WO2018198042A1

WO2018198042A1 - Process and device for recovering metal

Info

Publication number: WO2018198042A1
Application number: PCT/IB2018/052870
Authority: WO
Inventors: Michael Glass
Original assignee: Ultromex Limited
Priority date: 2017-04-25
Filing date: 2018-04-25
Publication date: 2018-11-01
Also published as: GB201706541D0; GB2577006A; GB201916971D0

Abstract

A process for recovering metal from slag or dross is described, which comprises the step of breaking down the slag or dross to break up the non-metallic material in the slag or dross.

Description

PROCESS AND DEVICE FOR RECOVERING METAL

The present invention relates to a process and device for recovering metal from slag (also known as salt slag, salt cake, ash, black dross) or dross (also known as black dross, white dross, skimmings) produced in the melting of metals.

More particularly the present invention may relate to a process for fulfilling two functions, each of which improve the economics of metal smelting. The present invention may be useful to remove waste from the raw material (high metal dross) coming into the smelter so that a higher metal content material can be fed into the smelter's furnace. Removing waste at this stage eliminates the energy, flux, and processing time (furnace capacity) consumed in otherwise processing this waste through the smelter's furnace as an integral part of the furnace charge and also greatly reduces the quantities of salt slag waste generated. The present invention may also be useful to recover metal bound up in the waste (slag or salt slag) ejected from a smelter's furnace. Within industry there are methods of achieving such processes however, the present invention provides a considerably higher level of efficiency, using less equipment, less energy consumption, occupying less factory space and for less operating cost.

Smelting is a process employing heat to recover metal in molten form. It typically involves heating metal ore, metals to be alloyed, metal scrap, or metal-containing waste materials (e.g. dross) in a furnace, often under the covering of a suitable flux, with free metal in liquid form collecting in the bottom of the furnace. The metal can be drained off leaving a waste material comprising of metal oxides and other waste compounds present in the raw material, any flux and other agents added to the furnace, and some metal that remains trapped within this bulk waste material. This waste may be referred to as dross if high enough in metal to be worth remelting (e.g. the material skimmed off to remove impurities from the surface of molten metal) or slag if the metal content is low. Slag may yet contain typically 5% to 10% metal and sometimes more.

Some smelters seek to recover some of the metal in their slags by crushing the slag and screening or hand picking whatever metal they are able to. Often the processes used to break up the slag also break down the metal sought, thereby generating unrecoverable metal fines. Slag and dross materials are typically classified as hazardous waste, e.g. in EU, and their disposal to landfill may be prohibited or at least be costly. There are however, potential uses for the bulk of this material, particularly if it does not contain salt. Thus separating out the waste before the addition of salt not only reduces the bulk quantity of waste generated but it also increases the potential for more of the waste to become a by-product, i.e. a useful material feedstock for other industries.

Smelting to produce virgin or recycled metals takes place across the world and so slag and dross wastes are generated in most countries and in large quantities.

In accordance with a first aspect of the present invention there is provided a method for separating slag and/or dross comprising (a) the use of a device as described hereinabove to separate metallic and non-metallic particles from the slag and/or dross.

Preferably, the process comprises a step of:

(b) separating the material obtained from step (a) according to metal content, size or shape. The step (a) metallic pieces may be removed from the product obtained by using the device.

The feed material may comprise slag and/or dross.

The step (b) may comprise using a magnet to separate magnetic material from non- magnetic material and/or the use of an eddy current separator.

The step (b) may comprise using a set of one or more screens. The screens may comprise at least one vibrating screen. The screens may comprise a series of screens, wherein each screen is selected to pass pieces of material of a

predetermined size or range of sizes. Separated material having a high metal content may be recovered by any suitable means, for example, an eddy current separator. Particles of material may be deemed to have a high metal content if they are either electrical conductors, or are of at least a predetermined size. Pieces of material of less than the predetermined size may be further processed for recovery of fine metal prills therefrom, for example by roller crushing and/or eddy current separator.

Prior to the step (a), a preparation step comprising crushing the slag or dross into pieces may be conducted. The crushed pieces may have a diameter of not more than 200mm, more preferably not more than 150mm, most preferably not more than 100 mm. The process may comprise first and second separating steps, and a compressing step between the first and second separating steps for compressing the material to break up non-metallic material and to flatten the metallic material. The broken up non-metallic material is then more likely to pass through a subsequent screen, while the flattened metallic materials are less likely to pass through those screens due to their shape and size.

It will be appreciated that nearly all of the products of the process, and sub- processes within the overall process have a use and can thus be recycled.

Conventionally, since separation of the components of slag and dross was previously uneconomical, the slag and dross mixture was previously of no

commercial value, and in fact would have significant disposal costs associated with it.

In accordance with an aspect of the present invention, there is provided a device for recovering metal from slag and/or dross comprising a housing defining a chamber having an inlet for receiving slag and/or dross and an outlet, wherein disposed in said chamber between said inlet and said outlet is a first blade mounted to the housing and within the chamber and at least one other blade being rotatably mounted on a rotor, said blades being co-operable with one another to reduce the non-metallic components of the slag and/or dross, said first and at least one other blade being separated by a predetermined distance.

Generally, some of the benefits of the invention are achieved by methods of material reduction and separation, rather than by remelting alone. This saves a substantial amount of energy, making recovery of smaller amounts of metal cost-effective.

Moreover, not only is the recovered metal of commercial value, the residual material absent the metal may also be of value.

Advantageously, the present invention provides a more efficient process for the recovery of metal from slag or dross comprising the step of (a) breaking down the slag or dross creating a mixture comprising metal which is liberated from the slag or dross matrix. It also results in any salt present in the slag or dross being broken down to a fine powder which both readily makes its way through various downstream screening stages, and is also suitable for dissolution for salt recovery purposes.

The differences in properties between metals and non-metals enable the device of the present invention to create the differentiated particle size in differing materials that enables their easy separation. More specifically, non-metallics & oxides are broken up by the device of the present invention while the trapped metal particles remain intact and are substantially unchanged and are liberated from the matrix. In contrast, reduction of slag by standard milling and shredding technology tends to reduce metal and the non-metal particles further, so reducing the likelihood of separation.

In accordance with an aspect of the present invention, there is provided a device for recovering metal from slag and/or dross comprising a housing defining a chamber having an inlet for receiving slag and/or dross and an outlet, wherein disposed in said chamber between said inlet and said outlet is a first blade mounted to the housing and within the chamber and at least one other blade being rotatably mounted on a rotor, said blades being co-operable with one another to reduce the non-metallic components of the slag and/or dross, said first and at least one other blade being separated by a predetermined distance. The present invention may comprise at least one baffle. The at least one baffle may be disposed within the chamber or exterior to the chamber.

In an embodiment, the at least one baffle is disposed exterior to the chamber and may help prevent material to be reduced from escaping via the inlet to a feed hopper. The device may comprise two or more baffles, preventing there being a clear line of sight for material to pass from the chamber, out through the inlet to a feed hopper.

In accordance with a further aspect of the present invention there is provided an apparatus for recovering metal from slag and/or dross comprising a device as described herein and an eddy current separator.

The apparatus may further comprise at least one screen.

The present invention will now be described, by way of example only, with reference to the following drawings, in which:

Fig. 1 schematically illustrates an embodiment of a process in accordance with the present invention for raising the metal purity of dross;

Fig. 2 schematically illustrates an embodiment of a process in accordance with the present invention for treating slag and/or dross (particularly, low quality dross); and

Fig. 3 shows a device in accordance with the present invention and for use in the process. Figs. 1 and 2 are schematics illustrating processes for raising the purity of dross and a salt slag process. Both processes involve the following steps:

1 . Breaking up of slag and / or dross using a crusher or other mechanical means to achieve a particle size of less than 200mm, preferably less than 150mm, more preferably less than 100mm.

2. Using a permanent magnet or electro-magnet to remove tramp magnetic metals. The magnetic separator may be an overband magnet which draws magnetic material up and away from a conveyor onto the overband magnet (to be released at another location).

3. Using a device as described hereinbelow and shown in Figs. 3 to break up the non-metallic components of the slag or dross whilst leaving the metallic components unchanged. The purpose of this step is to recover metal having a diameter of more than 0.5 mm. Firstly, the slag or dross is fed into a device as described hereinbelow. The device breaks down the non-metallic materials within the mixture to result in pieces of material of a size suitable for further screening. The screen is intended to remove large lumps (of probably principally metallic material). The device liberates metal from the slag or dross matrix by breaking up only the non-metallic materials (the metal being largely unaffected by the device) and create a mixture comprising pieces having varying sizes and metal content.

4. Separating the metallic and fractured non-metallic materials (NMP - non- metallic particles). This can be achieved in a variety of ways using conventional equipment such as, but not limited to, using one or more of the following: sieves / screens, eddy current separators, other techniques employing electromagnetic induction, cyclones, centrifuges, air separation and the like.

5. Having recovered the free metallic materials the remaining particles which are predominantly non-metallic and sufficiently small, anywhere between 0.5mm and 12mm, may be further processed by crushing the brittle non-metallic material into a powder whilst flattening any included ductile metallic material into discs using any crusher that minimises shearing and grinding which could lead to metal attrition. One embodiment would be the use of a single set or a cascade of sets of roller crushers. 6. Separating the crushed non-metallic particles from the rolled metallic discs using a sieve or other conventional separation equipment as listed in step 3.

The following subsequent step is relevant to the process illustrated in Fig. 2, as follows: 7. Particles which are predominantly non-metallic and greater than the size range selected for step 5 can be recirculated for further processing through step 3 or the process flow could incorporate an additional device in accordance with the present invention. An eddy current separator can perform this task.

Example

Example 1 : Concentration of aluminium dross to make ready for more efficient smelting.

Large lumps of dross containing 70% aluminium metal in large pieces (>400mm) and also 30% to 50% aluminium metal in the fines (<400mm) were treated by the device of the present invention and then screened at 8mm. The oversize material recovered by said screening was found to have been enriched to over 85% aluminium. The undersize material was further processed by passing through a roller crusher and screening at 0.5mm to separate the finely reduced oxides from the rolled aluminium platelets. The platelets were found to be 80% aluminium. The matrix fines generated by the process were found to contain less than 8% aluminium. The overall process reduced the dross bulk by over 30% whilst retaining all aluminium but for those prills smaller than 0.5mm. This equates to each furnace charge yielding 42% more aluminium for the same energy and time input whilst generating over 60% less salt slag waste. A device suitable for use in the present invention is shown in Fig. 3. The device 10 has a housing 12 having an inlet 14 and an outlet 16. The housing defines a chamber in which is housed a rotor 18 having a plurality of blades 20 disposed about its circumference. The rotor is operably connected to a motor to drive the rotation of the rotor and thus the blades 20.

Housing 12 is of general box construction and defines a chamber divided into an upper 22 and lower chamber 24. The housing 12 has re-inforced walls where shown in thicker lines to provide protection against particles moving with high velocity. The housing 12 has two side walls (not shown), and front and rear walls 26 and 28. Extending inwardly perpendicularly from the plane of front wall 26 is a blade 30, the free end of which is separated by a pre-determinable distance 32 from the free end of blades 20. The blade 30 and rotor divide the upper and lower chambers and the distance 30 will constrain the rate and to some degree the size of particle capable of passing therethrough to facilitate longer residence time in the upper chamber to enable more energy to be imparted to the feed material. Metallic components of the feed material will tend to remain intact and unchanged rather than be broken down by the action of the blades.

The position of blade 30 is adjustable to accommodate optimised blade position as blade tips wear and is spring loaded to enable large resilient particles to pass through to the lower chamber and avoid jamming or damaging the device.

In another embodiment, the position of the rotor may be adjustable.

Located between the inlet 14 and the rotors in the upper chamber are three baffles 34, 36 and 38 which are shaped and positioned to retain and recirculate the particles within the upper chamber. The baffles comprise two planar plates arranged to prevent a clear line of sight from the rotor to the opening of the inlet. The baffled feedbox is arranged such that material enters the chamber and is delivered to the rotor in a direction counter to the direction of the rotor and at a point preferably 180 degrees from the outlet. The outlet 16 is also located adjacent to the rear wall 28 and there is an angled end wall below the blades to deflect material passing between the fixed and rotating blades towards the outlet 16. Further the angled end wall is sufficiently resilient to withstand multiple impacts from metallic and non-metallic material travelling at high velocity. Material containing slag and/or dross containing metal is fed into a gravity fed hopper 40 and passes through inlet 14 and is fed towards the rotor and the blades mounted thereon such that the non-metallics shatter and the metallics remain intact. The arrows show the direction of movement of particles within the device during use. .

Claims

1 . A process for separating metal from non-metal in slag and/or dross the process comprising:

(a) comminuting particles of slag and/or dross; (b) separating the material obtained from step (a) according to metal content, size and/or shape.

2. A process according to claim 1 , wherein metallic pieces are removed from the product obtained by step (a).

3. A process according to claim 1 or 2 wherein an eddy current separator is used to separate the material obtained from step (a).

4. A process according to claim 3 wherein material separated using the eddy current separator is returned to be re-processed.

5. A process according to claim 4 wherein the material to be returned for reprocessing is predominantly non-metallic.

6. A process according to any one of the previous claims, wherein step (b) comprises using a magnet to separate magnetic material from non-magnetic material.

7. A process according to any one of the previous claims, wherein step (b) comprises using a set of one or more vibrating screens and/or ultrasonic vibrating screens.

8. A process according any one of the previous claims, comprising the use of a series of screens, wherein each screen is selected to pass pieces of material of a predetermined size or range of sizes.

9. A process according to claim 8 wherein pieces of material of less than the predetermined size are further processed for recovery of fine metal prills therefrom, the further processing comprising rolling and/or induction/eddy current separation.

10. A process according to any one of the preceding claims comprising a preparation step prior to step (a), the preparation step comprising reducing the slag or dross into pieces having a diameter of not more than 200 mm.

1 1 . A process according to any preceding claim comprising a preparation step prior to step (a), the preparation step comprising reducing the slag or dross into pieces having a diameter of not more than 1 50 mm.

12. A process according to any preceding claim comprising a preparation step prior to step (a), the preparation step comprising reducing the slag or dross into pieces having a diameter of not more than 1 00 mm.

13. A process according to any one of the preceding claims, comprising first and second separating steps, and a compressing step between the first and second separating steps for compressing the material to break up non-metallic material and to flatten the metallic material.

14. A process according to any one of the previous claims wherein step (a) is performed by a device capable of comminuting the particles of slag and/or dross into smaller particles by rotating at least one blade within a housing, the housing also containing a fixed blade and into which is fed said particles.

15. A process as claimed in claim 14 wherein the distance between the fixed blade and rotating blade is adjusted to comminute the particles to a predetermined size range.

16. A process of recovering metal from slag and/or dross substantially as hereinbefore described with reference to the accompanying drawings.

17. A device for recovering metal from slag and/or dross comprising a housing defining a chamber having an inlet for receiving slag and/or dross and an outlet, wherein disposed in said chamber between said inlet and said outlet is a first blade fixed relative to at least one other blade being rotatably mounted on a rotor, said blades being co-operable with one another to reduce the non-metallic components of the slag and/or dross, said first and at least one other blade being separated by a predetermined distance.

18. A device as claimed in claim 1 7 having at least one baffle.

19. A device as claimed in claim 1 7 further comprising at least one baffle disposed outside the housing and proximal to the inlet.

20. A device as claimed in claim 18 or 19 having three baffles.

21 . A device as claimed in any one of claims 17 to 20 wherein the distance between the first blade and at least one other blade mounted on a rotor is adjustable.

22. A device as claimed in claim 21 wherein the first blade is moveable relative to at least one other blade to adjust the predeterminable distance.

23. A device as claimed in claim 22 wherein the first blade is biased by biasing means in a position perpendicular to the axis of rotation of the rotor.

24. A device as claimed in claim 23 wherein the biasing means comprises a spring.

25. A device as claimed in claim 24 wherein the rotor is moveable to adjust the predeterminable distance.

26. A device as claimed in claim 25 wherein the predeterminable distance is between 1 mm and 10mm.

27. A device as claimed in any one of the preceding claims comprising a plurality of blades rotatably mounted on the rotor.

28. A device as claimed in claim 31 comprising six blades mounted on the rotor.

29. A device as claimed in any one of the preceding claims wherein the rotor rotates at a frequency of at least 1500 rpm.

30. A device as claimed in claim 29 wherein the rotor rotates at a frequency of at least 2500 rpm.

31 . A device as claimed in any one of the preceding claims wherein the blades are manufactured from tungsten carbide.

32. A device as claimed in any one of the preceding claims wherein located downstream of the outlet is a baffle to deflect the path of material exiting the chamber.

33. A device as claimed in claim 32 having a spout in communication with the lower chamber via the outlet and whose longitudinal axis is offset from the outlet.

34. A device as claimed in any one of the preceding claims wherein the inlet is disposed adjacent to a blade mounted on the rotor such that material is fed towards the rotating blade.

35. A device as claimed in claim 34 wherein material enters the chamber in a direction counter to the direction of the rotor and at a point between 90 degrees and 270 degrees from where material can leave the chamber.

36. A device as claimed in claim 35 wherein material enters the chamber in a direction counter to the direction of the rotor and at a point between 150 degrees and 180 degrees from where material can leave the chamber.