Patent Description:
The platinum group metals, i.e., ruthenium, rhodium, palladium, osmium, iridium, and platinum ("PGM"), are often recovered from used catalyst materials such as, for example, automotive catalytic converters. The catalyst materials are smelted in a furnace, typically with a flux material such as CaO, and the PGM are preferentially collected in an alloy pool below the slag. While the PGM are dilute in the furnace slag, nevertheless these losses can be significant due to the high volume of slag and a general inability to economically recover the dilute values. The PGM collector alloys may contain up to <NUM> wt% PGM, and usually contain more than <NUM> wt% iron. Enrichment is necessary if a higher PGM content is desired.

PGM enrichment of iron-rich, sulfide-lean collector alloy by pyrometallurgical converting was disclosed in<NPL>). PGM enrichment of sulfur-free or low-sulfur (<1wt%) PGM collector alloy was more recently proposed in patent documents <CIT> and <CIT>. The PGM-enriched alloys generally contain a relatively high proportion of iron (>10wt%). Patent documents <CIT> and <CIT> futher disclose a PGM converting process unsing an alloy pool.

There are a number of drawbacks associated with known converters and converting processes preventing them from being practically implemented to process PGM collector alloy generated from smelting catalyst materials. The converting process can be relatively slow. In the patent documents mentioned above, the collector alloy and slag-forming materials were melted for <NUM> hours prior to oxygen injection. Moreover, the converting process is exothermic, and the rate of oxygen addition is generally limited to avoid excessive temperatures. Further, the severe conditions in the converter, especially at high oxygen injection rates, lead to corrosion and short lifespans for refractory lining.

The industry has generally accepted that, similar to smelting, relatively high levels of added flux materials such as SiO<NUM> and MgO/CaO are needed for the formation of a low melting, light density slag to adequately remove impurities and improve the PGM content of the PGM-enriched alloy product from a converter. For example, the aforementioned patent documents disclose the addition of sulfur- and copper-free slag-forming material in minimum proportions of <NUM> or <NUM> part by weight per <NUM> part by weight collector alloy, where the slag-forming materials contain <NUM>-<NUM> wt% SiO<NUM> and <NUM>-<NUM> wt% MgO/CaO, or <NUM>-<NUM> wt% MgO/CaO and <NUM>-<NUM> wt% SiO<NUM>. Even so, as the content of the deleterious elements in the enriched alloy are reduced to very low levels, e.g., less than <NUM> wt% iron, the PGM losses in the slag also begin to rapidly rise.

The industry needs technology that can address one or more of the shortcomings of conventional converting processes for PGM collector alloys. Such technology would desirably achieve one or more of the following: improve the alloy melting rate, oxygen addition rate, and/or the processing rate or capacity of the converter; provide lower levels of iron and/or deleterious materials in the PGM-enriched collector alloy without excessive PGM losses in the slag; reduce PGM losses to the converter slag while achieving high levels of PGM enrichment in the alloy; improve reliability and/or durability of converter components; reduce converter maintenance requirements and/or operating interruptions; provide fluid cooling and/or temperature monitoring of the refractory lining in a rotary converter; and/or improve the efficiency and practicality of using converters incorporated as part of an overall process to recover and enrich PGM collector alloy, e.g., from catalyst or other PGM-containing materials.

There is provided, in accordance with various aspects of the present invention, processes for converting platinum group metal collector, a process for recovering and enriching platinum group metal, converting processes, and a rotary converter adapted for use in a converting process as set out in the appending independent claims. Features of embodiments are set out in the appending dependent claims.

There is also disclosed herein a converting process for recovering platinum group metals ("PGM") that addresses drawbacks of known converting processes. Applicant has observed that the high levels of added flux materials comprising <NUM> wt% or more of CaO/MgO and/or <NUM> wt% or more of SiO<NUM> in known PGM collector alloy converting processes can be reduced or avoided in the converting processes disclosed herein, and that limiting the amount of such flux in this manner leads to a reduced volume of converter slag, reduced alloy melting time, and increases converting capacity and/or throughput. Applicant has also observed that a relatively small amount of refractory protectant can be added after melting the alloy pool to inhibit refractory corrosion and extend refractory life, and that furnace slag from smelting catalyst material can be conveniently used as the protectant.

Additionally, applicant has observed that partially pre-oxidizing a portion (or all) of the collector alloy for the initial melt and/or converter feed can further reduce the time periods required for melting the initial alloy pool and converting the collector alloy. Further, applicant has observed that recycling a portion of the converter slag to the converter between cycles also provides a way to reduce PGM losses; and that high-grade slag can be selectively recovered for recycling to the converter, e.g., by magnetic separation of the converter slag. Moreover, recycling the slag in this manner can return readily reducible pre-oxidized metal values such as nickel to the converter, and thus effectively increase oxygen addition rates.

Additionally, applicant has observed that including recycled converter slag in the converter feed facilitates the oxidation of the alloy, e.g., by recycling some oxidized values such as nickel. Moreover, the presence of the recycled converter slag can moderate the temperature of the collector alloy. Also, the converter can, especially at times where it is advantageous to do so, be operated in such a way that PGM values may be relatively high in the slag since the high grade slag can be recycled. For example, in a final slag tapping prior to the alloy tapping, when it is desired to quickly tap the slag and the alloy to avoid the risk of premature alloy solidification, the final slag tapping may occur prior to complete disentrainment of alloy.

Applicant has further found that the converter can be integrated into an overall PGM recovery process by smelting catalyst material in a primary furnace to produce the collector alloy and/or by smelting the converter slag in a secondary furnace with slag from the primary furnace. The slag from either of the furnaces, preferably from the primary furnace, can be used as refractory protectant. Integration of the converter and the furnaces in this manner also inhibits the buildup of deleterious elements in the converter. Applicant has also devised a way to cool the refractory lining in the rotary converter using a heat transfer jacket through which water or an aqueous heat transfer fluid is circulated.

There is also disclosed herein a process for converting PGM collector alloy, comprising the steps of:.

There is also disclosed herein an unclaimed process for converting platinum group metal (PGM) collector alloy, comprising the steps of:.

There is also disclosed herein an unclaimed process for converting PGM collector alloy, comprising the steps of:.

There is also disclosed herein an unclaimed process for converting PGM collector alloy, comprising a cycle of the steps of:.

There is also disclosed herein an unclaimed process for recovering and enriching PGM, comprising the steps of:.

There is also disclosed herein a rotary converter suitable for PGM enrichment of a collector alloy, comprising:.

There is also disclosed herein an unclaimed converting process, comprising the steps of:.

Throughout the entire specification, including the claims, the words and phrases used herein shall have the meaning consistent with the words and phrases used by those skilled in the relevant art. The following definitions of specific terms used in this disclosure is intended to clarify the meanings of the terms in a manner consistent with their ordinary meaning. No special definition of a term or phrase different from the ordinary and customary meaning as understood by those skilled in the art is intended to be implied except where expressly set forth.

An "added" material as used herein in reference to a process refers to an imported ingredient or component that is added as an additional ingredient or component supplementary to that which is already present in the process. For example, in a process with a recycle, the recycled material is not an added material.

The term "and/or" refers to both the inclusive "and" case and the exclusive "or" case, and such term is used herein for brevity. For example, a composition comprising "A and/or B" may comprise A alone, B alone, or both A and B.

The term "alloy" refers to a substance having metallic properties and being composed of two or more chemical elements of which at least one is a metal.

The term "catalyst material" refers to metal on or in a support material, such as, for example, a metal washcoat on silica, alumina, or another ceramic, used to increase the rate of a chemical reaction without itself undergoing any permanent chemical change. Catalyst material can be spent, partially spent, or new, or active or inactive.

The term "collector alloy" refers to an alloy containing dilute quantities of one or more precious metals, which may optionally be partially oxidized. If the collector alloy is partially oxidized, "collector alloy" also refers to any oxidized material that may be present with the alloy. The term "raw collector alloy" refers to a collector alloy from a furnace that is untreated and comprises less than <NUM> wt% of oxides.

The term "comminute" refers to the reduction in average particle size of a solid material, e.g., by crushing, grinding, milling, cutting, vibrating, and so on.

The term "converter" refers to an apparatus used to oxidize elements in an alloy; the term "converting" refers to the conversion of oxidizable elements in an alloy to the corresponding oxides, and may be used interchangeably with the term "oxidation.

The term "feed" as used herein refers to any reactant, reagent, diluent, additive, and/or other component supplied to a reactor or other vessel during the process.

The term "flux" is used in its metallurgical sense to refer to a material added to a meltable or molten material to facilitate the agglomeration, separation, and removal of undesirable substances, like sand, ash, or dirt. In some embodiments, the term "flux" is specifically limited to materials comprising <NUM> wt% or more of silica and/or <NUM> wt% or more of calcium oxide, magnesium oxide, or a combination of calcium oxide and magnesium oxide, by weight of the flux material.

The term "in" refers to a first material or component that is within, on, or adjacent to a second material or component.

A "jacket" refers to a cavity external to a vessel for heat exchange between a fluid circulating through the jacket and the walls of the vessel. The jacket can be a shell creating an annular space around the vessel, a half-pipe coil jacket, a dimple jacket, plate coils, and so on.

The term "lance" refers to a pipe for supplying oxygen to a furnace, flame, or another high temperature area or region.

As used herein, the terms "less than" or "up to" a specific amount of a component, without specification of a lower limit, include zero, i.e., the component is optional.

As used herein, "mesh size" refers to the US Standard Sieve Series where "-" indicates passing through and "+" indicates retained on.

The term "metal" refers to an opaque lustrous elemental chemical substance that is a good conductor of heat and electricity and, when polished, a good reflector of light.

The term "metallic" refers to a metal or another substance with the properties of a metal.

The term "oxide" in reference to a metal refers to any oxide of the metal, e.g., "iron oxide" refers to Fe(II) oxides such as FeO and FeO<NUM>, mixed Fe(II,III) oxides such as Fe<NUM>O<NUM>, Fe<NUM>O<NUM>, and so on, Fe(III) oxides such as hematite, and so on.

The term "pot" refers to a vessel for holding a molten material.

The term "partial pre-oxidation" refers to conversion of some but not all, e.g., up to <NUM> percent by weight, of the oxidizable species in an alloy in a separate step prior to a main converting step.

The term "protectant" refers to a substance that provides protection.

The term "recovering" as used herein refers to the collection or isolation of a material.

The term "recycling" as used herein refers to returning a material already present in a cyclic process to a previous stage in the process; "recycle" refers to the material recycled.

The term "refractory" refers to a substance that is resistant to heat. A "ramming refractory" is one that is applied as a mix of aggregate, powder, binder, and/or other additives, and compacted using a ramming method, e.g., with an air rammer or masonry hammer.

The term "rotary" refers to an item or piece of equipment that is more or less continuously rotated or turned in operation.

The term "slag" refers to the oxidized material separated from metals and/or alloys during smelting or refining. "High grade slag" refers to a slag having a relatively higher PGM content than a "low grade slag. " For purposes herein, "high grade slag" has a PGM concentration of greater than <NUM> ppm, e.g., greater than <NUM> ppm PGM, and "low grade slag" has a PGM concentration of less than or equal to about <NUM> ppm. For example, slag having a <NUM> - <NUM> ppm PGM content is a high grade slag with respect to a low grade slag with <NUM> ppm PGM. High grade slag preferably comprises no less than <NUM> ppm PGM.

The term "smelting" refers to the extraction of metal from a material such as an ore by a process involving heating and melting.

The term "tap" refers to a pipe, spout, or lip for discharging a stream of fluid from a container.

The term "tapping" refers to the act of causing a fluid to flow from a pipe or container.

A "top blown rotary converter" or "TBRC" refers to a converter that can blow or inject a gas from above into or onto a molten phase in a rotatable pot.

According to embodiments of the present invention, a process for converting platinum group metal (PGM) collector alloy comprises the steps of: (a) introducing a converter feed into a pot of a converter holding a molten alloy pool, wherein the converter feed comprises: (i) <NUM> parts by weight of a collector alloy comprising no less than <NUM> wt% PGM, no less than <NUM> wt% iron, no less than <NUM> wt% nickel, and preferably no more than <NUM> wt% sulfur and no more than <NUM> wt% copper, based on the total weight of the collector alloy; and (ii) if an added flux material comprises <NUM> wt% or more of silica and/or <NUM> wt% or more of calcium oxide, magnesium oxide, or a combination of calcium oxide and magnesium oxide, by weight of the added flux material, less than <NUM> parts by weight of the added flux material; (b) injecting oxygen-containing gas into the alloy pool to convert iron and one or more other oxidizable elements from the collector alloy to corresponding oxides and enrich PGM in the alloy pool, preferably wherein the oxygen-containing gas injection is at least partially concurrent with the converter feed introduction; (c) allowing a slag comprising the iron oxide to collect in a low-density layer above the alloy pool; (d) tapping the low-density layer to recover the slag from the converter; and (e) tapping the alloy pool to recover the PGM-enriched alloy. The converter is preferably operated as a batch reactor. Preferably, the converter feed comprises less than <NUM> parts by weight (more preferably less than <NUM> parts by weight, and even more preferably less than <NUM> parts by weight) of any added flux material, per <NUM> parts by weight of collector alloy, regardless of silica, calcium oxide, or magnesium oxide content.

In any embodiment, the process can further comprise lining the pot with a refractory material; and supplying a refractory protectant to the pot holding the alloy pool at a rate not more than <NUM> parts by weight of the collector alloy, preferably no more than <NUM> parts by weight per <NUM> parts by weight of the collector alloy, more preferably at a rate between <NUM> and <NUM> parts by weight refractory protectant per <NUM> parts by weight of the collector alloy. In any embodiment, the refractory protectant can be supplied to the pot (i) after initially melting the alloy pool and prior to commencing step (b), (ii) during one or both of steps (a) and (b), and/or (iii) after stopping one or both of steps (a) and (b) to tap the low-density layer in step (d), prior to resuming said one or both of steps (a) and (b). The refractory protectant can be supplied to the pot together with the collector alloy introduced in step (a), or preferably is supplied to the pot separately from the collector alloy introduced in step (a), more preferably wherein the supply of refractory protectant to the pot is periodic.

The refractory protectant preferably comprises a component in common with the refractory material, such as alumina, for example. In any embodiment, the process can further comprise injecting the oxygen-containing gas into the alloy pool in step (b) through a lance extended into the alloy pool, wherein the lance comprises a consumable refractory material and is advanced into the pool as a tip of the lance is consumed. The consumable refractory material preferably comprises a component in common with the lining, preferably wherein the component in common comprises alumina. In any embodiment, the refractory material of the lining can comprise a ramming refractory comprising alumina, preferably wherein the ramming refractory comprises at least <NUM> wt% alumina.

In any embodiment, the process can further comprise sensing temperature in the refractory lining with radially spaced sensors mounted in the refractory lining; communicating temperature sensing information from the sensors to one or more transmitters; and transmitting signals containing the temperature sensing information from the one or more transmitters to a receiver. Preferably, the one or more transmitters are mounted externally on the pot and wirelessly transmit the signals to the receiver.

In any embodiment, the process can further comprise jacketing the pot, preferably adjacent the alloy pool, and circulating a coolant, preferably an aqueous heat transfer medium, e.g., water/ethylene glycol/propylene glycol, and the like, through the jacket during step (b), to remove heat from the alloy pool.

In any embodiment, the oxygen-containing gas can be injected into the converter alloy pool at a sufficient rate to maintain the alloy pool in a molten state at a temperature no higher than <NUM>, preferably at a temperature in a range from about <NUM> to <NUM>, more preferably <NUM> to <NUM>.

In any embodiment, the process can further comprise, prior to step (a), the step of: (I) partially pre-oxidizing a portion of the collector alloy from a raw state. Preferably, the partial pre-oxidation in step (I) comprises from <NUM> to <NUM> percent conversion of iron, more preferably from <NUM> to <NUM> percent iron conversion, and even more preferably from <NUM> to <NUM> percent iron conversion, based on the iron in the collector alloy portion prior to step (I). The collector alloy can be pre-oxidized by passing comminuted particles through an oxygen-rich flame; by partially converting the collector alloy and tapping the partially oxidized alloy, e.g., in an earlier converter cycle; by contacting particles of the collector alloy with an oxygen-containing gas at a temperature of at least <NUM>, for example between <NUM> and <NUM>, e.g., in a rotary kiln; fluidized bed roaster; and so on.

Preferably, the process can further comprise the steps of: (II) melting the partially pre-oxidized collector alloy in the pot to form a sufficient volume of the alloy pool for the injection of the oxygen-containing gas in step (b); and (III) then commencing the converter feed introduction into the pot in step (a) and the oxygen-containing gas injection into the alloy pool in step (b). As desired, the oxidized components in the partially pre-oxidized collector alloy from step (I) may be separated and removed in whole or in part prior to melting in step (II), or they can be allowed to remain in the partially pre-oxidized collector alloy melted in step (II).

In any embodiment, the pre-oxidizing step can comprise (I. A) passing comminuted collector alloy (e.g., a mesh size from about -<NUM>, preferably -<NUM> to + <NUM>) through an oxygen-rich flame, preferably wherein the flame exhibits a flame temperature of not less than <NUM>, more preferably <NUM> to <NUM>, and especially <NUM> to <NUM>. The oxygen rich flame is preferably produced by a burner for heating the pot, and the process can further comprise (I. B) depositing at least partially melted collector alloy particles from the flame into the pot. Preferably the process comprises (I. C) cooling and solidifying the particles to form a coating of the pre-oxidized collector alloy on an interior surface of a refractory lining of the pot, e.g., where step (II) comprises melting the coating. In this pre-oxidizing procedure the oxidized components in the partially pre-oxidized collector alloy from step (I) are preferably allowed to remain in the partially pre-oxidized collector alloy melted in step (II).

In any embodiment, the pre-oxidizing step can comprise operating the converter through a pre-oxidation cycle of steps (II), (III), (a), (b), (c), (d), and (e) to prepare a partially oxidized starter alloy, where a partially pre-oxidized collector alloy from an earlier cycle is preferably melted in step (II) and the alloy recovered from step (e) is used as the partially pre-oxidized starter. The starter alloy preparation cycle can further comprise melting a previously prepared charge of the partially oxidized starter alloy in the pot to form the alloy pool; periodically or continuously supplying the converter feed to the alloy pool in step (a) concurrently with the injection of the oxygen-containing gas in step (b); continuing the injection of the oxygen-containing gas to partially oxidize the alloy pool, preferably wherein from <NUM> to <NUM> percent, more preferably from <NUM> to <NUM> percent, of iron in the converter feed is oxidized, based on the weight of iron in the converter feed supplied to the converter alloy pool; tapping the slag from the converter pot, preferably a plurality of times; then recovering and solidifying the partially oxidized alloy pool. Preferably the solidified, partially oxidized collector alloy from the starter alloy preparation cycle is divided into a plurality of starter alloy charges for a like plurality of converter operating cycles and/or starter alloy preparation cycles.

In this pre-oxidizing converter cycle procedure the oxidized components in the partially pre-oxidized collector alloy from step (I) are preferably separated in step (c) and removed in step (d), and the partially pre-oxidized collector alloy can be recovered in step (e) of the pre-oxidizing cycle, cooled, and solidified prior to step (II). If desired, the slag recovered in step (d) of the pre-oxidizing cycle can be combined with and/or melted with the partially pre-oxidized alloy from step (e) in a subsequent step (I) of a collector alloy converting or pre-oxidation cycle.

In any embodiment, the pre-oxidizing step can comprise contacting particles of the collector alloy (e.g., a mesh size from about -<NUM>, preferably -<NUM> to +<NUM>) with an oxygen-containing gas at a temperature above <NUM>, e.g., between <NUM> and <NUM>, preferably by roasting in a rotary kiln, fluidized bed roaster, or any other roasting mechanism taking care not to melt and excessively aggregate the particles together.

In any embodiment, the process can further comprise the steps of: (A. <NUM>) separating the slag recovered in step (d) into a plurality of portions; (A. <NUM>) recycling a first one of the recovered slag portions from step (A. <NUM>) to the converter feed introduced to the pot in step (a). The converter feed preferably comprises the recycled slag in an amount of from about <NUM> to <NUM> parts by weight per <NUM> parts by weight of the collector alloy, more preferably from <NUM> to <NUM> parts by weight per <NUM> parts by weight of the collector alloy in the converter feed. The process preferably comprises (A. <NUM>) combining the collector alloy and the recycle slag for concurrent introduction in the converter feed in step (a), preferably from a single feed unit. The recycled slag in step (A. <NUM>) preferably comprises a high-grade portion of the recovered slag from step (d), i.e., a higher PGM content than an average overall PGM content of the recovered slag from step (d), and/or the recycled slag has a nickel oxide content greater than about <NUM> percent by weight of the recycled slag.

In any embodiment, the process can comprise the steps of: (B. <NUM>) cooling, solidifying, and comminuting the recovered slag from step (d) (e.g., crushing to a mesh size of -<NUM> (<NUM>/<NUM> in. ) may be suitable); (B. <NUM>) magnetically separating the crushed slag into a magnetically susceptible fraction and a non-magnetically susceptible fraction; (B. <NUM>) recycling the magnetically susceptible fraction to the converter feed in step (A. <NUM>); and (B. <NUM>) optionally recycling a portion of the non-magnetically susceptible fraction to the converter feed in step (A.

In any embodiment, the process can comprise the steps of: (C. <NUM>) prior to steps (a) to (e), beginning a converter operation cycle by melting a partially pre-oxidized collector alloy in the pot to form the alloy pool; (C. <NUM>) then, prior to step (e), repeating a sequence of steps (a), (b), (c), and (d) a plurality of times, wherein step (d) in each sequence follows step (c); and (C. <NUM>) after a final tapping of the low-density layer in step (d) in a last one of the sequences of step (C. <NUM>), tapping the alloy pool in step (e). Preferably in a step (C. <NUM>) all or part of the slag recovered from the final tapping in step (d) is recycled to the converter feed in step (A. <NUM>) regardless of magnetic susceptibility, and/or all or part of the non-magnetically susceptible fraction separated in step (B. <NUM>) from the final tapping in step (d) is recycled to the converter feed in step (A. The process preferably comprises the steps of: (D. <NUM>) for the tapping(s) of the low-density layer preceding the final tapping in step (C. <NUM>), allowing alloy entrained in the low-density layer to substantially settle into the alloy pool before the tapping of the respective low-density layer(s); and (D. <NUM>) for the final tapping in step (C. <NUM>), tapping the low-density layer within five minutes, optionally entraining alloy in the low-density layer.

In any embodiment, the process can comprise the steps of: (E. <NUM>) smelting a catalyst material in a primary furnace, preferably a non-converting furnace; (E. <NUM>) recovering a primary furnace slag and a first collector alloy from the primary furnace; (E. <NUM>) smelting the primary furnace slag in a secondary furnace, preferably a non-converting furnace; (E. <NUM>) recovering a secondary furnace slag and a second collector alloy from the secondary furnace; (E. <NUM>) supplying the first and second collector alloys to converter feed in step (a); and (E. <NUM>) supplying at least a portion of the slag recovered from the converter in step (d) to the secondary furnace for smelting with the primary furnace slag in step (E. The pot of the converter is preferably lined with a refractory material, and a portion of the primary furnace slag from step (E. <NUM>) can be supplied to the pot as a refractory protectant for steps (a) and (b), preferably at a rate not more than <NUM> parts by weight of the primary furnace slag per <NUM> parts by weight of the collector alloy, more preferably <NUM> parts by weight of the primary furnace slag per <NUM> parts by weight of the collector alloy, more preferably at a rate between <NUM> and <NUM> parts by weight of the primary furnace slag per <NUM> parts by weight of the collector alloy.

In any embodiment, the process can comprise any one or more or all of the following: (F. <NUM>) the oxygen-containing gas injection in step (b) is preferably continued until the alloy pool comprises no more than about <NUM> wt% iron, preferably no more than <NUM> wt% iron; and/or (F. <NUM>) the PGM-enriched alloy preferably comprises no less than <NUM> wt% PGM, preferably from <NUM> to <NUM> wt% PGM; (F. <NUM>) the PGM-enriched alloy preferably comprises no less than <NUM> wt% nickel, more preferably from <NUM> to <NUM> wt% nickel; and/or (F. <NUM>) the PGM-enriched alloy preferably comprises no more than <NUM> wt% iron; and/or (F. <NUM>) the PGM-enriched alloy preferably comprises no more than <NUM> wt% silicon, no more than <NUM> wt% phosphorus, no more than <NUM> wt% copper, and/or no more than <NUM> wt% sulfur; and/or (F. <NUM>) the collector alloy preferably comprises from <NUM> to <NUM> wt% PGM; and/or (F. <NUM>) the collector alloy preferably comprises no less than <NUM> wt% iron, preferably <NUM> to <NUM> wt% iron; and/or (F. <NUM>) the collector alloy preferably comprises no less than <NUM> wt% nickel, preferably <NUM> to <NUM> wt% nickel; and/or (F. <NUM>) the collector alloy preferably comprises no more than <NUM> wt% sulfur, more preferably <NUM> to <NUM> wt% sulfur; and/or (F. <NUM>) the collector alloy preferably comprises: no more than <NUM> wt% copper, more preferably <NUM> to <NUM> wt% copper; and/or no more than <NUM> wt% chromium, preferably <NUM> to <NUM> wt% chromium; and/or no more than <NUM> wt% silicon, more preferably <NUM> to <NUM> wt% silicon.

With reference to the drawings in which like parts are indicated by like numerals, <FIG> schematically shows a converting process 100A for converting PGM collector alloy according to embodiments of the present invention. A converter feed <NUM> is introduced into a pot <NUM> of a converter <NUM> holding a molten alloy pool <NUM>. The converter <NUM> can be any suitable converter for oxidizing the iron and other elements in the feed <NUM>, e.g., using oxygen in a gas bubbled into the alloy pool from the top or side or bottom (not shown), which results in the formation of a light-density slag phase <NUM>. The converter <NUM> is preferably a top blown rotary converter ("TBRC") having an inclined, generally cylindrical pot <NUM> holding the alloy pool <NUM> as shown that can be rotated by motor <NUM>, e.g., at <NUM> rotation per hour up to <NUM> rotations per minute, e.g., <NUM> rotations per hour, to facilitate mixing and agitation. The pot <NUM> is often lined with a refractory material <NUM>. TBRCs are known, for example, from patent document <CIT>, and they are typically custom-designed and built for specific applications by a number of engineering firms specializing in metallurgical processing.

In any embodiment, converter feed <NUM> can be a collector alloy obtained from smelting catalyst material, including the raw collector alloy and/or a partially pre-oxidized collector alloy, and preferably comprises no less than <NUM> wt% PGM, for example from <NUM> to <NUM> wt%; no less than <NUM> wt% iron, for example from <NUM> to <NUM> wt% iron; and no less than <NUM> wt% nickel, for example from <NUM> to <NUM> wt% nickel, based on the total weight of the converter feed <NUM>. The converter feed <NUM> may also comprise at least about <NUM> wt% of each of copper, sulfur, and chromium; for example, from <NUM> to <NUM> wt% copper, from <NUM> to <NUM> wt% sulfur, and from <NUM> to <NUM> wt% chromium, based on the total weight of the converter feed <NUM>. The converter feed <NUM> and/or its components can also comprise up <NUM> wt% silicon, for example, from <NUM> to <NUM> wt% silicon; and up to <NUM> wt% phosphorus, for example from <NUM> to <NUM> wt% phosphorus, all based on the weight of the converter feed <NUM>. Other elements may also be present, usually in amounts up to <NUM> wt%.

The converter feed <NUM> may optionally comprise an added flux material, but if the added flux material comprises <NUM> wt% or more of silica and <NUM> wt% or more of calcium oxide, magnesium oxide, or a combination of calcium oxide and magnesium oxide, by weight of the added flux material, the converter feed <NUM> preferably comprises less than <NUM> parts by weight of the added flux material per <NUM> parts by weight of the collector alloy, more preferably no more than <NUM> parts by weight of the added flux material per <NUM> parts by weight of the collector alloy.

The converter <NUM> can be provided with a preferably water cooled burner assembly <NUM> to melt the alloy pool <NUM>. The alloy pool <NUM> can be converter feed <NUM> and/or a collector alloy, which is preferably initially at least partially oxidized or converted, and can become increasingly oxidized or converted as the converting process progresses through a cycle of operation.

Oxidant gas such as oxygen <NUM> is preferably injected into the pot <NUM> via lance <NUM> as the pot is rotated about a longitudinal axis. The oxygen converts iron and other oxidizable elements in the alloy pool <NUM> to the corresponding iron and other oxides, e.g., iron to iron oxide, silicon to silica, phosphorus to phosphorous pentoxide, chromium to chromium oxide, copper to copper oxide, titanium to titanium oxide, and so on. The description herein refers to iron as an exemplary conversion species by way of example and not limitation for the purposes of brevity, clarity, and convenience. The rotation and gas injection provide agitation and mixing as the iron and other impurities are depleted from the alloy pool <NUM> by oxidation and collect as a floating, low density layer <NUM>, thereby enriching PGM in the alloy pool <NUM>. The low-density layer <NUM> is tapped periodically or continuously and recovered as slag <NUM>, for example, from a tap and/or by tipping the pot <NUM>. Nickel and PGM are generally not as easily oxidized, and these are enriched in the alloy pool <NUM> and similarly recovered from a tap and/or by tipping the pot <NUM> as a PGM-enriched nickel alloy <NUM>, which is often solidified in a mold to form ingots. Slag <NUM> is often cooled, solidified, comminuted, e.g., by crushing and/or milling, to facilitate handling. For example, a mesh size of -<NUM> (-<NUM>, -<NUM>/<NUM> in. ) may be suitable.

Preferably, a refractory protectant <NUM> is supplied to the converter <NUM> in an effective amount. The protectant <NUM> can retard loss of the refractory material from the lining <NUM>, thus extending the refractory life and reducing the frequency of replacement of the refractory lining <NUM>. The protectant <NUM> can contain a material common to the refractory lining <NUM>, e.g., alumina where the refractory <NUM> is alumina-based. Where the refractory <NUM> is alumina-based, the protectant <NUM> is preferably an aluminosilicate that melts at a lower temperature than the refractory, i.e., an aluminosilicate glass, which may conveniently be supplied from the furnace slags <NUM> and/or <NUM> (see <FIG>), preferably from the primary furnace slag <NUM>, for example, where the slags <NUM> and/or <NUM> also contain alumina. Where the refractory <NUM> is alumina-based, the amount of alumina in the protectant <NUM> should preferably not be less than <NUM> wt%, and the protectant <NUM> preferably comprises alumina in an amount of from <NUM> to <NUM> wt%, based on the total weight of the protectant.

An amount of protectant <NUM> needed to be effective is typically small in proportion to the converter feed <NUM>. Preferably the total amount of the added protectant is less than <NUM> wt%, based on the weight of the converter feed <NUM>, e.g., from <NUM> to <NUM> wt% of the converter feed. The protectant <NUM> can be added continuously, but is preferably added periodically in portions, e.g., as aliquots onto the top of the alloy pool <NUM>, following initial melting of the pool, and after each tapping of the slag <NUM>. Excessive amounts of protectant <NUM> provide limited additional protection and lead to higher volumes of slag <NUM>, whereas insufficient protectant <NUM> leads to higher refractory losses.

The lance <NUM> is frequently in a region of high temperature due to the oxygen addition and the exothermic nature of the converting reactions in close proximity, and is often consumable. Where the lance <NUM> is made of a consumable material, such as refractory material in common with the lining <NUM>, for example alumina, it may likewise benefit from the refractory protectant <NUM>. When the lance <NUM> is consumable, it is often advanced, periodically or continuously, as the tip of the lance is consumed, to maintain oxygen injection below an upper level of the alloy pool <NUM> and minimize unreacted oxygen escaping from the alloy pool <NUM> and/or slag <NUM>. In general, the rate of oxygen-containing gas injection is preferably as high as possible to rapidly complete the conversion, but not so high as to exceed the operating temperature limits of the TBRC <NUM> or as to cause unreacted oxygen to bubble up through the upper surface of the alloy pool <NUM> and/or low density layer <NUM>.

<FIG> schematically shows a PGM recovery process 100B incorporating a converter <NUM>, preferably the converter process 100A (see <FIG>), according to embodiments of the present invention. The PGM collector alloy is preferably obtained from smelting a catalyst material <NUM> in primary furnace <NUM>. The catalyst material <NUM> often comprises PGM on or in a support such as silica, alumina, clay, zeolite, cordierite, and the like, e.g., a washcoat of PGM-containing material on a ceramic support. The catalyst material <NUM> can be any PGM-containing material such as waste catalyst, for example, catalytic converters for automotive exhaust, catalyst from a refinery or chemical process industry, and the like.

If desired, the catalyst material can be conventionally processed to prepare it for smelting, e.g., by size reduction, removal of deleterious materials and/or inert materials that contain little or no PGM, such as by comminution, chemical treatment, magnetic separation, etc. Patent document <CIT>, for example, discloses comminution and magnetic separation of the catalyst material from automotive catalytic converters.

Smelting catalyst material such as in furnace <NUM> is well known, and uses a conventional furnace, e.g., a non-converting furnace such as an electric arc furnace, induction furnace, plasma arc furnace, fired furnace, and so on. For example, patent document <CIT> discloses processing catalyst material in an electric arc furnace to recover PGM, and patent documents <CIT> and <CIT> disclose smelting of chromite-bearing ores to recover PGM. The catalyst material, often with the addition of slag, flux, or collector metal, is generally continuously fed and when heated in the furnace forms slag <NUM> and a PGM-containing collector alloy. The collector alloy is relatively dense compared to the lighter slag, and collects in an alloy pool <NUM> below an upper layer of the slag <NUM>.

Slag <NUM> and collector alloy <NUM> are recovered, periodically or continuously, and often cooled and solidified for further processing. For example, collector alloy <NUM> is often poured into molds, and slag <NUM> is often granulated, dried in a rotary kiln, and packaged in bags or a suitable container. The slag <NUM> from the primary furnace <NUM> can contain residual PGM, often <NUM>-<NUM> wt% of the PGM in the catalyst material <NUM>, and is in turn preferably smelted in a secondary furnace <NUM>, which can be a furnace similar to furnace <NUM>, e.g., a non-converting furnace such as an electric arc furnace, induction furnace, plasma arc furnace, fired furnace, or the like, with the addition of metallurgical coke. The slag <NUM> recovered from furnace <NUM> is further depleted in PGM, and may be similarly cooled, solidified, granulated, dried, packaged, etc. The slag <NUM> can be disposed of as a byproduct or waste material. The PGM are concentrated and recovered in the collector alloy <NUM> from the secondary furnace <NUM>, and poured into molds and solidified in a manner similar to the collector alloy <NUM>.

In any embodiment, the first PGM collector alloy <NUM>, the second PGM collector alloy <NUM>, or preferably both, are introduced as converter feed <NUM> to converter <NUM>. The converter <NUM> shown in <FIG> can be any suitable converter for oxidizing the iron and other elements in the feed <NUM>, and preferably comprises the converter <NUM> as described above in process 100A in connection with <FIG>. The PGM collector alloys <NUM>, <NUM> are often comminuted, e.g., by crushing and/or milling, and fed to the converter <NUM> from a hopper <NUM> via a vibrating feeder <NUM> as shown in <FIG>.

Collector alloy <NUM> and collector alloy <NUM>, separately and/or collectively in converter feed <NUM>, preferably comprise no less than <NUM> wt% PGM, for example from <NUM> to <NUM> wt%; no less than <NUM> wt% iron, for example from <NUM> to <NUM> wt% iron; and no less than <NUM> wt% nickel, for example from <NUM> to <NUM> wt% nickel, based on the total weight of the converter feed <NUM>, collector alloy <NUM>, and/or collector alloy <NUM>. The first and/or second collector alloys <NUM>, <NUM>, may also comprise at least about <NUM> wt% of each of copper, sulfur, and chromium; for example, from <NUM> to <NUM> wt% copper, from <NUM> to <NUM> wt% sulfur, and from <NUM> to <NUM> wt% chromium, based on the total weight of the first and/or second collector alloys. The converter feed <NUM> and/or its components can also comprise up <NUM> wt% silicon, for example, from <NUM> to <NUM> wt% silicon; and up to <NUM> wt% phosphorus, for example from <NUM> to <NUM> wt% phosphorus, all based on the weight of the PGM-enriched nickel alloy. Other elements may also be present, usually in amounts up to <NUM> wt%.

Slag <NUM> from the converter <NUM> is often cooled, solidified, comminuted, e.g., by crushing and/or milling, to facilitate handling. Nickel and PGM are generally not as easily oxidized, and these are enriched in the alloy pool <NUM> and recovered as a PGM-enriched nickel alloy <NUM>, e.g., solidified in a mold to form ingots.

In any embodiment, the converter slag <NUM> can be smelted in the furnaces <NUM> and/or <NUM>. The slag <NUM> may contain residual PGM, and these values can be substantially recovered into the collector alloys <NUM> and/or <NUM>. Preferably, at least a first portion <NUM> of the converter slag <NUM> is processed in the secondary furnace <NUM> with the primary furnace slag <NUM>, since this may aid in limiting the accumulation of deleterious elements in the collector alloy <NUM> that can occur if the converter slag <NUM> is processed only in the primary furnace <NUM>.

In any embodiment, a second portion <NUM> of the converter slag <NUM> may be recycled to the converter feed <NUM>.

With reference to <FIG>, embodiments of the present invention provide a converter process <NUM> that partially pre-oxidizes collector alloy to speed up the converting process. In the converter process <NUM>, raw collector alloy <NUM> and/or <NUM> (<FIG>) are contacted in step <NUM> with an oxidant <NUM> at elevated temperature to obtain a partially pre-oxidized PGM collector alloy <NUM>. The oxidant <NUM> can be an oxygen-containing gas such as air, oxygen-enriched air, oxygen, oxygen-rich combustion gas, or the like. The elevated temperature is preferably not less than <NUM>, and more preferably not less than <NUM>.

In step <NUM>, the partially pre-oxidized alloy <NUM> is often melted in the pot <NUM> of the converter <NUM> (<FIG> or <FIG>) using, for example, burner assembly <NUM> (<FIG>), to form the alloy pool <NUM>. In the converting step <NUM>, converter feed <NUM> is introduced to the alloy pool <NUM> in the pot <NUM> and oxygen-containing gas <NUM> is injected. The converter feed <NUM> preferably comprises the partially pre-oxidized alloy <NUM>, the raw collector alloy <NUM>, <NUM>, or a combination thereof. Then in step <NUM>, the converter slag <NUM> can be tapped as needed, preferably a plurality of times, and in step <NUM>, the alloy pool <NUM> (<FIG>) is tapped, and PGM-enriched alloy <NUM> is recovered. Tapping involves stopping the rotation of the pot <NUM> and withdrawing molten material through a tap formed through a side wall (not shown) or by tipping the pot <NUM> and decanting the molten material and/or rabble, e.g., via a spout <NUM> (see <FIG>).

Pre-oxidation <NUM> as shown in <FIG> solves problems in known converting technology. For example, directly melting the PGM collector alloys <NUM>, <NUM> from the furnaces <NUM>, <NUM>, may produce an initial slag 128B (<FIG>) with undesirable melting characteristics. Also, the PGM collector alloys may be undesirably reactive with oxygen, resulting in an excessive exotherm, and/or requiring a relatively low rate of oxygen addition and an extended period of time for suitable conversion. Preferably, the partial pre-oxidation in step <NUM> achieves from <NUM> to <NUM> percent conversion of the iron to iron oxide in the collector alloy, more preferably from <NUM> to <NUM> percent iron conversion, and especially from <NUM> to <NUM> percent iron conversion. If desired, the oxidized iron can be removed from the partially pre-oxidized PGM collector alloy <NUM>, e.g., where prepared as a starter alloy in an earlier converter cycle from which slag is separated; or preferably the oxidized iron can remain in the partially pre-oxidized PGM collector alloy <NUM>, as in air oxidation in a kiln or especially by flame oxidation.

With reference again to <FIG>, the process <NUM> can provide a converter startup procedure. In any embodiment, a partially pre-oxidized collector alloy charge is often used to speed up the converting process, e.g., the initial melting, and/or produce an initial slag with a low melting temperature. In any embodiment, any metal that melts more quickly and/or at a lower temperature relative to the converter feed <NUM> (<FIG> and <FIG>) can be used as or in lieu of the partially pre-oxidized collector alloy <NUM>. In the converter startup procedure <NUM>, raw collector alloy <NUM> and/or <NUM> (<FIG>) are contacted in step <NUM> with an oxygen-containing gas <NUM> at elevated temperature to obtain a partially pre-oxidized PGM collector alloy <NUM>, which in turn is melted in step <NUM> using, for example, burner assembly <NUM> (<FIG>), to form the alloy pool <NUM> in the pot <NUM> of the converter <NUM> (<FIG> or <FIG>).

For example, the pre-oxidation <NUM> can be effected (<NUM>) by contacting particles of the raw collector alloy <NUM>/<NUM> (e.g., crushing to a mesh size of -<NUM> may be suitable, for example, -<NUM> or -<NUM>/+<NUM>) with an oxygen-containing gas at a temperature of at least <NUM>, for example between <NUM> and <NUM>, e.g., in a rotary kiln or fluidized bed roaster; (<NUM>) by partially converting the raw collector alloy in converter <NUM> (<FIG>) with oxygen-containing gas <NUM> at a temperature no less than <NUM>, preferably at least <NUM>, e.g., <NUM> to <NUM>, and tapping the partially oxidized alloy, e.g., in an earlier or previous converter cycle (see <FIG>); (<NUM>) by flame oxidation comprising passing comminuted particles <NUM> (e.g., crushing to a mesh size of -<NUM> may be suitable, for example, -<NUM> or -<NUM>/+<NUM>) through an oxygen-rich flame <NUM> (<FIG>), preferably at a temperature not less than <NUM>, more preferably <NUM> to <NUM>, and especially <NUM> to <NUM>; and so on. Some preferred embodiments of flame pre-oxidation are described in more detail in reference to <FIG> below.

With reference to <FIG>, there is schematically shown an example of starter alloy preparation procedure <NUM> to prepare partially pre-oxidized starter alloy in an amount sufficient for a plurality of batches. In step <NUM>, a charge of partially pre-oxidized collector alloy <NUM> (<FIG>), e.g., from an earlier starter alloy batch, is placed in the optionally emptied pot <NUM>. In step <NUM>, the starter alloy <NUM> is melted, e.g., using burner assembly <NUM> (<FIG>) to form the converter alloy pool <NUM>. In step <NUM>, converter feed <NUM> comprising the PGM collector alloy is supplied (periodically or continuously), and in step <NUM>, oxygen-containing gas <NUM> is injected into the alloy pool <NUM>. The oxygen injection is continued to partially oxidize the converter feed, preferably wherein from <NUM> to <NUM> percent of the iron is converted to iron oxide, more preferably where the iron conversion is from <NUM> to <NUM> percent, and especially from <NUM> to <NUM> percent iron conversion, based on the weight of iron in the total converter feed <NUM> and starter alloy supplied to the alloy pool <NUM>. In step <NUM>, the converter slag <NUM> can be tapped as needed to avoid over-filling the pot <NUM>, preferably a plurality of times.

Then in step <NUM>, the alloy pool <NUM> (<FIG>) is tapped, and starter alloy <NUM>' is recovered. The recovered starter alloy <NUM>' is often solidified and broken up into pieces, or it can be comminuted, e.g., by crushing, milling, etc., as desired, although this is not generally a requirement. For example, the solidified, partially oxidized collector alloy from the starter alloy preparation cycle can be divided into a plurality of generally equal-sized starter alloy charges for a like plurality of converter operating cycles and/or starter alloy preparation cycles. For example, one batch of starter alloy <NUM>' may provide sufficient starter alloy for a plurality of batches, e.g., <NUM>-<NUM>, and thus a starter batch prepared for seven batches might be prepared every seventh batch, i.e., using the seventh one of the starter batches after the sixth batch of PGM-enriched nickel alloy product.

With reference to <FIG>, there is schematically shown a simplified side view of a preferred TBRC <NUM> equipped with a water-cooled oxy-fuel burner assembly <NUM>, motor <NUM>, fume hood <NUM>, water cooled heat shield 121A, oxygen injection lance <NUM>, and rotary coupling <NUM>. The TBRC <NUM> has a fume hood <NUM> and a water cooled heat shield 121A that has openings to allow positioning of the burner <NUM> and lance <NUM>, entry of feed <NUM> (<FIG>) and protectant <NUM> (<FIG>), and tapping of the alloy pool <NUM> (<FIG>) and low density layer <NUM> (<FIG>) via tapping spout <NUM>. The motor <NUM> can be geared, e.g., via a chain 119A and sprockets 119B, 119C, and is capable of rotating the pot <NUM> at a suitable rate to provide agitation, e.g., <NUM>/<NUM> rotation per minute. Externally mounted transmitters <NUM> can be connected via wire <NUM> through conduit <NUM> to temperature sensors <NUM> (see <FIG>) mounted in or near the refractory <NUM> (see <FIG>) can send a temperature signal to a remote receiver <NUM>. A cooling fluid inlet and outlet can be in the form of flex hoses 147a and 147b to supply and return the cooling fluid from coolant system <NUM> via a dual flow rotary coupling <NUM> to a jacket <NUM> (see <FIG>).

With reference to <FIG> there is shown a side sectional view of the TBRC <NUM> comprising the pot <NUM>. A temperature sensor <NUM> such as a thermocouple is located in the refractory <NUM>, preferably adjacent an interior wall <NUM> of the pot <NUM>, and connected via wire <NUM> passing through conduit <NUM> to the externally mounted temperature transmitter <NUM>, which can transmit temperature information wirelessly to the remote receiver <NUM> (<FIG>). In any embodiment, the oxygen-containing gas is injected into the converter alloy pool at a sufficient rate to maintain the alloy pool in a molten state at a temperature no higher than <NUM>, e.g., a temperature in the alloy pool not less than <NUM>, preferably from about <NUM> to <NUM>. Lower temperatures risk premature solidification of the alloy pool <NUM>, whereas excessively high temperatures risk failure of TBRC <NUM> components. In any embodiment, the temperature of the refractory <NUM> can be monitored, e.g., for process control and/or to detect premature thinning.

In any embodiment, the pot <NUM> can be provided with a jacket <NUM> adjacent the slag layer and/or alloy pool to circulate coolant fluid such as an aqueous heat transfer medium, e.g., water/ethylene glycol/propylene glycol, and the like. For example, the fluid from a flex hose 147a can enter the jacket <NUM> through a central passage of a rotary coupling <NUM>, flow into an inner annular channel <NUM> adjacent the wall <NUM>, and out through an outer annular channel <NUM> (or in outer channel <NUM> and out inner channel <NUM>) to exit via the coupling <NUM> from flex hose 147b. In this manner, the life of the refractory <NUM> can be extended and/or the oxygen can be injected at a higher rate to facilitate faster processing and/or a greater converter throughput since the alloy pool can be in thermal communication with the jacket thorough the refractory lining to withdraw heat of reaction. If desired, the bottom of the pot <NUM> and jacket <NUM> can comprise a bottom flange (not shown) to facilitate assembly/disassembly.

With reference to <FIG>, there is shown a simplified side sectional view of the TBRC <NUM> of <FIG> and <FIG> schematically illustrating an embodiment of a burner assembly <NUM> for in situ pre-oxidation according to embodiments of the present invention. The burner assembly <NUM> is provided with a fuel/oxygen supply line(s) <NUM> to burner nozzle <NUM> to generate an oxygen-rich flame <NUM>. Collector alloy particles <NUM> are supplied through an adjacent feeding tube <NUM>, e.g., from an overhead vibrating feed unit (not shown). The collector alloy particles <NUM> fall from the feed tube <NUM> through the flame <NUM> where they are partially oxidized. The partially oxidized particles 157A then fall and accumulate in the pot <NUM>. Rotation of the pot <NUM> during operation distributes the particles 157A onto a surface of the refractory lining <NUM>. If the particles 157A are melted or partially melted in the flame <NUM>, they can form a coating on the refractory lining <NUM> when they cool and solidify. Free-flowing and/or fused particles 157A can then be melted when desired by increasing the firing rate of burner <NUM>. If the burner <NUM> is fired at a higher rate during pre-oxidation, the partially oxidized particles 157A can collect in a molten alloy pool 122A (see <FIG>).

The collector alloy particles <NUM> are often ground or milled into a particulated form to increase the surface area exposed to the flame <NUM>, but are preferably sufficiently large to pass through the flame <NUM> and settle on the pot <NUM>. The alloy particles <NUM> are also preferably sufficiently large to facilitate separation, e.g., by cyclone (not shown) or gravity, and avoid excessive entrainment in the discharged combustion gas. For example, a mesh size of -<NUM> or -<NUM>/+<NUM> may be suitable for gravity separation. Excessive fines, e.g., -<NUM> mesh, are preferably minimized or avoided. The flame <NUM> is preferably oxygen-rich to provide an oxidizing environment to partially oxidize the particles <NUM>, e.g., the burner <NUM> can be fired with a fuel gas such as natural gas or propane and a <NUM>% excess of oxygen relative to theoretical for complete combustion, preferably <NUM>-<NUM>% excess oxygen, more preferably <NUM>-<NUM>% excess oxygen. The combustion oxidizing gas is preferably oxygen-enriched air or more preferably ><NUM> volume percent oxygen so that the combustion temperature in the flame <NUM> is no less than <NUM>. The partial pre-oxidation should be sufficient to convert from <NUM> to <NUM> percent of the iron in the particles <NUM> to iron oxide in the particles 157A, preferably to convert from <NUM> to <NUM> percent of the iron, and more preferably to convert from <NUM> to <NUM> percent of the iron.

The collector alloy particles <NUM> can conveniently be pre-oxidized during an off shift, e.g., overnight, using a relatively low feed rate and a low burner rate, relative to operation. A charge of collector alloy particles <NUM> sufficient to form the desired alloy pool 122A (<FIG>) at the start of an operating cycle can be loaded in the feed unit (not shown). The particles <NUM> can accumulate in a bed, a coating, or as a molten pool inside of the pot <NUM>, which is kept hot by the flame <NUM>. After the charge is finished pre-oxidizing, continued firing of the burner <NUM> facilitates keeping the pot <NUM> and partially pre-oxidized collector alloy particles <NUM> warm, e.g., <NUM> to <NUM>, preferably <NUM> to <NUM>, so that a converting operating cycle can be quickly started. At the start of the day shift, the accumulated particles <NUM> can be molten or quickly melted to form the alloy pool 122A (see <FIG>) by increasing the firing rate of the burner <NUM> to quickly start a converting cycle.

A preferred operational cycle or batch of the converter <NUM> is shown in <FIG>. An operating cycle often begins by melting a charge of partially pre-oxidized collector alloy in the converter pot <NUM> to form the converter alloy pool 122A as shown in <FIG>. The pool 122A is preferably just sufficient to inject the oxygen below the surface, e.g., approximately <NUM>-<NUM> vol% of the available volume of the pot <NUM>, where the available volume is the volume of the pot <NUM> that can be filled without overflowing material out of the top at the angle at which the pot <NUM> is inclined for operation. However, because the PGM collector alloys <NUM>, <NUM> from the furnaces <NUM>, <NUM> may produce a slag (128B) with undesirable melting characteristics when melted, a partially pre-oxidized collector alloy charge is preferably used to speed up the initial melting and produce an initial slag with a low melting point. In any embodiment, any metal that melts more quickly and/or at a lower temperature relative to the converter feed <NUM> can be used as or in lieu of the partially pre-oxidized collector alloy.

After melting the initial pre-oxidized alloy charge 122A in <FIG>, the converter feed <NUM> is introduced and simultaneously the oxygen is injected. The feed material <NUM> is melted and the volume of the alloy pool 122B is enlarged as shown in <FIG>. Reaction of the oxygen converts iron and other materials into a slag phase 128B, which reduces the alloy pool volume. The slag phase 128B is less dense than the alloy pool 122B, and floats on top. Agitation from oxygen-containing gas injection and/or rotation of the pot <NUM> entrains particles or droplets <NUM> of the alloy into the slag phase 128B.

The reaction of the iron-containing alloy with oxygen is exothermic, and care is taken to avoid introducing the oxygen-containing gas at a rate that causes an excessive temperature, e.g., the oxygen is generally injected at a rate sufficient to maintain the alloy pool in a molten state, e.g., above <NUM>, and below a maximum temperature in the alloy pool no higher than <NUM>, e.g., a temperature of <NUM> to <NUM>. The introduction of the converter feed as a solid, including any flux, refractory protectant, recycle slag, etc., concurrently with the oxygen injection, helps to moderate the exotherm by the enthalpy required for melting the solids. Also, circulating a coolant through the jacket <NUM> also serves to remove some heat of reaction, allowing a higher oxygen injection rate.

Introduction of the feed <NUM> and oxygen-containing gas injection are continued until the pot <NUM> is filled to desired capacity with enlarged alloy pool 122C and slag phase 128C, as shown in <FIG>. The slag phases 128B and 128C during the pot fill stage generally contain some entrained alloy <NUM> dispersed in the slag phases 128B, 128C due to agitation and mixing by the oxygen injection and rotation of the pot <NUM>. The feed introduction and oxygen injection are often stopped for slag tapping. When the oxygen injection and rotation are stopped, the entrained alloy droplets or particles <NUM> are allowed to settle out of the slag phase 128D and return to the alloy pool 122D, as seen in <FIG>. After a quiescence period effective to promote the gravity settling and disentrainment of dispersed metal <NUM> from the slag 128C (<FIG>), and coalescence into the alloy pool 122D (<FIG>), preferably at least <NUM> minutes, the slag 128D can be removed with substantially less entrained alloy. The slag 128D is often tapped by tilting the pot <NUM> to pour out the slag phase 128D into molds (not shown), with minimal entrainment or tapping of the alloy pool 122D, i.e., with a clean margin for the slag phase 128D.

With the slag 128D removed, the pot <NUM> has additional volume to resume the feed supply and/or oxygen injection as in <FIG>. The cycle of filling the pot as in <FIG> and tapping the slag 128D, after a brief alloy disentrainment period as shown in <FIG>, is preferably repeated a plurality of times. After the desired charge of the converter feed <NUM> has been added, the oxygen-containing gas injection may continue until the level of desired conversion is achieved, e.g., at least <NUM>% conversion of the iron from the converter feed <NUM>, or preferably at least <NUM>% iron conversion, or more preferably <NUM>% iron conversion. After a final cycle of filling and/or oxygen injection, the alloy pool 122E is at its desired final volume and level of converting as in <FIG>, and the final slag layer 128E and alloy pool 122E are successively tapped and poured into respective molds.

When it is desired to tap the alloy 122E and final slag 128E as in <FIG>, however, it is preferred to immediately tap the slag 128E without waiting for the alloy phase <NUM> to substantially separate from the slag 128E. At the end of the oxygen injection, the converting reaction is more complete and the exotherm may moderate, tending to reduce the temperature of the alloy pool 122E. At the same time, the melting temperature of the PGM-enriched alloy has increased. Thus, it is preferred to tap the alloy 122E promptly to avoid premature solidification, e.g., by commencing final tapping of the slag 128E less than <NUM> minutes following termination of the oxygen injection. To avoid contaminating the alloy pool 122E with slag 128E, it is often preferred to tap the final slag 128E to provide the alloy pool 122E with a clean margin, i.e., by tapping an upper portion or surface at the upper margin of the alloy pool 122E with the slag 128E. However, as described above, this final slag tapping 128E represents a high grade slag that is preferably recycled to the converter feed <NUM> in a subsequent converter cycle, so that the PGM values can be recovered.

In a preferred embodiment as shown schematically in <FIG>, process <NUM> includes smelting catalyst material <NUM> in primary electric arc furnace <NUM>. Slag <NUM>, comprising mainly aluminosilicate, is recovered from the furnace <NUM>, granulated in water in granulator <NUM>, dried in rotary kiln <NUM>, and repackaged in bag-filling station <NUM>. The PGM collector alloy <NUM> is cast into molds <NUM>, solidified, and crushed in crusher <NUM>.

The dried slag <NUM> from the primary furnace <NUM> is smelted in second, finishing electric arc furnace <NUM>. Slag <NUM> recovered from the furnace <NUM> is granulated in granulator <NUM> and recycled as byproduct <NUM> for an appropriate use, e.g., as aggregate. The PGM collector alloy <NUM> from the secondary furnace <NUM> is cast into molds <NUM>, solidified and crushed in crusher <NUM>.

Milled collector alloys <NUM> and <NUM> from crusher <NUM> are placed in hopper <NUM> which supplies feed material to vibrating feeder <NUM> to TBRC <NUM>. The TBRC <NUM> is equipped with a burner assembly <NUM>, oxygen injection lance <NUM>, fume hood <NUM>, and motor (see <FIG>) to rotate the pot <NUM> of the TBRC <NUM>. If desired, the pot <NUM> can be provided with a water-cooling jacket, lined with an alumina-based ramming refractory, and provided with any of the other features of the TBRC <NUM> as described above in connection with <FIG>, <FIG>, <FIG>.

To start a converting cycle, as the TBRC <NUM> is rotated, a portion of the converter feed from the hopper <NUM> is fed through the feeder <NUM> to fall through an oxygen-rich flame (cf. flame <NUM> in <FIG>) of the burner assembly <NUM> and is partially pre-oxidized. The pre-oxidation is continued until accumulating a charge of the partially pre-oxidized collector alloy that when melted would create an alloy pool of sufficient size to allow oxidation to begin, generally filling about <NUM>-<NUM>% of the available volume of the pot. alloy pool 122A in <FIG>. Alternatively, a previously prepared starter alloy, a kiln-oxidized collector alloy, a fluidized bed oxidized collector alloy, or the like could be used as the partially pre-oxidized collector alloy. If necessary, the partially pre-oxidized collector alloy charge is melted using the burner <NUM> to a temperature of at least <NUM>, preferably at least <NUM>. A portion of the total protectant comprising the dried aluminosilicate slag <NUM> from the primary furnace <NUM> is preferably placed on top of the alloy pool as slag protectant <NUM>.

While the pot of the TBRC <NUM> is rotated, the burner is typically shut off and oxygen <NUM> is injected into the alloy pool using lance <NUM> at a rate to maintain a temperature sufficient to avoid solidification of the alloy pool but at a sufficient rate to maintain the temperature in the alloy pool no higher than <NUM>, e.g., <NUM> to <NUM>. PGM collector alloys <NUM>, <NUM> from the furnaces <NUM>, <NUM> are placed in hopper <NUM>, and fed into the TBRC <NUM> at a generally steady rate via vibrating feeder <NUM>. The TBRC <NUM> is filled with material as slag is formed, and the alloy pool is grown by the feed into the TBRC. alloy pool 122B and slag 128B in <FIG>. When the volume of the pot was filled sufficiently (cf. alloy pool 122C and slag 128C in <FIG>), the pot rotation, oxygen injection, and alloy feed can be stopped. After waiting several minutes, typically at least <NUM> minutes, to allow phase separation (cf. alloy pool 122D and slag 128D in <FIG>), slag <NUM> is tapped into molds <NUM> by tipping the TBRC <NUM>, taking care to maintain a clear margin in the slag <NUM> and avoid tapping excessive amounts of the alloy.

The oxygen injection and converter feed into the remaining alloy pool are then resumed until the TBRC <NUM> is again filled, and slag <NUM> tapped as described above. The cycle is repeated several times until the alloy pool has grown to a desired volume for tapping. The last slag <NUM> tapped just before tapping the alloy is preferably performed promptly after stopping the oxygen injection and collector alloy feed to avoid premature solidification in the pot, taking care that substantially all of the slag <NUM> is tapped, e.g., providing a clear margin for the alloy pool. Minor amounts of alloy may optionally be entrained in the slag. alloy pool 122E, slag 128E, and alloy <NUM> in <FIG>. However, the final slag tapping is preferably recycled to the converter feed <NUM> in a subsequent cycle or batch to minimize PGM losses. The PGM-enriched alloy <NUM> is then tapped into ingot molds <NUM>, cooled, and solidified.

After the slag molds <NUM> are cooled, the solidified slag <NUM> is often fed through slag crusher <NUM> and magnetic separator <NUM>. The non-magnetic fractions from the final slag tapping and the earlier tappings can be sorted into containers <NUM> and <NUM>, respectively. The non-magnetic fraction <NUM> can be smelted in the secondary furnace <NUM> with the slag <NUM> from the primary furnace.

The magnetic fractions <NUM> from all of the converter slag and the non-magnetic fraction <NUM> from the final slag tapping are preferably placed in the feed hopper <NUM> for a subsequent TBRC batch. Alternatively, the entirety of the final slag tapping can be placed directly in the hopper <NUM> with the collector alloy(s) <NUM>, <NUM>, bypassing the magnetic separator <NUM>.

In another aspect, in reference to <FIG>, embodiments of the present invention provide a PGM collector alloy converting process <NUM> comprising: in step <NUM>, introducing a converter feed <NUM> (<FIG>) comprising PGM collector alloy <NUM> and/or <NUM> (<FIG>) into a pot <NUM> of a converter <NUM> (<FIG>) holding an alloy pool <NUM> (<FIG>); in step <NUM>, injecting oxygen-containing gas <NUM> (<FIG>) into the alloy pool; in step <NUM>, recovering slag <NUM> (<FIG>) from the pot <NUM>; in step <NUM>, smelting the recovered slag <NUM> in a furnace <NUM> and/or <NUM> (<FIG>), preferably a secondary furnace <NUM>; in step <NUM>, recovering collector alloy <NUM> and/or <NUM> (<FIG>) from the furnace <NUM> and/or <NUM>; optionally in step <NUM>, introducing the collector alloy <NUM> and/or <NUM> recovered from the furnace <NUM> and/or <NUM> in step <NUM> to the converter feed <NUM> to the pot <NUM> with the alloy pool <NUM>; and in step <NUM>, recovering PGM-enriched alloy <NUM> (<FIG>) from the pot <NUM>. The converter feed <NUM> preferably comprises the collector alloys <NUM> and/or <NUM> which comprise no less than <NUM> wt% PGM, no less than <NUM> wt% iron, and no less than <NUM> wt% nickel, based on the total weight of the collector alloy. The converter feed <NUM> may optionally comprise an added flux material, but if an added flux material comprises <NUM> wt% or more of silica and <NUM> wt% or more of calcium oxide, magnesium oxide, or a combination of calcium oxide and magnesium oxide, by weight of the added flux material, the converter feed preferably comprises less than <NUM> parts by weight of the added flux material per <NUM> parts by weight of the collector alloy. Preferably, the PGM-enriched alloy comprises no less than <NUM> wt% PGM, no less than <NUM> wt% nickel, and no more than <NUM> wt% iron, more preferably from <NUM> to <NUM> wt% PGM and from <NUM> to <NUM> wt% nickel.

In another aspect, in reference to <FIG>, embodiments of the present invention provide a PGM collector alloy converting process <NUM> comprising: in step <NUM>, lining a converter pot <NUM> with a refractory material <NUM> (<FIG>); in step <NUM>, holding an alloy pool <NUM> (<FIG>) in the pot <NUM>; in step <NUM>, supplying a refractory protectant <NUM> (<FIG>) to the pot <NUM> with the converter alloy pool <NUM>; in step <NUM>, introducing a converter feed <NUM> (<FIG>) comprising PGM collector alloy <NUM> and/or <NUM> (<FIG>) into the pot <NUM> with the alloy pool <NUM>; in step <NUM>, injecting oxygen-containing gas <NUM> (<FIG>) into the alloy pool <NUM>; in step <NUM>, recovering slag <NUM> (<FIG>) from the pot <NUM>; and in step <NUM>, recovering PGM-enriched alloy <NUM> from the pot <NUM>. The refractory protectant <NUM> preferably comprises a refractory component in common with the refractory material <NUM>. The component in common can comprise alumina, for example. The converter feed <NUM> preferably comprises the collector alloys <NUM> and/or <NUM> which comprise no less than <NUM> wt% PGM, no less than <NUM> wt% iron, and no less than <NUM> wt% nickel, based on the total weight of the collector alloy.

The converter feed <NUM> may optionally comprise an added flux material, but if an added flux material comprises <NUM> wt% or more of silica and <NUM> wt% or more of calcium oxide, magnesium oxide, or a combination of calcium oxide and magnesium oxide, by weight of the added flux material, the converter feed preferably comprises no more than <NUM> parts by weight of the added flux material per <NUM> parts by weight of the collector alloy. Preferably, the converter feed <NUM> comprises less than <NUM> parts by weight (more preferably less than <NUM> parts by weight, and even more preferably less than <NUM> parts by weight) of any added flux material, per <NUM> parts by weight of collector alloy <NUM>, <NUM>, regardless of silica, calcium oxide, or magnesium oxide content. Preferably, the PGM-enriched alloy comprises no less than <NUM> wt% PGM, no less than <NUM> wt% nickel, and no more than <NUM> wt% iron, more preferably from <NUM> to <NUM> wt% PGM and from <NUM> to <NUM> wt% nickel.

In another aspect, in reference to <FIG>, embodiments of the present invention provide a PGM collector alloy converting process <NUM> comprising: in step <NUM>, contacting a raw collector alloy <NUM>/<NUM> (<FIG>) with oxidant <NUM> to form a partially pre-oxidized PGM collector alloy <NUM> (see also <FIG>); in step <NUM>, placing a charge of converter feed 116A, comprising the partially pre-oxidized collector alloy <NUM> and optionally comprising the raw collector alloy <NUM>/<NUM>, in a pot <NUM> of a converter <NUM> (<FIG>); in step <NUM>, melting the charge of the converter feed 116A to form an initial alloy pool 122A (<FIG>), e.g., using a burner assembly <NUM>; in step <NUM>, introducing a converter feed 116B (<FIG>) comprising raw collector alloy <NUM>/<NUM> (<FIG>) and/or partially pre-oxidized collector alloy <NUM> into the pot <NUM> with the alloy pool 122A; in step <NUM>, injecting oxygen-containing gas <NUM> (<FIG>) into the alloy pool; in step <NUM>, recovering slag <NUM> (<FIG>) from the pot <NUM>; and in step <NUM> recovering PGM-enriched alloy <NUM> from the pot <NUM>. The collector alloys <NUM> and/or <NUM> preferably comprise no less than <NUM> wt% PGM, no less than <NUM> wt% iron, and no less than <NUM> wt% nickel, based on the total weight of the collector alloy.

The converter feeds 116A, 116B may optionally comprise an added flux material, but if an added flux material comprises <NUM> wt% or more of silica and <NUM> wt% or more of calcium oxide, magnesium oxide, or a combination of calcium oxide and magnesium oxide, by weight of the added flux material, the converter feeds 116A, 116B preferably comprise no more than <NUM> parts by weight of the added flux material per <NUM> parts by weight of the (raw and/or partially pre-oxidized) collector alloy. Preferably, the converter feeds 116A, 116B comprise less than <NUM> parts by weight (more preferably less than <NUM> parts by weight, and even more preferably less than <NUM> parts by weight) of any added flux material, per <NUM> parts by weight of the (raw and/or partially pre-oxidized) collector alloy, regardless of silica, calcium oxide, or magnesium oxide content. Preferably, the starter charge forms an alloy pool comprising a volume of from <NUM> to <NUM> vol% of available pot volume, or the depth is otherwise sufficient to receive a lance for the oxygen-containing gas injection. Preferably, the PGM-enriched alloy comprises no less than <NUM> wt% PGM, no less than <NUM> wt% nickel, and no more than <NUM> wt% iron, more preferably from <NUM> to <NUM> wt% PGM and from <NUM> to <NUM> wt% nickel.

In yet another aspect, in reference to <FIG>, embodiments of the present invention provide a PGM collector alloy converting process <NUM> comprising: in step <NUM>, holding an alloy pool <NUM> in a pot <NUM> (<FIG>); in step <NUM>, introducing a converter feed <NUM> (<FIG>) comprising PGM collector alloy into the pot <NUM> with the alloy pool <NUM>; in step <NUM>, injecting oxygen-containing gas <NUM> (<FIG>) into the alloy pool <NUM>; in step <NUM>, recovering slag <NUM> from the pot <NUM>; in step <NUM>, separating the slag <NUM> into first and second portions <NUM>, <NUM>; optionally, in step <NUM>, smelting the first portion <NUM> in a furnace <NUM> and/or <NUM> (<FIG>); introducing the second portion <NUM> to the converter feed <NUM> to the pot <NUM>; and in step <NUM>, recovering PGM-enriched alloy <NUM> from the pot <NUM>.

In any embodiment of the process <NUM>, the converter feed <NUM> can comprise a weight ratio of recycled slag <NUM> to collector alloy <NUM> and/or <NUM> (see <FIG>) of from <NUM>:<NUM> to <NUM>:<NUM>, preferably from <NUM>:<NUM> to <NUM>:<NUM>. Preferably, all or part of the second portion <NUM> of the recovered slag has a higher PGM and/or nickel content relative to a PGM and/or nickel content of the first portion <NUM>, and/or the second portion <NUM> of the recovered slag has a nickel content greater than about <NUM> wt%. For example, the separation in step <NUM> can be according to magnetic susceptibility where the first portion <NUM> comprises the non-magnetically susceptible fraction and the second portion <NUM> comprises the magnetically susceptible fraction. As another example, the second portion <NUM> can comprise a slag 128D with entrained alloy <NUM> as shown and discussed in connection with <FIG>. The converter feed <NUM> preferably comprises the collector alloys <NUM> and/or <NUM> which comprise no less than <NUM> wt% PGM, no less than <NUM> wt% iron, and no less than <NUM> wt% nickel, based on the total weight of the collector alloy.

The converter feed <NUM> may optionally comprise an added flux material, but if an added flux material comprises <NUM> wt% or more of silica and <NUM> wt% or more of calcium oxide, magnesium oxide, or a combination of calcium oxide and magnesium oxide, by weight of the added flux material, the converter feed <NUM> preferably comprises less than <NUM> parts by weight of the added flux material per <NUM> parts by weight of the collector alloy. Preferably, the converter feed <NUM> comprises less than <NUM> parts by weight (more preferably less than <NUM> parts by weight, and even more preferably less than <NUM> parts by weight) of any added flux material, per <NUM> parts by weight of collector alloy <NUM>, <NUM>, regardless of silica, calcium oxide, or magnesium oxide content.

In a further aspect, with reference to <FIG>, embodiments of the present invention provide a PGM collector alloy converting process <NUM> comprising: in step <NUM>, holding an alloy pool <NUM> in a pot <NUM> (<FIG>); in step <NUM>, introducing a converter feed <NUM> comprising PGM collector alloy <NUM> and/or <NUM> (see <FIG>) comprising iron and nickel into the pot <NUM> with the alloy pool <NUM>; in step <NUM>, injecting oxygen-containing gas <NUM> (<FIG>) into the alloy pool <NUM>, preferably at least partially concurrently with the feed introduction in step <NUM>; in step <NUM>, recovering slag <NUM> from the pot <NUM>; in step <NUM>, solidifying and comminuting the recovered slag <NUM>; in step <NUM>, separating the slag <NUM> into a high grade fraction for a recycling step <NUM> and a low grade fraction <NUM>, where the high grade fraction has a higher PGM content than the low grade fraction <NUM>; in step <NUM>, introducing a recycle portion of the recovered slag comprising the magnetically susceptible fraction <NUM> to the converter feed <NUM> for introduction into the pot <NUM>; and in step <NUM>, recovering PGM-enriched alloy <NUM> from the pot <NUM>. In any embodiment, the separation step <NUM> can optionally comprise a magnetic separation step <NUM> to magnetically separate the comminuted slag into a non-magnetically susceptible fraction <NUM> and a magnetically susceptible fraction <NUM> comprising high grade slag. In any embodiment, the recycle portion of the recovered slag in step <NUM> can optionally include a first, high grade portion <NUM> of the non-magnetically susceptible fraction <NUM>. For example, the high grade portion <NUM> can comprise slag 128E (<FIG>) from a final tapping. A second, low grade part <NUM> of the non-magnetically susceptible fraction <NUM> is not recycled, and can be removed from the converting process, e.g., for smelting in the secondary furnace <NUM>. In any embodiment, the converter feed <NUM> can comprise a weight ratio of slag <NUM> and <NUM> to collector alloy of from <NUM>:<NUM> to <NUM>:<NUM>, preferably from <NUM>:<NUM> to <NUM>:<NUM>. Preferably, the total recycle portion <NUM> and <NUM> of the recovered slag <NUM> has a higher PGM content and/or nickel content relative to a non-recycled portion <NUM>. Often, the recycle portion of the recovered slag has a total nickel content not less than about <NUM> wt%.

In a further aspect, with reference to <FIG>, embodiments of the present invention provide a converting process <NUM> for converting a converter feed <NUM> comprising a collector alloy comprising no less than <NUM> wt% PGM, no less than <NUM> wt% iron, and no less than <NUM> wt% nickel, based on the total weight of the collector alloy. The converter feed <NUM> may optionally comprise an added flux material, but if an added flux material comprises <NUM> wt% or more of silica and <NUM> wt% or more of calcium oxide, magnesium oxide, or a combination of calcium oxide and magnesium oxide, by weight of the added flux material, the converter feed preferably comprises less than <NUM> parts by weight of the added flux material per <NUM> parts by weight of the collector alloy. Preferably, the converter feed <NUM> comprises less than <NUM> parts by weight (more preferably less than <NUM> parts by weight, and even more preferably less than <NUM> parts by weight) of any added flux material, per <NUM> parts by weight of collector alloy, regardless of silica, calcium oxide, or magnesium oxide content.

The process <NUM> comprises: (a) in step <NUM>, placing a charge of a partially pre-oxidized PGM collector alloy <NUM> (<FIG>) in a converter pot <NUM> (<FIG>); (b) in step <NUM>, melting the charge of the partially pre-oxidized PGM collector alloy <NUM> in the pot <NUM>, e.g., using a burner assembly <NUM> (<FIG>), to form an alloy pool 122A (<FIG>); (c) in step <NUM>, periodically or continuously introducing a charge of converter feed <NUM> into the pot <NUM>; (d) in step <NUM>, injecting oxygen-containing gas <NUM> into the alloy pool to form slag 128B (<FIG>); (e) in preparation for one or more periodic non-final slag tappings, in step <NUM>, allowing alloy <NUM> entrained in the slag 128C to substantially settle into the alloy pool 122D as seen in <FIG>, e.g., for a period of no less than <NUM> minutes; (f) then in step <NUM>, tapping slag 128D from the pot <NUM>; (g) repeating step <NUM> in (d) one or more times followed by steps <NUM> and <NUM> until a final time; (h) following the final step <NUM>, in step <NUM>, tapping the slag 128E with entrained alloy <NUM> as seen in <FIG>.

The converter feed introduction step <NUM> in (c) and the oxygen-containing gas injection step <NUM> in (d) are preferably stopped for the periodic slag tapping steps <NUM> in (e) and <NUM> in (h). Preferably, the oxygen-containing gas injection step <NUM> is continued until the alloy pool 122E comprises <NUM> wt% iron or less, more preferably <NUM> wt% iron or less, by weight of the alloy pool. In any embodiment, all or part of the converter slag 128E recovered from the final slag tapping in (h) can be introduced to the converter feed <NUM>, e.g., in a later batch.

In a still further aspect, with reference to <FIG>, embodiments of the present invention provide a process 100B for recovering PGM from catalyst material, comprising: smelting a catalyst material <NUM> in a primary furnace <NUM> to form slag <NUM> and a first collector alloy <NUM>; recovering slag <NUM> from the primary furnace <NUM>; smelting the primary furnace slag <NUM> in a secondary furnace <NUM> to form a second collector alloy <NUM> in the secondary furnace <NUM>; recovering slag <NUM> from the secondary furnace <NUM>; recovering the first and second collector alloys <NUM>, <NUM> from the respective first and secondary furnaces <NUM>, <NUM>; introducing converter feed <NUM> comprising the first and second collector alloys <NUM>, <NUM> into a pot <NUM> holding a converter alloy pool <NUM>, wherein the first and second collector alloys <NUM>, <NUM> preferably comprise at least <NUM> wt% PGM, at least <NUM> wt% iron, and at least <NUM> wt% nickel, based on the total weight of the converter feed <NUM>; injecting oxygen-containing gas <NUM> into the converter alloy pool <NUM>; recovering converter slag <NUM> from the pot <NUM>; smelting at least a first portion <NUM> of the converter slag <NUM> in the secondary furnace <NUM> together with the primary furnace slag <NUM>; and recovering PGM-enriched nickel alloy <NUM> from the pot <NUM>. Optionally, a second portion <NUM> of the converter slag <NUM> is introduced to the converter feed <NUM> with the first and second PGM collector alloys <NUM>, <NUM> to the pot <NUM>. Preferably, the oxygen-containing gas injection is continued until the converter alloy pool <NUM> comprises <NUM> wt% iron or less, more preferably <NUM> wt% iron or less, by weight of the converter alloy pool.

Further still in another aspect, in reference to <FIG>, <FIG>, and <FIG>, embodiments of the present invention provide a TBRC <NUM> comprising an inclinable pot <NUM>; a burner assembly <NUM> for heating the pot <NUM>; fluid inlet and outlet connections 147a, 147b to circulate cooling fluid through a jacket <NUM>; a refractory lining <NUM> in the pot <NUM> for holding an alloy pool <NUM> (<FIG>); a motor <NUM> to rotate the pot <NUM>; and a lance <NUM> for injecting oxygen into the alloy pool <NUM>. Preferably, the TBRC <NUM> further comprises a plurality of temperature transmitters <NUM> operably connected to a plurality of temperature sensors <NUM> positioned in radially spaced relationship in the refractory lining <NUM> adjacent an interior wall <NUM> of the pot <NUM>. Preferably, the TBRC <NUM> further comprises a feed channel <NUM> to supply particles to a flame <NUM> from a burner <NUM> of the burner assembly <NUM>. In any embodiment, the TBRC <NUM> may further comprise a fume hood <NUM> and/or a water-cooled heat shield 121A.

In the following examples, process <NUM> according to <FIG> was used. Catalyst material <NUM> was smelted in electric arc furnace <NUM> having a nominal capacity of <NUM>/h (<NUM> tph), a transformer rated at <NUM> MVA, with a secondary voltage of <NUM> V and a secondary current of <NUM> A. Slag <NUM>, comprising mainly aluminosilicate, was recovered from the furnace <NUM>, granulated in water in granulator <NUM>, dried in rotary kiln <NUM>, and repackaged in bag-filling station <NUM>. The PGM collector alloy <NUM> was cast into molds <NUM>, solidified, and crushed in crusher <NUM> to -<NUM> mesh (-<NUM>/<NUM> in.

The dried slag <NUM> from the primary furnace <NUM> was smelted in second, finishing electric arc furnace <NUM> having a nominal capacity of <NUM>/h (<NUM> tph), a transformer rated at <NUM> MVA, with a secondary voltage of <NUM> V and a secondary current of <NUM> A. Slag <NUM> recovered from the furnace <NUM> was granulated in granulator <NUM> and recycled in step <NUM> for an appropriate use, e.g., as aggregate. The PGM collector alloy <NUM> from the secondary furnace <NUM> was cast into molds <NUM>, solidified, and crushed in crusher <NUM> to -<NUM> (<NUM>/<NUM> in.

A charge of partially pre-oxidized PGM collector alloy <NUM> was prepared from collector alloy <NUM> and/or <NUM> as described in the example. The pre-oxidized alloy <NUM> was placed in the pot <NUM> of a water-cooled TBRC <NUM> lined with an alumina-based ramming refractory, and melted with a gas burner <NUM> to a temperature of at least <NUM>. The pre-oxidized alloy pool was sufficient to inject oxygen below the surface of the alloy pool, generally filling about <NUM>-<NUM>% of the available volume of the pot <NUM>. A portion of the aluminosilicate slag <NUM> from the primary furnace <NUM> was placed on top of the alloy pool as refractory protectant <NUM> at the start of each oxygen injection cycle. Unless otherwise stated, the total amount of protectant <NUM> used for each TBRC operating cycle was <NUM>-<NUM> (<NUM>-<NUM> lbs), apportioned between oxygen injection cycles, e.g., following the initial alloy pool melt and each non-final slag tapping.

While the pot <NUM> was rotated, the burner <NUM> was shut off and oxygen <NUM> was injected into the alloy pool using lance <NUM> at a rate to maintain a temperature sufficient to avoid solidification of the alloy pool but at a sufficient rate to maintain the temperature in the alloy pool no higher than <NUM>, e.g., <NUM> to <NUM>, while circulating cooling water through the TBRC jacket. Unless otherwise noted the oxygen injection rate was <NUM><NUM>/h (<NUM> SCFM). The PGM collector alloy <NUM>, <NUM> from the furnaces <NUM>, <NUM> (<NUM> unless otherwise noted) and recycle slag <NUM>, <NUM> (<NUM> unless otherwise noted) that had been placed in hopper <NUM> was fed into the pot <NUM> via vibrating feeder <NUM> at a generally steady rate of <NUM>/h, except when stopped during slag tappings, unless otherwise noted. The pot <NUM> filled as slag was formed and the alloy pool grown by the feed into the pot <NUM>. When the volume of the pot <NUM> was filled sufficiently, the pot rotation, oxygen injection, and alloy feed were stopped. After waiting several minutes to allow phase separation and alloy disentrainment from the slag layer, slag <NUM> was tapped into molds <NUM> by tipping the pot <NUM>, taking care to avoid tapping any of the alloy phase, erring on the side of leaving some slag on the top of the alloy phase.

The oxygen injection and alloy feed into the remaining alloy pool were then resumed until the pot <NUM> was again filled, and slag <NUM> tapped as described above. The cycle was repeated several times until the alloy pool had grown to a desired volume for tapping. The final slag tapping just before tapping the alloy was performed promptly after stopping the oxygen injection and collector alloy feed, taking care that substantially all of the slag <NUM> was tapped, erring on the side of alloy entrainment in the slag. The PGM-enriched alloy <NUM> was then tapped into ingot molds <NUM>, cooled, and solidified.

After the slag molds <NUM> were cooled, the solidified slag <NUM> was fed through slag crusher <NUM> and magnetic separator <NUM>. The non-magnetic fractions from the final slag tapping and the earlier tappings were sorted into containers <NUM> and <NUM>, respectively. The non-magnetic fraction <NUM> was smelted in the secondary furnace <NUM> with the slag <NUM> from the primary furnace. The magnetic fractions <NUM> from all of the converter slag and the non-magnetic fraction <NUM> from the final slag tapping were placed in the feed hopper <NUM> with collector alloy <NUM> and/or <NUM> for a subsequent TBRC batch. The same result would have obtained if the entirety of the final slag tapping were placed directly in the hopper <NUM>, bypassing the magnetic separator <NUM>. Assays reported below were determined using a combination of inductively coupled plasma spectroscopy (ICP) and desktop X-ray fluorescence (XRF). Unless otherwise noted, typical assays are reported below.

Example <NUM>: Smelting catalyst material in primary furnace. In this example, catalyst material from automotive catalytic converters is smelted in the electric arc furnace <NUM>. Iron oxide is added as needed to provide a minimum iron content in the feed of at least <NUM> wt%, based on the total weight of the feed to the furnace <NUM>. Lime (CaO) is added in an amount of <NUM> wt%. After smelting, <NUM> tonne slag and <NUM> collector alloy are typically recovered, cooled, and solidified. The collector alloy and slag have the following typical assays set out in Tables <NUM> and <NUM>.

Example <NUM>: Smelting slags in secondary furnace. In this example, <NUM> tonne (<NUM> t) of the Example <NUM> slag from the primary furnace <NUM> and <NUM> (<NUM> t) of non-magnetic converter slag <NUM> from Example <NUM> (Table <NUM> below) are smelted in the furnace <NUM>. Metallurgical grade coke is added in an amount of <NUM> wt%. After smelting, <NUM> tonne (<NUM> t) slag and <NUM> collector alloy are recovered, cooled, and solidified. The collector alloy and slag have the typical assays set out in Tables <NUM> and <NUM>.

Example <NUM>: Pre-oxidation of collector alloy - starter alloy. In this example, <NUM> of a starter alloy from a previous starter alloy preparation cycle were loaded into the TBRC and melted after <NUM> using the burner <NUM>. The beginning starter alloy has the typical assay shown in Table <NUM>. The collector alloy (<NUM>) from Example <NUM> (Table <NUM>), recycle slag (<NUM>, or [<NUM>/(<NUM>+<NUM>)]*<NUM> = <NUM> parts recycle slag per hundred collector alloy), and refractory protectant (<NUM>, or [<NUM>/(<NUM>+<NUM>)]*<NUM> = <NUM> parts protectant per hundred collector alloy) were supplied to the TBRC. The refractory protectant was the furnace slag from Example <NUM> (Table <NUM>). The recycle slag has the typical assay as shown in Table <NUM>.

The oxygen injection rate during the converting was <NUM><NUM>/h <NUM> SCFM), and the slag was tapped several times, after waiting for several minutes to allow alloy disentrainment. The final slag tapping was done in the same way, which it is noted is different from the usual converter cycle to produce PGM-enriched alloy product where slag contamination of the alloy is minimized. After <NUM> of oxygen injection, corresponding to <NUM>% oxidation, the alloy was tapped, solidified, and crushed for use as the starter alloy in subsequent TBRC converting cycles. The product starter alloy has the typical assay as shown in Table <NUM>.

Example <NUM>: Converting with starter alloy. In this example, <NUM> of the starter alloy produced from Example <NUM> (Table <NUM>) were loaded into the TBRC and melted after <NUM> using the burner <NUM>. The converter feed was made up of collector alloy (<NUM>) from Example <NUM> (Table <NUM>), and the recycle slag (<NUM>, or [<NUM>/(<NUM>+<NUM>)]*<NUM> = <NUM> parts recycle slag per hundred collector alloy) used in Example <NUM> (Table <NUM>). Refractory protectant (<NUM>) supplied to the TBRC was the furnace slag from Example <NUM> (Table <NUM>), or [<NUM>/(<NUM>+<NUM>)]*<NUM> = <NUM> parts protectant per hundred collector alloy. The oxygen injection rate during the converting was <NUM><NUM>/h (<NUM> SCFM), and the slag was tapped several times as needed, after waiting for several minutes each time to allow alloy disentrainment. The final slag tapping was started within <NUM> minutes of stopping oxygen injection without waiting for complete alloy disentrainment. After <NUM> of oxygen injection, corresponding to <NUM>% iron conversion, the alloy was tapped and formed into ingots. The PGM-enriched alloy (<NUM>) has the typical assay as shown in Table <NUM>.

The slag tappings were cooled, solidified, crushed, milled, and magnetically separated. The magnetically susceptible fraction was collected and combined with the non-magnetic fraction of the final slag tapping (<NUM> total) for use as recycle slag in a subsequent converting cycle. The non-magnetic fraction of the non-final slag tappings were collected (<NUM> total) for smelting in the secondary furnace similarly to example <NUM>. The recycle slag and smelting slag have the typical assays shown in Tables <NUM> and <NUM>:.

This example shows that PGM collector alloy can be enriched with a high oxygen injection rate without a large amount of added flux materials, using only recycle converter slag from a previous cycle and primary furnace slag as a refractory protectant. This example demonstrates the use of partially pre-oxidized starter alloy to reduce the TBRC cycle operation time and improve PGM enrichment. This example also demonstrates the feasibility of converting PGM collector alloy using a water-cooled, jacketed TBRC.

Example <NUM>: Converting with flame pre-oxidized collector alloy. In this example, <NUM> of collector alloy were flame pre-oxidized using the burner <NUM>. The collector alloy was loaded into the hopper for pre-oxidation during a night shift. The two-burner assembly <NUM> was set at <NUM> MMBtu/h each (<NUM> MMBtu/h total) with <NUM>% excess oxygen to produce a flame temperature greater than <NUM>. The collector alloy was fed into the TBRC using an apparatus similar to that shown in <FIG> so that the particles passed through the flame and fell into the TBRC, forming a coating on the refractory. The next morning, the pre-oxidized collector alloy was melted after <NUM> by increasing the firing rate of the burners to <NUM> MMBtu/h total.

Next, the converter feed was made up of collector alloy (<NUM>) from Example <NUM> (Table <NUM>), and recycle slag (<NUM>, or [<NUM>/(<NUM>+<NUM>)]*<NUM> = <NUM> parts recycle slag per hundred collector alloy) produced from Example <NUM> (Table <NUM>). The refractory protectant (<NUM>) was furnace slag from Example <NUM> (Table <NUM>), or [<NUM>/(<NUM>+<NUM>)]*<NUM> = <NUM> parts protectant per hundred collector alloy. The oxygen injection rate during the converting was <NUM><NUM>/h (<NUM> SCFM), and the slag was tapped several times as needed, after waiting each time for several minutes to allow alloy disentrainment. The final slag tapping was started within <NUM> minutes of stopping oxygen injection without waiting for complete alloy disentrainment. After <NUM> of oxygen injection, corresponding to <NUM>% iron conversion, the alloy was tapped and formed into ingots. The PGM-enriched alloy (<NUM>) has the typical assay as shown in Table <NUM>.

The slag tappings were cooled, solidified, crushed, milled, and magnetically separated. The magnetically susceptible fraction was collected and combined with the non-magnetic fraction of the final slag tapping (<NUM> total) for use as recycle slag in a subsequent converting cycle. The non-magnetic fraction of the non-final slag tappings was collected (<NUM> total) for smelting in the secondary furnace (see Example <NUM>). The recycle slag and smelting slag have the typical assays shown in Tables <NUM> and <NUM>.

This example shows that partial pre-oxidation by flame oxidation of collector alloy, relative to Example <NUM>, allows a larger quantity of the collector alloy to be processed in the TBRC with higher oxygen injection rates and a shorter cycle time to obtain a higher purity of enriched PGM alloy.

Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments. Accordingly, it will be appreciated by the skilled person that modifications may be made within the scope the following claims.

Claim 1:
A process for converting platinum group metal, PGM, collector alloy, comprising the steps of:
(a) introducing a converter feed (<NUM>) into a pot (<NUM>) of a converter (<NUM>) holding a molten alloy pool (<NUM>), preferably comprising nickel, wherein the converter feed (<NUM>) comprises:
(i) <NUM> parts by weight of a collector alloy comprising no less than <NUM> wt% PGM, no less than <NUM> wt% iron, and no less than <NUM> wt% nickel, and preferably no more than <NUM> wt% sulfur and no more than <NUM> wt% copper, based on the total weight of the collector alloy; and
(ii) if an added flux material comprises <NUM> wt% or more of silica and <NUM> wt% or more of calcium oxide, magnesium oxide, or a combination of calcium oxide and magnesium oxide, by weight of the added flux material, less than <NUM> parts by weight of the added flux material;
(b) injecting oxygen-containing gas into the alloy pool (<NUM>) to convert iron and one or more other oxidizable elements from the collector alloy to the corresponding oxides and enrich PGM in the alloy pool (<NUM>), wherein the introduction of the converter feed (<NUM>) and the injection of the oxygen containing gas are at least partially concurrent;
(c) allowing a slag comprising the iron oxide to collect in a low-density layer (<NUM>) above the alloy pool (<NUM>);
(d) tapping the low-density layer to recover the slag from the converter (<NUM>); and
(e) tapping the alloy pool (<NUM>) to recover the PGM-enriched alloy.