EP2978866A1 - Method and apparatus for recovering pgm and ferro-chrome from pgm bearing chromite ore - Google Patents

Method and apparatus for recovering pgm and ferro-chrome from pgm bearing chromite ore

Info

Publication number
EP2978866A1
EP2978866A1 EP14720990.2A EP14720990A EP2978866A1 EP 2978866 A1 EP2978866 A1 EP 2978866A1 EP 14720990 A EP14720990 A EP 14720990A EP 2978866 A1 EP2978866 A1 EP 2978866A1
Authority
EP
European Patent Office
Prior art keywords
slag
furnace
smelting furnace
metal alloy
concentrate
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP14720990.2A
Other languages
German (de)
French (fr)
Inventor
Lauri NÄRHI
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Outotec Finland Oy
Original Assignee
Outotec Finland Oy
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Outotec Finland Oy filed Critical Outotec Finland Oy
Publication of EP2978866A1 publication Critical patent/EP2978866A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B11/00—Obtaining noble metals
    • C22B11/02—Obtaining noble metals by dry processes
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B1/00—Preliminary treatment of ores or scrap
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B34/00—Obtaining refractory metals
    • C22B34/30—Obtaining chromium, molybdenum or tungsten
    • C22B34/32—Obtaining chromium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B5/00—General methods of reducing to metals
    • C22B5/02—Dry methods smelting of sulfides or formation of mattes
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
    • C22B7/04—Working-up slag
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B19/00—Combinations of different kinds of furnaces that are not all covered by any single one of main groups F27B1/00 - F27B17/00
    • F27B19/04—Combinations of different kinds of furnaces that are not all covered by any single one of main groups F27B1/00 - F27B17/00 arranged for associated working
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F9/00—Making metallic powder or suspensions thereof
    • B22F9/02—Making metallic powder or suspensions thereof using physical processes
    • B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
    • B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
    • B22F9/082—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Definitions

  • the invention relates to a method and an ap ⁇ paratus for recovering platinum group metals and fer- rochrome from PGM bearing chromite ore.
  • Platinum group metals include platinum, rhodium, palladium, ruthenium, iridium, osmium. PGMs frequently occur together with chromites.
  • the platinum industry in South Africa is increasingly moving from traditional Meren- sky reef to UG2 reef as a raw material.
  • the UG2 reef contains most of the world's known PGM reserves, and it also has high chromite content.
  • the UG2 concentration process used by the platinum industry in South Africa produces lots of chromite-containing tailings. Ferrochrome producers can use these tailings as raw material. South Africa suffers from shortage of electricity, which is why lo ⁇ cal producers cannot use all chromite-containing tail ⁇ ings of platinum industry but tailings are exported to China. The Chinese are building a lot of ferrochrome capacity now, which is worrying for the South African producers.
  • One of the targets of the present invention is to provide a process that allows the South Africans to use their UG2 reserves more completely in their own country .
  • US 6,699,302 Bl disclos ⁇ es a method for processing metal sulfide concentrate that contains at least one metal selected from the group consisting of the PGMs, nickel, cobalt and zinc.
  • the method comprises dead-roasting the metal sulfide concentrate, smelting the dead-roasted concentrate un ⁇ der reducing conditions in an electrically stabilized open-arc furnace, and collecting the metals from the smelting step in the form of an alloy or vapor. Chrome is an unwanted element and it is removed from the met ⁇ al alloy in a converter.
  • the purpose of the present invention is to eliminate or at least reduce the problems of the prior art .
  • a further purpose is to provide a new process for effective utilization of PGM bearing chromite ore.
  • the new method comprises preparing a concen ⁇ trate that contains most of the PGMs and chromite of the ore, subjecting the concentrate to a heating step to dry and/or preheat the concentrate, and smelting the concentrate under reducing conditions in a DC smelting furnace to produce molten metal alloy that contains the PGMs of the feed and molten slag that contains the chromium of the feed.
  • the molten slag is tapped from the smelting furnace into an AC slag fur ⁇ nace, where reduction of the oxides of iron and chro ⁇ mium contained in the slag takes place so that ferro ⁇ chrome is produced.
  • the heating step additionally comprises roasting the concentrate to remove sulfur and/or volatiles con ⁇ tained in the concentrate.
  • the slag properties are controlled with flux.
  • the method comprises adding flux and/or reductant into the smelting furnace and/or into the slag furnace.
  • the reducing conditions in the smelting furnace and/or in the slag furnace are controlled with the addition of reductant.
  • the slag properties in the smelting furnace and/or in the slag furnace are controlled with the addition of flux .
  • Advantageously molten metal alloy is tapped from the smelting furnace, after which PGMs are recovered from the metal alloy by hydrometallurgical pro- Derivatives or a combination of pyrometallurgical and hy ⁇ drometallurgical processes.
  • molten metal alloy from the smelting furnace is tapped to a Peirce-Smith converter, after which the converted metal alloy is subjected to atomization and hydromet ⁇ allurgical process steps.
  • molten metal alloy is tapped from the smelting furnace directly to an atomizer, after which the atom- ized metal alloy is subjected to hydrometallurgical process steps.
  • the new apparatus comprises a DC smelting furnace for producing a molten metal alloy containing the PGMs of the feed and a molten slag containing the chromium of the feed, and an AC slag furnace for pro ⁇ ducing a ferrochrome alloy from the molten slag tapped from the DC smelting furnace.
  • the apparatus further comprises a heating unit for drying and/or preheating the concentrate before it is fed to the smelting furnace.
  • the heating unit is pref ⁇ erably selected from a group comprising a fluidized bed reactor, a rotary kiln, a drying tower, or similar .
  • the slag furnace can be an open bath alterna ⁇ tive current furnace, or similar.
  • the apparatus further comprises a Peirce-Smith converter for removing iron from the molten metal alloy tapped from the smelting furnace.
  • the apparatus further comprises an atomizer for atomizing the molten metal alloy tapped from the smelting furnace or from the converter.
  • the present invention proposes using molten slag from a PGM smelter as a raw material in ferro ⁇ chrome production.
  • both PGMs and ferrochrome are produced at the same time, which gives flexibility for the use of raw material and makes the concentration of PGM and chromite con- taining ore easier.
  • the process also saves energy com ⁇ pared to current recovery processes.
  • the ferrochrome containing slag fraction need not to be cooled and re ⁇ heated before introduction into ferrochrome process.
  • the present invention allows adjusting the Cr/Fe ratio in the ferrochrome by controlling how much iron is reduced in the smelting furnace.
  • Typical use of pure UG2 ore results in Cr/Fe ratio of around 1.35, which means that the Cr content in the ferrochrome is below 50%.
  • Higher Cr contents are preferred by the end users of ferrochrome, i.e. stainless steel industry.
  • the enclosed Figure 1 is a flow chart illus ⁇ tration of one embodiment of a process according to the present invention.
  • PGM bearing chromite ore is fine grinded to liberate the PGM particles.
  • the fine grinded ore is concentrated in a concentrator 10, where the target is to remove gangue while keeping iron, chromium, base metals and PGMs in the concentrate.
  • the process is simpler than the concentration processes currently used in PGM recovery, because there is no need to sep- arate chrome and iron from the base metals and PGMs.
  • the concentrate is subjected to heat treat ⁇ ment in a heating unit 12, where the concentrate is dried, if necessary, and possibly preheated before it is fed to a smelting furnace 14.
  • the heating unit 12 can be, for instance, a fluidized bed reactor, a rota ⁇ ry kiln, or a drying tower. If the raw material contains lots of sulfides and/or volatiles, roasting can be carried out in the heating unit 12 to oxidize the metal sulfides. CO gas generated in subsequent smelt- ing and slag furnaces 14, 16 can be used as a heat source in the heating unit 12.
  • the preheated concentrate is charged as a feed into a DC smelting furnace 14.
  • carbonaceous reductant such as anthracite or coke
  • some flux may be charged, if necessary.
  • the concentrate is melted and the PGMs, base metals and part of the iron contained in the feed are reduced to elemental metal, which is separated as a molten metal alloy be ⁇ low the lighter slag phase.
  • most of the feed goes into the slag phase.
  • all Cr and most of Fe, AI 2 O 3 , S 1O 2 , MgO and CaO of the feed go in ⁇ to the slag phase.
  • Reduction in the smelting furnace 14 is limited by controlling the amount of carbon charged to the furnace 14. The target is only to get the PGMs into metal phase together with just a part of the iron. Iron droplets capture the PGMs and other base metals, forming molten metal alloy. Ni and Cu can also be present in the molten metal alloy produced in the smelting furnace 14.
  • Liquid slag is tapped from the DC smelting furnace 14 to an AC slag furnace 16.
  • Liquid metal al ⁇ loy is tapped from the bottom of the DC smelting fur- nace 14 to further refining steps in pyrometallurgical and/or hydrometallurgical processes.
  • the slag furnace 16 is preferably an open bath alternative current furnace where electrodes are buried in a burden of lumpy materials comprised of molten slag received from DC smelting furnace. Carbo ⁇ naceous reductant and flux are charged to the AC fur ⁇ nace to control the reduction reactions and to opti ⁇ mize the amount and quality of slag.
  • Typical ferro- chrome furnace operations comprise reduction of oxides of iron and chromium into metal phase.
  • the resulting slag mainly contains AI 2 O 3 , MgO, CaO and S i0 2 - Metal alloy received from the slag furnace 16 contains Fe, Cr, some C and Si. All the rest of the feed is re ⁇ tained in the slag.
  • Products received from the slag furnace 16 are ferrochrome metal and slag.
  • the temperature of the slag tapped from the AC slag furnace 16 is 1650-1750°C and the temperature of the ferrochrome tapped from the AC slag furnace 16 is 1550-1600°C.
  • PGM rich metal alloy tapped from the smelting furnace 14 can either be directly passed to hydromet- allurgical treatment steps or it can be converted in a Peirce-Smith converter 18 before passing to hydromet- allurgical treatment.
  • the purpose of converting is to remove iron and other impurities from the metal alloy.
  • the recovery of PGMs can comprise, for instance, atom- ization in an atomizer 20 and leaching.
  • the basic idea of the present innovation is to smelt the concentrate in a DC smelting furnace 14, where PGMs are reduced, and then to produce FeCr alloy from the slag of the DC smelting furnace in a separate AC slag furnace 16. This gives flexibility as regards the raw materials and simplifies the concentrating process 10.
  • Benefits of the new process comprise simplic ⁇ ity of the preceding concentration process as there is no need to remove chromite at an early stage.
  • FeCr and PGMs are produced at the same time, less concen ⁇ tration, cooling and melting is needed and the process is more energy efficient.
  • the safety of the process is improved as there is no risk of crust formation or ex- plosion.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Mechanical Engineering (AREA)
  • Organic Chemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Manufacturing & Machinery (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Environmental & Geological Engineering (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Geology (AREA)
  • Geochemistry & Mineralogy (AREA)
  • General Engineering & Computer Science (AREA)
  • Manufacture And Refinement Of Metals (AREA)

Abstract

In a method for recovering PGMs and ferrochrome from platinum group metals bearing chromite ore, a concentrate is prepared that contains most of PGMs and chromite of the ore and the concentrate is subjected to a heating step to dry and/or preheat the concentrate, after which the preheated concentrate is smelted under reducing conditions in a DC smelting furnace (14) to produce molten metal alloy containing the PGMs of the feed and molten slag containing the chromium of the feed. The molten slag is tapped from the smelting furnace (14) into an AC slag furnace (16), where iron and chromium are reduced to produce a ferrochrome alloy. PGMs are recovered from the metal alloy tapped from the smelting furnace (14) utilizing hydro-metallurgical processes.

Description

METHOD AND APPARATUS FOR RECOVERING PGM AND FERRO- CHROME FROM PGM BEARING CHROMITE ORE
FIELD OF THE INVENTION
The invention relates to a method and an ap¬ paratus for recovering platinum group metals and fer- rochrome from PGM bearing chromite ore.
BACKGROUND OF THE INVENTION
Most of the world' s known platinum reserves are located in South Africa, which produces most of the world's platinum. South Africa is also the world's largest single producer of ferrochrome. Platinum group metals, or PGMs, include platinum, rhodium, palladium, ruthenium, iridium, osmium. PGMs frequently occur together with chromites. The platinum industry in South Africa is increasingly moving from traditional Meren- sky reef to UG2 reef as a raw material. The UG2 reef contains most of the world's known PGM reserves, and it also has high chromite content.
There are some challenges in using UG2 based raw material with current PGM recovery processes. One of the challenges is that traditional smelting furnac¬ es cannot use a concentrate that contains over 2.5% Cr. If the chromium content is too high, Cr tends to create crust in the smelting furnace and the explosion risk is high. Traditional six-in-line smelting furnac¬ es are susceptible to build-ups of high-melting chro¬ mite spinels if the Cr203 content of the feed is too high. Also the furnace control is very challenging. Furthermore, concentration process is rather complicated when the target is to separate the chromite from the PGMs. Traditionally, UG2 ore has been concentrated by removing chromite from the ore as far as possible to reach low chromite content in the PGM smelting furnace feed. It is very difficult to totally remove chromite from the concentrate by flotation. Chrome melts at temperatures above 1600°C, whereas PGM smelt¬ ing furnaces operate at 1400-1500°C. The presence of chromium in the feed leads to lower furnace reduction efficiency and chromite can also damage the smelting furnace .
The UG2 concentration process used by the platinum industry in South Africa produces lots of chromite-containing tailings. Ferrochrome producers can use these tailings as raw material. South Africa suffers from shortage of electricity, which is why lo¬ cal producers cannot use all chromite-containing tail¬ ings of platinum industry but tailings are exported to China. The Chinese are building a lot of ferrochrome capacity now, which is worrying for the South African producers. One of the targets of the present invention is to provide a process that allows the South Africans to use their UG2 reserves more completely in their own country .
Attempts have been made to develop pyrometal- lurgical processes that tolerate higher chromite con¬ tents in the PGM concentrate. US 6,699,302 Bl disclos¬ es a method for processing metal sulfide concentrate that contains at least one metal selected from the group consisting of the PGMs, nickel, cobalt and zinc. The method comprises dead-roasting the metal sulfide concentrate, smelting the dead-roasted concentrate un¬ der reducing conditions in an electrically stabilized open-arc furnace, and collecting the metals from the smelting step in the form of an alloy or vapor. Chrome is an unwanted element and it is removed from the met¬ al alloy in a converter.
Although the process of US 6, 699, 302 Bl can use raw materials with high chromium content, chrome is finally discarded from the process. Furthermore, the process is designed only for use with sulfide raw materials . The industry lacks a process that effectively combines the recovery of PGMs and ferrochrome from a PGM bearing chromite ore, such as UG2. PURPOSE OF THE INVENTION
The purpose of the present invention is to eliminate or at least reduce the problems of the prior art .
A further purpose is to provide a new process for effective utilization of PGM bearing chromite ore.
SUMMARY
The method according to the present invention is characterized by what is presented in claim 1.
The apparatus according to the present inven¬ tion is characterized by what is presented in claim 10.
The new method comprises preparing a concen¬ trate that contains most of the PGMs and chromite of the ore, subjecting the concentrate to a heating step to dry and/or preheat the concentrate, and smelting the concentrate under reducing conditions in a DC smelting furnace to produce molten metal alloy that contains the PGMs of the feed and molten slag that contains the chromium of the feed. The molten slag is tapped from the smelting furnace into an AC slag fur¬ nace, where reduction of the oxides of iron and chro¬ mium contained in the slag takes place so that ferro¬ chrome is produced.
According to one embodiment of the invention the heating step additionally comprises roasting the concentrate to remove sulfur and/or volatiles con¬ tained in the concentrate.
According to one embodiment of the invention the slag properties are controlled with flux. Advantageously the method comprises adding flux and/or reductant into the smelting furnace and/or into the slag furnace.
According to one embodiment of the invention the reducing conditions in the smelting furnace and/or in the slag furnace are controlled with the addition of reductant.
According to one embodiment of the invention the slag properties in the smelting furnace and/or in the slag furnace are controlled with the addition of flux .
Advantageously molten metal alloy is tapped from the smelting furnace, after which PGMs are recovered from the metal alloy by hydrometallurgical pro- cesses or a combination of pyrometallurgical and hy¬ drometallurgical processes.
According to one embodiment of the invention molten metal alloy from the smelting furnace is tapped to a Peirce-Smith converter, after which the converted metal alloy is subjected to atomization and hydromet¬ allurgical process steps.
According to another embodiment of the invention molten metal alloy is tapped from the smelting furnace directly to an atomizer, after which the atom- ized metal alloy is subjected to hydrometallurgical process steps.
The new apparatus comprises a DC smelting furnace for producing a molten metal alloy containing the PGMs of the feed and a molten slag containing the chromium of the feed, and an AC slag furnace for pro¬ ducing a ferrochrome alloy from the molten slag tapped from the DC smelting furnace.
According to one embodiment of the invention the apparatus further comprises a heating unit for drying and/or preheating the concentrate before it is fed to the smelting furnace. The heating unit is pref¬ erably selected from a group comprising a fluidized bed reactor, a rotary kiln, a drying tower, or similar .
The slag furnace can be an open bath alterna¬ tive current furnace, or similar.
According to one embodiment of the invention the apparatus further comprises a Peirce-Smith converter for removing iron from the molten metal alloy tapped from the smelting furnace.
According to another embodiment of the inven- tion the apparatus further comprises an atomizer for atomizing the molten metal alloy tapped from the smelting furnace or from the converter.
Instead of using tailings from a PGM concentrator, the present invention proposes using molten slag from a PGM smelter as a raw material in ferro¬ chrome production. According to the new method both PGMs and ferrochrome are produced at the same time, which gives flexibility for the use of raw material and makes the concentration of PGM and chromite con- taining ore easier. The process also saves energy com¬ pared to current recovery processes. The ferrochrome containing slag fraction need not to be cooled and re¬ heated before introduction into ferrochrome process.
The present invention allows adjusting the Cr/Fe ratio in the ferrochrome by controlling how much iron is reduced in the smelting furnace. Typical use of pure UG2 ore results in Cr/Fe ratio of around 1.35, which means that the Cr content in the ferrochrome is below 50%. Higher Cr contents are preferred by the end users of ferrochrome, i.e. stainless steel industry.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawing, which is included to provide further understanding of the invention and constitutes a part of this specification, illustrates an embodiment of the invention and together with the description helps to explain the principles of the in¬ vention .
The enclosed Figure 1 is a flow chart illus¬ tration of one embodiment of a process according to the present invention.
DETAILED DESCRIPTION OF AN EMBODIMENT
PGM bearing chromite ore is fine grinded to liberate the PGM particles. The fine grinded ore is concentrated in a concentrator 10, where the target is to remove gangue while keeping iron, chromium, base metals and PGMs in the concentrate. The process is simpler than the concentration processes currently used in PGM recovery, because there is no need to sep- arate chrome and iron from the base metals and PGMs.
The concentrate is subjected to heat treat¬ ment in a heating unit 12, where the concentrate is dried, if necessary, and possibly preheated before it is fed to a smelting furnace 14. The heating unit 12 can be, for instance, a fluidized bed reactor, a rota¬ ry kiln, or a drying tower. If the raw material contains lots of sulfides and/or volatiles, roasting can be carried out in the heating unit 12 to oxidize the metal sulfides. CO gas generated in subsequent smelt- ing and slag furnaces 14, 16 can be used as a heat source in the heating unit 12.
The preheated concentrate is charged as a feed into a DC smelting furnace 14. At the same time, carbonaceous reductant, such as anthracite or coke, is charged to the smelting furnace 14. Also some flux may be charged, if necessary.
In the DC smelting furnace 14 the concentrate is melted and the PGMs, base metals and part of the iron contained in the feed are reduced to elemental metal, which is separated as a molten metal alloy be¬ low the lighter slag phase. However, most of the feed goes into the slag phase. For instance, all Cr and most of Fe, AI2O3 , S 1O2 , MgO and CaO of the feed go in¬ to the slag phase. Reduction in the smelting furnace 14 is limited by controlling the amount of carbon charged to the furnace 14. The target is only to get the PGMs into metal phase together with just a part of the iron. Iron droplets capture the PGMs and other base metals, forming molten metal alloy. Ni and Cu can also be present in the molten metal alloy produced in the smelting furnace 14.
In the direct current (DC) smelting furnace
14 the charged material is directly exposed to an electric arc, and the current between a cathode and an anode passes through the charged material. Energy is supplied by open plasma arc. The temperature in the smelting furnace 14 is relatively high, which is why reactions are quick. The plasma arc agitates the slag phase and creates strong currents, which further im¬ proves reactions. A carbon monoxide atmosphere is cre¬ ated in the closed furnace. One more advantage of us- ing a DC smelting furnace is that it allows charging fine grinded material.
Liquid slag is tapped from the DC smelting furnace 14 to an AC slag furnace 16. Liquid metal al¬ loy is tapped from the bottom of the DC smelting fur- nace 14 to further refining steps in pyrometallurgical and/or hydrometallurgical processes.
The slag furnace 16 is preferably an open bath alternative current furnace where electrodes are buried in a burden of lumpy materials comprised of molten slag received from DC smelting furnace. Carbo¬ naceous reductant and flux are charged to the AC fur¬ nace to control the reduction reactions and to opti¬ mize the amount and quality of slag. Typical ferro- chrome furnace operations comprise reduction of oxides of iron and chromium into metal phase. The resulting slag mainly contains AI2O3 , MgO, CaO and S i02 - Metal alloy received from the slag furnace 16 contains Fe, Cr, some C and Si. All the rest of the feed is re¬ tained in the slag. Products received from the slag furnace 16 are ferrochrome metal and slag. Typically, the temperature of the slag tapped from the AC slag furnace 16 is 1650-1750°C and the temperature of the ferrochrome tapped from the AC slag furnace 16 is 1550-1600°C.
PGM rich metal alloy tapped from the smelting furnace 14 can either be directly passed to hydromet- allurgical treatment steps or it can be converted in a Peirce-Smith converter 18 before passing to hydromet- allurgical treatment. The purpose of converting is to remove iron and other impurities from the metal alloy. The recovery of PGMs can comprise, for instance, atom- ization in an atomizer 20 and leaching.
The basic idea of the present innovation is to smelt the concentrate in a DC smelting furnace 14, where PGMs are reduced, and then to produce FeCr alloy from the slag of the DC smelting furnace in a separate AC slag furnace 16. This gives flexibility as regards the raw materials and simplifies the concentrating process 10.
Benefits of the new process comprise simplic¬ ity of the preceding concentration process as there is no need to remove chromite at an early stage. As FeCr and PGMs are produced at the same time, less concen¬ tration, cooling and melting is needed and the process is more energy efficient. The safety of the process is improved as there is no risk of crust formation or ex- plosion. There are fewer restrictions for raw materials and no limits for the Cr content of the feed. Nei¬ ther Cr nor PGMs are lost in the process.
It is obvious to a person skilled in the art that with the advancement of technology, the basic idea of the invention may be implemented in various ways. The invention and its embodiments are thus not limited to the examples described above; instead they may vary within the scope of the claims.

Claims

1. A method for recovering platinum group metals and ferrochrome from PGMs bearing chromite ore, comprising the steps of:
- preparing a concentrate that contains most of the PGMs and chromite of the ore,
- subjecting the concentrate to a heating step to dry and/or preheat the concentrate,
- smelting the concentrate under reducing conditions in a DC smelting furnace (14) to produce molten metal alloy containing the PGMs of the feed and molten slag containing the chromium of the feed,
- tapping the molten slag from the smelting furnace (14) into an AC slag furnace (16),
- reducing the oxides of iron and chromium contained in the slag in the AC slag furnace (16) to produce ferrochrome alloy.
2. The method according to claim 1, wherein the heating step also comprises roasting the concen- trate to remove sulfur and/or volatiles contained in the concentrate.
3. The method according to claim 1 or 2, wherein the slag properties are controlled with flux.
4. The method according to any one of claims 1 to 3, comprising adding flux and/or reductant into the smelting furnace (14) and/or into the slag furnace (16) .
5. The method according to claim 4, wherein the reducing conditions in the smelting furnace (14) and/or in the slag furnace (16) are controlled with the addition of reductant.
6. The method according to any one of claims 3 to 5, wherein the slag properties in the smelting furnace (14) and/or in the slag furnace (16) are con- trolled with the addition of flux.
7. The method according to any one of claims 1 to 6, comprising tapping molten metal alloy from the smelting furnace (14) and recovering PGMs from the metal alloy.
8. The method according to claim 7, compris¬ ing tapping molten metal alloy from the smelting fur- nace (14) to a Peirce-Smith converter (18) and/or subjecting the converted metal alloy to atomization and hydrometallurgical process steps.
9. The method according to claim 7, compris¬ ing tapping molten metal alloy from the smelting fur- nace (14) to an atomizer (20) and subjecting the atomized metal alloy to hydrometallurgical process steps.
10. An apparatus for recovering platinum group metals and ferrochrome from PGMs and chromite containing ore concentrate, comprising a DC smelting furnace (14) for producing a molten metal alloy containing the PGMs of the feed and a molten slag con¬ taining the chromium of the feed, and an AC slag fur¬ nace (16) for producing a ferrochrome alloy from the molten slag tapped from the DC smelting furnace (14) .
11. The apparatus according to claim 10, com¬ prising a heating unit (12) for drying and/or preheating the concentrate before it is fed to the smelting furnace (14), which heating unit (12) is selected from a group comprising a fluidized bed reactor, a rotary kiln, a drying tower, or similar.
12. The apparatus according to claim 10 or 11, wherein the slag furnace (14) is an open bath alternative current furnace, or similar.
13. The apparatus according to any one of claims 10 to 12, further comprising a Peirce-Smith converter (18) for removing iron from the molten metal alloy tapped from the smelting furnace (14) .
14. The apparatus according to any one of claims 10 to 13, further comprising an atomizer (20) for atomizing the molten metal alloy tapped from the smelting furnace (14) or from the converter (18) .
EP14720990.2A 2013-03-25 2014-03-25 Method and apparatus for recovering pgm and ferro-chrome from pgm bearing chromite ore Withdrawn EP2978866A1 (en)

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FI20135284A FI125099B (en) 2013-03-25 2013-03-25 Process and apparatus for the recovery of platinum metals and ferrochrome from chromite ore containing platinum metals
PCT/FI2014/050214 WO2014154945A1 (en) 2013-03-25 2014-03-25 Method and apparatus for recovering pgm and ferro-chrome from pgm bearing chromite ore

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US10323302B2 (en) * 2016-11-18 2019-06-18 Heraeus Deutschland GmbH & Co. KG Process for the production of a PGM-enriched alloy
US11772158B2 (en) 2018-03-01 2023-10-03 Aurum Integra Inc. Method for selectively oxidizing metals of an alloy
US10435767B2 (en) 2019-04-29 2019-10-08 Techemet, LP Low-flux converting process for PGM collector alloy
US10472700B1 (en) 2019-04-29 2019-11-12 Techemet, LP Converting process with partial pre-oxidation of PGM collector alloy
CN112760549B (en) * 2020-12-30 2022-02-22 邬海宇 Process for smelting rare and noble metal ferroalloy in intermediate frequency furnace
WO2023096525A1 (en) * 2021-11-28 2023-06-01 Татьяна Михайловна ПАРПОЛИТО Furnace for producing ferrochromium alloys

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US4295881A (en) * 1979-04-23 1981-10-20 Texasgulf Inc. Process for extraction of platinum group metals from chromite-bearing ore
EP1157139B1 (en) * 1999-02-26 2002-10-09 Mintek Treatment of metal sulphide concentrates by roasting and arc furnace smelt reduction
DE102006052181A1 (en) * 2006-11-02 2008-05-08 Sms Demag Ag A process for the continuous or discontinuous recovery of a metal or metals from a slag containing the metal or compound of the metal

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FI125099B (en) 2015-05-29
WO2014154945A1 (en) 2014-10-02
CN105164285A (en) 2015-12-16
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ZA201507020B (en) 2017-01-25
CA2907005A1 (en) 2014-10-02

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