THIS INVENTION relates to the recovery of particulate material from slurries.

Recovering fine particulate materials, such as fine iron ore slimes or fine coal slimes, from slurries is often problematic. Any method which can economically recover particulate material, including fine slimes from slurries, can thus provide substantial economic benefits.

According to one aspect of the invention, there is provided a method of recovering particulate material from a slurry, the method including passing ultrasonic waves through the slurry; and separating by gravimetric or magnetic techniques at least a portion of the particulate material from the slurry.

Preferably, the particulate material is separated from the slurry whilst the slurry is being subjected to ultrasonic wave energy. In other words, the ultrasonic waves are preferably passed through the slurry simultaneously with the particulate material being separated from the slurry.

The particulate material may be metallic or non-metallic material. Examples of metallic materials are haematite, schweelite, cobaltite and pentlandite tantalite. An example of non-metallic particulate material is coal fines. The particulate material may thus be magnetic or paramagnetic or non-magnetic.

In one embodiment of the invention, the particulate material is magnetic or paramagnetic, e.g. haematite, and the particulate material is magnetically separated from the slurry.

The method of the invention may be implemented as a batch process. Instead, preferably, the method of the invention is implemented as a continuous process, with a continuous slurry feed and continuous particulate material separation.

The slurry may have a particulate material concentration of up to about 50 % by mass. Preferably, the particulate material concentration is between about 20 % by mass and about 40 % by mass, e.g. about 30 % by mass. These values are particularly, though not necessarily exclusively, suitable for a haematite iron ore slurry.

The ultrasonic waves may have a frequency of between about 19000 Hz and about 50000 Hz, preferably between about 19000 Hz and about 22000 Hz.

The ultrasonic waves may have a wavelength of between about 100 mm and about 30 mm.

The ultrasonic waves may be passed through the slurry, and the particulate material may be separated from the slurry, without stirring the slurry to any significant extent.

The particulate material may have an average particle size of up to about 900 μm, preferably up to about 700 μm, more preferably up to about 500 μm.

The method may include passing ultrasonic waves through the slurry with one or more chemical dispersants being present in the slurry.

The ultrasonic waves may be passed continuously through the slurry. Instead, the ultrasonic waves may be pulsed through the slurry.

According to another aspect of the invention, there is provided separation apparatus to separate particulate material from a slurry, the apparatus including a reservoir or conduit for slurry; at least one ultrasonic wave source operable to radiate ultrasonic waves into the reservoir or conduit; and a separator to separate particulate material from the slurry.

11. The separator may be a magnetic separator, operable magnetically to separate particulate material from slurry in the reservoir or conduit. Instead, the separator is a gravimetric separator, operable to receive slurry from the reservoir or conduit and gravimetrically to separate particulate material from the slurry.

When the separator is a magnetic separator, it may provide a magnetic field strength of at least 3000 Gauss, more preferably at least 4000 Gauss, even more preferably at least 5000 Gauss, e.g. about 6000 Gauss.

The ultrasonic wave source may be operable to generate ultrasonic waves at a frequency of between about 19000 Hz and about 50000 Hz, preferably the ultrasonic wave source is operable to generate ultrasonic waves at a frequency between about 19000 Hz and about 22000 Hz.

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

Figure 1 shows a three-dimensional view of laboratory scale apparatus used as a control in testing the invention; Figure 2 shows a three-dimensional view of laboratory scale apparatus used to test the invention; and

Figure 3 shows a three-dimensional partially sectioned view of production scale separation apparatus to separate particulate material from a slurry in accordance with the invention.

Referring to Figure 1 of the drawings, reference numeral 10 generally indicates laboratory scale apparatus used as a control in testing the invention. The apparatus 10 includes a reservoir or tank 12, an electrically driven mixer 14 and a handheld magnet 16. Magnets 16 of three different strengths were used, namely magnets with a Gauss strength of 3000, a Gauss strength of 4000 and a Gauss strength of 6000.

Referring to Figure 2 of the drawings, laboratory scale apparatus embodying the invention is generally indicated by reference numeral 20. The apparatus 20 includes a reservoir or tank 22 and a hand-held magnet 24. The apparatus 20 further

includes an ultrasonic wave source 26 comprising an ultrasonic wave generator 28 and a pair of wave actuators or transducers 30 located at opposite ends of the tank 22, which is rectangular in outline in plan view.

As will be noticed, the apparatus 20 does not include a mixer corresponding to the mixer 14 of the apparatus 10.

The apparatus 10, 20 were used to illustrate, on a laboratory scale, the effectiveness of the invention. An iron ore (haematite) slurry, with a maximum particle size of about 300 μm and a solids concentration of about 30 % by mass, was poured into the tanks 12, 22. Each tank 12, 22 has a length of about 200 mm, a width of about 120 mm and a height of about 120 mm and the slurry was poured into the tanks 12, 22 so that the tanks 12, 22 were close to being full. Each tank 12, 22 held about 2 litres of slurry with an iron (Fe) concentration in the solids of about 48 % by mass.

The slurry in the tank 12 was mildly agitated by means of the mixer 14, with the mixer 14 drawing an estimated 40 W. The hand-held magnet 16 was then inserted into the tank 12, as indicated by arrow 17, and held there for a period of between about 30 seconds and about 60 seconds, before being withdrawn. The haematite magnetically attached to the magnet was removed and collected. This procedure was repeated sixteen times for each magnet strength and the collected haematite was then analysed. Best results were obtained for a magnet with a Gauss strength of 6000. The analysis showed that the apparatus 10, with a 6000 Gauss magnet, was able to concentrate the haematite to 63 % Fe by mass with a mass recovery of 58 %, i.e. an Fe recovery of 76 %.

The same procedure as described above with reference to the apparatus 10, was repeated with the apparatus 20, except that the slurry inside the tank 22 was not stirred and that ultrasonic waves at a frequency of 35000 Hz generated by the ultrasonic wave generator 28 were passed through the slurry in the tank 22 by means of the wave actuators 30. Power input into the tank 22 was estimated to be 120 W.

The following table provides the results for the experiments conducted using the apparatus 20, for magnets of Gauss strength 3000, 4000 and 6000.

* by calculation

As will be noted, surprisingly, the Fe recovery with the apparatus 20 is substantially higher than for the apparatus 10, with also the mass recovery and concentrate grade being higher for the apparatus 20 than for the apparatus 10. There is thus also less adherence of non-metallic or non-magnetic particles to the magnet 24.

Referring to Figure 3 of the drawings, reference numeral 50 generally indicates separation apparatus to separate magnetic or paramagnetic particulate material from a slurry, in accordance with the invention. The apparatus 50 is of a commercial or production scale.

The apparatus 50 includes a tank 52 for slurry with a pump 54 and a feed line 56 leading into the tank 52, and a tailings discharge line 58 leading from a bottom of the tank 52. More than one feed line 56 may be employed, if desired. It is envisaged that the tank will have dimensions of about 6 m x 2 m x 2 m. A plurality, e.g. about thirty

(only some of which are shown), temporarily magnetisable discs 60 are arranged axially along a drive shaft 62, with the discs 60 being axially spaced. Drive means, typically in the form of an electric motor 64 is drivingly attached to the drive shaft 62. A plurality of permanent high strength magnets 61 are arranged on both sides of each disc 60, along a lower arc thereof, and define a zone or space between them where the discs 60 are magnetised as they rotate through the space. An ultrasonic wave generator 66, preferably generating ultrasonic waves of variable, selected frequency, and wave actuators or transducers 68 are provided, with the wave actuators 68 being located at both ends of the elongate tank 52.

A discharge chute 70 for recovered particulate material (e.g. haematite) is arranged along a longitudinally extending portion of a rim of the tank 52.

It is envisaged that about 100 tons per hour of a 30 % solids haematite iron ore slurry will be treated by the apparatus 50. The slurry is pumped by means of the pump 54 and the feed line 56 into the tank 52. By means of the electric motor 64, the magnetic discs 60 are slowly rotated and simultaneously, by means of the wave generator 66 and wave actuators 68, ultrasonic waves of about 30000 Hz or higher are fed into the slurry inside the tank 52. Without wishing to be bound by theory, the Applicant believes that the action of the ultrasonic waves is to separate fine mineral particles from each other (i.e. the ultrasonic waves disperse the particles), by mechanical and/or surface property charge mechanisms, allowing magnetised portions of the magnetic discs 60 to attract the magnetic or paramagnetic and well-dispersed particles, leaving the non-magnetic or unwanted particles in the slurry. Unwanted material is discharged through the tailings discharge line 58 while the recovered magnetic particles are separated from the discs 60 where the discs 60 rotate out of the space between the magnets 61 (i.e. where the discs become demagnetised) and drop into the discharge chute 70.

The feed slurry can be varied to any pulp density that can be suitably pumped and fed into the tank 52, but for optimum dispersion and magnetic recovery of iron ore particles with a particle size up to about 500 μm the Applicant believes that the pulp density should be in the region of about 20 % to 30 % solids by mass. For lighter semi-magnetic ore particles, such as schweelite, cobaltite and pentlandite tantalite, other feed pulp densities may be optimum and higher magnetic strengths may be required.