This disclosure concerns the recovery of PGM (platinum group metals) from spent homogeneous catalysts present in an organic phase.

Specifically, a pyrometallurgical process is provided whereby the PGM, and RIi in particular, are concentrated in a metallurgical phases, rendering them accessible for refining according to known processes.

Several methods have been developed wherein soluble organonietallic compounds, often containing PGM, and RJi in particular, are used as catalysts in a homogenous catalytic reaction. These compounds are useful for various reactions such as hydrogenation, hydroformylation, and hydrocarboxylation of olefins.

Since aforesaid compounds are chemically very stable, the catalyst solution can be recycled in the reaction system after separating it from the reaction products by distillation. However, since various high boiling by-products are formed in the aforesaid reaction, and also since the catalyst used in the reaction is partially inactivated, a portion of the catalyst-containing residue obtained at the recovery of the reaction products by distillation must be discarded. This is needed to prevent the accumulation of high boiling by-products and of inactivated catalyst.

The catalyst-containing residue, also referred to as spent catalyst, contains expensive PGM that are to be recovered from an ecologic as well as from an economic point of view.

Several methods have been proposed for the recovery of PGM from such spent catalysts. Generally, the methods are categorized as either wet or dry, according to the type of processing put to use.

In wet methods, such as known from EP-A-0147824, rhodium is removed and recovered by extracting it from the crude spent product by means of phosphine sulphonates or carboxylates as complexing reagents. Other methods, including piecipitation of piecious metals as sulfides, iediiction by addition of a ieducing agent such as Te accoiding to US-4687514, oi absoiption on active caibon, have been desciibed

Wet methods, although allowing foi the iecupeiation of the PGM, do not solve the pioblem of discaiding oi otheiwise using the oiganic waste pioducts in an ecological way Moieovei, the yield of the piocess ciitically depends on bieaking down the initial PGM complexes, which can be veiy stable

In diy methods, such as known fiom OS-3920449, metals aie lecoveied fiom a organic solvent solution containing a soluble complex of the noble metal and an oiganophosphoius compound by burning the oiganic solvent solution in a combustion zone The combustion pioducts aie immediately intioduced into an aqueous absoibing solution to catch the paiticles of the noble metal and phosphoius oxide foimed in the combustion US-5364445 pi o\ ides a similai method foi ieco\ eπng ihodium compi ising the steps of adding a basic compound to the oiganic solution containing a ihodium complex and at least one type of oiganophosphoius compound as a hgand and an oiganophosphoius compound, combusting the iesultant mixtuie to ash undei a contiolled tempeiatuie of less than 1000 ⁰ C, and cleaning the ash using a solution containing a ieducing agent

A antage of the com entional diy piocesses lies in the burning of the oiganic fiactions Heat iecupeiation and off gas filtiation aie not stiaightfoiwaid Theie is moieovei a significant πsk of loosing PGM in the in the soot oi in the ashes

The objective of the invention is theiefoie to guaiantee a high yield foi the lecoveiy of the valuable metals, while destiucting envnonmentally haimful oiganic waste pioducts The PGM, and RIi in paiticulai should be obtained in an easily lecoveiable and puufyable phases The oiganics should be valued foi then embodied eneigy

To this end, a piocess foi lecoveπng PGM fiom a spent homogeneous catalyst is disclosed, compiising the steps of - providing a molten bath furnace, having a submerged injector equipped for liquid fuel firing;

- providing a molten bath comprising a metallic and/or matte phase, and a slag phase;

- feeding the spent homogeneous catalyst and an O ₂ bearing gas through the injector, a major part (i.e. more than 50% by weight) of the PGM being recovered in the metallic and/or matte phase;

- separating the PGM-beaπng metallic and/or matte phase from the slag phase.

Typically, more than 90% of the PGM is recovered in the metallic and/or matte phase;

The spent homogeneous catalyst contains preferably more than 10 ppm of PGM, preferably Rii This minimum amount is needed to insure the economy of the process.

It is advantageous to collect the PGM in a metal-bearing molten phase, such as a metallic and/01 matte phase comprising a total metal content of at least 50% by weight of any one or more of Cu, Ni. Co. Fe, and Pb. This phase comprises preferably at least 50% of Cu. PGM are efficiently collected in these metals and they can be further refined using known techniques.

When a sufficient amount of spent catalyst is available, it is advantageous to completely replace the liquid fuel. This tends to maximize the PGM concentration in the metallic and/or matte phase by avoiding dilution across batches.

Advantageously, during the step of feeding the spent homogeneous catalyst and an O ₂ bearing gas through the injector, a complex metallurgical charge is introduced into the furnace and smelted, thereby producing a metallic and/or matte phase, slag and flue dust. In this way, the energy content of the waste organic material in the catalyst is effectively utilized for heating and/or reduction of the metallurgical charge in the furnace. The flue dust can be recycled as part of the complex charge to the smelting operation. The said complex metalluigical chaige typically comprises Pb, Cu, and Fe as oxides and/or as sulfides. Pyiometalluigical piocesses foi collecting PGM in a metallic phase aie widely applied foi iecycling substiate-bound catalysts The catalysts aie heieby directly fed to a molten bath furnace, possibly aftei a simple pie-tieatment such as moistening, to avoid the entiainment of fine pai tides with the off gas

Spent homogeneous catalysts, howevei, compπse volatile oiganic compounds and theiefoie cannot be fed to a furnace in the usual way, neithei as such, noi aftei e g impiegnation on a solid caiiiei Indeed, such a pioceduie would mvaiiably lead to the ev aporation and loss of significant quantities of 01 games including PGM complexes

According to the piesent disclosuie, it has howevei been shown that losses thiough evaporation can be gieatly ieduced oi even avoided by injecting the spent homogeneous catalyst dueclly into the molten bath through a fuel injector, being eithei a submeiged lance oi a tuyeie

By a submeiged lance is meant a pipe designed to mtioduce compiessed gas, typically oxygen-em iched an, into a metallurgical bath accoiding to a geneially downwaid diicction A lance is often mounted \ eitically above the bath, with its tip dipping below the bath level in the furnace

By a tuyeie is meant a pipe designed to mtioduce compiessed gas typically oxygen- enπched an into a bath, accoiding to a geneially honzontal oi upwatd diiection A tuyere is by natuie submeiged, as it is positioned below the bath level thiough a hole piercing the bottom oi the wall of the furnace

Lances and tuyeies can be equipped with a fuel injectoi This mjectoi can e g be located in a coaxial position at oi neai the tip of the pipe The fuel bums with the oxygen within the bath, theieby contπbuting to the heat input to the opeiation In the piesent disclosuie. only lances and tuyeies equipped foi burning liquid fuel aie consideied

By PGM are meant Ru, Os, Rh, Ii , Pd, and Pt Spent homogeneous catalyst can be very sticky, having a viscosity of more than

400 mPa s Such pioducts should be pieconditioned to avoid clogging in pumps and pipes. This may involve preheating and/or diluting them with an organic solvent

When dealing with a Cu-based alloy, grinding and leaching the copper is perfomied to collect the PGM in a iesidue The further piocessiiig of the PGM residue can be performed by classical method, e.g. by cupellation and electrowinning

Examples The process is peifoimcd in a cylindπcal steel furnace, lined with MgO-Ci ₂ O ₃ biicks. having an internal diameter of 0.7 m The furnace is further provided with tap holes foi slag and metal, and in the top section with openings foi exhaust gasses and for insertion of an injection lance.

The lance compπses a RVS steel outer tube for air/oxygen injection with a diameter of 48 mm, and an inner coaxial tube with a diametei of 17 mm fot fuel injection The innei tube is equipped with a spiaying nozzle at its tip.

The metalluigical chaige is added ovei the course of 5 hours. This consists of 500 kg lead iich slag as a staiting bath; and

4000 kg (wet weight) Pb/Cu/Precious metals complex charge.

The lance paiameteis aie

Total gas flow iate 265 NmVh ₁ An flow iate 224 NmVh,

O ₂ flow rate 41 NmVh,

Oxygen enrichment 33, 1%;

Fuel (Compaiative Example 1) or RJi spent (Example 2) flow rate 22 kg/h. and

Flame stoechiometiy (λ) 2, 18 The process is run at a bath temperature of 1200 ⁰ C. The flame stoechiometry is can be adapted so as to ensure sufficiently strong reducing conditions as indicated by a Cu concentration in the slag of less than 5%.

The off gasses and flue dust are cooled from 1200 ⁰ C to about 120 ⁰ C, first in a radiation chamber, and then in an adiabatic cooler. The flue dust is collected in a baghouse. The SO ₂ in the off gasses is neutralized in a NaOH scrubber.

Comparative Example 1 In a comparative example (reference), only conventional fuel is injected. The metallurgical charge comprises a limited amount of RJi, which is a typical background for the materials recycled in this type of operation. The feed, production, and the Rh distribution across the phases, are shown in Table 1. The charge contains 17.8% of humidity, which means that a wet weight of 4000 kg is actually fed to the furnace. Both the slag and the charge further contain uncritical amounts of metals (a total of 2 Io 5% of Ni. Zn, and Sn, as oxides), metalloids (a total of 4 to 8% of As. Sb. and Te. as oxides), and other oxides (a total of 4 to 8% of AI7O ₃ and MgO). The S in the charge is a mixture of sulfides and sulfates. Table 1 : Comparative example with typical RIi background in the charge, and injection of conventional fuel

The RJi collects with a yield of moie than 95% in the matte/alloy phase The piecioυs metals can be fuithei sepaiated and lefined. accoidmg to conventional means

Example 2

In this example accoidmg to the invention, a metalluigical chaige with the same composition is piocessed, but with injection of Rh beaiing spent catalyst instead of fuel This paiticulai spent catalyst is a homogeneous catalyst in an oiganic phase, has a Rh content of 743 ppm a heat value of 38 MJ/kg. and a flash point highei than 70 ⁰ C The feed, pioduction, and the RIi distnbution acioss the phases, aie shown in Table 2

Table 2 Example accoidmg to invention with Rh backgiound, and injection of

RIi spent catalysis

A global RJi yield in the matte/alloy phase of nearly 94% is observed.

From a comparison between Examples 1 and 2, it can be calculated that more than 92% of the Rh added through the catalyst is recovered in the matte and/or alloy. In this context, a yield of more than 90% is considered as satisfactory.

The minor amounts of Rh in the flue dust can be recovered by recycling all or part of the flue dust to the furnace. Such recycles are performed as a matter of routine when operating this type of furnace. The additional residence time of part of the RIi in this recycling loop does not significantly affect the economy of the process.