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PRODUCT News
February 2015
MODERN MINING
47
Demagnetising coils are commonly used
in the minerals processing industry to
demagnetisemagnetised slurry. Themedia
used in the Dense Medium Separation
(DMS) process is magnetic to allow for sim-
ple recovery and regeneration processes.
In the past, traditional demagnetising
coils have been plagued by inefficien-
cies. Longi-Multotec now offers a solution
that – it claims – addresses these issues
and provides continuous, high frequency
demagnetisation.
“It is well known that recovery of the
media by means of magnetic separators
induces a residual magnetisation, which
causes flocculation of the magnetised
particles and increases the viscosity of the
medium. It is possible to reduce or even
eliminate these effects by demagnetising
the magnetic over-dense product stream,”
says Stuart Callum, Process Engineer at
Multotec’s Solid Liquid and Magnetic
Separation business line.
“The process of demagnetisation
requires an alteration of an applied mag-
netic field from north to south, while
monotonically decreasing the field inten-
sity steps. This elimination of the magnetic
hysteresis will bring about scrambling of
the magnetic domains striving towards a
zero net resultant charge.”
DMS efficiency may be improved by
lowering and then controlling medium
viscosity as well as medium stability and
density control. These improvements are
clearer in cyclones, where gravitational
forces are higher, compared to DMS drums.
“Over the years, demagnetising coils
have been developed to improve the fre-
quency of alternating magnetic fields,
as well as to decrease the distance over
which the field is dissipated. These prod-
ucts were aimed at allowing more energy
efficient and compact designs. Ironically,
however, this drive has led to inefficien-
cies in process performance,” says Willem
Slabbert, Applications and Process
Manager at Multotec’s Solid Liquid and
Longi-Multotec offers new generation demagnetising coil
Magnetic Separation business line.
The constant wave, high frequency
demagnetising coil has been designed to
overcome the inefficiencies of previous
generations of coils by generating a con-
tinuous wave of a consistently decreasing
magnetic field across distance in the direc-
tion of fluid flow, at high frequencies of up
to 200 Hz. This allows continuous demag-
netisation of slurry through all consecutive
slurry elements.
“Even though the actual magnetic coil
remains the same, new advances in electri-
cal component technology allow improved
control over the electrical energy supply
to the coil. The performance advancement
of the new generation Longi-Multotec
demagnetising coil will allow more effi-
cient demagnetisation, which will facilitate
better viscosity management and in turn
will improve cyclone performance in
terms of separation efficiency and quality,”
Slabbert concludes.
Multotec Group, tel (+27 11) 923-6193