Tackling Acid Mine Drainage And Generating Returns
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Mineral processing specialist Multotec says its continuous ionic filtration (CIF) process could change the mining sector’s outlook on wastewater treatment and also offer an income stream while treating contaminated water to achieve potable water quality.
According to Multotec environmental process engineer, Carien Van der Walt, the technology augments existing solutions such as reverse osmosis by achieving higher water recoveries and delivering a zero liquid discharge solution.
“It is a significantly improved version of the familiar and widely accepted ion exchange methodology,” says van der Walt, “and has been tested and proven in treating wastewater in various applications around the world.”
With local representation rights from Australian water treatment and metals recovery specialist Clean TeQ, Multotec sees the process as an ideal long term solution to Acid Mine Drainage (AMD) in South Africa, especially as options are being explored to upgrade the output of the three Witwatersrand AMD treatment plants to achieve a potable standard.
“Adding a secondary solution that fits onto the backend of the current treatment plants is not only cost effective, but also much faster to implement,” she says.
Among the system’s novel features is the continuous and counter-current movement of resin – in contrast to a conventional fixed bed arrangement –that allows the process to operate closer to ideal equilibrium conditions to improve process efficiency. The movement of resin counter-current to the solution also creates a concentration gradient, which drives the ion exchange reaction, thereby reducing reagent consumptions and improving recovery.
“The movement of the resin also eliminates the potential for scaling and fouling,” she says. “Any suspended particles in the feed water do not interfere with the primary desalination operation of the technology, and are filtered out.”
Van der Walt highlights that, while a single-stage CIF module can be used for a range of treatment applications, Multotec focuses on the Dual-stage Iconic Desalination (DeSALx) process in South Africa, to produce water with low total dissolved salts (TDS) and a neutral pH.
“The DeSALx process uses two stages of CIF to desalinate brackish water, and produce potable water,” she says. “In the first stage, a cationic resin is used to remove cations from the water, while an anionic resin is used in the second stage to remove anions.”
The resins are regenerated with sulphuric acid and lime respectively for the cation and anion sections. Due to the continuous movement of the resin through the system, the process is able to handle any in-column formation of precipitated gypsum, eliminating the need for expensive regeneration chemicals. This also means the spent regeneration solution (or brine) is precipitated gypsum slurry, which can be recycled to the front-end of any existing neutralization process, thereby closing the loop and facilitating a zero-liquid discharge process.
Using the same principles as CIF, the Clean-iX metals recovery technology is available to remove and recover metals present at low concentrations in mine-impacted waters – creating a revenue stream from a range of metals including gold, silver, platinum, nickel, copper, uranium and rare earth metals.
“Revenue from these additional by-product metals can help off-set the cost of installing a water treatment plant and eliminates a waste sludge or brine that has to be environmentally managed and contained,” says van der Walt.
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