Method for the recovery of platinum group metals from catalysts comprising silicon carbide

Abstract

The invention concerns a process suitable for the recovery of platinum group metals (PGM) present in PGM-bearing catalysts comprising silicon carbide (SiC). More particularly, the process for the recovery of PGM present in PGM-bearing catalysts comprising SiC, comprises the steps of preparing a metallurgical charge by mixing the PGM-bearing catalysts with an Fe-oxide compound in an amount sufficient to oxidize at least 65% of the SiC, and feeding the metallurgical charge and slag formers to a smelting furnace operating in conditions susceptible to form a liquid Fe-based bullion, which contains PGM, and a liquid slag. Good to excellent PGM yields are obtained.

Claims

1. A process for the recovery of platinum group metals (PGM) present in PGM-bearing catalysts comprising SiC, comprising the steps of: preparing a metallurgical charge, by mixing the PGM-bearing catalysts with an Fe-oxide compound in an amount sufficient to oxidize at least 65% of the SiC; and, feeding the metallurgical charge and slag formers to a smelting furnace operating in conditions susceptible to form a melt comprising a liquid Fe-based bullion, which contains PGM, and a liquid slag.

2. The process according to claim 1, wherein the PGM-bearing catalysts comprise spent automotive catalysts and/or spent catalyzed diesel particulate filters.

3. The process according to claim 1, comprising the additional step of slagging part of the Fe present in the Fe-base bullion by blowing oxygen into the melt, thereby concentrating the PGMin the remaining Fe-based bullion.

4. The process according to claim 1, further comprising feeding a Ni-compound to the smelting furnace and blowing oxygen into the melt, whereby at least 50% by weight of the Fe present in the Fe-base bullion is slagged, thereby concentrating the PGM in a Ni- or FeNi-based bullion.

5. The process according to claim 1, wherein the SiC amounts to more than 2.5% by weight of the PGM-bearing catalysts.

6. The process according to claim 1, wherein more than 80% by weight of the metallurgical charge is the PGM-bearing catalysts comprising SiC together with the Fe-oxide compound.

7. The process according to claim 1, comprising the additional step of separating the Fe-based bullion which contains PGM from the slag.

8. The process according to claim 1, wherein the Fe-oxide compound is Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, CaFeO.sub.4 or K.sub.2FeO.sub.4.

9. The process according to claim 1, where, in the step of preparing the metallurgical charge, the PGM-bearing catalysts are comminuted to particles having a d50 of less than 2000 m.

10. The process according to claim19, wherein the Fe-oxide compound is comminuted to particles having a d50 of less than 2000 m.

Description

EXAMPLE 1

(1) In this experiment, Fe-oxide is added to PGM-bearing catalysts comprising SiC in a 1:1 stoichiometric amount, i.e. 1 mol of Fe.sub.2O.sub.3 per mol of SiC.

(2) 750 g of a slag-forming flux comprising 34% SiO.sub.2, 26% Al.sub.2O.sub.3, 14% CaO, and 7% MgO is melted and heated to 1550 C. under an N.sub.2-atmosphere. When everything is melted, N.sub.2-gas is blown at a rate of 50 L/h into the slag.

(3) 560 g PGM-bearing catalyst (d.sub.50 of 100 82 m) comprising 42% SiC, 30% SiO.sub.2, 20% Al.sub.2O.sub.3, 0.6% CaO, 3% MgO, 1741 ppm Pt, 1114 ppm Pd, and 41 ppm Rh is mixed with 954 g Fe.sub.2O.sub.3 (d.sub.50 of 250 m) until a homogeneous mixture is obtained (Table 1). This mixture is then charged stepwise, about 50 g at a time with 5 minutes in-between the additions, to give time for the mixture to dissolve into the slag and for the reaction to take place. After everything is charged, the blowing of N.sub.2-gas continues at a rate of 50 L/h for 2 hours. After that, the furnace remains at 1550 C. for 30 minutes to allow for phase separation.

(4) 559.8 g of a high-density Fe-bullion containing PGM (lower layer) and 1567 g of a low-density slag (upper layer) are formed (Table 2). The Fe-bullion comprises 98% Fe, 0.7% C, 1730 ppm Pt, 1111 ppm Pd and 41 ppm Rh. Hence, the Fe-bullion collects the PGM with a global yield of more than 99%.

(5) TABLE-US-00001 TABLE 1 Composition of the feed Weight Pt Pd Rh Fe.sub.2O.sub.3 SiC SiO.sub.2 Al.sub.2O.sub.3 CaO MgO Feed (g) (ppm) (ppm) (ppm) (%) (%) (%) (%) (%) (%) Slag 750 34 26 14 7 Charge 1514 644 412 15 63 15 11 7 0.2 1

(6) TABLE-US-00002 TABLE 2 Composition of the products Weight Pt Pd Rh Fe C SiO.sub.2 Al.sub.2O.sub.3 CaO MgO Product (g) (ppm) (ppm) (ppm) (%) (%) (%) (%) (%) (%) Slag 1567 <5 <5 <5 9 45 32 6 4 Bullion 559.8 1730 1111 41 98 0.7

EXAMPLE 2

(7) Fe-oxide is added to PGM-bearing catalysts comprising SiC in a slightly under-stoichiometric amount, i.e. 0.8 mol of Fe.sub.2O.sub.3 per mol of SiC.

(8) 750 g of a slag-forming flux comprising 34% SiO.sub.2, 26% Al.sub.2O.sub.3, 14% CaO, and 7% MgO is melted and heated to 1550 C. under an N.sub.2-atmosphere. When everything is melted N.sub.2-gas is blown at a rate of 50 L/h into the slag.

(9) 560 g PGM-bearing catalyst (d50 of 100 m) comprising 42% SiC, 30% SiO.sub.2, 20% Al.sub.2O.sub.3, 0.6% CaO, 3% MgO, 1741 ppm Pt, 1114 ppm Pd, and 41 ppm Rh is mixed with 763 g Fe.sub.2O.sub.3 (d.sub.50 of 250 m) until a homogeneous mixture is obtained.

(10) This mixture is then charged stepwise, about 50 g at a time with 5 minutes in-between the additions, to give time for the mixture to dissolve into the slag and for the reaction to take place. After everything is charged, the blowing of N.sub.2-gas continues at a rate of 50 L/h for a total of 2 hours. After that, the furnace remains at 1550 C. for 30 minutes to allow for phase separation.

(11) 370.1 g of a high-density Fe-bullion containing PGM (lower layer) and 1638 g of a low-density slag (upper layer) are formed. The Fe-bullion comprises 87% Fe, 1.6% C, 2585 ppm Pt, 1659 ppm Pd and 62 ppm Rh. Hence, the Fe-bullion collects the PGM with a global yield of more than 98%.

(12) The best yields are obtained with a stoichiometric amount of Fe.sub.2O.sub.3 with respect to the amount of SiC present in the mixture. However, a slightly under-stoichiometric amount can also collect the PGM with a sufficient yield.

COMPARATIVE EXAMPLE 3

(13) Fe-oxide is added to PGM-bearing catalysts comprising SiC in an under-stoichiometric amount, i.e. 0.6 mol of Fe.sub.2O.sub.3 per mol of SiC.

(14) 750 g of a slag-forming flux comprising 34% SiO.sub.2, 26% Al.sub.2O.sub.3, 14% CaO, and 7% MgO is melted and heated to 1550 C. under an N.sub.2-atmosphere. When everything is melted N.sub.2-gas is blown at a rate of 50 L/h into the slag.

(15) 560 g PGM-bearing catalyst (d.sub.50 of 100 m) comprising 42% SiC, 30% SiO.sub.2, 20% Al.sub.2O.sub.3, 0.6% CaO, 3% MgO, 1741 ppm Pt, 1114 ppm Pd, and 41 ppm Rh is mixed with 572 g Fe.sub.2O.sub.3 (d.sub.50 of 250 m) until a homogeneous mixture is obtained.

(16) This mixture is then charged stepwise, about 50 g at a time with 5 minutes in-between the additions, to give time for the mixture to dissolve into the slag and for the reaction to take place. After four additions, the molten bath becomes slightly viscous. After everything is charged, blowing of N.sub.2-gas continues at a rate of 50 L/h for a total of two hours. After that, the furnace remains at 1550 C. for 30 minutes to allow for phase separation. At the end the bath is somewhat viscous.

(17) 377.9 g of a high-density Fe-bullion containing PGM (lower layer) and 1457 g of a low-density slag (upper layer) are formed. The Fe-bullion comprises 74% Fe, 1.6% C, 1500 ppm Pt, 1416 ppm Pd and 54 ppm Rh. Hence, the Fe-bullion has collected Pt with a yield of 58%, Pd with a yield of 86% and Rh with a yield of 88%. The global PGM yield amounts to 69%, which is considered insufficient.

(18) Using only a 60% stoichiometry, the bath becomes somewhat viscous. This is assumed to be due to unreacted solid SiC particles. An inadmissible amount of PGM is then lost to the slag.

COMPARATIVE EXAMPLE 4

(19) Fe-oxide is added to PGM-bearing catalysts comprising SiC in a highly sub-stoichiometric amount, i.e. 0.3 mol of Fe.sub.2O.sub.3 per mol of SiC, and O.sub.2-gas is blown through the mixture instead of N2-gas as in examples 1, 2, and 3.

(20) 1595 g of a slag-forming flux comprising 36% SiO.sub.2, 11% Al.sub.2O.sub.3, 38% CaO, and 9% MgO is melted and heated to 1500 C. under an N.sub.2-atmosphere. The Fe-oxide being insufficiently present, and in an attempt to oxidize the SiC, a more than stoichiometric amount of O.sub.2-gas is blown at a rate of 100 L/h into the slag.

(21) 613 g PGM-bearing catalyst (d.sub.50 of 150 m) comprising 57% SiC, 26% SiO.sub.2, 13% Al.sub.2O.sub.3, 0.7% CaO, 2% MgO, 1056 ppm Pt, 384 ppm Pd, 11.58 ppm Rh is mixed with 450 g Fe.sub.2O.sub.3 (d50 of 250 m) until a homogeneous mixture is obtained. This amount of Fe-oxide accounts for around 30% of what would be needed to completely transform the amount of SiC present.

(22) The mixture is then charged stepwise, about 50 g at a time with 5 minutes in-between the additions, to give time for the mixture to dissolve into the slag and for the reaction to take place. The mixture dissolves for the most part, but a small part forms a dross on top of the slag phase. The molten bath becomes very viscous. After 100 minutes the blowing is stopped. The furnace remains at 1500 C. for 30 minutes to allow for phase separation.

(23) 3.2 g of an Fe-bullion (lower layer) and 2642 g of a heterogeneous slag phase (upper layer) are formed. Said heterogeneous slag phase still contains alloy droplets, which could not be separated anymore, e.g. by tapping, and therefore contribute to PGM-losses to the slag. The formed Fe-bullion comprises 81% Fe, 2.4% Pd, but no Pt and no Rh. Hence, the Fe-bullion collects PGM with a global yield of only 4.3%. This yield is totally unsatisfactory. The slag is viscous and still comprises unreacted SiC particles.

(24) Also, blowing O.sub.2-gas through the mixture is not effective to achieve the same result as with Fe-oxide.

COMPARATIVE EXAMPLE 5

(25) PGM-bearing catalysts comprising SiC and Fe-oxides are separately added to the slag in a stoichiometric amount, i.e. 1 mol of Fe.sub.2O.sub.3 per mol of SiC, thus without prior mixing or blending. 750 g of a slag-forming flux comprising 34% SiO.sub.2, 26% Al.sub.2O.sub.3, 14% CaO, and 7% MgO is melted and heated to 1550 C. under an N.sub.2-atmosphere. When everything is melted, N.sub.2-gas is blown at a rate of 50 L/h into the slag.

(26) 560 g PGM-bearing catalyst (d50<100 m) comprising 42% SiC, 30% SiO.sub.2, 20% Al.sub.2O.sub.3, 0.6% CaO, 3% MgO, 1741 ppm Pt, 1114 ppm Pd, and 41 ppm Rh is then charged stepwise, about 30 g at a time, to the slag phase. After each addition of catalyst material, about 50 g of Fe.sub.2O.sub.3 (d50 of 250 m) is added to the molten bath, for a total of 954 g. 5 to 10 minutes are provided for the materials to dissolve into the slag and react between additions. After 5 additions, a layer of foam forms on top of the bath, which remains there until the end of the experiment.

(27) After everything is charged, the blowing of N.sub.2 continues at a rate of 50 L/h for a total of 2 hours. After that, the furnace remains at 1550 C. for 30 minutes to allow for phase separation.

(28) 463 g of a high-density Fe-bullion containing PGM (lower layer) and 1691 g of a low-density slag (upper layer) are formed. The Fe-bullion comprises of 98% Fe, 0.2% C, 1381 ppm Pt, 999 ppm Pd and 39 ppm Rh. Hence, the Fe-bullion has collected Pt with a yield of 66%, Pd with a yield of 74% and Rh with a yield of 78%. The global PGM yield amounts to 69%, which is considered insufficient.

(29) When PGM-bearing catalysts comprising SiC and Fe.sub.2O.sub.3 are not mixed before feeding the metallurgical charge, foaming is observed, and the oxidation of SiC is incomplete. As a result, an inadmissible amount of PGM is lost to the slag.