MechChem Africa February 2017

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. Mine water treatment that improves profitability

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-

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

Multotec’s dual stage continuous desalination process consists of cation removal followed by anion removal, with each section consisting of three columns.

34 ¦ MechChem Africa • February 2017

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