PASTE & TAILINGS 2020
Filtering down
Todd Wisdom, FLSmidth Director of Tailings Solutions,
talked to Paul Moore about filtered tailings in relation
to best practice, equipment and application
IM: Am I right in saying that filtered tailings still
have a moisture content but that they can be
moved by conveyor?
TW: Both thickened and paste tailings are
saturated with water. Filter cake can be
saturated or not saturated depending on
whether air is used to dewater the cake. Some
filters like belt presses and centrifuges cannot
blow air through the cake. Saturated and
unsaturated filter cake can usually be conveyed
but may have a low surcharge angle which is
important to understand so the conveyor can be
correctly sized. FLSmidth has developed a
TW: Thickeners are very important in a filtration
solution. Gravity is free and doesn’t fail.
Removing water prior to the filter reduces
CAPEX and OPEX significantly. Any kind of filter
is more expensive than a thickener. The
attached chart is based on a study we did that
shows how increasing underflow solids effects
overall CAPEX and OPEX.
FLSmidth developed a proprietary test to
determine conveyability of the filtered tailings –
these show the same material; in both cases
the material is conveyable but has different
properties that must be understood to ensure
proper conveyor design
slurry dam failing but those alone don’t seem
to be enough to be able to make a filtered
tailings project go ahead from what I have seen.
We would reccomend the attached flowsheet.
Note that water ratio is defined as tonne of
fresh water required/tonne of ore feed to the
concentrator.
proprietary test to determine the conveyability of
the filtered tailings – see the attached before and
after testing photos of the same material. Note
that in both cases the material is conveyable but
has different properties that must be understood
to ensure proper conveyor design.
IM: Thickeners are usually associated with
thickened or paste tailings projects - what role
do/can they play in filtered tailings projects?
IM: Can you outline the type of project where
you would recommend a filtered tailings
approach versus thickened tailings and what a
typical flowsheet for this would look like?
TW: The main drivers for filtered tailings are the
cost of water, above $4/m 3 you can make a
filtered tailings project have a positive IRR on its
own. The other factor is meeting regulatory
requirements. There are also the social license
to operate and risk/consequence aspect of a
IM: Is the reason that thickened tailings have
been more of a focus to do with the fact that
slurry transport is cheaper and easier to
handle?
TW: Partially, if you don’t go all the way to
paste tailings in a thickener you can easily use
centrifugal pumps to transport the slurry to the
TSF which is cheaper. You also get the benefit
that the slurry will flow by gravity and selflevel
so you don’t need complicated
The left hand chart illustrates how increasing underflow solids effects overall CAPEX and OPEX; the flowsheet on the right is a typical recommended
filtered tailings flowsheet from FLSmidth
P8 International Mining | SEPTEMBER 2020 Supplement