METHOD FOR RECOVERING NOBLE METAL FROM HETEROGENEOUS CATALYSTS CONTAINING NOBLE METAL

Abstract

A method for recovering noble metal from a heterogeneous catalyst comprising a solid carrier material and palladium, platinum or rhodium, present at least partially in elemental form, said method comprising the steps of converting the noble metal to an oxidation state>0 by treating the heterogeneous catalyst with an oxidizing agent in the presence of hydrochloric acid so as to form a two-phase system A comprising a hydrochloric aqueous phase A1 and a solid phase comprising the carrier material which is insoluble therein, optionally, at least partially separating the hydrochloric aqueous phase A1 from the two-phase system A and adding a further aqueous phase to the remaining residue of the two-phase system A so as to form a two-phase system B comprising a hydrochloric aqueous phase and a solid phase comprising the carrier material insoluble therein.

Claims

1. A method for recovering noble metal of and/or from a heterogeneous catalyst comprising a solid carrier material and at least one noble metal which is selected from the group consisting of palladium (Pd), platinum (Pt), and rhodium (Rh), and is present at least partially in elemental form, comprising the successive steps of: (a) converting the at least one noble metal present at least partially in elemental form into an oxidation state>0 by treating the heterogeneous catalyst with oxidizing agent in the presence of hydrochloric acid to form a two-phase system A comprising a hydrochloric aqueous phase A1 and a solid phase comprising the carrier material that is insoluble therein, (b) optionally at least partially separating the hydrochloric aqueous phase A1 from the two-phase system A, and adding a further aqueous phase to the remaining residue of the two-phase system A to form a two-phase system B comprising a hydrochloric aqueous phase B1 and a solid phase comprising the carrier material that is insoluble therein, (b) if step (b) has taken place, optionally, once or multiple times, repeatedly at least partially separating the hydrochloric aqueous phase from the two-phase system formed in the preceding step, and adding a further aqueous phase to form a further two-phase system comprising a hydrochloric aqueous phase and a solid phase comprising the carrier material that is insoluble therein, and (c) cathodic electro-deposition of the at least one noble metal either (c1) from the hydrochloric aqueous phase A1 of the two-phase system A or (c2) from the hydrochloric aqueous phase B1 of the two-phase system B or (c3) from the hydrochloric aqueous phase of the two-phase system formed finally in step (b).

2. The method according to claim 1, wherein the further aqueous phase is a hydrochloric acid solution, hydrochloric acid, or water.

3. The method according to claim 1, comprising the successive steps (a) and (c) in variant (c1) without steps (b) and (b).

4. The method according to claim 1, comprising the successive steps (a), (b), and (c) in variant (c2) without step (b).

5. The method according to claim 1, comprising the successive steps (a), (b), (b), and (c) in variant (c3).

6. A method for recovering palladium of and/or from a heterogeneous catalyst comprising a solid carrier material and palladium present at least partially in elemental form, comprising the successive steps of: (a) converting the palladium present at least partially in elemental form into an oxidation state>0 by treating the heterogeneous catalyst with oxidizing agent in the presence of hydrochloric acid to form a two-phase system A comprising a hydrochloric aqueous phase A1 and a solid phase comprising the carrier material that is insoluble therein, (b) optionally at least partially separating the hydrochloric aqueous phase A1 from the two-phase system A, and adding a further aqueous phase to the remaining residue of the two-phase system A to form a two-phase system B comprising a hydrochloric aqueous phase B1 and a solid phase comprising the carrier material that is insoluble therein, (b) if step (b) has taken place, optionally, once or multiple times, repeatedly at least partially separating the hydrochloric aqueous phase from the two-phase system formed in the preceding step, and adding a further aqueous phase to form a further two-phase system comprising a hydrochloric aqueous phase and a solid phase comprising the carrier material that is insoluble therein, (c) adjusting a basic pH of the hydrochloric aqueous phase A1 of the two-phase system A or of the hydrochloric aqueous phase B1 of the two-phase system B or of the hydrochloric aqueous phase of the two-phase system formed finally in step (b), in the range of 8 to 14 using ammonium hydroxide, and (c) cathodic electro-deposition of the palladium from the hydrochloric aqueous phase of the two-phase system basically adjusted in step (c).

7. The method according to claim 1, wherein the heterogeneous catalyst is a spent heterogeneous catalyst.

8. The method according to claim 1, wherein the heterogeneous catalyst has been subjected to one or more pretreatment steps before step (a).

9. The method according to claim 1, wherein the oxidizing agent is selected from chlorates, nitrates, bromates, iodates, chlorites, bromites, iodites, hypochlorites, perchlorates, peroxide compounds, chlorine, and/or ozone.

10. The method according to claim 1, wherein the noble metal recovery takes place in the sense of an almost complete removal from the carrier material.

11. The method according to claim 1, wherein the cathodic electro-deposition is carried out with spatial separation of the partial reactions.

12. The method according to claim 1, wherein the cathodic electro-deposition takes place until a noble metal concentration of <50 wt.ppm in the hydrochloric aqueous phase is reached.

Description

EXEMPLARY EMBODIMENTS

Example 1

[0079] 100 g of a heterogeneous catalyst (balls with 3 mm diameter; 0.511 wt. % of palladium on aluminum oxide) corresponding to 500 mg of palladium were mixed with 1 L of 6N hydrochloric acid. This two-phase system was flowed through with chlorine at 10 NI/h at 60 C. for 15 min while stirring. Subsequently, chlorine was removed by holding at 90 C. for 30 min. After letting the solid constituents settle, 865 ml of the liquid phase were removed. From the removed liquid phase, 476 mg of palladium could be recovered hydrometallurgically. The two-phase residue was diluted with 160 ml of water and 7 g of ammonium chloride were added. Subsequently, 28 wt. % ammonium hydroxide solution was added until a pH of 8.8 was reached. In a subsequent electrolytic deposition at 25 C. and a current density of 33 mA/cm2 by means of graphite electrodes at 4 V, elemental palladium was deposited at the cathode at an electrochemical efficiency of 25%. The yield of total recovered palladium was 99.5%. Palladium analysis of the carrier material by means of ICP-OES showed a residual content of <10 wt.ppm of palladium based on the total weight of the carrier material.

Example 2

[0080] 50 g of a heterogeneous catalyst (powder having a particle size of 100 m to 1 mm); 2 wt. % of palladium on aluminum silicate) corresponding to 1000 mg of palladium was heated for 5 h at 800 C. in an air atmosphere and subsequently annealed for 2 h at 500 C. under H.sub.2 atmosphere and subsequently mixed with 1 L of 6N hydrochloric acid. This two-phase system was flowed through with chlorine at 6 NI/h at 60 C. for 15 min while stirring. Subsequently, chlorine was removed by holding at 85 C. for 30 min. After letting the solid constituents settle, 850 ml of the liquid phase were removed. From the removed liquid phase, 890 mg of palladium could be recovered hydrometallurgically. The two-phase residue was diluted with 150 ml of water and 7 g of ammonium chloride were added. Subsequently, 28 wt. % ammonium hydroxide solution was added until a pH of 8 was reached. In a subsequent electrolytic deposition at 25 C. and a current density of 33 mA/cm.sup.2 by means of graphite electrodes at 4 V, elemental palladium was deposited at the cathode at an electrochemical efficiency of 25%. The yield of total recovered palladium was 99.5%. Palladium analysis of the carrier material by means of ICP-OES showed a residual content of <10 wt.ppm of palladium based on the total weight of the carrier material.

Example 3

[0081] 100 g of a heterogeneous catalyst (powder having a particle size of 100 m to 1 mm); 0.5 wt. % of palladium and 0.5 wt. % of platinum on aluminum oxide) corresponding to 500 mg of palladium and 500 mg of platinum were mixed with 1 L of 6N hydrochloric acid. This two-phase system was flowed through with chlorine at 6 NI/h at 60 C. for 30 min while stirring. Subsequently, chlorine was removed by holding at 85 C. for 30 min. After letting the solid constituents settle, 850 ml of the liquid phase were removed. From the removed liquid phase, 470 mg of palladium and 450 mg of platinum could be recovered hydrometallurgically. The two-phase residue was diluted with 150 ml of water. In a subsequent electrolytic deposition at 85 C. and a current density of 33 mA/cm.sup.2 by means of graphite electrodes at 1.8 V, elemental palladium and elemental platinum were deposited at the cathode at an electrochemical efficiency of 12%. The yield of total recovered noble metal (palladium and platinum) was 99.5%. Platinum and palladium analysis of the carrier material by means of ICP-OES showed a residual content of <10 wt.ppm of palladium and <10 wt.ppm of platinum based on the total weight of the carrier material.

Example 4

[0082] 100 g of a heterogeneous catalyst (balls with 3 mm diameter; 0.511 wt. % of palladium on aluminum oxide) corresponding to 500 mg of palladium were mixed with 1 L of 6N hydrochloric acid. This two-phase system was flowed through with chlorine at 10 NI/h at 60 C. for 15 min while stirring. Subsequently, chlorine was removed by holding at 90 C. for 30 min. After letting the solid constituents settle, 865 ml of the liquid phase were removed. From the removed liquid phase, 476 mg of palladium could be recovered hydrometallurgically. The two-phase residue was diluted with 150 ml of water. In a subsequent electrolytic deposition at 85 C. and a current density of 33 mA/cm.sup.2 by means of graphite electrodes at 1.8V, elemental palladium was deposited at the cathode at an electrochemical efficiency of 12%. The yield of total recovered palladium was 99.5%. Palladium analysis of the carrier material by means of ICP-OES showed a residual content of <10 wt.ppm of palladium based on the total weight of the carrier material.