Jan Svoboda. Magnetic Techniques for the Treatment of Materials

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540 CHAPTER 6. INDUSTRIAL APPLICATIONS

Figure 6.60: Distribution of heavy non-ferrous metals, per mass and per value,

in a scrap metal mix (adapted from [S91]).

to electronic scrap treatment [B46, G26]. In view of large density dierences

between non-magnetic or weakly magnetic metals to be separated, only modest

separation selectivity and a rather simple design of the FHS separator is re-

quired. It is fairly easy to design a ferrohydrostatic separator that can generate

apparent densities exceeding 10 000 kg/m

, required to ﬂoat, for instance, lead,

in a modestly magnetic (e.g. M

= 0.02 T) ferroﬂuid.

A separator shown in Fig. 6.61 can treat up to 1 t/h of scrap material and

it can be further scaled-up to double this throughput. Recovery of 95% of most

heavy non-ferrous metals can achieved, with purity ranging from 98 to 100%.

[M24]. A typical example of a copper concentrate obtained by FHS is shown in

Fig. 6.62. Inclusion of ferrohydrostatic separation in the ﬂowsheet for sorting

of heavy non-ferrous metals is illustrated in Fig. 6.63.

As has been discussed in Section 5.6, there are two basic types of separators

with magnetic ﬂuids. A ferrohydrostatic separator with constant apparent den-

sity of ferroﬂuid along the vertical axis produces two products, namely ﬂoat and

sink. The selectivity and accuracy of separation in this type of separator can

be very high. On the other hand, separators that use paramagnetic liquids or

separators with ferroﬂuid with wedge-shaped pole-pieces generate a distribution

of apparent density along the vertical. Although it is possible, at least in the-

ory, to obtain several density products in one pass of a material through such a

separator [e.g. A44], selectivity is inevitably limited. Interparticle interactions,

distribution of density of the materials to be separated, and a continuum of the

apparent density of the magnetic ﬂuid along the vertical axis are some of the

reasons that make this approach impractical.

While it is unlikely that the latter approach will ﬁnd industrial applica-

6.6. RECOVERY OF METALS FROM WASTES 541

Figure 6.61: A pilot-plant-scale ferrohydrostatic separator for sorting of heavy

non-ferrous metals.

Figure 6.62: A photograph of the - 12 mm copper concentrate obtained by FHS

as a sink product at the density of 8200 kg/m

and a ﬂoat fraction

at 10 300 kg/m

[M24].

542 CHAPTER 6. INDUSTRIAL APPLICATIONS

Non-ferrous

material

DMS 2.0 sg

< 2.0 sg

> 2.0 sg

DMS 3.0 sg

> 3.0 sg

< 3.0 sg

ECS

Plastics

Rubber

Magnesium

Thin gauge Al

Cu wire

Stones

Thick gauge Al

Zn 7.0 sg

Bronze 7.4-8.9 sg

SS steel 7.9 sg

Brass 8.4-8.7 sg

Copper 8.9 sg

Lead 11.3 sg

FHS concentrates

FHS

Figure 6.63: A ﬂowsheet for sorting non-ferrous metals into individual metal

concentrates, using FHS.

tion, sorting of non-ferrous metals by ferrohydrostatic separation holds a signif-

icant promise. A successful production-scale demonstration of this technology,

availability of ferrohydrostatic separators with a throughput of 2 to 5 t/h, and

availability of technical-grade ferroﬂuid at reasonable cost are prerequisites for

introduction of this technology into the recycling process.

6.7 The applications of ferrohydrostatic separa-

tion

The range of potential applications of ferrohydrostatic separation is extensive

and, in view of the unique capabilities of the FHS technology, this technique

can change conventional practices of materials treatment. The main limitation

is, however, the cost of ferroﬂuid, limited throughput of the existing separators

and rather poor e!ciency of separation of particles smaller than 500 m. The

viability of every application will be determined mainly by the losses of the

ﬂuid, its cost compared to the value of the products of separation, and by the

e!ciency of of the ferroﬂuid recycling, if it is used [S92].

The FHS technology is presently being used, on industrial scale, for the

recovery of gold and other platinum-group metals and in the diamond industry.

On laboratory and pilot-plant scale, the technology is being applied to the

recovery of non-ferrous metals from scrap, as discussed in Section 6.6.2, and

to the treatment of wastes and tailings, slags, coal analysis and recovery of base

metals.

6.7. THE APPLICATIONS OF FERROHYDROSTATIC SEPARATION 543

LIMS

HIMS

FHS

Gravity concentrate

Mags

Non-mags

Au concentrate

Final tails

Mags

Throughput: > 25 kg/h

Recovery of gold:

Total: 98.6%

in FHS: 99.5%

Grade: 97 - 99% Au

Particle size: - 5 mm + 40 um

Ferrofluid loss: 5 l/t

Figure 6.64: Recovery of gold by FHS at Aldanzoloto, Russia (adapted from

[S55]).

Table 6.29: Beneﬁciation of gold-bearing alluvial sands by FHS [G27].

Product Yield [%] Grade [g/t Au] Recovery [% Au]

Feed 100 473 100

Concentrate 0.1 452 000 95.5

Tailings 15.7 78 2.6

Magnetics 84.2 11 1.9

6.7.1 Recovery of gold and other platinum-group metals

At least ﬁfty ferrohydrostatic separators, based either on electromagnets [S55],

or permanent magnets [S54], are in operation in the territories of the former

Soviet Union. The separators are used to recover gold from gravity concentrates

and to treat previously accumulated tailings after the amalgamation of the gold

concentrates. A typical ﬂowsheet of the treatment of the gravity concentrate is

shown in Fig. 6.64. Table 6.29 summarizes the results of the ﬁnal concentration

of black alluvial sand by an electromagnet-based GMUO FHS [G27].

Tables 6.30, 6.31 and 6.32 oer a detailed summary of the results of beneﬁ-

ciation of table gold concentrates in individual stages as outlined in Fig. 6.64.

Results of the concentration of gold from tailings in the Amur Region (Rus-

sia), using permanent-magnet based FHS, are shown in Table 6.33.

544 CHAPTER 6. INDUSTRIAL APPLICATIONS

Table 6.30: Beneﬁciation of the gold gravity concentrate by a low-intensity mag-

netic separator (Severvostokzoloto Co.), B = 0.13 T.

Product Yield [%] Grade [g/t Au] Recovery [%Au]

Feed 100 222146 100

Magnetics 31.81 1502 0.22

Non-magnetics 68.19 325074 99.78

Table 6.31: Beneﬁciation by a high-intensity magnetic separation of the non-

magnetic fraction from LIMS (Severvostokzoloto Co.).

Product Yield [%] Grade

[g/t Au]

Recovery [%Au]

per stage overall per stage overall

Feed 100 68.19 325074 100 99.78

Magnetics 59.47 40.55 1864.6 0.34 0.34

Non-magnetics 40.53 27.64 799248 99.66 99.44

Table 6.32: Concentration of gold from the non-magnetic fraction of a high-

intensity magnetic separator by FHS (Severvostokzoloto Co.).

Product Yield [%] Grade

[g/t Au]

Recovery [%Au]

per stage overall per stage overall

Feed 100 27.64 799248 100 99.44

Au concentrate 93.42 25.82 99.92 99.36

Tailings 6.58 1.82 9280.68 0.08 0.08

Table 6.33: Recovery of gold from tailings by permanent-magnet based FHS.

Cut-point density: > 9000 kg/m3 [S54].

Size distribution Recovery [%Au]

+ 0.315 mm, 8% 99.7

- 0.315 mm, 82% 71; 93.1 free gold

Full sample, 100% 89.1, 93.8 free gold

6.7. THE APPLICATIONS OF FERROHYDROSTATIC SEPARATION 545

Table 6.34: Recovery of ﬁne diamonds from the sorthouse feed at Yakutalmaz

(Russia).

Parameter Speciﬁcation

Throughput 5to10kg/h

Feed size 0.2 to 2 mm

Recovery of diamonds 99%

Input power 0.47 kW

Mass of the separator 450 kg

6.7.2 Applications in the diamond winning industry

Beneﬁts of the unique capabilities of ferrohydrostatic separation for diamond

winning were readily recognized and it was also realized that, in contrast to

sorting of non-ferrous metals, separators with high selectivity operating at rel-

atively low apparent densities (up to 4500 kg/m

) were required. One of the

ﬁrst industrial applications of the technology was the installation of six GMUO

FHS-40/3 units at Yakutalmaz Co. (Yakutia, Russia) in 1992. The separators

were used at the sorthouse for the ﬁnal recovery of ﬁne diamonds. Typical

performance data are summarized in Table. 6.34. Although the units operated

satisfactorily, the FHS plant was later closed down, for reasons that were mainly

of non-technical nature.

In order to meet the needs of the modern diamond-winning industry, De

Beers Diamond Research Laboratory of De Beers Consolidated Mines (Pty.)

Ltd. (South Africa) developed a range of sophisticated cost-eective FHS sepa-

rators as has been discussed in Sections 2.8 and 5.6. In order to maintain accu-

rate control of the apparent density, the separators employ a closed-loop control

system. Such a control system automates the separation process and provides

a user-friendly interface. An operator selects the desired cut-point density from

a computer screen and the system automatically controls the plant at the set

point.

In order to ensure high selectivity of separation, a proprietary detection

system, which detects any changes in the density, is employed. The output of

the detection system is used by the closed-loop controller to control the power

supply output to maintain the ferroﬂuid at the constant apparent density.

Diamonds, by virtue of their high value, are highly sought after as an ex-

change medium in criminal activities. This results in signiﬁcant pressure being

applied to workers in the diamond mining industry to pilfer diamonds. It was

therefore imperative to put into place mechanisms, which prevented people from

accessing diamondiferous material during mining and recovery processes. Fig-

ures 2.108 and 6.65 show a two-stage automated and secure ferrohydrostatic

separator built by De Beers for the recovery of diamonds [S23].

Secure and selective ferrohydrostatic separators can be used for the recovery

of diamonds at various points of the diamond recovery process. Recovery of

diamonds from DMS concentrates, X-ray tailings, X-ray concentrates and from

546 CHAPTER 6. INDUSTRIAL APPLICATIONS

Figure 6.65: A two-stage ferrohydrostatic separator for the recovery of dia-

monds.

the sorthouse feed and tailings are some of the applications.

In addition to diamond recovery, ferrohydrostatic separators are used for

the treatment of geological samples. Mass reduction of samples before hand-

sorting, sorting of indicator minerals into individual narrow density fractions

and replacement of toxic and expensive heavy liquids are the main beneﬁts.

The Rhomag

ferrohydrostatic separator, developed at De Beers and shown in

Fig. 2.109, is used for treatment of exploration materials.

As a result of the ability of FHS to separate materials into narrow, well-

deﬁned density fractions over a wide range of densities, using a single ﬂuid

density, which can be changed by varying the magnetic ﬁeld strength, the tech-

nique is particularly suitable for densimetric analysis. Densimetric analysis of

the DMS feed and products by FHS allows to set the operating conditions of

DMS and to assess its e!ciency. Caution must, however, be exerted to take

into account the magnetic properties of the material. As has been discussed in

Section 3.8.4, particles with non-zero magnetic susceptibility exhibit an eective

density dierent from their natural density. A failure to take into account this

increment in density would result in distortion of the density distribution of the

material.

6.7.3 The fractionation analysis of coal

Sink-and-ﬂoat analysis of coal has been one of the areas of potential applica-

tions of FHS. Densimetric analysis of coal is usually carried out in bromoform

6.7. THE APPLICATIONS OF FERROHYDROSTATIC SEPARATION 547

Table 6.35: Comparison of densimetric analysis of coal in heavy liquids and FHS

[G17]. Concentration of impurities in FHS fractions is shown as a

dierence (in heavy liquids.

Separation density Size fraction [mm] Concentration

of impurities

[%]

2100 kg/m

- 100 + 50 0

-50+25 0

-25+13 0.7

-13+1 1.8

1800 kg/m

- 100 + 50 0

-50+25 0

-25+13 0.9

-13+1 1.4

and aqueous solutions of zinc chloride. Both heavy liquids are toxic and expen-

sive to acquire and to dispose of. Such a hands-on operation, involving several

liquids, to cover the entire density region from 1800 to 2400 kg/m

is tedious

and environmentally unfriendly. The obvious advantage of using magnetic ﬂu-

ids to separate coal into narrow density fractions has been appreciated, over

the last twenty years, by numerous researchers. Gubarevich [G17] employed a

ferrohydrostatic separator with kerosene-based ferroﬂuid to investigate the frac-

tionation of coal, ranging from 1 to 100 mm in size. The results, shown in Table

6.35, were compared with densimetric analysis obtained with heavy liquids.

It can be seen that while the best results were obtained with the coarse

fractions, even in the ﬁne fractions the concentration of impurities was low.

The selectivity of separation was found to be high, with Hs ranging from 0.015

to 0.045, depending on the ferroﬂuid density. The high accuracy of separation is

assisted by the fact that most coals are very feebly magnetic ("

frdo



25×10

9

/kg). It was also observed that chemical interaction between the ferroﬂuid

and organic and mineral matter in the coal was negligible.

Based on the above experiments, an industrial-scale continuous FHS sepa-

rator (FGS-2) was developed by the GMUO Institute, Lugansk, the Ukraine.

The separator, shown in Fig. 6.66, underwent several pilot-plant tests, with

duration of each exceeding 600 hours. Typical results are summarized in Table

6.36. In spite of satisfactory performance, several attempts to commercialize

this technology failed as a result of geopolitical changes in the former USSR at

that time.

548 CHAPTER 6. INDUSTRIAL APPLICATIONS

Figure 6.66: FGS-2 separator for fractionation of coal. 1-electromagnet, 2-coils,

3-pole-tips, 4-hopper, 5-bottomless separation chamber with hy-

draulic support, 6-lift.

Table 6.36: Typical results of pilot-plant-scale densimetric analysis of coal using

FGS-2 [G17].

Density range 1300 to 2200 kg/m

Cross-contamination [%] of FHS products - 100 + 13 mm 0.5%

-13+1mm 2%

Throughput 200 kg/h

Carry-over of ferroﬂuid into products 1to4kg/t

Loss of ferroﬂuid after regeneration 0.4 kg/t

6.7. THE APPLICATIONS OF FERROHYDROSTATIC SEPARATION 549

Figure 6.67: Comparison of densimetric analysis of coal using FHS and ZnCl

Particle size: - 3 + 0.3 mm (adapted from Fujita et al. [F34]).

Fujita et al. [F34] described the design of a batch ferrohydrostatic separator

for densimetric analysis of coal. The results, an example of which is shown

in Fig. 6.67 were encouraging. The separation curves for three size fractions,

namely - 25 + 13 mm, - 13 + 3.3 mm and - 3.3 + 0.3 mm were similar for

both separation methods, namely FHS and zinc chloride. The carry-over of the

water-based ferroﬂuid into the products of separation was less than 5 kg per

tonne of the feed material, in agreement with the value given by Gubarevich

[G17]. Further regeneration of the ferroﬂuid reduced the loss to about 0.5 kg/t.

Ferrohydrostatic separators can thus be used as accurate tools for densi-

metric analysis of coal. FHS lends itself to automation, the rate of treatment

is high and the detrimental eect of chemical and physical interaction of the

heavy liquids with the coal matter is reduced. FHS thus possesses numerous

advantages compared to conventional methods. As has been discussed by Svo-

boda [S93], further development of FHS technology that will result in more

accurate and large-scale equipment for coal fractionation and in availability of

cost-eective ferroﬂuids, combined with strong interest of the coal preparation

fraternity, will inevitably result in the introduction of the FHS technique to the

coal fractionation practice.