Pyrometallurgical process for treating a feed material

Abstract: A process of pyrometallurgically treating a feed material such as a sulphide ore or concentrate is provided. The process includes the steps of: (a) producing a liquid body (50) of feed material; (b) creating a first reaction zone (58) and a second reaction zone (60) which is in contact with the first reaction zone (58) and is in the liquid body (50); (c) introducing feed material in particulate form and an oxidising gas into the first reaction zone (58); (d) allowing in-flight oxidation of feed material to take place in the first reaction zone (58); (e) allowing at least some of the reaction products of the inflight oxidation to pass into a second reaction zone (60); and (f) allowing sulphidation or reduction of the reaction products to take place in the second reaction zone (60).

Description: This invention relates to a pyrometallurgical process for treating a feed material. High temperature smelting processes are examples of pyrometallurgical processes. Such processes are often carried out in two vessels, the one vessel being used to heat the feedstock (feed material) and thereby melt it, and the second vessel being used to oxidise the molten feedstock. The use of two vessels carries with it several disadvantages, one of which is the difficulty of transferring molten feedstock from one vessel to the other. Lances have been developed in Australia which enable fuel and oxidising gas to be introduced into feedstock for a smelting process. A typical lance of this type is described in Australian Patent No. 520351 and consists of an outer tube and an inner tube. Liquid fuel for the process passes down the inner tube and exits through a nozzle into a mixing zone. In the case of the solid fuel lance, there is no nozzle. Oxidising gas passes along the passage defined between the inner and outer tubes and into the mixing zone. The oxidising gas acts as a coolant for the outer tube. The cooling effect of this gas on the outer tube allows slag or other material which is splashed on to this tube from the molten mass to freeze and so insulate and protect the tube. These operations can all take place in a single vessel. Further, the use of such a lance produces a jet of fuel/oxidising gas with a result that the molten feedstock is vigorously, and even violently, agitated. The process described above using the lance of Australian Patent No. 520351 is an "in-bath" process in that the feed material is digested and partially oxidised in the slag which is in a state of high turbulence effected by the injection, at high speed, of oxidising gas from the lance. An "in-flight" process is also known in which feed material in a dry and finely particulate form is combusted in a stream of oxygen-enriched air in a vertical shaft. The products of combustion fall on to a molten bath below where slag and matte fractions separate. Such "in-flight" processes are carried out in large furnaces which are expensive to produce and to operate. According to the present invention, there is provided a process of pyrometallurgically treating a feed material which includes the steps defined in claim 1. A lance most suitable for use in introducing reactants, feed material and/or fuel to a vessel for carrying out a pyrometallurgical process of this invention has a discharge end which is characterised by an outer passage for delivering an oxidising gas, and an inner passage for delivering reactants or feed material for the process in a solid, liquid or gaseous form, or a mixture thereof, and optionally an intermediate passage located between the inner and outer passages for delivering fuel, the discharge outlet of the intermediate passage being such as to produce a diverging flow of fuel which is discharged therefrom. Figure 1 illustrates a sectional side view of the discharge end of a lance for use in a pyrometallurgical process of the invention; and Figure 2 illustrates a sectional side view of a furnace in which a pyrometallurgical process of the invention may be carried out. The process of the invention is a pyrometallurgical one in which a feed material is subjected to an in-flight oxidation step and at least some of the reaction products of this in-flight oxidation pass into the second reaction zone where they are subjected to sulphidation or reduction. The second reaction zone is located in the liquid body of feed material. The feed materials which may be treated in this process may be ores or concentrates of various compositions. For example, the ore or concentrate may be a sulphide such as chalcopyrite or pyrrhotite. With the use of such ores or concentrates, a slag phase and a matte phase will form in the liquid body of feed material. With such feed materials resulphidation of oxidised products produced in the first reaction zone takes place in the second reaction zone. The feed material may also be an oxide such as zinc or lead oxide. Such oxides may take the form of an ore, flue dust or a concentrate. Oxidation of some of the components of such a feed material will occur in the first reaction zone and reduction of some of the oxidised product so produced and other oxides will occur in the second reaction zone. Slag and matte phases will also form in the liquid body of feed material. Where the molten bath contains a slag phase and a matte phase, the second reaction zone may be created in the slag phase only. Thus, in this form of the invention the reactions which occur in the second reaction zone are, in effect, "in-slag" reactions. The feed material and oxidising gas are preferably introduced into the first reaction zone through the discharge end of a lance which comprises an inner passage through which the feed material passes and an outer passage surrounding the central passage and through which the oxidising gas passes. The inner passage and its discharge end must be of such a cross-section as to allow for the passage of particulate feed material therethrough. Typically, this feed material will have a particle size not exceeding 100 microns, although larger particle sizes can be used. Solid, particulate fuel such as coal or anthracite, may be mixed with the particulate feed material. Fluxes may also be included in this feed material. The inner passage is preferably circular in cross-section with the outer passage providing an annulus surrounding the inner passage. The discharge end of the lance may be placed above the molten bath or in the molten bath. When the discharge end of the lance is placed in the molten bath, the oxidising gas will form a depression in the bath which defines at least part of the boundary of the first reaction zone. To achieve this, the oxidising gas will typically leave the lance at a velocity not exceeding 100 meters per second, preferably at a velocity of between 50 and 70 meters per second. Figure 1 illustrates an embodiment of a lance which can he used in the process of the invention. Referring to this figure, there is shown the discharge end of a lance comprising three concentric tubes 10, 12 and 14 of different diameters. Tube 12 is located inside of tube 10 and tube 14 is located inside of tube 12. The tubes are typically made of mild steel, although a portion extending immediately behind end 32 which is typically submerged in the molten bath may be made of stainless steel construction. Three passages are defined between the tubes. There is an outer passage 16 defined between the tubes 10 and 12; there is an inner passage 18 defined within the tube 14; and there is an intermediate passage 20 defined between the tubes 12 and 14. Flow swirlers 22 capable of creating turbulence in a gas flow are provided in the passage 16. These swirlers are secured to the outer surface of tube 12. The passages 16, 18 and 20 have discharge outlets 24, 26 and 28 respectively, which open into a mixing zone 30. The lance as illustrated by the drawing may be used for introducing feed material, fuel and oxidising gas into a vessel for a smelting or other pyrometallurgical process. The oxidising gas passes down the passage 16, the feedstock mixed with oxidising gas passes down the passage 18 and the fuel passes down the passage 20. The discharge outlet 28 of the passage 20 is very narrow, typically about 0,5mm in width, so that when the fuel is delivered at a suitable pressure down the passage 20 it is discharged through the outlet 28 in the form of a diverging cone, as illustrated by the dotted lines. The rapid flow imparted to the fuel, due to the narrow passage also prevents its overheating, hence cracking. The outlet thus serves as a ring nozzle creating an intimate mixture of the fuel with the oxidising gas which is discharged from the outlet 24 leading to increased fuel efficiency. In use, feed material in particulate form will be introduced into a smelting vessel. The lance will be so located in this vessel that the end 32 is just above the material. Fuel is delivered down the passage 20 and oxidising gas down the passage 16. Mixing takes place in the zone 30 and the mixture of gases is then ignited. The heat produced causes the particulate feed material to melt and create a progressively increasing liquid body or molten bath of the feed material in the vessel. Some of the molten material will splash on to the lance This molten material will freeze on the outer surface of the tube 10 which is cooled by the oxidising gas passing down the passage 16. Cooling is enhanced by the action of the swirlers on the flow of oxidising gas. This frozen material acts as an insulant and protects the tube 10. Once the molten bath has been established to a satisfactory extent, the lance can be lowered so that the end 32 of the lance is located in the molten bath. This is illustrated by Figure 2 of the accompanying drawings. Referring to this figure, the reaction vessel 40 is a refractory lined furnace which contains a reaction volume 42 within it. The lance 44 passes through the top 46 of the vessel 40 and extends into the reaction volume so that the discharge end 48 (32 in Figure 1) extends into the molten bath 50 of the feed material. The molten bath 50 consists of two phases - a slag phase 52 and a matte phase 54. Feed material is introduced into the lance at 56 and oxidising gas at 58. The feed material passes down the inner passage of the lance and the oxidising gas down the outer passage of the lance, as described above with reference to Figure 1. When smelting certain sulphidic concentrates, it is not necessary at this stage of the process to use any fuel, as sufficient heat is generated by the oxidisation reactions to maintain the required temperature. The oxidising gas leaves the discharge end 48 of the lance at such velocity that a depression 58 is produced in the slag phase 52. This depression 58 defines a first reaction zone in which feed material which leaves the discharge end 48 of the lance is subjected to in-flight oxidation. Excellent oxidation rates are achieved in this zone. A region or zone 60, illustrated by dotted lines, is created within the slag phase 52. This zone is one of turbulence and defines a second reaction zone in which oxidised reaction products and other oxides from the first reaction zone 58 are subjected to re-sulphidation or reduction, depending on the nature of the feed material. Thus, there is an in-flight oxidation which takes place in the zone 58 and an in-slag re-sulphidation or reduction which takes place in the molten bath in the zone 60. The products of the re-sulphidation or reduction pass downwards through the slag phase 52 and into the matte phase 54. The slag and matte phases may be tapped from time to time through outlet 62. Outlet 64 is used for exhausting gases such as sulphur dioxide which are produced in the process. Figure 2 illustrates an embodiment in which the discharge end of the lance is located in the slag phase of the molten bath. The process can also operate with this discharge end immediately above the molten bath. In this case, the first zone will be defined between the discharge end 48 of the lance and the surface of the depression which is formed in the slag phase. However, under these conditions, higher dust losses will occur. It is to be noted that the creation of two zones where different reactions take place does not occur in a smelting process using a lance of the type described in Australian Patent No. 520351. With the use of such a lance, a jet of gas and/or fuel leaves the lance creating a high degree of turbulence in the molten bath. Feed material is not delivered through the lance such that there is in-flight oxidation. In the present invention, smelting is more efficient in that higher reaction rates are achieved and the use of a finely particulate feed material means there is no undigested material suspended in the slag. Further, there is significant turbulence only in the zone 60 leading to lower refractory wear rates. Finally, penetration of the oxidising gas into the matte phase can be controlled better as the lance discharge end can be situated further above the matte phase than is possible with the lance of the Australian patent. The flow rates, pressures and particle sizes of feed material will vary according to the nature of the materials used. Examples of typical flow rates, pressures and particle sizes are: 1. Mass flowrate of feed material (including flux and coal) : 50 to 200 kg/hr at air pressures up to 200 kPa (gauge). 2. Volume flowrate of lance oxygen-enriched air : 50 to 200 Nm³/hr at pressures up to 200 kPa (gauge). 3. Volume flowrate of air transporting the solids (in (1) above) : 20 to 50 Nm³/hr. 4. Volume flowrate of diesel : 5 to 15 litres/hr at 20°C up to 700 kPa. 5. Particle sizes of: Sulphide concentrate: 70 to 80% minus 74 micrometers. Fluxes (either silica or burnt lime) : 70 to 80% minus 74 micrometers. Coal or anthracite : 80 to 90% minus 74 micrometers. The invention will now be further illustrated by the following examples of smelting processes carried out using a lance and furnace as described above and illustrated by Figures 1 and 2. 1. EXAMPLE OF A TYPICAL COPPER/NICKEL SULPHIDE SMELTING OPERATION Heating of the furnace is obtained by combustion. During start-up a small amount of LPG gas is injected via the lance for pre-heating the furnace As soon as the furnace hearth is at 700°C, the gas is replaced with diesel and the furnace is heated up to operating temperature (1350°C) with oxygen enriching the air. The average diesel flowrate used is 10 1/h at a pressure of 680kPa. The average oxygen enrichment is 10 Nm³/h during the pre-heating cycle. Once the operating temperature is achieved, a pneumatic feed system is activated and controlled amounts of particulate concentrate and flux are fed pneumatically via a flexible hose to the passage 18 of the lance and into the furnace. The pneumatic feeding system is operated at an air pressure of 150 kPa and an air flowrate of 20-40 Nm³/h, depending on the flux and concentrate mixture. A depression or first reaction zone 58 is formed in the molten bath. In this zone, in-flight oxidation of the sulphides in the concentrate takes place. The products of this reaction, namely a mixture of base metal oxides and sulphides then enter the slag phase (zone 60) whereupon further reactions between the base metal oxides and finely dispersed molten matte globules take place. As a result of the intense agitation in the zone 60, the reactions occur rapidly and equilibrium is quickly reached, which results in a very short retention time. The SO₂ in the off gas is monitored for acid production, and is maintained at a concentration of between 5 and 15%, after cooling air has been introduced. A liquid matte containing about 20% iron and a liquid slag containing the gangue material and flux are formed. It is also possible to reduce the iron level in the matte to any desired level, thereby minimising the need for a subsequent converting operation. Before tapping, concentrate feeding is terminated, the lance is raised 0,5m to 1m from the furnace hearth to allow the bath to settle and so minimise matte entrainment in the slag. The furnace is tapped by oxygen lancing the taphole open, the matte and slag are tapped into cast iron bogeys, cooled, separated, weighed and sampled for chemical analyses. In this example, oxidation in the in-flight zone takes place on the surfaces of the various sulphide particle types whereupon a range of oxides are produced. The reactions are: 3FeS + 50₂ → Fe₃O₄ + 3SO₂ 0.5(Ni,Fe)₉S₈ + 6.870₂ → 1.125NiFe₂O₄ + 1.125NiO + 4SO₂ CuFeS₂ + 3O₂ → 0.5Cu₂O.Fe₂O₃ + 2SO₂ Because these reactions are highly exothermic, it is possible for particle temperatures to exceed well beyond 1500°C with the result that the sulphide situated below the particle surface undergoing oxidation dissociates and melts, an example being: CuFeS 2(s) → 0.5Cu₂S (1) + FeS (1) + 0.25S 2(g) where the subscripts in parentheses, namely s, 1 and g, mean solid, liquid and gas respectively. In this way a molten bleb of Cu-Fe-S is formed. Similarly, molten blebs of Fe-S and Ni-Fe-S are formed with the other sulphide types present in the sulphide concentrate. The products of the reactions taking place in the in-flight zone are therefore a range of oxides and molten sulphides. On entering the slag, in-slag reactions take place where the FeS component of the molten sulphide blebs reacts with the iron, nickel and copper oxides resulting in the reduction of trivalent iron ions to the divalent state as well as the resulphidation of the nickel and copper oxides. Some of the reactions are: FeS + 3Fe₃O₄ → 10FeO + SO₂ and FeS + Cu₂O → Cu₂S + FeO These reactions are promoted by the presence of silica, which is included in the sulphide concentrate, which promotes the in-slag reactions because of the favourability of the reaction: 2FeO + SiO₂ → Fe₂SiO₄ where fayalite (Fe₂SiO₄) is the product. 2. EXAMPLE OF THE USE OF THE LANCE FOR THE TREATMENT OF STIBNITE CONCENTRATE AND ARSENIC MIDDLINGS MATERIAL To facilitate safe and efficient furnace start-up the diesel fuel supply of the lance is temporarily replaced by butane (LP gas). The gas is ignited and the lance lowered onto a bed of coke on the furnace bottom. Once the coke is red hot the diesel replaces the LP gas and the furnace is then heated to approximately 1200°C by means of the diesel with oxygen enrichment. It is important to have cooling air flowing through the outer passage 16 of the lance at all times. An air flow of 100 to 130 Nm³/h is used at a pressure of 120kPa. A diesel flow in the passage 20 of 5 to 15 l/h is used at a pressure of 680kPa. Once the furnace is at 1200°C the feeder vessel is pressurised to 150kPa, the rotary vane feeder is started and pneumatic feeding commences. If stibnite concentrate is processed, the stibnite entering the hot furnace at the tip of the lance along passage 18 immediately reacts with the oxygen to form volatile crude antimony oxide, which is removed, condensed and collected in a baghouse. The impurities in the concentrate, approximately 15%, smelt down to form a slag bath. A small proportion of the antimony will dissolve in the molten slag as antimony oxide. Since about 85% of the feed material is volatile, the furnace vessel will take a long time to fill up. Once the furnace is filled to about 0,5m, a reduction step in which the antimony oxide is reduced to the metal is carried out by adding about 20kg of coke over a 20 minute period. The lance should be raised about five minutes before tapping to allow bath to settle and so prevent metal entrainment in the slag. The furnace is tapped by oxygen lancing the taphole open. The slag and metal bullion are tapped into cast iron bogeys, cooled, separated, weighed and sampled for chemical analyses. If arsenic middling material is treated, the process is similar to that of the stibnite concentrate. The only difference being that more gangue material is present and much more slag is formed.

Claims: A process of pyrometallurgically treating a feed material comprising the steps of: (a) producing a liquid body of feed material (50); (b) providing a lance (44) for delivering feed material in particulate form and an oxidising gas, the lance having a discharge end (48); (c) placing the discharge end (48) of the lance (44) in or immediately above the liquid body (50); (d) delivering oxidising gas through the discharge end (48) of the lance (44) at a velocity suitable to form a depression (58) in the liquid body, the depression defining at least part of the boundary of a first reaction zone; (e) introducing feed material in particulate form and an oxidising gas into the depression (58) through the discharge end (48) of the lance (44) and allowing in-flight oxidation of the feed material to take place in the depression (58); (f) allowing at least some of the reaction products of the in-flight oxidation to pass into a second zone which is in the liquid body and is in contact with the first reaction zone; and (g) allowing sulphidation or reduction of the reaction products to take place in the second reaction zone (60). A process according to claim 1 wherein the feed material is a sulphide ore or concentrate. A process according to claim 1 wherein the feed material comprises an oxide or a mixture of oxides. A process according to any one of the preceding claims wherein the liquid in the second reaction zone (60) is in a state of turbulence. A process according to any one of the preceding claims wherein the particulate feed material has an average particle size not exceeding 100 microns. A process according to any one of the preceding claims wherein the oxidising gas is selected from oxygen, oxygen-enriched air and air. A process according to any one of the preceding claims wherein the molten bath (50) contains a slag phase (52) and a matte phase (54) and the second reaction zone (60) is created in the slag phase (52) only. A process according to any one of the preceding claims wherein the feed material and oxidising gas are introduced into the first reaction zone (60) through the discharge end (48) of a lance comprising an inner passage (18) through which the feed material passes and an outer passage (16) surrounding the inner passage (18) and through which the oxidising gas passes. A process according to claim 8 wherein the inner passage (18) is circular in cross-section and the outer passage (16) provides an annulus surrounding the inner passage (18). A process according to claim 8 or claim 9 wherein the oxidising gas leaves the lance (44) at a velocity not exceeding 100 meters per second. A process according to claim 8 or claim 9 wherein the oxidising gas leaves the lance (44) at a velocity of between 50 and 70 meters per second. A process according to any one of claims 8 to 11 wherein an intermediate passage (20) is provided between the inner and outer passages (18, 16) and the intermediate passage (20) is used for delivering fuel, the discharge end (28) of the passage (20) being such as to produce a diverging flow of fuel which is discharged therefrom. A process according to any one of claims 8 to 12 wherein the outer passage (16) is provided with formations (22) adapted to create turbulence in the flow of gas passing along the passage (16).

Inventors: BODENSTEIN JOHANNES JACOBUS, EHLERS KRAUSE LUDWIG, PERRY KEVIN PHILIPPE DANIEL, BODENSTEIN, JOHANNES JACOBUS, EHLERS, KRAUSE LUDWIG, PERRY, KEVIN PHILIPPE DANIEL
Applicants: JOHANNESBURG CONS INVEST, JOHANNESBURG CONSOLIDATED INVESTMENT COMPANY LIMITED
Application year: 1991
Main classification: C22B5
IPC codes: C22B15, C22B23, C22B9, F27D3, C21B7, C22B1, C22B5, C21B13