More particularly, this invention relates to a process for treating ore or ore concentrate and to roasting apparatus suitable for roasting or treating ore or ore concentrate.

According to a first aspect of the invention, there is provided a process for treating ore or ore concentrate, the process including introducing particulate ore or ore concentrate and a carrier gas at a low elevation into a substantially vertically extending treatment zone such that the particles are entrained in the carrier gas, thereby carrying the particles upwards through the treatment zone to a high elevation where they are removed from the treatment zone together with the carrier gas; and roasting or treating the particles at elevated temperature while they are moving upwards through the treatment zone.

The metal may be a base metal. The ore or ore concentrate may include a mineral or metal selected from the group consisting of zinc, copper, nickel, iron, cobalt, a precious metal or mineral, and mixtures thereof. The ore or ore concentrate may be a mineral or metal bearing ore which includes sulphur, and the carrier gas may include oxygen. In principle, the ore or ore concentrate may be any particulate material resulting from the processing of ore, which reacts exothermically with the carrier gas to allow the roasting or reaction to proceed autogenously, even if an auxiliary fuel is to be added to the ore or ore

concentrate. Treating the particles may thus include oxidising or reducing the particles.

The carrier gas may include a gas selected from the group consisting of air, nitrogen, sulphur dioxide, carbon dioxide, oxygen, carbon monoxide, hydrogen, chlorine, and mixtures thereof.

The roasting of metal sulphide-bearing ore or ore concentrate particles in the presence of oxygen is an autogenous, exothermal reaction which will proceed once the particles have reached a required initiation temperature.

The process may include the step of controlling roasting conditions in the treatment zone by modifying the composition of the carrier gas. Thus, the temperature of the treatment zone may be controlled by controlling the partial pressure of the oxygen in the treatment zone. The partial pressure of the oxygen in the treatment zone may be controlled by introducing a gas selected from the group consisting of air, nitrogen, carbon dioxide, oxygen, and mixtures thereof at one or more selected elevations into the treatment zone. In one embodiment of the invention, nitrogen is added to the carrier gas, which is air, to decrease the concentration or partial pressure of oxygen. This is done where the process requires partial oxidation of the particles for use in a downstream process such as acid leaching. One such application for the process is the treatment of iron pyrites.

The carrier gas may be introduced into the treatment zone under pressure. Thus, the treatment zone may be maintained at a pressure of between 1 bar (g) and 30 bar (g). Typically, the treatment zone is maintained at a pressure of between 3 bar (g) and 20 bar (g).

The particles may be roasted or treated in the treatment zone for a period of between 1 s and 30s. However, it is to be appreciated that this period depends on the particular ore or ore concentrate, and may thus fall outside the range provided.

The treatment zone may have a height of between 3m and 30m.

Typically, the treatment zone has a height of between 3m and 20m.

The ratio of the volumetric flow rate of the carrier gas, expressed in Nm3/s, to a cross-sectional area of the treatment zone, expressed in m2, may be between 2: 1 and 36: 1. Typically, the ratio is between 10: 1 and 20: 1, e. g. about 12: 1.

The particles may have a particle size between 0,1/. im and 6000, um.

Typically, the particles have a particle size between 0,1, um and 250nom.

The particles may be roasted at a temperature of between 600°C and 1200°C, e. g. about 1000°C.

The treatment zone may be defined by a vertically extending vessel.

It will be appreciated by a person skilled in the art that the carrier gas moves upwardly in the vessel at a velocity which is influenced, amongst other things, by the diameter of the vessel and the pressure differential across the vessel. The particles, which are entrained in the carrier gas, move upwards at a net velocity being the difference between the carrier gas velocity and the particle free settling velocity. The formation of a fluidised bed is thus to be avoided by ensuring that conditions in the treatment zone are such that the particles are entrained and carried through the treatment zone. The particle free settling velocity is influenced, amongst other things, by the density, and thus by the pressure, of the carrier gas in the treatment zone. The residence time of the particles in the treatment zone and the temperature of the treatment zone may thus be controlled by manipulating the pressure of the treatment zone.

The linear velocity of the carrier gas through the treatment zone may be between 0,2m/s and 1 Om/s. Typically, the linear velocity of the carrier gas is between 2m/s and 5m/s, e. g. about 3,5m/s.

The process may include the step of dedusting product which leaves the treatment zone at pressure in small treatment units. Instead, the product may be released under pressure and treated in a low pressure device.

The process may include recovering energy from the carrier gas after it leaves the treatment zone. At least some of the recovered energy may be used to preheat the carrier gas prior to introducing it into the treatment zone.

Instead, or in addition, at least some of the recovered energy may be used to compress the carrier gas prior to introducing it into the treatment zone.

According to a second aspect of the invention, there is provided roasting or treating apparatus suitable for roasting or treating ore or ore concentrate, the apparatus including a vessel defining a treatment zone having a height and a horizontal cross- sectional area such that the ratio of the horizontal cross-sectional area to the height is at least 1: 6; and feed means for feeding particulate ore or ore concentrate and a carrier gas at a low elevation into the vessel, the vessel having an outlet for removing the carrier gas and particulate ore or ore concentrate at a high elevation from the vessel.

The feed means may include a carrier gas feed pipe opening out at a low elevation into the vessel, and particulate ore or ore concentrate supply means or storage means configured to feed particulate ore into the carrier gas feed pipe. Instead, the feed means may include a carrier gas feed pipe opening out at a low elevation into the vessel, and particulate ore or ore concentrate supply means or storage means configured to feed particulate ore or ore concentrate into the vessel at a low elevation, but above the opening of the carrier gas feed pipe.

The vessel may be a pressure vessel configured to operate at an internal pressure of between 1 bar (g) and 30 bar (g). Typically, the vessel is

configured to operate at an internal pressure of between 3 bar (g) and 20 bar (g), e. g about 15 bar (g).

The vessel may have an internal refractory lining. The apparatus may include heating means for heating the refractory lining and/or the particulate ore or ore concentrate and the carrier gas fed into the vessel to a temperature of at least 600°C. The heating means may be in the form of a gas or fuel oil burner located at a bottom of the vessel.

The vessel may be cylindrical. The treatment zone may have a height of between 3m and 30m, and a diameter of between 0,2m and 2m.

Typically, the treatment zone has a diameter of between 0,2m and 1,5m, and a height of between 3m and 20m, e. g a height of about 15m.

The vessel may include at least one gas inlet at an elevation above the elevation at which the feed means is configured to feed carrier gas into the vessel. Typically, the vessel includes a plurality of vertically spaced gas inlets.

The apparatus may include heat exchange means in flow communication with the outlet of the vessel and with the feed means, such that in use heat is transferred from the carrier gas exiting the vessel to the carrier gas being fed to the vessel.

The apparatus may include separation means downstream of the vessel outlet for separating particles from the carrier gas, and an expansion turbine downstream of the separation means for recovering energy from the carrier gas.

The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which

Figure 1 shows a schematic representation of one embodiment of roasting apparatus in accordance with the invention, for use in a process for treating ore concentrate; and Figure 2 shows a schematic representation of another embodiment of roasting apparatus in accordance with the invention, for use in a process for treating ore concentrate.

Referring to Figure 1 of the drawings, reference numeral 10 generally indicates roasting apparatus in accordance with the invention for treating or roasting ore concentrate. The roasting apparatus 10 includes a vertically extending pressure vessel 12 which defines a vertically extending treatment zone. The treatment zone has a height dimension as indicated by the arrow 14 of 30 metres.

The apparatus 10 includes feed means for feeding particulate ore concentrate and a carrier gas at a low elevation into the vessel 12. The feed means includes a carrier gas feed pipe 16 which opens out at a low elevation into the vessel 12, defining a carrier gas inlet 18. The carrier gas inlet 18 can also be used to drain solids from the vessel 12. A pressure regulator 20 is positioned in the carrier gas feed pipe 1 6, which leads from a carrier gas supply source generally indicated by reference numeral 22.

The vessel 12 has an outlet 24 at a high elevation.

The feed means also includes particulate ore concentrate storage means 26, which is connected by four feed pipes 28 to the vessel 12. The feed pipes 28 opens out into the vessel 12 at a low elevation, but above the carrier gas inlet 18.

An alternative feed arrangement is indicated by reference numeral 29. In this feed arrangement, the ore concentrate is fed into the carrier gas feed

pipe 16 through an ejector or similar device. The carrier gas thus acts in this case as a pneumatic transport medium for the ore concentrate particles.

A conduit 30 leads from the outlet 24 to cyclones 32 which are arranged in series for removal of the ore concentrate particles from the carrier gas which emanates from the pressure vessel 12, and for reducing the pressure of the carrier gas. The carrier gas which emanates from the cyclones 32 are fed into a plant generally indicated by reference numeral 34, which, depending on the application, could be a conventional sulphuric acid plant, a custom-designed sulphuric acid plant which receives the carrier gas at a desired, elevated pressure, or an ore cleaning system.

In use, finely milled ore concentrate particles (75/ym), in this case containing ZnS, are fed from the particulate ore concentrate storage means 26 via the feed pipes 28 into the vessel 12. The carrier gas, which is nitrogen enriched compressed air, flows under pressure (25 bar) from the carrier gas supply source 22 via the carrier gas feed pipe 16 into the vessel 12, and moves upwardly through the vessel 12, at a linear velocity which is higher than the free settling velocity of the ore concentrate particles in the carrier gas, thereby entraining the ore concentrate particles to form a carrier gas/ore concentrate particle mixture which is conveyed upwards through the vessel 12. The ore concentrate particles are roasted at a temperature of about 900°C in the treatment zone, before they are removed, together with the carrier gas, through the outlet 24. In the cyclones 32, the roasted ore concentrate particles are separated from the carrier gas, and the pressure of the carrier gas is reduced.

It will be appreciated that there are any number of variables which affect the efficiency of the roasting reaction inside the vessel 12. A vessel with a predetermined diameter and height can be designed for each ore-type. In designing a vessel which will optimise the roasting reaction, regard is firstly to be had to the specific ore which is to be treated.

For ZnS, it is known that a suitable residence time, that is the time which the particles must remain in the treatment zone, defined by the vessel 12, to fully react is in the region of about 10 seconds. The velocity, V (net) at which the ore particles move upwardly in the vessel can be approximately determined by the formula V (net) = V (g)-V (E)............................. (1) with V (E) = the particle free settling velocity, which is influenced by the size of the particle and its specific gravity and which can be easily calculated by one skilled in the art; and V (g) = the carrier gas velocity, that is the velocity at which the carrier gas moves upwardly in the vessel 12. The carrier gas velocity V (g) is influenced by the pressure at which the gas is introduced into the vessel 12, the pressure differential across the vessel 12, and the diameter of the vessel 12 and can be measured or calculated.

It will further be appreciated that if the pressure of the carrier gas is increased, mass flow of carrier gas into the vessel is increased. In this process, the increased mass flow of carrier gas into the vessel is used to control the temperature inside the vessel, thereby substantially obviating the need for the addition of water to temper the roasting process as energy released by the roasting reaction will be used in heating up the addition mass of carrier gas.

In order to control the roasting reaction, even with an increased mass flow of carrier gas into the vessel, the composition of the carrier gas may be modified. In this example, the carrier gas comprises compressed air with nitrogen added to the air to decrease the concentration or partial pressure of oxygen in the vessel.

The required reaction diameter for a given vessel can be determined if the following variables are known: Typical conditions for roasting of ZnS, for an output of 25 000 kg/h, at 25 bar and 1000° C: Typical mass flow rate of compressed air = 47 000 kg/h.

Volumetric flow rate of compressed air through the vessel = 36306 Nm3/h.

Actual volumetric flow rate of compressed air through the vessel = 6577m3/h.

Typical mass flow rate of diluent nitrogen = 8530 kg/h.

Volumetric flow rate of nitrogen through the vessel = 6824 Nm3/h.

Actual volumetric flow rate of nitrogen through the vessel = 1223m3/h.

The total volumetric flow rate of compressed air and diluent nitrogen- 7800m3/h The height of the vessel 12 = 30 m.

The required residence time = 10 seconds.

The particle size of the ZnS particles = 75 um.

The density of ZnS particles = 4000kg/m3 The free settling velocity as determined by formula (1) = 0.27 m/sec.

Required gas velocity for a 30 m reactor or vessel with a 10 second residence time = 3,27m/s.

Thus, if Area = Flow/Velocity, then Vessel diameter = (7800 m3/h/3600/3.27 x 4/ru) 0 5 918 mm.

Similarly, the required gas velocity for a 20 m reactor or vessel with a 10 second residence time = 2.27m/s.

Thus, if Area = Flow/Velocity, then Vessel diameter = (7800 Am3/h/3600/2.27x4/77) 1102 mm.

Referring to Figure 2 of the drawings, reference numeral 100 generally indicates another embodiment of roasting apparatus in accordance with the invention, for treating or roasting particulate ore concentrate. The roasting apparatus 100 includes a cylindrical vessel 102 defining a vertically extending treatment zone having a height of about 15m and a diameter of about 1 m. The apparatus 100 also includes feed means, generally indicated by reference numeral 104 for feeding particulate ore concentrate and a carrier gas at a low elevation into the vessel 102. The vessel 102 has an outlet 106 for removing the carrier gas and particulate ore concentrate at a high elevation from the vessel 102.

The feed means 104 includes a carrier gas feed pipe 108 opening out at a low elevation into the vessel 102, and particulate ore concentrate storage means 110. A screw conveyor 112 is provided to feed particulate ore concentrate from the particulate ore concentrate storage means 110 into the vessel 102 at a low elevation, but above the opening of the carrier gas feed pipe 108 into the vessel 102. An alternative feed arrangement for the particulate ore concentrate is shown in broken lines and identified by reference numeral 105.

In this arrangement, the particulate ore concentrate is gravity fed directly into the carrier gas feed pipe 108.

A gas or fuel oil burner 114 extends into the vessel 102 through a bottom of the vessel 102, which has an internal refractory lining (not shown).

From the outlet 106, a product line 116 leads to a heat exchanger 118, and from the heat exchanger 118 to a separation unit 120. A roasted ore concentrate line 122 emerges from the separation unit 120, as well as an acid plant feed line 124. A pressure regulator 126 is provided in the acid plant feed line 124.

The acid plant feed line 124 feeds into a sulphuric acid plant, generally indicated by reference numeral 128, from which a sulphuric acid

product line 130 leads, as well as an offgas line 132. The offgas line 132 enters an expansion turbine 134, from where an offgas vent 136 leads to atmosphere.

The roasting apparatus 100 also includes a supply of compressed air 138, a supply of compressed oxygen 140 and a supply of compressed nitrogen 142. As will be appreciated, other gases such as chlorine or hydrogen, may be provided, depending on the reactions required. The supplies of compressed air, oxygen and nitrogen 138,140,142 may form part of a conventional air separation unit. As can be seen in Figure 2, the supplies of compressed air, oxygen and nitrogen 138,140 and 142 are all connected to the carrier gas feed pipe 108, but also to six gas inlets 144, which enters the vessel 102 at vertically spaced positions.

In use, the carrier gas, in the form of compressed air at a pressure of 20 bar from the supply of compressed air 138, is fed via the carrier gas feed pipe 108, through the heat exchanger 118, into the bottom of the vessel 102.

In the heat exchanger 118, hot carrier gas emanating from the vessel 102 via the product line 116 exchanges heat with the carrier gas in the carrier gas feed pipe 108, thereby preheating the carrier gas to a required temperature.

However, in the majority of roasting, oxidation or reduction reactions for which the apparatus 10 can be used, it would be undesirable to preheat the carrier gas.

A bypass 119 can then be employed.

Particulate metal or mineral bearing ore concentrate which requires roasting is fed from the particulate ore concentrate storage means 110 by means of the screw conveyor 112 into the vessel 102, where the ore concentrate particles are entrained and carried upwards through the vessel 102 as hereinbefore described. The roasting of sulphide bearing ore concentrate, and many other ore concentrates, are autogenous, exothermic processes. In order to initiate the roasting process, the burner 114 is used initially to heat the refractory lining of the vessel 102 and incoming carrier gas and particulate ore to a suitably high temperature to allow the roasting process to continue without

any further energy input. Once the treatment zone is at a suitably high temperature to allow the roasting process to continue without further energy input, the burner 114 is switched off.

In the vessel 102, the ore concentrate particles are roasted whilst moving upwards through the vessel 102. A desired temperature in the treatment zone is maintained by increasing the pressure of the carrier gas and/or by adding air, oxygen or nitrogen into the vessel 102 by means of the gas inlets 144. The linear velocity of the carrier gas through the vessel 102 is manipulated by controlling the pressure differential across the vessel 102 by means of the pressure regulator 126. As will be appreciated, by means of injecting air, nitrogen or oxygen into the vessel 102 at different elevations, the reaction conditions inside the vessel 102 at different elevations can be manipulated.

From the vessel 102, the roasted ore concentrate particles and the carrier gas leave through the product line 116 and, if desired, exchanges heat with the carrier gas being fed to the vessel 102, in the heat exchanger 118 as hereinbefore described. The cooled particulate ore concentrate and carrier gas are fed into the separation unit 120, where roasted ore concentrate particles are separated from the carrier gas and discharged through the roasted ore concentrate product line 122. The carrier gas is fed along the acid plant feed line 124 into the sulphuric acid plant 128, where it is treated to produce sulphuric acid, which is discharged through the sulphuric acid product line 130.

Offgas from the sulphuric acid plant 128 is fed by means of the offgas line 132 to an expansion turbine 134, where the pressure of the offgas is reduced to about atmospheric pressure, before the offgas is vented to atmosphere via the offgas vent 136. As will be appreciated, the energy recovered from the offgas by means of the expansion turbine 134 can be used to compress air for use as carrier gas, or for driving the compressor of an air separation unit.

The applicant believes that the process of the invention, as illustrated, has several advantages, the first being that the temperature is

controlled by pressure or addition of nitrogen or other diluent gas without addition moisture being introduced into the vessel which may adversely affect the process. Also, the process provides a means to reduce capital costs of pyrometallurgical equipment. The process has various applications and could be used on existing plants, especially where an existing oxygen plant and/or a nitrogen plant is in operation. Product is released from the vessel under pressure and can be used in applications where further treatment of the product is conducted at high pressure, such as in an acid plant, thereby resulting in a saving of costs. The applicant also believes that the process and apparatus, as illustrated, obviates the need for blending of minerals prior to roasting, as is often the case with conventional roasting processes and apparatus, in order to obtain a blend of sufficiently high grade.

The process and apparatus of the invention, as illustrated, provides the necessary residence time for roasting ore or ore concentrate, without the need for establishing and maintaining a fluidised bed.

It is expected that the process, as illustrated, will allow control over reaction conditions to limit the formation of undesirable roasting products, which can impede downstream ore or ore concentrate leaching processes.

Furthermore, due to smaller equipment, lower heat losses can be expected, which may be desirable in some roasting processes.