The used activation compositions are generally known to the skilled person (can be purchased from Atotech Deutschland GmbH & Co. KG as Pal laganth® Activator , Neolink® Activator, Adhemax® Activator) and comprises palladium in a total amount ranging from 100 mg / L to 30 mg / L, based on the total volume of the activation composition.

[0067] Example

[0068] The method for recovering palladium from a rinsing composition is now explained in more detail. The embodiment will not limit the scope of the invention.

[0069] In the following embodiment of the present invention shower heads, door handles and trim panels as palladium-activated substrates were used. The non-conductive substrates were activated with a known palladium-tin colloids activator composition (e.g. Neolink® IME) which typically operates with 60 mg / L palladium.

[0070] After the activation step, the palladium-activated substrates, which are arranged on a product carrier, were spray rinsed with tap water to provide the acidic rinsing composition according to step (a). In the present example eight product carriers per hour were rinsed with 7.5 liters of tap water per product carrier for 20 sec which leads to a total of 60 L / h acidic rinsing composition for the recovering method. This step was repeated with further freshly prepared palladium-activated substrates and tap water. The overall consumption of the spray rinsing with tap water for this example results in an acidic rinsing composition volume of 60l / h x 24 h x 14d = 20,0001 (means for a period of 2 weeks). Each provided acidic rinsing composition according to step (a) had almost the same concentrations after each spray rinsing step. This is beneficial for the subsequent palladium recovery steps.The spray rinsing therefore achieves an already constant concentration of the obtained acidic rinsing composition over time, which preferably corresponds to a dilution of about 1:10 of the concentration of used activator composition. The results showed that this acidic rinsing composition has the following concentrations of 5 mg / l Pd, 0.5 g / l Sn2+(Sn(ll)) and Sn4+(Sn(IV)) ions and about 30 ml / l HCI 37% (whereby at this point the HCI only comes from the palladium activation composition). The resulting pH was between 1 and 1.2. No acidifier agent was added at this point.

[0071] The provided acidic rinsing compositions will be completely fed into the inventive palladium recovery method wherein it is important that the provided acidic rinsing compositions of step (a) are not collected in a large tank without further treatment due to the mentioned stability problems.

[0072] Therefore, according to step (b) each of the provided acidic rinsing compositions of step (a) was directly treated by adding an acidifier agent and thereby collected in a tank. In the present example, 20 ml / l hydrochloric acid (37 w.-%) as acidifier agent was added over 30 min to obtain a stabilized acidic rinsing composition. The pH was between 0.8 and 0.9.

[0073] After step (b), a part of the stabilized acidic rinsing composition could be stored for at least 24 hours without observed precipitation or turbidity. In the present example, the stabilized acidic rinsing composition was transferred to step (c) within 60 to 120 min. According to step (c), the stabilized acidic rinsing composition was oxidized by carefully adding 1.5 g / L H2O2 (35 w.-% in water) as oxidizing agent to obtain the oxidized rinsing composition comprising dissolved palladium ions, and dissolved Sn4+ions. The amount of oxidizing agent was equimolar or with a slight access to the total amount of palladium, tin and Sn2+ions to be oxidized by the oxidizing agent. Because the oxidized rinsing composition after oxidation comprising high amounts of dissolved Sn4+ions, the stability of the oxidized rinsing composition is reduced and a quick proceeding with step (d) is recommended, at latest within 24 hours.

[0074] According to step (d), the oxidized rinsing composition comprising 5 mg Pd ions / l was loaded onto the ion exchange resin (Resin PRU, Atotech Deutschland GmbH & Co. KG) with volume quantity of 4 I (absorption capacity = 20 g Pd / I resin), which corresponds to an oxidized rinsing composition volume of 16 m3. The loading speed was 100 BV / h, which results in an effective charging time of 40 hours (i.e. the loading capacity for a column with 4 litres of resin is 20 g / l resin x 4 I = 80 g Pd; for the oxidized rinsingcomposition with 5 mg Pd / I this is 80 g / 0.005 g / 1 = 16,000 litres of oxidized rinsing composition volume; which are loaded onto the pump in 16,000 I / (4 l / BV x 100 BV / h is 400 L / h) = 40 hours and this then means 40 hours 124 hours / d = 1.7 days real exposure time for the rinse water with the resin).

[0075] With the invention palladium recovery method high palladium ions loads were achieved at the ion exchange resin (up to 20g Pd / I resin), because the residence time of the oxidized rinsing composition is kept very short with a small unavoidable excess of H2O2. Therefore, the ion exchange resin was fully loaded within 10 days.

Claims

C LA I M S1. A method for recovering palladium from a rinsing composition, the method comprising the steps(a) providing an acidic rinsing composition derived from a spray rinsing of a palladium-activated substrate with an aqueous solution, wherein the acidic rinsing composition comprises metallic palladium, metallic tin and tin ions; (b) treating the acidic rinsing composition with an acidifier agent to obtain a stabilized acidic rinsing composition having a pH of < 0.9;(c) treating the stabilized acidic rinsing composition with an oxidizing agent to obtain an oxidized rinsing composition comprisingdissolved palladium ions, anddissolved Sn4+ions,(d) contacting the oxidized rinsing composition with an ion exchange resin to adsorb palladium ions on said resin to obtain a treated rinsing composition comprising the dissolved Sn4+ions, and a loaded ion exchange resin comprising palladium ions.

2. The method for recovering palladium from a rinsing composition, the method comprising additional steps(pre-a1) contacting a non-conductive substrate with an activation composition comprisingpalladium-tin colloids and tin ions,to obtain a palladium-activated substrate; and(pre-a2) spray rinsing the palladium-activated substrate with an aqueous solution to obtain a rinsed palladium-activated substrate and an acidic rinsing composition comprising palladium-tin colloids and tin ions.

3. The method of claim 1 or 2, wherein the acidic rinsing composition has a pH of 1.0 to 1.8.

4. The method of any of the preceding claims, wherein the acidifier agent is concentrated hydrochloric acid.

5. The method of any of the preceding claims, wherein the aqueous solution comprises or is tap water or DI water.

6. The method of any of the preceding claims, wherein the added oxidizing agent is provided in an equimolar concentration or in an excess over the overall concentration of palladium, tin and tin(ll) ions, wherein the excess is less than 10 percent, preferably less than 5 percent.

7. The method of any of the preceding claims, wherein the oxidizing agent is selected from the group consisting of persulfate, permanganate and peroxides.

8. The method of any of the preceding claims, wherein the method comprises between step (c) and step (d) an additional step(pre-d) rendering the oxidizing agent inactive preferably by adding an aqueous solution of iron (II) salts and / or permanganate.

9. The method of any of the preceding claims, wherein in step (d) the ion exchange resin is provide in an ion exchange column and the ion exchange resin is loaded with a loading speed of 50 - 100 BV / h.

10. The method of claim 9, wherein the volume of ion exchange resin within the column is from 2 I - 5 I.

11. The method of any of the preceding claims, wherein the ion exchange resin is a cation exchange resin, which preferably comprises functional groups selected from the group consisting of urea-groups, thiol-groups, thioronium-groups, and thioureagroups.

12. The method of any of the preceding claims, wherein the oxidized rinsing composition is a solution being free of colloids.

13. The method of any of claims 2 - 12, wherein the activation composition according to step (pre-a1) has a pH of below 1.

14. The method of any of claims 2 - 13, wherein the non-conductive substrate is selected from the group consisting of plastics, resin-containing laminates, glasses, ceramics, semi-conductors, and mixtures thereof.

15. The method of any of the preceding claims comprising an additional step(e) combusting the loaded ion exchange resin to obtain palladium.

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