GB2256819A

GB2256819A - Separating solids

Info

Publication number: GB2256819A
Application number: GB9113397A
Authority: GB
Inventors: Frank K West
Original assignee: MULTISERV INT Ltd
Current assignee: MULTISERV INT Ltd
Priority date: 1991-06-21
Filing date: 1991-06-21
Publication date: 1992-12-23
Anticipated expiration: 2011-06-21
Also published as: GB2256819B; GB9113397D0; ZA924037B

Abstract

A slag containing a metal fraction is passed through a magnetic separator A to provide a fraction(s) containing an enhanced content of metal and a waste product with reduced metal content. The metal containing fraction(s) is then passed through a separator B containing a trough 10 having an endless path and containing dry sand, the floor 11 of the path being air permeable and including a depthwise partition 12, the metal and non-metal components being separated according to their density. <IMAGE>

Description

SEPARATION The invention relates to separation and in particular to the separation of the metal and non-metal fractions of a metallurgical slag or waste product from a metal recovery process. In particular, the invention is concerned with the separation of metallic fractions from non-metallic slag fractions. The metal-rich fraction can be sold or used as revert feed for the furnace and the slag fraction is a waste product of reduced metal content which may be put to use or discarded.

It is known to use a magnetic separator to recover strongly magnetic alloys from slags and wastes. It is also known to recover non-magnetic or weakly magnetic alloys by the use of a wet gravity concentrator of the type used in the mineral processing industry. For a number of reasons e.g. climatic and/or environmental it is not always possible to use wet processing in the treatment of slags or wastes. An alternative technique involves the use of a dry gravity concentration device which however requires the feed to be crushed to a fine particle size e.g. less than about 5mm and which results in a fine particulate end product of reduced economic value.

It is one object of the invention to provide a method of dry separating the metallic fraction from the non-metallic fractions of a slag or waste product.

According to the invention in one aspect there is provided a method of dry separating a slag containing at least one metal fraction to provide a vendible product, the method comprising the steps of: 1) passing lumps of the metal bearing slag through a magnetic separator so as to provide a) one or more fractions containing an enhanced content of metal, and b) waste product with reduced metal content 2) passing the or each of the fractions under category (a) through a separator comprising a trough defining an endless path, the trough containing a particulate material as an entraining medium, the base of the trough being air permeable for only a portion of its length, a substantially depthwise partition being present over the air permeable portion, the partition being arranged to supply two separate discharge paths, the fraction to be treated being supplied to the trough along a distributor located away from the air permeable portion so as to cause the slag to pass over the partition and to one discharge path and the metal to pass over the partition to a second discharge path.

Preferably, the magnetic separator comprises an endless belt passed over a magnet, separate receptacles being present at the discharge end of the separator each to receive a different fraction. Most preferably the magnet is a powerful magnet which is rotating at a speed which may be varied. It is preferred that the speed of travel of the belt is variable. Preferably, splitter means is present to isolate the different fractions and direct them to the respective receptacles.

The material to be treated may be any slag containing a metal or alloy. Preferably the material is a ferroalloy e.g. ferrochrome, ferronickel; or an aluminium alloy or the like. It is an advantageous feature of the invention that the material to be treated can be in lump form e.g. from about 5mm to above 75mm in diameter. The lumps may be supplied to the magnetic separator at up to say 20 tonnes/hour/metre width of belt.

In order that the invention may be well understood it will now be described by way of example with reference to the accompanying diagrammatic drawings, in which Figure 1 is a plan view of one embodiment of apparatus; and Figure 2 shows the process schematically.

The apparatus comprises a magnetic separator A and a solids separator B. The magnetic separator A comprises an endless belt 1 travelling between a supply feeder 2 and a bank of discharge hoppers 3A, 3B, 3C. The speed of travel of the belt 1 may be varied by means, not shown. The discharge hoppers are separated by dividers 4 and a splitter 5, the position of which can be varied is present to direct material into individual hoppers.

Below the belt 1 is a powerful magnet 6 arranged to use the paramagnetism in weakly magnetic materials or eddy currents generated in non-magnetic metal (including alloy) contained in the slag to be treated. The magnet 6 is mounted on a rotary drive shaft 7 and the rate of rotation may be varied. The distance between the magnet and the material to be treated is minimised. In use, crushed lumps of a slag, say ferrochrome slag, about 6mm to 40mm are fed from the feeder 2 on to the belt 1 and then carried towards the discharge end and the hoppers. As the lumps pass over the rotating magnet 6, they are attracted towards the magnet which itself is rotating. The susceptible lumps are thus separated from the lumps which are not susceptible, and travel into the hopper 3A whereas the less magnetised or non-magnetised lumps travel to the other hoppers.

The hopper 3A will tend to contain substantially pure or clean metal with little or no adherent slag and the hopper 3B will tend to contain lumps of slag which contain a reduced metal content; the hopper 3C will tend to contain lumps which have little or no metal.

The solids separator B comprises a horizontal trough 10 which is generally circular as seen in plan. A length 11 of the floor of the trough is air permeable i.e. holes are present. A depth wise partition 12 is present above the air permeable portion and leads to an upwardly inclined ramp 13 and a downwardly inclined ramp 14. A supply belt 15 is present above one end of the air permeable portion of the floor and the partition 12 is present towards the other end. The trough contains a dry sand. In use, air is blown through the holes in the floor to fluidise the sand.

Scrap from hoppers 3A and 3B is separately supplied from the belt 15 to the trough and is carried along to the partition 12. The metal and the non-metal components of the slag will separate according to their density, the heavier metal travelling down the lower ramp and the lighter non-metallics travelling up the ramp.

In this way, the metal containing fractions from the magnetic separator are upgraded to form substantially all metal-rich lumps. The process is illustrated schematically in Figure 2.

The invention is further illustrated by the following example which is a non-limitative nature. About 1.5 tonnes of ferrochrome slag arising from normal production methods was processed into lumps about 10 to 35mm in diameter and was treated by the method of the invention. The material was passed through a magnetic separator A on a belt about 46mm (18 inches) in width at the rate of about 9 tonnes/hour, which took about 22 minutes.

The material was separated into three fractions: (a) predominantly clean metal ("concentrate") 257kg (b) metal and adherent slag ("middlings") 248kg (c) predominantly slag with some metallic particles ("rejects") 1021kg Fractions (a) and (b) were separately processed in the solids dry gravity separator B and at the rate of about 2 tonnes/hour the following results were obtained: fraction (a) concentrate the sink i.e. the metal 163kg the float i.e. the slag 83kg 249 (the discrepancy between 257 and 249 kg is probably due to measurement errors and losses).

fraction (b) the middlings the float i.e. the slag 168kg the sink i.e. the metal 84kg 252 (the discrepancy between 252 and 249 is probably measurement errors and losses).

As a result of the two stage treatment there was available an upgraded metal fraction which was a vendible product in that it could be sold for use as is or could be used as revert feed for the furnace. The upgraded fraction was in lumps and substantially free of fines. The products were found to contain more than 60% Cr content for sink products. This product is suitable for direct sale. The float fraction from the gravity concentrator contained some middling material containing metal and would be suitable for a revert charge to the ferrochrome furnace.

The invention is not limited to the embodiment shown. The material to be treated need not be ferrochrome but can be another ferroalloy; the number of fractions formed may be varied; steps may be repeated. The susceptible material may be attracted to the magnet or it may be repelled.

Claims

1. A method of dry separating a slag containing at least one metal fraction to provide a vendible product, the method comprising the steps of: 1) passing lumps of the metal bearing slag through a magnetic separator so as to provide: a) one or more fractions containing an enhanced content of metal, and b) waste product with reduced metal content, 2) passing the or each of the fractions under category (a) through a separator comprising a trough defining an endless path, the trough containing a particulate material as an entraining medium, the base of the trough being air permeable for only a portion of its length, a substantially depthwise partition being present over the air permeable portion, the partition being arranged to supply two separate discharge paths, the fraction to be treated being supplied to the trough along a distributor located away from the air permeable portion so as to cause the slag to pass over the partition and to one discharge path and the metal to pass over the partition to a second discharge path.

2. A method according to Claim 1, wherein the magnetic separator comprises a travelling endless belt passed over a magnet, separate receptacles being present at the discharge end of the separator each to receive a different fraction.

3. A method according to Claim 2, wherein the magnet is rotated.

4. A method according to Claim 2 or 3, wherein splitter means is present to isolate the different fractions and direct them to the respective receptacles.

5. A method according to any preceding Claim, wherein the belt is run at a speed of up to about 20 to 15 tonnes/hour per metre width of the belt.

6. A method according to any preceding Claim, wherein the density of the solids separator is adjusted according to the fraction being treated.

7. A method according to any preceding Claim, wherein the slag contains at least one weakly magnetic metal.

8. A method according to Claim 7, wherein the slag contains a ferroalloy or aluminium alloy or the like.

9. A method according to Claim 8, wherein the slag contains ferrochrome.

10. A method according to any preceding Claim, wherein the slag to be treated is in the form of lumps of an average diameter of between about 5 to 75mm, preferably about 10 mm and about 35 mm.