[0001] The present disclosure relates to improvements in, or relating to, the treatment of by-products of ferrous metal processing, such as steel waste.

[0002] The present invention concerns the treatment of by-products of ferrous metal processing. More particularly, but not exclusively, this invention concerns a method of treating particulate by-product of ferrous metal processing. The invention also concerns an apparatus for treating particulate by-product of ferrous metal processing.

[0003] Iron and steel processing produce many solid particulate by-products. Some of those by-products may be used without further treatment. However, many of the by products may only be used after suitable treatment, and in some cases that treatment is not economically viable, given the market value of the treated product. In such cases the by-product will typically be stored in landfill.

[0004] For example, steel is typically made by adding scrap steel to molten iron in a process often called the basic oxygen process, or by melting scrap in an electric arc furnace. The scrap steel often has a relatively high zinc content, and the steel making process results in the generation of particles comprising iron and zinc. Such particles are of varying size and zinc content, larger particles often known as “grit” (typically having a lower zinc content), and smaller particles often known as “dust”, typically a free-flowing powder with particles of small size (comprising particles having a mean greatest dimension of 1-lOOOmicrons), with a higher zinc content. Zinc may be recovered from the waste material by thermal processes. One such process in the waelz process, which involves heating the zinc-containing waste in a rotary kiln with a carbon-containing reductant to a temperature of 1000-1500°C. The zinc is reduced to elemental zinc that is volatised, and then oxidised to ZnO, which is recovered. Another process used to recover zinc is the rotary hearth process. Pelletised material is heated and reduced, with dust containing high levels of zinc being recovered. [0005] The capital outlay involved in purchasing such thermal processing equipment is high, and the performance of such methods is energy-intensive and expensive, given the heating involved. It is therefore only financially viable to use such methods to treat waste with the relatively high zinc content. Waste with a zinc content lower than that which is viable to treat is not treated, and is effectively treated as toxic waste and stored in landfill. [0006] Similarly, steel may be subject to what is known as a pickling process in which the surface of the steel is exposed to a pickling liquid, typically an acid such as hydrochloric, sulphuric or phosphoric acid that cleans the surface of the steel. The by product of the pickling process is a pickling liquor that contains particulate removed from the surface of the steel. The liquid may be removed from the pickling liquor to isolate the particulate, forming what is often called filter cake. The filter cake often has a large iron content and therefore it may be desirable to use such material in a blast furnace or the like. However, oftentimes the filter contains unacceptably high levels of contaminants (e.g. chlorine or sulphur-containing species) that prevent use in a blast furnace. It would therefore be desirable to remove the contaminant.

[0007] The present invention seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved method for the treatment of said particulate by-product.

SUMMARY OF THE INVENTION

[0008] In accordance with a first aspect of the present invention, there is provided a method of treating particulate by-product of ferrous metal processing, the method comprising exposing said particulate by-product to ultrasound, said particulate by product being located in a carrier fluid.

[0009] The embodiment of the present invention facilitates the treatment of particulate by-product of ferrous metal processing, such as steel or iron waste. The particulate by product is typically not dissolved in the carrier fluid. The by-product and carrier fluid may form a slurry, for example. [0010] The method of the present invention may help facilitate a reduction of the amount of one or more target species in said by-product. In this connection, the method may comprise forming a target species-depleted component and a target-species enhanced component. Exposure to ultrasound may facilitate the formation of the target species- depleted component and the target-species enhanced component. The target-species depleted component may, for example, comprise particulate. The target-species enhanced component may, for example, comprise particulate and/or a solution in which the target species is dissolved. For example, the method may reduce the amount of chlorine- containing species in a steel waste, with the target chlorine-containing species being dissolved as chloride in the carrier fluid to produce a chloride-enhanced component in the form of a chloride solution. The particulate is chlorine-species depleted, and may be used in an environment that does not tolerate high concentrations of chlorine- containing species (e.g. in a blast furnace). If the method reduces the amount of zinc in a steel waste, the target species zinc may be in the form of a solid (for example, as elemental zinc or zinc oxide). The zinc-depleted particulate may then be used in an environment that does not tolerate high concentrations of zinc. The use of the word “target” herein merely indicates that it is desirable to remove said species from the by-product. The target- enhanced component may be a waste material that is disposed of (for example, kept in landfill) or may be used or further processed into a useful product. Those skilled in the art will realise that “depleted” indicates that the amount of target species has been reduced, but not necessarily removed completely.

[0011] Any suitable size of particulate may be treated, although those skilled in the art will realise that particles of a larger size (e.g. a greatest dimension of 5mm) may be less effectively treated on account of their having a relatively small surface area for the volume of material that is treated. Material treated using the method of the first aspect of the present invention may have a very broad particle size distribution. Optionally, the particulate may comprise a portion of particles having a greatest dimension of no more than 50 microns, optionally of no more than 30 microns, optionally of no more than 20 microns and optionally or no more than lOmicrons. Optionally, the particulate may comprise at least 10% by number, optionally at least 20% by number, optionally at least 30% by number and optionally at least 40% by number of particles having a greatest dimension of no more than 50 microns, optionally of no more than 30 microns, optionally of no more than 20 microns and optionally or no more than lOmicrons.

[0012] Those skilled in the art will realise that the method of the present invention does not necessarily remove all of the target material from the particulate.

[0013] The carrier fluid may comprise a liquid. The liquid may be an aqueous liquid i.e. it comprises water. Those skilled in the art will realise that other liquids may be used, but water is inexpensive and readily-available.

[0014] The amount of by-product used in the method of the first aspect of the present invention may vary, for example, based on the presence of other non-by-product components. For example, if the by-product is provided as a mixture with other solid material (such as coal or coke waste), then the amount of by-product relative to the amount of fluid will be reduced. In his connection, the amount of solid comprising by product and non-by-product (if present) may be at least 25% by volume, based on the total volume of the solid and carrier fluid, optionally at least 30% by volume, optionally at least 40% by volume, optionally at least 50% by volume, optionally at least 60% by volume and optionally at least 70% by volume, based on the total volume of the solid and carrier fluid. The amount of solid comprising by-product and non-by-product (if present) may be no more than 95% by volume, based on the total volume of the solid and carrier fluid, optionally no more than 90% by volume, optionally no more than 85% by volume and optionally no more than 80% by volume, based on the total volume of the solid and carrier fluid. Optionally, there may be substantially no non-by-product present and therefore the volume % above relate to the by-product.

[0015] The temperature of the carrier fluid and/or particulate during exposure to ultrasound may be no more than 90°C, optionally no more than 80°C, optionally no more than 70°C, optionally no more than 60°C, optionally no more than 50°C and optionally no more than 40°C.

[0016] The temperature of the carrier fluid and/or particulate during the exposure to ultrasound may be at least 5°C, optionally at least 10°C, optionally at least 15°C and optionally at least 20°C. [0017] Those skilled in the art will realise that exposing the particulate to ultrasound may generate heat, and therefore exposure to ultrasound may take place at an above-ambient temperature without taking other steps (such as using a heater to heat the carrier fluid) to heat the particulate and/or carrier fluid. Alternatively, the method may comprise heating the carrier fluid and/or particulate by-product.

[0018] The temperature of the carrier fluid and/or particulate during the exposure to ultrasound may be ambient temperature. The exposure to ultrasound may therefore be performed without heating either the fluid or the particulate.

[0019] The frequency of the ultrasound may be at least 10kHz, optionally at least 15kHz and optionally at least 20kHz. The frequency of the ultrasonic waves may be no more than 100kHz, optionally no more than 80kHz, optionally no more than 60kHz and optionally no more than 40kHz.

[0020] The frequency of the ultrasound may be from 15kHz to 60kHz.

[0021] The particulate by-product may be exposed to ultrasound for at least 5 minutes, optionally for at least 10 minutes, optionally for at least 20 minutes, optionally for at least 30 minutes.

[0022] The particulate by-product may be exposed to ultrasound for no more than 300 minutes, optionally for no more than 240 minutes, optionally for no more than 180 minutes, optionally for no more than 120 minutes and optionally for no more than 60 minutes.

[0023] The particulate by-product may be exposed to ultrasound for from 5 to 300 minutes, optionally from 10 to 240 minutes, optionally from 10 to 120 minutes, optionally from 20 to 120 minutes and optionally from 30 to 60 minutes.

[0024] The mean power density of the ultrasound may be at least lOW/litre of fluid, optionally at least 15W/1., optionally at least 20W/L, optionally at least 30W/1., optionally at least 40W/1. and optionally at least 50W/1. The mean power density of the ultrasound may be calculated by dividing the power of the ultrasound generator(s) that emit ultrasound into the fluid by the volume of fluid into which the ultrasound is emitted. [0025] The mean power density of the ultrasound may be no more than 500W/litre of fluid, optionally no more than 400W/L, optionally no more than 300W/1., optionally no more than 200W/1. and optionally no more than lOOW/1.

[0026] The frequency of the ultrasound may be varied. The particulate by-product may be exposed to more than one frequency of ultrasound. For example, the particulate by product may be exposed to ultrasound having a first band of frequencies and subsequently exposed to ultrasound having a second band of frequencies, the second band of frequencies being different from the first band of frequencies. Optionally, there may be no overlap between the first band of frequencies and the second band of frequencies. Optionally, the method may comprise exposing the particulate by-product to ultrasound having a first band of frequencies in a first ultrasound treatment region and exposing the particulate by-product to ultrasound having a second band of frequencies in a second ultrasound treatment region. The first and second ultrasound treatment regions may be provided by a conduit or other elongate reaction chamber. The first ultrasound treatment region may be provided by a first reaction vessel and the second ultrasound treatment region may be provided by a second reaction vessel.

[0027] The ultrasound may be pulsed, for example.

[0028] The method may comprise dispersing said by-product in a carrier fluid, thereby forming particulate by-product located in the carrier fluid. The method may comprise admixing said by-product and carrier fluid. The method may comprise admixing by product particulate and carrier fluid. The method may comprise admixing by-product and carrier fluid, thereby forming particulate by-product of ferrous metal processing located in a carrier fluid. The by-product may initially not be in particulate form (for example, it may be in the form of large “chunks” or of a “cake” of solid material), or may be in the form of large breakable pieces. Admixing with the carrier fluid may cause the formation of particles of by-product and/or cause the formation of particles with a lower mean size. Admixing at least part of said fluid with at least part of the by-product may take place in a mixing zone. The mixing zone is optionally upstream of an ultrasound treatment region in which the particulate by-product is exposed to ultrasound. [0029] The by-product of ferrous metal processing may comprise any by-product generated during the production and/or processing of ferrous metals, such as steel or iron. The by-product may comprise one of more by-product of iron or steel making (for example, electric arc furnace or basic oxygen steel making) or iron or steel processing (for example, steel rolling, hot or cold; or steel pickling). The by-product may be derived, or obtained from, a slurry, sludge or dispersion of particulate, said sludge, slurry or dispersion being generated during the production and/or processing of ferrous metals.. Alternatively, such a slurry, sludge or dispersion may be exposed to ultrasound.

[0030] The by-product may comprise steel waste, such as solid material produced by steel making (such as flue dust or solid material is steel making sludge or slurry), solid material produced by steel rolling (for example, solid material in cold or hot rolling mill sludge, or mill scale), solid material produced by cleaning metal (for example, pickling filter cakes or solid material in pickling liquor).

[0031] The by-product (for example, steel waste) may be found mixed with other solid material, such as coke and/or coal dust, and/or solid material produced by the processing of coal or coke, in particular, by the sizing or screening of coal or coke.

[0032] As mentioned above, the method of the present invention may comprise forming a target species-depleted component and a target species-enhanced component. The method may comprise separating the target species-depleted component from the target species- enhanced component. Such separating may take place in a separation zone, for example. Separating the target species-depleted component from the target species-enhanced component may comprise applying a magnetic field. This may facilitate the separation of magnetic components from non-magnetic components. Separating may comprise separating the target species-depleted component from the target species-enhanced component by gravitational separation. This may be used to separate dense components from less dense components. Separating may comprise filtration. This may be used to separate solid components from liquid components and/or liquid-dissolved components. [0033] Those skilled in the art will realise that the method may comprise forming more than one target species-depleted component and/or more than one target-species enhanced component. [0034] Exposing the particulate by-product to ultrasound may provide a solid, target species-depleted component, optionally in the form of particulate. The method may comprise agglomerating said solid, optionally into pellets. The pellets may be of any suitable size and shape. The mean greatest dimension of the pellets of the agglomerate composition may be at least 2mm, optionally at least 5mm and optionally at least 10mm. The mean greatest dimension may be up to 100mm, optionally up to 80mm, optionally up to 60mm, optionally up to 50mm and optionally up to 40mm. The mean greatest dimension may be from 10mm to 50mm, for example. The pellets of the agglomerate composition may be substantially spherical, in which case the mean diameter of the pellets of the agglomerate composition may be at least 2mm, optionally at least 5mm and optionally at least 10mm. The mean diameter may be up to 100mm, optionally up to 80mm, optionally up to 60mm, optionally up to 50mm and optionally up to 40mm. The mean diameter may be from 10mm to 50mm, for example. Pellets of such size have been found to be advantageous.

[0035] The particulate by-product may comprise iron. The particulate may comprise at least 5wt% iron, optionally at least 10wt% iron, optionally at least 15wt% iron and optionally at least 20wt% iron. The particulate may comprise no more than 80wt% iron, optionally no more than 70wt% iron, optionally no more than 60wt% iron, optionally no more than 50wt% iron, optionally no more than 40wt% iron, optionally no more than 35wt% iron, optionally no more than 30wt% iron and optionally no more than 25wt% iron. The wt% above are based on the weight of the particulate by-product.

[0036] At least some of the iron may be in the form of an iron oxide, such as FeiCb or Fe304. At least some of the iron may be in the form of iron metal i.e. elemental iron. [0037] The particulate by-product may comprise one or more of calcium (optionally in the form of calcium oxide), magnesium (optionally in the form of magnesium oxide), manganese, alumina, silica, lead and chromium.

[0038] The method of the present invention may be used to generate a zinc-depleted component (optionally the particulate from which at least some zinc has been removed) and a zinc-enhanced component (optionally particles comprising zinc). This may be the case, for example, for the treatment of flue dust from an electric arc furnace. Without wishing to be bound by theory, it is anticipated that the zinc-enhanced component comprises zinc oxide.

[0039] The particulate by-product comprising zinc may be, or be derived from, steel waste, such as the so-called “steel dust” (for example, waste dust collected from the off gases of steel making converters or furnaces, such as oxygen blown converters or electric arc furnaces, and any heavier drop-out material).

[0040] The particulate by-product may comprise iron and zinc. The particulate may optionally comprise one or more of chromium, lead, aluminium, manganese and calcium. [0041] The particulate by-product may comprise no more than 40wt% zinc, optionally no more than 35wt% zinc, optionally no more than 30wt% zinc, optionally no more than 25wt% zinc and optionally no more than 20wt% zinc. Such relatively high levels of zinc may be found, for example, in waste generated by electric arc furnace steel making.

[0042] The particulate by-product may comprise at least 5wt% zinc, optionally at least 10wt% zinc, optionally at least 15wt% zinc and optionally at least 20wt% zinc. The zinc may be in the form of zinc oxide.

[0043] The particulate by-product may comprise at least 0.5wt% zinc, optionally at least 1.0wt% zinc and optionally at least 1.5wt% zinc. The particulate may comprise no more than 5wt% zinc, optionally no more than 4wt% zinc, optionally no more than 3wt% zinc, optionally no more than 2.0wt% and optionally no more than 1.5wt% zinc. Such relatively low levels of zinc may, for example, be generated by blown oxygen steel making.

[0044] The particulate by-product may comprise at least 30wt% iron, optionally at least 40wt% iron and optionally at least 50wt% iron.

[0045] The method of the present invention may be used to reduce the zinc content of a particulate to a level sufficiently low to allow the particulate to be used in a steel-related process, such as in a blast furnace, as opposed to being treated as waste. For example, sufficient zinc may be removed from blown oxygen convertor waste to facilitate use of the zinc-depleted waste in a blast furnace.

[0046] The method of the present invention may provide a zinc-depleted component and a zinc-enhanced component. The method may comprise separating the zinc-depleted component from the zinc-enhanced component. Separating the zinc-depleted component from the zinc-enhanced component may comprise applying a magnetic field to the zinc- depleted component and the zinc-enhanced component. The zinc-depleted component may optionally comprise magnetic material, such as ferrous material. The zinc-enhanced component may also comprise magnetic material, but not as high a percentage as the zinc-depleted component. Separating the zinc-depleted component from the zinc- enhanced component may comprise using a density separation method. For example, a jig may be used to separate the zinc-enhanced component from the zinc-depleted component. [0047] The target species in the particulate by-product may optionally comprise one or more of a chlorine-containing species, a sulphur-containing species, a nitrogen-containing species, a phosphorous-containing species, a fluorine-containing species and a citrate- containing species. The target species optionally comprises one or more of a chlorine- containing species or a sulphur-containing species. The target species optionally comprises a chlorine- containing species. The chlorine- containing species optionally comprises chloride ions, but other species are possible. The target species is optionally capable of being removed by an aqueous carrier fluid. Exposing the particulate by product to ultrasound in the presence of an aqueous carrier fluid may produce a target species-depleted material. The target species optionally comprises an anion.

[0048] The particulate by-product may comprise, and optionally be, a by-product of the pickling of iron or steel.

[0049] The iron in the particulate by-product may be in any oxidation state but typically the majority of iron is iron (II) or iron (III). The particulate by-product optionally comprises both iron (II) and iron (III), for example, comprising a core or inner portion comprising iron (II), and an outer portion comprising iron (III). The method of the present invention may oxidise iron (0) to iron (II) and/or iron (III), and/or oxidise iron (II) to iron (III).

[0050] The particulate by-product optionally comprises at least 20wt% iron, optionally at least 30wt% iron and optionally at least 40wt% iron. The particulate by-product optionally comprises up to 60wt%, optionally up to 55wt% iron and optionally up to 50wt% iron. The particulate by-product optionally comprises more than lwt% target species.

[0051] After exposure to ultrasound, the target species-depleted (and optionally oxidised) component may optionally comprise at least 50wt% iron and optionally no more than 1.0wt% of said target species. The target species-depleted (and optionally oxidised) material may comprise at least 55wt% iron and optionally at least 60wt% iron.

[0052] The method may comprise contacting the particulate by-product with an oxidising agent, optionally before and/or during and/or after exposure to ultrasound. The method may comprise contacting the particulate by-product with a gaseous oxidising agent, such as a gas comprising oxygen, such as air. The gaseous oxidising agent may be used to agitate the particulate by-product.

[0053] The method may be a batch process in which a portion of particulate is exposed to ultrasound. For example, a portion of particulate and associated carrier fluid may be exposed to ultrasound in a receptacle provided with ultrasound emitters, and then the portion of particulate and associated carrier fluid may be transferred to a separator, with a second portion of particulate and associated carrier fluid being transferred into the receptacle.

[0054] The method may be a continuous process. A continuous process is a flow production process in which the particulate is optionally in continuous motion.

[0055] The method may comprise one or more continuous process parts and one or more batch process parts. For example, exposure to ultrasound may take place in a continuous process in which particulate and associated carrier fluid moves continuously while being exposed to ultrasound. The separation may be a batch process. For example, a batch of particulate and associated carrier fluid may be transferred into a separator, and the separator used to separate particulate from the associated carrier fluid.

[0056] In accordance with a second aspect of the present invention, there is provided an apparatus for the treatment of particulate by-product of ferrous metal processing, the apparatus comprising: an ultrasound treatment arrangement comprising at least one ultrasound generator configured to emit ultrasound into an ultrasound treatment region configured to contain particulate by-product of ferrous metal processing in a carrier fluid; and a separator configured to receive ultrasound-treated carrier fluid and/or particulate from the ultrasound treatment region.

[0057] Those skilled in the art will realise that neither the particulate by-product nor the carrier fluid in which it is located is part of the apparatus of the second aspect of the present invention.

[0058] The apparatus may comprise more than one ultrasound generator.

[0059] More than one ultrasound generator may be configured to emit ultrasound into a volume of the ultrasound treatment region (i.e. more than one generator may emit ultrasound into one place, optionally at the same time).

[0060] The ultrasound treatment region may be elongate. For example, the ultrasound treatment region may be defined by a conduit or other elongate chamber. The use of an elongate treatment region facilitates the use of a continuous (as opposed to a batch) treatment process. If the apparatus comprises more than one ultrasound generator, then at least two of those ultrasound generators may be mutually spaced along the ultrasound treatment region.

[0061] The ultrasound treatment arrangement may comprise a first ultrasound treatment region and a second ultrasound treatment region. The first and second ultrasound treatment regions may be provided by an elongate chamber or conduit. One or more ultrasound treatment conditions in the second ultrasound treatment region may be different from in the first ultrasound treatment region. Alternatively, the first ultrasound treatment region may be provided by a first ultrasound treatment chamber and the second ultrasound treatment region may be provided by a second ultrasound treatment chamber. The second ultrasound treatment chamber may be downstream of the first ultrasound treatment chamber. One of more ultrasound treatment conditions may be different in the second ultrasound treatment chamber from in the first ultrasound treatment chamber. For example, an ultrasound generator configured to emit ultrasound into the second ultrasound treatment chamber may be configured to emit ultrasound of a frequency band that is different from the frequency band that an ultrasound generator configured to emit ultrasound into the first ultrasound treatment region is configured to emit.

[0062] The apparatus may comprise a mixer for admixing a carrier fluid with by-product of ferrous metal processing to produce particulate by-product located in the carrier fluid. The apparatus is typically configured to facilitate transfer of the mixed carrier fluid and particulate from the mixer to the ultrasound treatment region.

[0063] The mixer may comprise a slurrifier.

[0064] The separator may comprise one or more of a magnetic separator, a density separator, a centrifugal separator and a filter. A magnetic separator may facilitate separation of iron- containing components from non-magnetic components. A density separator may facilitate separation of dense components from less dense components. A filter may facilitate separation of solid, non-dissolved components from a carrier fluid (such as a liquid). A centrifugal separator is typically used to separate solids from liquids. [0065] The apparatus may comprise an agglomerator, for example, to form granules, tablets, briquettes or the like, optionally from particulate from the separator. The agglomerator may be downstream of the separator, and may be configured to receive particulate from the separator.

[0066] The apparatus may comprise a neutralising region upstream of the ultrasound treatment arrangement. In the neutralising region neutralising agent may be added. The neutralising region may be configured to receive a dispersion from a steel pickling apparatus and to add neutralising agent (e.g. alkali) to an acidic dispersion.

[0067] Those skilled in the art will realise that the method of the first aspect of the present invention may use any of the features of the apparatus of the second aspect of the present invention. Furthermore, the method of the first aspect of the present invention may use the apparatus of the second aspect of the present invention.

[0068] Those skilled in the art will further realise that the apparatus of the second aspect of the present invention may comprise one or more of the features of the method of the first aspect of the present invention.

DESCRIPTION OF THE DRAWINGS [0069] Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

[0070] Figure 1 shows a schematic representation of a method according to a first embodiment of the invention, the method being a method of reducing the amount of zinc in flue dust;

[0071] Figure 2 shows a schematic representation of an apparatus according to another embodiment of the invention, the apparatus being an apparatus suitable for reducing the amount of zinc in flue dust;

[0072] Figure 3 shows a schematic representation of a further method according to a further embodiment of the invention, the method being a method of reducing the chloride content of pickling line filter cake and oxidising iron in the solid component;

[0073] Figure 4 shows a schematic representation of another apparatus according to another aspect of the invention, the apparatus being an apparatus suitable for reducing the chloride content of pickling line filter cake and oxidising iron in the solid component; [0074] Figure 5 shows a schematic view of a method according to another embodiment of the invention, the method being a method of treating pickling line liquor to reduce the chloride content in the solid component and oxidise iron in the filter cake solid component; and

[0075] Figure 6 shows a schematic view of an apparatus according to another embodiment of the invention, the apparatus being an apparatus for treating pickling line liquor to reduce the chloride content in the solid component and oxidise iron in the solid component.

DETAIFED DESCRIPTION

[0076] A first embodiment of a method of the invention will now be described with reference to Figure 1. The method is denoted generally by reference numeral 100. Water and electric arc furnace (EAF) flue dust were mixed 101 in a volume ratio of 1 :3 to form a slurry. The slurry was put into an ultrasonic bath (a GT ultrasonic cleaner) and exposed 102 to ultrasound for about 1 hour at a bath temperature of about 80°C. The ultrasound had a frequency of 40kHz. The nominal power of the ultrasound generators was 100W. The nominal volume of the bath was 3 litres, though the volume of material that could be held in the bath was probably 1.5-2 litres. The zinc content of the EAF dust prior to treatment was 25wt%.

[0077] A scum was formed on the surface of the water, and a light coloured material is observed on the top of a darker material at the bottom of the bath. It is strongly suspected that the light coloured material on top of the darker material is primarily zinc oxide. It is strongly suspected that the darker material is a zinc-depleted iron-containing particulate that may be used in a blast furnace or similar. The water is removed and the zinc oxide separated 103 from the darker coloured material. The method described above is a batch process in which a batch of particulate is treated, and then removed and then separated. Those skilled in the art will realise that this need not be the case, and a continuous method may be used. The darker material in the bottom of the bath was analysed using x- ray fluorescence and x-ray diffraction, which confirmed that the zinc content had been reduced.

[0078] Figure 2 is a schematic representation of an apparatus that may be used to treat EAF flue dust. The apparatus is denoted generally by reference numeral 1000, and comprises a mixer 1001 for mixing the flue dust with a fluid (in this case, water) to form a dispersion of the flue dust in water, an ultrasound treatment arrangement 1002 configured to receive particulate dispersed in a fluid from the mixer 1001 in an ultrasound treatment region 1009 defined by a conduit 1003. The ultrasound treatment arrangement 1002 comprises ultrasound emitters, only four of which are shown 1004a-d, for emitting ultrasound into the ultrasound treatment region 1009, and a separator 1005 configured to receive treated particulate and fluid from the ultrasound treatment region 1009. The mixer 1001 may, for example, be a trommel wash that permits mixing of the particulate and fluid, while facilitating removal of unwanted large particles. The ultrasound treatment portion 1009 is defined by a conduit 1003. In the present case, the conduit 1003 is linear, with multiple ultrasound emitters 1004a-d arranged along the length of the conduit 1003. Those skilled in the art will realise that the conduit need not be linear and may, for example, be tortuous or serpentine. A heater (not shown) may be provided to heat the fluid in the conduit 1003. The separator 1005 is, in this case, a jig separator. This facilitates the separation of materials of different density. Apparatus 1000 may be used in a batch or continuous mode. In batch mode, a batch of a mixture of particulate and fluid is passed into the conduit 1003. The batch of mixture is exposed to ultrasound in the conduit 1003. After treatment, the batch is then fed to the separator 1005. In continuous mode, liquid is continuously fed from the mixer and through the conduit 1003, the mixture being treated as it passes through the conduit 1003. The jig separator 1005 facilitates the separation of the zinc oxide from the remaining particulate, with the zinc oxide tending to remain on the jig separator screen while the remaining particulate falls through the screen into the bottom of the jig separator 1005. The zinc oxide and the particulate may then be dewatered.

[0079] A further embodiment of a method of the invention will now be described. A slurry of steel making dust was formed by mixing 3 volumes of steel making dust with 1 volume of water. The steel making dust was generated by a blown oxygen process, and had an iron content of more than 50wt% and a zinc content of about 0.45wt%. The slurry was subjected to ultrasound treatment substantially as described above with reference to the treatment of EAF dust. The treated material was analysed by x-ray fluorescence and x-ray diffraction, and the zinc content was found to have decreased.

[0080] A further embodiment of a method of the invention will now be described by reference to Figure 1. A slurry of ferrous chloride pickling line filter cake was made by mixing 101 equal volumes of water and ferrous chloride filter cake obtained from a steel making pickling line. The slurry was put into an ultrasonic bath (the same as that described above with reference to the treatment of EAF dust) and exposed 102 to ultrasound at a bath temperature of 80°C. Oxidation of the iron in the filter cake was observed to take place over a period of about 20 minutes, with the treated material becoming a lot darker in colour. The ferrous chloride material formed what is believed to be haematite. The solid material was separated 103 from the liquid and dried. It could then be used in the iron and steel making process. The time taken for the formation of the darker material was significantly shorter than if no ultrasound was used. Furthermore, the time taken to form the darker material was also significantly shorter than the time taken if attempts were made to oxidise the iron by bubbling air through the water in the absence of ultrasound (it is estimated that the method of the present invention was 60% faster than by using air pumped into the water). Furthermore, unwanted chlorine-containing species (such as chloride ions) are removed from the particulate, making it suitable for subsequent use in a blast furnace.

[0081] It is possible to use both ultrasound and air pumped into the water to treat the filter cake.

[0082] Another embodiment of a method and an apparatus of the present invention will be described by way of example only with reference to Figures 3 and 4, of which Figure 3 is a schematic representation of a method denoted generally by reference numeral 200 and Figure 4 is a schematic representation of an apparatus denoted generally by reference numeral 2000. Pickling line filter cake is broken up and mixed 201 in a trommel wash mixer 2001 with water. The dispersion so formed is then transferred to an ultrasound treatment region 2002 in which the dispersion is exposed 202 to ultrasound. The ultrasound treatment region is essentially defined by a conduit (not shown) as described above in relation to Figure 2. Haematite is formed and unwanted chlorine-containing species removed. The treated dispersion is then transferred to a separator 2005 for separating 203 the particulate from the liquid. In this case, the separator 2005 is a centrifuge that removes the liquid from the particulate. The particulate collected from the centrifuge is agglomerated 204 in an agglomerator 2006 with a curable resin precursor and the precursor pellets so formed are then cured 205 in a curer 2007 to form pellets that may be used in a blast furnace.

[0083] Those skilled in the art will realise that the dispersion of particulate in liquid will already be formed. For instance, pickling line filter cake is typically formed by removing liquid from a dispersion of particles removed from steel during the pickling process (pickling being exposure to a typically acidic cleaning chemical), the filter cake then being put into landfill. It is therefore possible to treat the dispersion without removing the liquid, and then re-dispersing the particulate. A further embodiment of the method of the invention and an apparatus of the invention will therefore now be described with reference to Figs. 5 and 6. In this connection, the method is denoted generally by reference numeral 300 and the apparatus is denoted generally by reference numeral 3000. Acidic pickling line liquor is obtained from a steel pickling line. The method 300 comprises neutralising 306 the acidic pickling line liquor in a neutralising zone 3010, and feeding the neutralised liquor into an ultrasound treatment region 3020 in which the pickling line liquor is exposed 302 to ultrasound. The ultrasound treatment region is 3020 is essentially the same as that described above in relation to Fig. 2. The treated dispersion is passed to a separator 3030 in which the solid component of the dispersion is separated 303 from the liquid component. In this case, the separator 3030 comprises a filter press that reduces the liquid content of the composition. If desired, the liquid content of the solid component may be reduced more using a drying bed or centrifuge, for example. [0084] Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

[0085] One of the exemplary methods above demonstrates the removal of zinc from a powder. Those skilled in the art will realise that the method of the present invention may be used to remove zinc from larger particles. Those skilled in the art will also realise that the method of the present invention may be used to remove zinc from a mixture of particles having different sizes.

[0086] One of the exemplary methods above demonstrates the removal of zinc using warm water. Those skilled in the art will realise that liquids other than water may be used, and will also realise that the liquid need not be heated, although exposure to ultrasound may in itself cause some heating of the liquid.

[0087] One of the exemplary methods described above demonstrates the removal of zinc using a batch process. Those skilled in the art will realise that the removal of zinc may be achieved in a continuous process in which the particulate to be treated moves is exposed to ultrasound treatment as it flows through an ultrasound treatment zone.

[0088] The examples above describe the removal of zinc from flue dust, and the removal of chloride from pickling line filter cake, and oxidation of the iron therein. Those skilled in the art will realise that other particulate substrates could be treated by ultrasound. [0089] The exemplary method described above illustrates the removal of zinc from steel making dust. Those skilled in the art will realise that other substrates could be treated. [0090] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.