MechChem Africa February 2017

MechChem Africa

•

February 2017

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

) ions, two H

ions

are discharged into the water for each Ca

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

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

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