MATERIAL

FIELD OF INVENTION

THIS INVENTION relates to a method of, and process for treating a silicon carbide (SiC) bearing material, in particular an automotive catalyst containing a catalyst supported on a substrate made from or containing SiC (in other words, a catalyst made with SiC substrates).

BACKGROUND OF THE INVENTION

Landfills have restrictions concerning the type of materials that can be disposed thereon. Although the disposal of catalytic converters which may house either spent catalyst components, or “off-specification” catalyst components, or “as-new” catalyst components, may not be a problem in most landfills, it will be appreciated that most catalyst components contained in the catalytic converters contain precious and noble metals, such as, PGMs including platinum, palladium, and rhodium, which are extremely rare to locate in natural resources and would be wasted if disposed in landfills and not recovered using well known pyrometallurgical and hydrometallurgical processes.

Usually, the pyrometallurgical treatment of crushed catalyst made from SiC substrates is carried out in a primary smelting furnace that may be either an electric thermal pyrometallurgical furnace or an autogenous, oxygen injected, bath smelting furnace. The catalyst components are fed to the smelting furnace that is arranged to form a dense sulfide matte or alternatively an iron carrier metal containing the precious PGMs, which carrier metal or matte will then be processed downstream using hydrometallurgical techniques. The catalyst components would need to be physically pre-processed and adequately sized. The substrates of the catalytic convertors are usually removed from the casing of the catalytic convertors and are thereafter subjected to crushing and/or milling into a particular size.

Unfortunately, feeding physically pre-processed catalysts into a smelting furnace without subjecting them to a pre-treatment step usually poses a problem in the operation of smelter furnaces dedicated for the recovery of PGMs. For example, it is known that a carbon content in catalysts, typically catalyst made from SiC substrates, of greater than 2 % can cause issues with the operation of the smelting furnaces. The high carbon content is responsible for the conversion of iron oxide in the slag phase into elemental iron, which settles into the iron carrier metal or matte layer. In operations with either iron or sulfide matte as a carrier, the furnace temperatures will increase rapidly and potentially exceed the high temperature limitations of the furnaces. In electric furnaces, the depletion of iron in the slag phase results in more resistance for the electric power running through the slag, resulting in higher temperatures in both the upper slag layer and in the denser carrier metal or matte layers in the furnace. As a result of the change in the electrical resistance of the slag layer, the computer-controlled operating system of the electric smelting furnace will automatically force the electrodes deeper into the furnace bath to compensate for the change in the resistance in the slag. When the electrodes are driven deeper into the bath, this results in more heat going into the matte layer, and this puts the furnace at a risk for a run out (i.e., leak) if the temperatures exceed the normal operating temperatures for the furnace. In addition to elemental carbon presence in the catalyst posing a problem in electric smelting furnaces, the presence of silicon carbide (SiC) in the catalyst can also pose a serious issue with the safe and proper operation of electric smelting furnaces. The silicon carbide compound, under normal smelting conditions, usually breaks apart into the individual silicon and carbon molecules. At the normal smelting conditions, silicon acts as a reducing agent (just like carbon, only much stronger at 3 times the reduction rate of elemental carbon) which increases the iron removal rate from the slag. Not only does this deplete the iron in the slag but it increases the iron concentration in the iron carrier metal or matte phase (as the iron concentration increases, the viscosity increases making it difficult to remove matte from the furnace). The chemical reaction involving the reduction of silicon carbide is quite exothermic which will increase temperatures rapidly and the furnace thermal balance would be difficult to control. Because of the limitations involved in using catalyst which are made from silicon carbide substrates and have a high carbon content, electric smelting furnaces are limited in the quantity of carbon/silicon that can be contained in a catalyst.

The present invention seeks to address at least some of the abovementioned problems.

SUMMARY OF THE INVENTION

In view of the deficiencies of the current available processes used to extract precious metals from catalysts with silicon carbide substrates, a more efficient and economical means must be developed. The present invention is related to a method of and a process for treating a catalyst made from SiC substrates in order to reduce the amount of carbon in the substrate, so that the end product can be fed into a smelting furnace without posing any of the problems mentioned above.

In this specification, the term “automotive catalyst made with silicon carbide (SiC) substrates” means a catalyst supported on a substrate made from or containing SiC.

In the context of the present invention, the term “SiC bearing material” means a SiC substrate supporting a catalyst. Therefore, this term and “automotive catalyst made with SiC substrates” may be used interchangeably.

The catalyst may be a spent/deactivated catalyst, an “off-specification” catalyst, or a “as-new” catalyst of a catalytic convertor manufactured with a silicon carbide monolith. The term “off-specification” catalyst shall mean a catalyst that is contaminated or otherwise fails to meet the applicable industrial specifications used to qualify the quality and properties of the catalyst.

The term “as-new” catalyst shall mean a catalyst that is not spent/deactivated but is still in a good condition for re-use.

The catalyst may contain precious metals and/or noble metals.

In the context of the present invention, it will be understood that the term “melt pool” typically refers to a dense iron or sulfide matte layer that settles to the bottom of the vessel and an immiscible less dense slag layer forms on top of the iron or sulfide matte layer. However, it will be appreciated that the melt pool may initially comprise of slag and overtime may then comprise of the sufide matte and the slag.

According to broad first aspect of the invention, there is provided a method for treating a SiC bearing material, the process including: generating a flame having a predetermined flame velocity and producing a predetermined amount of heat, wherein the generated flame and heat are for burning and oxidizing the SiC bearing material in the presence of at least a fluxing agent, thus producing a carbon containing gas product and a slag product.

In particular, the method of treating the SiC bearing material may include: feeding feed material into a melt pool contained in a vessel, wherein the feed material includes the SiC bearing material along with at least a fluxing agent; and delivering an oxyfuel gas into the vessel above the melt pool to generate a flame inside the vessel, wherein the flame is generated above the melt pool and is arranged to burn and oxidize the SiC bearing material, thus forming a carbon containing gas and a slag.

The oxyfuel gas may be delivered into the vessel by a lance having a nozzle tip arranged at a predetermined spacing above the melt pool.

The flame may have a predetermined flame velocity to ensure that the flame is separated from the tip of the lance and to cause agitation of the melt pool. The oxyfuel gas may be a mixture of an oxygen carrying gas flowing through the lance at a predetermined velocity and a fuel gas flowing through the lance at a predetermined velocity.

In another version, the oxygen carrying gas and the fuel gas may be delivered separately into the vessel, for example, through the same lance.

The oxygen carrying gas may comprise of at least 95% of oxygen. It will be appreciated therefore that the ejection of the oxyfuel gas or oxygen carrying gas into the vessel creates an oxidizing environment within the vessel.

The fuel gas may be natural gas, butane, propane or a mixture of natural gas, butane and propane.

In feeding the feed material into the melt pool, droplets of the melt pool may form and may ascend above the surface of the melt pool along with splashes of the melt pool, a reaction zone may be defined in the region above the melt pool where the splashes project and the droplets ascend.

In the reaction zone, the flame may heat the melt pool, feed material and oxygen (obtained from the oxyfuel gas and which generates an oxidizing environment within the vessel) thereby promoting the oxidation of the SiC bearing material contained in the feed material.

Typically the oxidation of the SiC bearing material will initiate as the feed material is ejected from the lance and interacts with the flame, and the oxidation will continue as the feed material is injected into the melt pool and causes droplets of the melt pool to ascend above the upper surface of the melt pool into the reaction zone, which droplets may carry the feed material and may be subjected to the heat from the flame.

It will also be appreciated that the flame velocity may cause the melt pool to be agitated, which agitation may further promote the oxidation of the SiC bearing material.

The melt pool may comprise of slag, wherein the slag may comprise calcium aluminosilicate. The temperature of the melt pool prior to feeding the feed material into the melt pool may be about 1350 °C (2460°F).

However, the melt pool may, as the oxidation of the SiC bearing material continues and depending on the composition of the feed material, transition into a denser tramp metal with a less dense slag above or alternatively a denser sulfide matte (CU2S + NiaS2) with a less dense slag above.

The feed material may also include a cooling agent. The feed material may optionally include matte that is exogenous to the oxidation step (i.e., not formed by the oxidation step).

The feed material may be a blended feed material. Accordingly, the method may include a prior step of blending the SiC bearing material, fluxing agent, cooling agent, and optionally the exogenous matte.

Alternatively, the method may include co-feeding the SiC bearing material, fluxing agent, cooling agent, and optionally the matte into the melt pool.

The feeding of the feed material into the melt pool may be effected by gravity feeding.

The feeding may be effected by injecting, by means of a lance, the feed material into the melt pool.

The lance used to deliver the oxyfuel gas into the vessel may be the same lance used for injecting the feed material into the melt pool.

In generating the flame, oxyfuel gas flowing at a predetermined rate may be ejected through a tip of a lance that is arranged to face the melt pool and spaced away from the melt pool by a predetermined amount of spacing, the lance may accordingly generate the flame from the ejected oxyfuel gas for providing a predetermined amount of heat for burning and oxidizing the SiC bearing material.

The lance may be arranged in an inclination with respect to the vertical and a tip thereof may be spaced away, by a predetermined amount of spacing, from the upper surface melt pool.

The lance may be arranged vertically and a tip thereof may be spaced away, by a predetermined amount of spacing, from the upper surface of the melt pool.

The upper surface of the melt pool may be inclined relative to the vertical.

Alternatively, the upper surface of the melt pool may be arranged horizontally.

The oxidation step may include arranging the lance such that a nozzle tip thereof faces the melt pool, wherein the nozzle tip is disposed above the melt pool and arranged to maintain a predetermined spacing from the melt pool so as to create a reaction zone between the tip of the lance and surface of the melt pool, such that, in use, when the jet of oxyfuel gas ejected/blasted from the lance nozzle tip is combusted, the tip produces the flame having desired characteristics to provide a predetermined amount of heat for burning and oxidizing the SiC bearing material in the melt pool and/or reaction zone.

The method may further include the step of agitating the melt pool during the oxidation step.

In one embodiment, the vessel may be in the form of a rotary kiln.

According to a second aspect of the invention there is provided a furnace arrangement for treating a SiC bearing material, the furnace arrangement comprising: a vessel defining a chamber for holding a melt pool, in use; and a lance locatable within the furnace, the lance having a tip that is spaced from and arranged to face the melt pool, the tip being arranged to maintain a predetermined spacing from the melt pool such that, in use, when a jet of oxyfuel gas, flowing at a predetermined velocity, ejected from the lance tip is subsequently combusted, the tip produces a flame having desired characteristics to provide a predetermined amount of heat for burning and oxidizing the SiC bearing material that is in the melt pool and/or injected into the melt pool, in use.

The lance may have a bluff body face.

The lance may be adjustable, i.e., retractable relative to the height of the melt pool. The lance may be arranged to feed solid feed material and the oxyfuel gas into the vessel.

The furnace arrangement may comprise agitation means for agitating the melt pool, in use.

The agitation means may be a rotation means connected to the vessel for rotating the vessel about its rotational axis, which rotation will consequently result in the agitation of the melt pool.

The furnace arrangement may comprise a displacement means arranged to displace, by tilting movement, the furnace from a rest configuration to either a first or second tilted positions for discharging the slag and matte, respectively.

The displacement means may be by means of a hydraulic drive unit.

The furnace may comprise a tap hole on a side thereof for dispensing the matte or tramp metal when displaced to the second tilted position.

The furnace may comprise an opened upper end defining a mouth of the furnace through which the lance is insertable into the chamber of the furnace, the furnace being arranged to dispense/discharge slag when displaced to the first tilted position. According to another aspect of the invention, there is provided a use of a slag produced in accordance with the first aspect of the invention as a feed material for a smelting furnace.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be described in more detail by way of non-limiting example, with reference to the process for implementing the method of the invention, and to the accompanying drawings, in which:

Figure 1 shows a process block flow diagram for implementing a method of treating a SiC bearing material in accordance with an embodiment of the invention;

Figure 2 shows a process block flow diagram for implementing a method of treating a SiC bearing material in accordance with another embodiment of the invention;

Figure 3 to 5 show a furnace arrangement in accordance with the invention, the furnace arrangement including a furnace and a lance, the furnace being shown in a rest oxidation configuration/position, slag pouring configuration/position and matte pouring configuration/position, respectively;

Figure 6 shows a ternary phase diagram for the CaO - SiO2 - AI2O3 system in accordance with the present invention;

Figure 7 shows a furnace diagram with an exemplary lance position, reaction zone and taphole arrangements; and

Figure 8 shows a detailed process flow in accordance with the invention. DETAILED DESCRIPTION OF THE INVENTION

The disclosure may be understood more readily by reference to the following description taken in connection with the accompanying Figures and examples, all of which form a part of this disclosure. It is to be understood that this disclosure is not limited to the specific products, methods, conditions or parameters described and/or shown herein, and that the terminology used herein is for the purpose of describing particular examples by way of example only and is not intended to be limiting of any claimed invention. Similarly, unless specifically otherwise stated, any description as to a possible mechanism or mode of action or reason for improvement is meant to be illustrative only, and the disclosure herein is not to be constrained by the correctness or incorrectness of any such suggested mechanism or mode of action or reason for improvement.

In the disclosure the singular forms “a,” “an,” and “the” include the plural reference, and reference to a particular numerical value includes at least that particular value, unless the context clearly indicates otherwise. Thus, for example, a reference to “a material” is a reference to at least one of such materials and equivalents thereof known to those skilled in the art, and so forth. When a value is expressed as an approximation by use of the descriptor “about,” it will be understood that the term “about” indicates approximations that can vary depending on the desired properties sought to be obtained by the disclosed subject matter and is to be interpreted in the specific context in which it is used, based on its function. The person skilled in the art will be able to interpret this as a matter of routine. In some cases, the number of significant figures used for a particular value may be one non-limiting method of determining the extent of the word “about.” In other cases, the gradations used in a series of values may be used to determine the intended range available to the term “about” for each value.

Where present, all ranges are inclusive and combinable. That is, references to values stated in ranges include every value within that range.

Referring to Figures 1 and 2 of the drawings, which shows a process for treating a SiC bearing material in accordance with a method of the invention, the process is designated generally by reference numeral 10.

The process 10 includes the following stages:

- a mixing/blending stage 12;

- an oxidation stage 14;

- a matte granulation stage 16;

- a slag granulation stage 18;

- a smelting stage 20; and

- an off-gas treatment stage 22.

The process 10 also includes the following feedlines, transfer lines, and exit lines:

- a SiC bearing material feedline 24;

- a fluxing agent feedline 26;

- a matte feed line 28; coolant agent feedline 30; silica sand feed line 32;

- a blended feed material transfer line 34;

- an oxygen feedline 36;

- a fuel gas feed line 38;

- a matte product transfer line 40;

- a matte granules exit line 42;

- a slag product transfer line 44;

- a slag granules transfer line 46;

- an off-gas line 48;

- a dust exit line 50; and

- a fume gas exit line 52.

Referring to Figures 1 and 2, there is provided a process 10 in accordance with the present invention for treating a SiC bearing material, i.e., an automotive catalyst made with silicon carbide (SiC) substrates.

The process 10 includes a material blending stage (comprising a blending unit or blender) 12. In the blending stage 12, particulate automotive catalyst made with silicon carbide (SiC) substrates (feed line 24) is mixed with one or more fluxing agents (feed line 26), as described more completely below. The catalyst may arrive at the blending stage 12 in a raw form and require processing to facilitate blending. Such processing may include taking the catalyst material (i.e., the automotive catalyst made with silicon carbide (SiC) substrates) and processing it to a suitable particle size or consistency for mixing. Shredding, crushing, and grinding may be carried out in a sequential operation by which the lump size is reduced step by step. Screening, which is a mechanical separation of particles according to size, may be carried out in conjunction with the crushing and grinding. Alternatively, the automotive catalyst made with silicon carbide (SiC) substrates 24 may be processed before arriving at the blending stage 12, such that the automotive catalyst made with silicon carbide (SiC) substrates is provided to the blending stage 12 in suitable form for blending.

In the blending stage 12, the particulate automotive catalyst made with silicon carbide (SiC) substrates 24, having a nominal particle size of about -5mm (-3/16”), is blended with one or more fluxing agents 26, a coolant agent 30, silica 32 and matte 28, in the case of the process shown in Figure 1 , which may be obtained from a smelter stage 20 downstream or may be outsourced.

The feed blend recipe is formulated according to:

24 - Automotive Catalyst Made with Silicon Carbide (SiC) Substrates: Mass is determined based on production plans and furnace lining condition;

26 - Fluxing Agent: Preferably lime (CaO) having a particle size of about -1/8” is fed at about 75% of the mass of the automotive catalyst 24. The automotive catalyst may have varying amounts of alumina and the flux ratio may be changed based on slag basicity and to some extent varied in consideration of the silica sand 32 addition.

30 - Coolant agents: Various materials are fed to maintain a furnace slag temperature range of about 1 ,350 °C (2,460 °F) to 1 ,550 °C (2,820 °F). Feldspars (such as, plagioclase feldspars) which may have similar chemistry to slag 44 produced from the oxidation stage 14 may also be sourced as a coolant agent.

28 - Matte: a matte (CU2S and Ni2S3), which provides a good collector for PGMs and precious metals, of up to about 15% (by mass) of the automotive catalyst made with silicon carbide SiC substrates 24 is fed into the blending stage 12.

32 - Silica sand: Slag chemistry may be optimized by controlling the addition of silica sand. The automotive catalysts made with silicon carbide SiC substrates 24 has a composition of alumina AI2O3 of about 10% to 20% by weight. Referring to Figure 6, the lime addition and silica addition reduce the melting point of the alumina AhOs that may be about 2020 °C (3670 °F).

The blended material is transferred via product transfer line 34 into the oxidation stage 14 in which the removal of carbon from the automotive catalyst made with silicon carbide substrates will be effected. The oxidation stage 14 comprises a furnace arrangement 100 including a refractory lined, vertical rotary furnace (i.e. vessel) 102, shown in Figures 3 to 5, which is, in use arranged at an inclination with respect to the vertical. The inclination of the rotary furnace 102 is such that the mouth 106 of the furnace 102 and a base thereof are arranged at an angle relative to the vertical, which arrangement is preferred to ensure that the melt pool that forms inside the furnace 102 is also arranged at an incline within the vessel.

The furnace 102 defines a chamber 100A for holding a melt pool 100B, as shown in Figure 7, which melt pool has an upper surface 100C which is also arranged at an inclination with respect to the vertical. The rotary furnace 102 has an axis of rotation A and is arranged to rotate in either direction as shown by rotation arrows B and C.

The furnace 102 is typically arranged to operate between about 1350 °C (2460 °F) and 1550 °C(2820 °F). The furnace arrangement 100 also includes a water cooled, retractable lance 104 which is fed into the chamber 100A of the furnace 102 via an opened mouth 106 of the furnace 102 at a top end of the furnace 102. As shown in Figure 7, the lance 104 is arranged at an inclination with respect to the vertical and is disposed substantially at the center of the chamber 100A above the melt pool. It is envisaged that the lance 104 can be offset from the center of the furnace 102 and may be arranged in other configurations relative to the upper surface of the melt pool. By tilting the furnace 102 and accordingly arranging the lance 104 at an angle as well, as shown in Figure 7, the surface area for the SiC and/or melt pool is increased and its exposure to the oxidative atmosphere (created by the oxygen ejected/blasted from the lance 104 into the vessel 102) is also increased. The furnace 102 further includes a tapping hole 108 defined on one of the sides of the furnace 102, as shown in Figures 3 to 5 and 7. As shown in Figure 3, an off-gas duct 1 10 covers the mouth 106 of furnace 102 for collecting off-gases produced from the oxidation stage 14. The blended material, in transfer line 34, is fed either via gravity through feed ports (not shown) in the roof of the furnace or through the mouth 106 of the furnace, or by injection through the water cooled, retractable lance 104 inserted into the chamber via the mouth 106 of the vessel (i.e. furnace) 102, as shown for example in Figures 3 to 5.

As mentioned above, the furnace 102, shown in Figures 3 to 5, is typically cylindrical and is constructed with a steel shell and an internal refractory lining.

A technical grade of oxygen of about 95% purity and fuel gas, such as, natural gas, butane, or propane, are delivered into the furnace 102, of the oxidation stage 14 via feed lines 36 and 38, respectively, by the same retractable water-cooled lance 104 that is used to feed the blended feed material 34 into the vessel 102, as shown in Figures 1 to 3. The feeding and delivery of the oxyfuel gas (i.e., oxygen and natural gas) into the chamber 100A generates a high velocity flame 100D and extreme temperatures at the tip 105 of the lance 104 as shown in Figure 7.

The process 10 has the flexibility to operate as a batch process however, continuously feeding the blended feed material 34 pneumatically through the lance 104 results in a more stable and efficient carbon burning (i.e., oxidation) process.

Once a melt pool of molten calcium aluminosilicate slag is initially formed and a minimum temperature of about 1350 °C(2460 °F) is established in the furnace 102, the oxygen and fuel gas flow rates through the lance 104 are raised to operating conditions, such as those shown in the table below, which are dependent on the size of the furnace 102, the configuration (i.e., size) of the lance 104, the blended feed rate in line 34 injected into the furnace 102 via the lance 104, and the oxygen gas and fuel gas (i.e. oxyfuel gas) feed rates in lines 36 and 38 injected into the furnace 100 via the lance 104.

Although not shown, it is envisaged that the blended feed 34 may be fed into the furnace 102 via a separate solid injection lance or by other injection means, for example a tuyere. The lance 104 in this envisaged embodiment may be an oxyfuel burner lance that is arranged to provide oxygen into the furnace and generate a flame in the vessel 102 when combusted with the natural gas flowing through the same lance 104.

In the oxidizing stage 14, the carbon component of the silicon carbide (SiC) will oxidize rapidly reporting to the furnace off-gas line 48 as carbon monoxide (CO) and carbon dioxide (CO2) while the silicon oxidizes to silica SiO2 and forms a slag. The oxidation process continues, in the oxidation stage 14, until the furnace 102 approaches its volumetric capacity and the feed is temporarily suspended. Although not shown clearly in the drawings, the furnace 102 may be continuous rotated, about its rotation axis A in either direction B or C, as shown in Figure 7, in order to agitate the melt pool 100B as the oxidation process proceeds.

Referring to Figures 3 to 5, the furnace 102 will be displaced, by tilting, from a rest, blowing position to a slag pouring position and a matte pouring position. As shown in Figure 3, in the rest, blowing position, the furnace is arranged angularly with respect to the vertical and the oxyfuel gas in lines 36 and 38 and the blended feed in line 34 are fed through the lance 104 into the furnace 102. The SiC bearing material in the feed material 34 is oxidized in the melt pool and/or reaction zone (which will be described below) by the high velocity flames generated at the tip 105 of the lance 104. The high velocity flames may have, for example, a minimum flame velocity of about 100 ft/sec (30.5 m/sec). It will be appreciated by those skilled in the art of the invention that the minimum flame velocity mentioned herein is only exemplary and the scope of the preset invention should not be limited to this exemplified value since it is envisaged that other lower values may be used as long as they achieve the objects of the present invention.

In the slag pouring position, as shown in Figure 4, the furnace is tilted to allow the slag 44 to be discharged from the furnace 102 through the opened mouth 106 of the furnace 102 into a slag pot 112. In the matte pouring position, as shown in Figure 5, the furnace 102 is further tilted in the opposite direction to discharge the matte, containing precious metals and noble metals contained in the catalyst made from SiC substrates, through the taphole 108 provided on the side of the furnace 102, into a matte collecting pot 114.

In the case of the process 10 shown in Figure 2, the furnace 102 will not be tilted to the matte pouring position as only slag is produced by the process 10. However, as the operation of the process 10 continues, a matte obtained from the smelter stage 20 downstream may be included in the blending stage 12 as described above in order to form a melt pool comprising both of slag and matte, as described above in relation to Figure 1 .

The tilting of the furnace 102 as mentioned above from the rest position to the slag pouring position and the matte pouring positions may be effected by tilting means such as, a hydraulic drive unit (not shown). The cycle is then typically repeated with occasional operator intervention required to take temperatures, inspect the furnace 102 and manipulate the insertion of the lance 104 as required. The melting point of the silicon carbide (SiC), alumina and trace levels of other metal oxides is considerably higher than the operating temperature of the furnace 102. The fluxing agents 24 and silica 32 formulated in the feed blending stage 12 serve to lower the melting point of the furnace contents and a mixed bath (i.e., melt pool) of molten slag and molten metals or matte are formed. Because the molten metals and matte are denser than the slag, they will sink under gravity and settle out to form a pool of molten metal at the base of the furnace 102 thereby leaving the slag on top of the molten metal.

The unique combination of the oxyfuel gas velocity, lance tip configuration (i.e., lance nozzle tip diameter size), energy delivery supplied by the flame and the energy/heat generated in the reaction zone, and the agitation of the melt pool by the flame and/or continuous rotation of the vessel 102, results in continuous carbon oxidation without forming accretions on the lance 104 or causing a premature failure of the lance 104.

A reaction zone is formed between the tip 105 of the lance 104 and the upper surface 100C of the melt pool 100B, as shown in Figure 7. Generally, as the blended feed material 34 is fed into the melt pool 100B during the oxidation process, a high temperature reaction zone is formed directly under the lancel 04. It will be appreciated that the lance tip 105 is positioned above the melt pool by a predetermined amount of spacing so that the resultant flame velocity of the flame would be able to agitate the melt pool and accordingly cause oxidation of the SiC bearing material contained in the melt pool.

As the feed material is ejected from the lance 104, the feed material 34 is subjected to the high flame temperature as well as the flame from the tip 105 of the lance 104 which causes the SiC bearing material to oxidize or partly oxidize. As the feed material 34 descends and injects into the melt pool 100B, some of the melt pool 100B will project above the upper surface 100C of the melt pool 100B in the form of splashes and droplets carrying the feed material. The splashes and droplets in the reaction zone will be subjected to the flame temperature and the flame 100D. The flame 100D generated from the tip 105 of the lance 104 would then heat up the feed material in the reaction zone resulting in the oxidation of the silicon and carbon in the SiC bearing material.

During the oxidation reaction of the SiC, the CaO fluxing agent will form a slag that will be stripped away from the SiC surface and the oxidation of the silicon and carbon will continue. The oxidation will continue as the droplets and splashes descend back into the melt pool and further continue as a result of the agitation of the melt pool 100B by the flame velocity and the heat in the reaction zone. Referring to the table below, estimated furnace size, feed rates and lance configurations have been developed based on extensive testing and have shown that the use of the high velocity flames obtained from the lance tip can aid in the oxidation of carbon in an automotive catalyst made from SiC substrates. In the present invention, reference to a lance generally refers to commonly known burner lances which are generally used in metallurgical furnaces. These lances are not consumable and are arranged to feed both solid feed material and an oxyfuel gas through them. These lances generally have a bluff body face and have been developed to achieve a separated flow at their tips.

The slag 44 produced in the oxidation stage 14 by the furnace 102 may have properties resembling those of naturally occurring calcium-alumina-silicate minerals, coded as 190401 in the European Waste Catalogue (EWC). The compositions of the slag 44 may differ with respect to phase and may either be anorthite or gehlenite. The base slag is an AI2O3, CaO, SiO2 slag. The slag 44 obtained from the oxidation stage 14 may further contain noble metals and precious metals which were contained in the catalyst made from SiC substrates.

As mentioned above, one or more fluxing agents 26 were added in feed material 34 in order to give the slag the desired melting point, viscosity, density, or chemical properties. The fluxing agents 26 may be formulated to lower the melting temperature as well as improve viscosity of the molten slag. In the present invention, lime (CaO) was preferably used as the fluxing agents 26. However other fluxing agents such as, one or more of CaSO4 and CaCOa could also be used either alone or in combination with the other fluxing agents mentioned herein or with the preferred lime.

The melting point for the slag can be predicted to some extent with the use of ternary phase diagrams presented in Figure 6. The silica (SiO2), lime (CaO) and alumina (AI2O3) content determine the phase formation and therefore liquidus temperature (i.e., melting point) and viscosity. Typical automotive catalyst made with silicon carbide (SiC) substrates 24 which are blended with lime 26 at about 75% of the weight of the automotive catalyst made with silicon carbide (SiC) substrates 24 will form slag in the gehlenite phase boundary. Referring again to Figure 6, silica (SiO ₂ ) 32 was added as required in the blending stage 12 to form a lower melting point anorthite phase slag.

One critical aspect of the invention was the development of the feed flux selection and the lance 104 reaction zone characteristics in the furnace 102. Silicon carbide (SiC) has many unique characteristics and the compounds propensity to form a thin silica (SiO2) protective layer at high temperatures under oxidizing conditions may be one reason the material is suitable in the production of certain catalytic converters. As related to the discovery of the present invention, active oxidation of silicon carbide (SiC) occurs at oxygen pressures of less than about 1 (one) Bar (14,7 psi), according to the following equations:

SiC(s) + O (g) = SiO (I ) CO(g )

In active oxidation, the SiO formed gets vaporized after its formation leading to loss of mass. Passive oxidation proceeds at oxygen pressures close to one Bar (14.7 psi), according to the following reaction:

SiC(s) + 3/2 O ₂ (g) = SiO ₂ (s) + CO(g), and promotes the formation of a protective layer around the SiC.

The silica (SiO ₂ ) formed during passive oxidation can be deposited over the surface of silicon carbide preventing further destruction of the SiC. Such protective action continues up to the melting point of silica (SiO ₂ ), about 31 10 °F (1710 °C). The test work completed during the development of the process 10, in particular the oxidation of the SiC in the furnace 102, identified the following critical basis of design:

• Oxygen pressure, and lance tip gas velocities (i.e., velocity of the jet of oxyfuel gas ejected from the lance tip);

• Fuel proportioning, i.e., natural gas to oxygen ratios;

• Lance tip to top of bath (i.e., melt pool) optimum dimension (i.e., spacing between lance tip and the top of the bath);

• Rotation of the vessel/agitation of the melt pool to promote oxidation; and

• Flux composition.

It was found that the operation of the lance 104 impacted the effectiveness of the SiC oxidation. The critical parameters for optimizing carbon burning (i.e., oxidation of the carbon in the SiC) included:

Lance Insertion Position: The manipulation of the lance 104 insertion depth/height into the furnace 102 may consider the melt pool depth (i.e., position of the tip 105 of the lance relative to the upper surface 100C of the melt pool), blended feed material 152 rates, and total oxyfuel and blended feed material flow volumes through the lance 104;

Fuel & Oxygen Flows: The oxyfuel gas fired lance 104 had a separated flow at the tip of the lance. Plant scale carbon burning trials indicate that about 80,000 kcal per ton of automotive catalyst made with silicon carbide (SiC) substrates with about twice the stoichiometric oxygen flow, yielded a stable and efficient carbon burning (i.e., oxidation) reaction. Due to the highly exothermic reactions taking place at the lance tip 105, the amount of fuel gas may decrease considerably as the instantaneous feed rate is increased. The lance configurations proven effective in the pilot testing and full-scale plant trials operated at lance nozzle jet gas velocities at about 250 ft/sec (76 meters/sec). The MTBF, mean-time-between-failure, of the water- cooled lances may be significantly increased if proper flame separation is maintained at the tip 105 of the lance 104. In the present invention, it was found that the flame 100D was properly separated from the tip 105 of the lance 104 as a result of the predetermined flowrates of the oxyfuel gas velocity and the design of the lance tip 105.

The furnace 102 temperature is controlled by the addition of the cooling agent 30 into the feed blend 34. The exothermic nature of the furnace 102 reactions may benefit from automatic mass rate control by modulating the cooling agent 30 addition rate based on off-gas 48 temperatures and slag 44 temperatures.

The feed blend material 34 may optionally be further blended with off-gas dust 50 obtained from an off-gas treatment stage 22 downstream as will be described below. Referring again to Figures 1 and 2 and Figure 8, the process 10 includes an off-gas treatment stage 22 for treating a carbon containing off-gas in line 48 typically fed into the off-gas treatment stage via the duct 1 10. The off-gas stream 48 may have a carbon monoxide (CO) content of 5% on a volume basis and trace levels of nitrogen oxides, NOx.

During high temperature combustion of fuels, above about 1300°C (2370°F), the formation of nitric oxide (NO), nitrogen dioxide (NO2) and to a lesser extent nitrous oxide (N2O) may occur. In the off-gas treatment stage 22, comprising a thermal oxidizer 55, urea (HNCO) is injected in the thermal oxidizer 55 to convert the nitrogen oxides to nitrogen, carbon dioxide, and water according to the following reaction:

2CO(NH ₂ ) ₂ + 6NO 5N ₂ + 2CO ₂ + 4H ₂ O 4HNCO + 6NO 5N ₂ + 4CO ₂ + 2H ₂ O 4NH ₃ + 4NO + O ₂ 4N ₂ + 6H ₂ O

The off-gas treatment stage 22 is carried out to prevent air pollution and to recover valuable elements through oxidation reactions of carbon monoxide. The off-gas stream 48 may contain a limited amount of char and dust carried over in the oxidation (i.e., carbon burning) stage 14. The produced off-gas stream 48 enters a thermal oxidizer 55 of the off-gas treatment stage 22, which converts the off-gas and char into a fully oxidized flue gas. The thermal oxidizer 55 inlet (not shown) may function as the ignition stage for the combustion of carbon monoxide. Combustion air is added to the off-gas 48 by a combustion air fan 56 and the mixed gases may be ignited by a pilot gas burner 54 that runs continuously. The thermal oxidizer 55 may taper to a solids discharge point as the off-gas 48 heated to above the autothermal ignition point of about 1450 °F (790 °C) flows upwards past cooling water sprays 58 and 59. The thermal oxidizer 55 may operate at a temperature in a range of from about 850°C (1560 °F) to about 1 100°C (2010 °F). Water may be fed into the thermal oxidizer 55 water spray nozzles 58 for evaporative cooling of the thermal oxidizer 55. The injection of water is used to control the temperature and prevent a temperature of the thermal oxidizer 55 from rising too high. A modulating gas preheat burner 57 of the thermal oxidizer 55 would be switched off during full operational steady state of the process 10 as the combustion of the carbon monoxide generates more than enough heat required for the operation of the thermal oxidizer 55. To control the amount of heat generated in the thermal oxidizer, water is injected into the gas flow just above the gas entry point and urea solution 60 is also sprayed in for Nox abatement. A further spray water addition is made at the high-level discharge 59 from the thermal oxidizer 55.

From the thermal oxidizer 55, the off-gas enters a high temperature-rated duct 61 equipped with a dilution air damper 62. The off-gas temperature may be continuously monitored to allow for control of the dilution air damper position to keep the off-gas entering a baghouse 63 to below about 235 °C (450 °F). The baghouse 63 may be equipped with an automated bag cleaning system comprising of air jets 64 that release compressed air sequentially to disengage the dust 50 from the baghouse surfaces.

The dust 50 may be collected and recycled to the blending stage 12 or fed into a smelting stage 20 downstream.

The generated off-gas (i.e., carbon containing gas) 48 may be evacuated from the furnace 102 by an induced draught (ID) fan 65, which drafts the entire process by creating a slight suction pressure inside the furnace 102. This reduces the exposure of carbon monoxide in the process while maintaining containment of the offgas resulting in higher recoveries and a cleaner process 1 0. The ID fan 65 relies on variable speed controls. The ID fan may maintain the furnace 102 at about - 0.2” WC (water column) and controlled automatically to adjust for the furnace 102 offgas volumes. The off furnace off-gas 48 extracted by off-gas ID fan 65 may also include particulate material as a result of physiochemical carryover of the furnace 102 feed material 34. Stable off-gas draft control may minimize dust carryover. The final process tail gas 52 is discharged to the atmosphere depending on off-gas composition and area environmental regulations.

Referring again to Figures 1 , 4 and 5, slag 44 and/or matte 40 is periodically poured out of the furnace 102. Samples may be taken for analysis in order to control the formulation of the slag 44 and matte or tramp metal 40 in the furnace 102. The results of the analysis may be fed back to the process operator. The volume of the tapped slag 44 and matte or tramp metal 40 may be controlled in order to retain the holding volume of the furnace 102. This volume range control may be used for continuous oxidation operations, called a tidal zone operation, where the movement of the matteslag line is limited to a defined height in the furnace 102. The design point volume of the tapped slag 44 and matte or tramp metal 40 may equate to the volume of the furnace’s slag/matte tidal zone.

The slag 44 obtained from the furnace 102 may be cooled before being transferred via transfer line 44 into the slag granulation stage 18. Similarly, the matte obtained from the furnace 102 may be cooled before being transferred via transfer line 40 to the matte granulation stage 16. In the matte and slag granulation stages 16 and 18, respectively, the cooled matte and slag are granulated. The matte granulation stage product may exit the matte granulation stage 16 via exit line 42 and may further be processed downstream, for example by feeding it into a convertor along with the matte obtained from a smelter downstream.

The slag granulation stage product, comprising of granulated slag, may be transferred via transfer line 46 into a smelting stage 20 where the granulated slag will be blended with other fluxing agents, iron oxide, and other catalyst material such as those not made from SiC substrates but made from, for example, cordierite and similar material, before feeding the resultant blended material into a smelting furnace.

The abovementioned process 10 for performing the method has been tested in pilot plants and has proven effective in reducing the amount of carbon contained in the SiC bearing material. As mentioned above, the resultant slag 46, having a lower carbon content compared to the amount of carbon which was initially contained in the catalyst made from SiC substrates, will be fed into a smelter stage 20 downstream for further processing.