Jan Svoboda. Magnetic Techniques for the Treatment of Materials

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560 CHAPTER 7. INNOVATION AND FUTURE TRENDS

Figure 7.8: Sala-Metso Minerals HGMS carousel high-gradient magnetic sepa-

rator, model 480 (courtesy of Metso Minerals).

magnetic ﬁeld is limited by the saturation magnetization of the yoke material

and the scale-up is di!cult. In order to treat a meaningful quantity of material,

the working gap between the poles of an electromagnet must be large, which

results in a signiﬁcant drop in the magnetic ﬁeld and the machine becomes

massive. To generate a su!ciently large magnetic ﬁeld at large volumes, an

iron-clad solenoid must be used [M5], as has been discussed in Sections 2.4.3

and 4.4.

Sala HGMS While the design of a cyclic HGMS based on the iron-clad

solenoid is a straightforward process, continuous solenoid separators require a

more complex approach. Sala Magnetics, Inc. developed a carousel HGMS [O5]

that employed a sophisticated saddle-shaped iron-clad solenoid surrounding the

carousel ring. The separator shown in Figs. 2.64 to 2.67 and 7.8 can, in con-

trast to its predecessors, generate a background magnetic ﬁeld as high as 2 T,

allows a close control of ﬂow velocity through the matrix and can be relatively

easily scaled-up.

In spite of the obvious advantages of this second-generation HGMS, the Sala

separator did not enjoy commercial success at that time. Although the separa-

tor was earmarked for several large-scale applications, the cost was apparently

prohibitive and the market was reluctant to accept the product in spite of its

progressive features.

7.3. MAGNETIC SEPARATION AND INNOVATION 561

Figure 7.9: SOL high-gradient magnetic separator.

SOL HGMS In the SOL separator, designed and built by Krupp GmbH

[S99, S1], the saddle-shaped solenoid was replaced by a simple axially orientated

solenoid, as shown in Fig. 7.9. In order to provide a reasonably long retention

time of the slurry in the magnetic ﬁeld, the magnet had to be su!ciently long.

The air gap of the magnet was, therefore, long and the magnetomotive force

needed to generate the required magnetic ﬁeld was very high. Moreover, because

the coil was much longer that its diameter, the beneﬁcial eect of the steel

cladding was negligible.

As a result of this misconceived approach to the magnet design, the SOL

separator could generate only a modest magnetic ﬁeld at very high energy input

per tonne of treated material. For these reasons the separator failed to gain

acceptance by the industry.

VMS HGMS Probably the most onerous problem in the operation of HGMS

separators is a permanent retention of particles in the matrix. Frequent shut-

downs of the separators for cleaning or replacement of a blocked matrix severely

impair the economic and metallurgical performance of the units. Numerous pre-

ventive measures that were investigated and applied in practice [S1] were found

to be of interim e!cacy only. The long-term solution was oered by machines

that employed a back-ﬂushing system.

The VMS magnetic separator developed by the Ore Research Institute,

Prague, Czech Republic [C7], addressed the problem of matrix clogging by re-

placing the conventional horizontal rotor by a vertically rotating ring, as shown

562 CHAPTER 7. INNOVATION AND FUTURE TRENDS

in Fig. 2.68. In addition to the reverse ﬂush, the main advantages of the VMS

separators, which employ an iron-clad solenoid, are excellent ability of scale-up

and a high background magnetic ﬁeld at modest input power.

The VMS separators were earmarked for incorporation into the Krivoy Rog

and Kursk Magnetic Anomaly iron ore beneﬁciation plants in the former USSR.

The proposed capacity of the plants was 30 Mt/a and it was envisaged that at

least forty VMS separators, each with a capacity of 100 t/h, would be required.

Numerous di!culties were experienced, associated mainly with the disinte-

gration of the Eastern Block in the late 1980s and early 1990s. In particular, the

completion costs escalated as a result of rampant inﬂation in the former USSR

during those transition years. In 1991 the Czechoslovak government decided to

pull out from this joint venture and write o US$300 million already invested in

the project. The beneﬁciation complex was never fully commissioned and po-

litical circumstances were, therefore, responsible for the failure of a promising

innovative technology to be implemented on production scale.

SLON HGMS In spite of its commercial misfortune, the concept of the VMS

separator proved beyond doubt that the use of an iron-clad solenoid and the ap-

plication of the reverse ﬂush of the matrix enhances the e!ciency, scalability

and availability of continuous high-gradient magnetic separators. The techni-

cal success of VMS separators prompted further innovative eort. The SLON

HGMS developed at the Ganzhou Non-ferrous Metallurgy Research Institute,

Ganzhou, China, and shown in Fig. 2.74, is based on the VMS concept [X1].

In order to improve the e!ciency of separation even further, SLON employs

an iron-clad solenoid located in the bottom section of the vertical ring carrying

the matrix. This feature allows a pulsation of the slurry within the matrix to be

introduced, which results in better selectivity of separation. The separator that

is used, at the present time, to beneﬁciate weakly magnetic iron and ilmenite

ores enjoys considerable commercial success in China and is making inroads into

the international markets.

Magnetic separation and superconductivity

Superconductivity has been seen as a panacea in magnetic separation, partic-

ularly because of its ability to generate a magnetic ﬁeld exceeding 2 T, the

maximum ﬁeld that can be generated by most resistive electromagnets. Ad-

ditional advantages include low running costs, low mass and large volumes in

which the high magnetic ﬁeld can be generated.

Although numerous small-scale superconducting magnets were built in the

late 1970s [S1], production-scale machines were slow to emerge. The ﬁrst in-

dustrial superconducting separator was designed and built by the Institute for

Refrigeration Engineering (VUPCHT), Prague, Czech Republic [F6]. This 5 T

unit, shown in Fig. 2.83, was a reciprocating canister machine for beneﬁciation

of kaolin.

The design of the magnetic system, the choice of the operating magnetic ﬁeld

strength and of the matrix were based on a theoretical description of particle

7.3. MAGNETIC SEPARATION AND INNOVATION 563

Figure 7.10: Installation of Cryoﬁlter superconducting separators at Cadam,

Brazil (courtesy of Outokumpu Technology, Inc.).

capture by a single magnetized wire. Such theoretical models, very popular in

the late nineteen seventies and early eighties, failed to describe correctly the

dependence of particle capture on key operational parameters. This approach

sometimes resulted in costly and unnecessarily complicated design of magnetic

separators and the VUPCHT separator was no exception.

Initially, the performance of the VUPCHT separator was encouraging. How-

ever, the subsequent deterioration in e!ciency, and drop in throughput, as a

result of matrix blockage, led to closure of the plant. The fate of the VUPCHT

superconducting separator demonstrates how unproven academic reasoning and

erroneous interpretation of laboratory data, with limited relevance to practical

operation, can result in failure to implement a new technology.

Not surprisingly, the subsequent production-scale superconducting HGMS,

developed by Eriez Magnetics, Inc. and shown in Fig. 2.80, was based on a

conventional cyclic design [S16]. The magnet generated a 2 T magnetic ﬁeld,

su!cient to treat most minerals. The fast-ramp magnet allowed the maximum

ﬁeld to be reached in less than 60 s, which enabled a reasonable duty factor to

be obtained without resorting to a mechanically more complicated reciprocating

matrix system.

Further developments in superconducting technology and better understand-

ing of mechanisms of HGMS led to a revival of the reciprocating matrix concept.

After Carpco Inc. acquired, in 1991, the Magnetic Separation Group from Cryo-

genic Consultants Ltd., development of reciprocating canister superconducting

magnets gained momentum. Several types of separators of dierent sizes were

564 CHAPTER 7. INNOVATION AND FUTURE TRENDS

developed and installed at kaolin processing operations. The ﬁrst large 5 T ma-

chine, with a diameter of the reciprocating tube of 500 mm and throughput of

up to 50 t/h was delivered in 1993 to Caulim di Amazonia (Cadam), a Brazilian

kaolin company. The machine requires 1000 litres of liquid helium per year,

which is transferred annually. No liquid nitrogen is required and a small re-

frigerator, running at 10 kW, provides cooling at an intermediate temperature

[W36]. The reduction in energy costs compared to conventional HGMS units

amounts to about 95%. Further installations, including the largest separator

of 1000 mm diameter, Cryoﬁlter 5T/1000, under the Outokumpu Technology

label after Outokumpu acquired Carpco Inc. in 1998, took place in several other

kaolin operations. Figure 7.10 illustrates the two units delivered to Cadam.

Open-gradient magnetic separators

An unsuccessful attempt, potentially of breakthrough signiﬁcance, to implement

an innovative technique was the application of open-gradient magnetic separa-

tion to beneﬁciate pyroxenite ore. OGMS, instead of employing a matrix to

generate a magnetic ﬁeld gradient, uses the actual magnet windings to create

the ﬁeld gradient and magnetic force that deﬂect magnetizable particles. A

schematic diagram of such a "falling curtain" superconducting OGMS is shown

in Fig. 2.85.

As has been discussed in Section 2.5.3, Cryogenic Consultants Ltd. built a

production-scale linear race-track magnet OGMS that was earmarked for the

dry concentration of apatite from phlogopite [R19]. The magnet suered from

repeated quenches resulting from electromagnetic stresses [K31]. In spite of

considerable expenses to resolve the problems and to salvage the project, the

separator was never commissioned. This case illustrates the consequences of an

attempt to introduce an immature technology into a production environment.

Separation in magnetic ﬂuids

It has been discussed in Section 2.8.2 that AVCO Corp., NASA [M12], Hitachi

[N4] and other organizations successfully demonstrated, in 1970s, that it was

possible to achieve a very high selectivity of separation of non-ferrous metals

from automobile scrap in ferroﬂuids at industrially meaningful separation rates.

In spite of the positive outcomes of these campaigns, further production-scale

implementation of the FHS technique did not happen. It can be speculated that

the reason for non-acceptance of FHS by the market at that time was that the

need for scrap recycling was not yet well developed. The perceived high cost of

ferroﬂuid and the need to recycle it probably contributed to the fact that the

introduction of FHS to the metal recycling industry was not successful.

At a somewhat later stage, a wide range of ferrohydrostatic separators was

developed by the GMUO Institute in Lugansk, in the former USSR [G5]. The

application of these units included the density separation of coal and non-ferrous

metals and the recovery of diamonds, gold and other platinum-group metals.

7.3. MAGNETIC SEPARATION AND INNOVATION 565

Figure 7.11: The GMUO ferrohydrostatic separator FHS-40M.

Figure 7.11 shows an FHS-40M ferrohydrostatic separator designed for the re-

covery of ﬁne diamonds from the ﬁnal sorting concentrate.

In 1992 six of the FHS separators that had been supplied to Yakutalmaz in

Yakutia, Russia, for the recovery of diamonds, underwent, successfully, detailed

acceptance tests and it was decided to install them in production at Yakutalmaz

to replace the toxic heavy liquid Clerici solution. It appears, however, that

this new technology was treated with suspicion by the workforce. FHS was

apparently seen as a threat to various beneﬁts and perks. The management was

forced to abandon this novel technique.

More fortunate was the GMUO FHS separator for the recovery of gold from

placer gravity concentrates. It was reported that in 1993 this technology, which

eliminates the need to use mercury amalgamation, was operating in nine Russian

gold mining operations [S55]. Even more successful appears to be permanent

magnet-based Geos ferrohydrostatic separators. It was reported that in 1995

these systems were in operation in 19 gold-processing plants in Russia [S54].

It can be seen that separation in ferroﬂuids, in spite of a few patches of

misfortune, is on its way to successful implementation on production scale. The

existing applications are in areas where a high density dierence between the

566 CHAPTER 7. INNOVATION AND FUTURE TRENDS

fractions to be separated allows a low level of sophistication of the equipment.

Considerable progress has, however, been made in the development of selective

FHS separators with automated density control with the main emphasis on

application in the diamond-winning industry. Scale-up of the technology has

also been addressed, technology for the recovery and recycling of ferroﬂuid has

been developed, and low-cost ferroﬂuids are being produced on a production

scale [S23]

These recent developments in FHS and new waste legislation in various First

World countries open again the door for the application of FHS in the recycling

of metals and metallic products and the recovery of non-ferrous metals [S92].

Concluding summary

Our walk through the innovation landscape in magnetic separation illustrates

the enormous eort that was expended over the years in order to convert a wealth

of novel ideas into workable techniques and to introduce them into material

treatment operations. The cases discussed above illustrate that there have been

numerous successful innovations in magnetic separation. Permanent magnetic

roll separators, matrix separators as conceived by Jones, iron-clad solenoids as

aspin-o of a search for the elusive magnetic monopole by the MIT scientists,

the replacement of the Jones horizontal rotor in HGMS by a vertically rotating

ring carrying the matrix and the introduction of eddy current techniques to

the separation of non-ferrous metals are examples of the remarkable success of

innovation and technology transfer.

On the other hand, there is an equal share of unmistakable failures. The

reasons for these failures cover a wide spectrum of risks that accompany any

eort to implement new technology. The derailers that were responsible for the

failures in technology transfer can be identiﬁed from our analysis:

• The excessive cost of a product, in order to recover the research and devel-

opment costs in the shortest possible time, not compatible with the market

needs and with the availability of an alternative technique or product.

• Incorrect assessment of technical feasibility. A technique was not feasible

or viable from ﬁrst principles and in spite of this, it was still developed

and oered to the industry.

• Political turmoil and changes on a regional level prevented implementation

of a novel and su!ciently mature technology. In spite of ﬁnancial losses

and time delay, this setback became a basis for even further innovation.

• Premature application of unproven technology. Scale-up of the research

results was attempted with limited consideration of the production-scale

complexities.

• Poor engineering of an ambitious and complex technique.

• Insu!cient market need in relation to the complexity and cost of the

technique.

7.4. CURRENT STATUS OF MAGNETIC SEPARATION TECHNOLOG

567

• Resistance to change from the workforce and fear of job and perk losses.

It is also interesting to note from the above analysis that the mining and

material-handling companies that were trying to introduce innovation in their

operations by implementing the magnetic separation technology usually did not

carry out the research and development in-house, but rather preferred to procure

proven, or seemingly proven, equipment or techniques. While this is a safe and

cheaper way of acquiring a novel technology, it also carries some risks. The user

becomes dependent on the supplier’s expertise, credibility and integrity, and

additional expenses might be incurred in order to align a novel technology with

the work system into which it is being introduced.

7.4 The current status of magnetic separation

technology

In order to review the current status of magnetic separation technology, it is

instructive to apply Stokes’s quadrant model of research, development and tech-

nology transfer, shown in Fig. 7.4. Without doubt, the ultimate objective of

research and development of a novel technique should be to place it in the ﬁrst,

Pasteur’s quadrant. A technique that ﬁnds itself in this quadrant is charac-

terized by well developed theoretical foundations as well as by clearly outlined

practical use or application.

The current status of magnetic separation technology, using Stokes’s quad-

rant concept, is schematically depicted in Fig. 7.12. It can be seen that

techniques such as low-intensity magnetic separation, permanent magnet-based

high-intensity magnetic separation and large-particle eddy-current separation,

while widely employed on production scale, are based on an empirical and heuris-

tic approach rather than on good knowledge of the fundamentals [S97]. The

magnetic aspects of the applications of magnetic techniques in biosciences are

also of empirical nature rather than based on good understanding of the funda-

mentals of magnetism.

On the other hand, production-scale applications of open-gradient magnetic

separation, dry HGMS, ferrohydrostatic separation and to some extent wet

HGMS are rare, although the fundamental theoretical principles are reason-

ably well established. Flocculation of weakly magnetic materials and magnetic

tagging, two techniques of potentially considerable industrial, environmental

and social signiﬁcance, ﬁnd themselves only in the early stages of fundamental

research.

7.5 What the future holds?

It transpires from our discussion that the future focus of magnetic techniques

of material handling should be towards a good understanding of the physical

principles, combined with clear goals for industrial applications.

568 CHAPTER 7. INNOVATION AND FUTURE TRENDS

Consider at ion for use ?/

Appr oach

Blue skies Practical

Quest for

under -

st anding?

Knowledge of

fundamentals

Empirical

heuristic

Target status

of magnetic

separation

OGMS

FHS

Wet

HGMS

Dry

HGMS

Low temperature

superconducting

LIMS

WHIMS

Permanent

magnet HIMS

Large

particle

ECS

Biomedical

Flocculation of

ferromagnetic

materials

Flocculation

of weakly

magnetic

materials

Demagneti-

zation

Magnetic

tagging

Figure 7.12: The current status of magnetic separation technology (adapted

from Svoboda [S97]).

Presently, the magnetic techniques of manipulation of matter stand at a

crossroads. The dominant drivers of the early 21st century dier markedly from

those of the late 20th. The priorities of nuclear power, defence and beneﬁciation

of mineral resources by brute force have been replaced by those associated with

economic growth, discovery of new materials, environmental and knowledge

management and health care. Processes and products from the last century

cannot, therefore, meet the criteria of the 21st century and a new approach will

have to be developed.

7.5.1 Mineral processing

The minerals industry faces problems of declining grades of ores, increasing pro-

portions of deleterious impurities and a need to reduce the particle size in order

to liberate the valuable components. New technologies capable of meeting these

challenges have to be designed for environmental and sustainability reasons.

Magnetic separation, unlike many other technologies of mineral treatment,

can operate in a dry mode. It can perform successfully in arid and arctic regions

and even in extraterrestrial conditions. Problems of water consumption and

e"uent disposal can thus be largely eliminated. Using sophisticated magnet

design or advanced permanent magnet materials, the energy consumption can

be reduced signiﬁcantly. In addition to lower operating costs, reduction of waste

heat, CO

and other emissions will be, therefore, achieved.

7.5. WHAT THE FUTURE HOLDS? 569

In contrast to conventional ﬂotation and ﬂocculation, magnetic separation

does not require chemicals that are responsible for steadily increasing operating

costs and environmental concerns. Similarly, the use of heavy liquids, usually

toxic and costly to acquire and to dispose of, in density separation and coal

preparation, can be eliminated by using magnetism-based techniques.

7.5.2 Biomedical applications

There are three main areas in the biomedical ﬁeld in which magnetic techniques

are likely to play a role. The development of magnetic carriers and magnetic

ﬂuids as drug carriers and adsorbents is at the top of the list. Future applica-

tions also include the production of DNA sequences, development of magnetic

a!nity adsorbents for isolation and removal of selected biological compounds,

the identiﬁcation of unwanted toxic organisms in foodstus, and gene cloning.

Drug delivery and the localization of magnetic ﬂuids in target areas will beneﬁt

from new developments of powerful permanent magnet materials.

Although magnetic separation is the most common approach to exploit mag-

netic properties in biosciences, the design of existing commercially available

separators is still based more on a trial-and-error approach than on specialized

knowledge of the fundamentals of magnetism. Future magnetic separation sys-

tems will have to be able to discriminate between targets precisely, will have to

be selective and will be required to leave targets functionally unharmed.

7.5.3 Recycling and waste processing

The recovery of materials from solid waste is technically, and in particular eco-

nomically, complicated. Nevertheless, beneﬁcial uses for stockpiled by-products

are being found, and recycling is experiencing increasing emphasis. While the

process design from the environmental point of view is based on short-term

thinking, sustainability requires a longer view, perhaps 50 years into the future.

It is a tough problem, in which recycling and waste treatment, in addition to

renewability, dematerialization and product life extension, is an important part

of the scenario.

The potential for improved success in the recovery of materials from solid

waste increased considerably with the availability of eddy-current separators for

small particles. The high intrinsic value of non-ferrous metals will inevitably

lead to further improvements in the separation of ﬁne and very ﬁne particles of

non-ferrous metals. This development, combined with availability of even more

powerful permanent magnets that would allow the increase in the magnetic ﬁeld

strength in eddy-current separators, will extend the range of applicability of this

technique and its viability [V11].

Magnetic carrier and tagging technology allow for rapid and selective sep-

arations of colloidal non-magnetic mineral particles and macromolecules using

magnetic means. To date, this technology has been associated with small-scale

high-value medical and analytical applications. However, with the development

of new inexpensive magnetic support particles and genetic advances in mass