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MechChem Africa
•
February 2017
A
ccording toMultotec environmen-
talprocessengineer,Carienvander
Walt, continuous ionic filtration
technology augments existing so-
lutions such as reverse osmosis, by achieving
higher water recoveries while delivering a
zero liquid discharge solution.
“CIF
®
is a significantly improved version of
the familiar andwidely accepted ionexchange
methodology,” says Van der Walt, “and it has
been tested and proven in treating wastewa-
ter in various applications around the world.”
The technology was developed by the
All Russian Research Institute: Chemical
Technology (ARRICT), originally for uranium
and rare earth extraction and recovery. Using
ion exchange resins, the technology enables
uranium ions tobe loadedonto the resin from
a solution, and then regenerated in order to
produce a concentrated uranium solution.
This solution can be processed even further
to produce a saleable uranium product, “and
there are nowmore than ten uranium recov-
ery plants inKazakhstan andRussia that have
beenusingthetechnologyadvantageouslyfor
many years,” Van der Walt adds.
In 2000, the Australian water treatment
and metals recovery specialist, Clean TeQ,
which is now commercialising the process,
obtained the exclusive license to the technol-
ogy. Some three years ago, Multotec recog-
nised the benefits and became the exclusive
partner for the technology in Africa. “It fits in
well with our range of solid-liquid separation
technologies, such as our centrifuges and
filter presses,” she tells
MechChem Africa
.
Describing how ion exchange technology
works, Van der Walt says that ion exchange
resins consist of polymer beads chemically
engineered to suit specific ion exchange re-
actions. “The reactions take place on the
surfaces and within the porous structure of
these tiny spheres. Typically for water treat-
ment applications, an ion exchange resinused
for removingcationicelements startsoutwith
hydrogen ions (H
+
) attached to the polymeric
structure of the beads. When brought into
contact with contaminatedwater containing,
for example, calcium (Ca
2+
) ions, two H
+
ions
are discharged into the water for each Ca
2+
ion that attaches itself to a bead.
Most traditional ion exchange treatment
systems rely on a static resinbed, which is laid
out similarly to a sand filtration system, the
water being passed through the bed, usually
from above.
“As the ion exchange reaction proceeds,
the resin in the fixed resin bed becomes
saturated and then has to be regenerated.
This is, therefore, an intermittent batch pro-
Minerals processing specialist Multotec believes its continuous ionic filtration (CIF
®
)
process could help change the mining sector’s outlook on wastewater treatment.Via
its Clean-iX
®
process, valuable metals can be recovered first, followed by wastewater
being passed through the patented dual-stage ionic desalination (DeSALx
®
) process,
to produce potable water quality.
Peter Middleton
talks to Carien van der Walt.
Multotec’s dual stage continuous desalination process consists of cation removal followed by anion
removal, with each section consisting of three columns.
Mine water treatment
that improves profitability
cess that has to be halted at regular intervals
while the resin bed is flushed, washed and
treated to remove the accumulated Ca
2+
ions
and replace themwithH
+
ions again,” Van der
Walt explains.
The difference between CIF and tradi-
tional ion exchange processes? “The key dif-
ference is thatwe do not use a fixed resin bed.
Instead, we are moving ion exchange resins
through the system in the opposite direction
to the water flow,” Van der Walt responds.
Explaining how the continuous process
works, she says: “By moving the resin in the
counter current direction to the solution,
we enable continuity and we get a chemical
advantage by creating a natural driving force
for the loading and regeneration reactions
to occur.”
Thewater being treated enters at the bot-
tomof the first column, called the adsorption
column. Cation exchange resin, that is, resin
with H
+
ions around its surface, enters the
exchangecolumn fromthe top. Duringa trans-
fer cycle, the fresh resin moves downward
creating a concentration gradient within the
bedas soonas the contaminatedwater comes
into contact with the resin.
“Because ion-exchange reactions are equi-
libriumreactions and therefore reversible, Le
Chatelier’s principle of dynamic equilibrium
can be used to optimise the process. As the
water rises up the column and through the
resin, it becomes less and less contaminated,
while the resin becomes more loaded with
ions as it moves down.
“So at the bottom of the column, water
with a high concentration of dissolved ele-
ments comes into contact with the most Ca
2+
loaded resin. As the water rises, it becomes
less and less contaminated. At the same time,
however, the resin becomes less and less
loaded, which keeps the concentration well
to the left of the equilibrium point, so decon-
tamination occurs at an ideal condition over
the full length of the column.
“Chemically speaking, we say that the