Water scarcity is probably the biggest driver for mining companies to strive towards zero liquid discharge (ZLD) during water and wastewater treatment. Therefore, new technologies and innovative solutions are the current and best future trends.
One examle of new technology is the continuous ionic filtration (CIF®) system by CleanTeQ, which is available to Africa and South Africa through Multotec. This ZLD treatment system can typically be used in mines with acidic sulphate-dominant mine water, and has a range of applications to produce fit-for-purpose recycled water and potentially valuable chemical by-products and metals.
Carien van der Walt, process engineer – environment SSM Division, Multotec Process Equipment, describes the CIF® technology as a unique, novel form of ion exchange, working as a dual-stage system when treating mine water. There are a set of columns for cation removal and another set for the anion removal process.
She explains that the system works via continuous, counter-current movement of resin and solution. “This means that resin moves in one direction, while solution moves in another direction. Fresh resin contacts the most concentrated solution and vice versa. The concentration gradient drives the reaction,” says Van der Walt.
This dual-stage system takes out the cations (for example, calcium and magnesium) and the anions (for example, sulphates and nitrates) to produce the brine, or slurry, which goes back to the front end of the system to be neutralised. With this dual-stage system, one regenerates the cation system with sulphuric acid and the anion system with lime, both relatively low cost chemicals.
“The calcium loaded onto the cation resin will produce calcium sulphate (also known as gypsum) during regeneration with sulphuric acid, whilst the sulphates loaded onto the anion resin will also produce gypsum during regeneration with lime, thereby producing a calcium sulphate slurry. This slurry will go back to the front end of the neutralisation step to precipitate out whatever calcium and magnesium is still remaining in the closed loop,” explains Van der Walt. The total process results in fit-for-purpose water, whether it is process or potable water.
Van der Walt adds that the size of the system can be designed according to the amount of dissolved solids that need to exit the system. For process-quality water, the system will be smaller than for potable water, in which case the system will be designed for a greater resin capacity
The dual-stage system also acts as a filter, as the process removes suspended solids from the feed stream as well as dissolved solids. It is the continuous movement of the resin through the system, coupled with an external resin washing step that allows for the high suspended solids handling capabilities of the process. The system can also operate in series to remove multiple species, to recover valuable products from the water. Furthermore, the system also purifies the water with its ability to operate in high scaling or high solids environments.
Besides the fact that this system is unique, it also offers benefits to the end users that include:
In most cases, there is no need to pre-treat or pre-filter the water that enters the CIF® process. “Water is fed directly into the adsorption column where dissolved salts are removed via ion exchange. Suspended particles that enter the system are filtered out within the process and therefore do not interfere with the desalination operation,” says Van der Walt.
The system is also self-cleaning, as the continuous movement of resins means that the process is not subject to the normal scaling and fouling failure modes associated with membrane technology. The ion exchange resins are continually cleaned and chemically regenerated before being reused, to ensure that the primary treatment process continues to operate.
Van der Walt says that innovation is the key for the future of water and wastewater management. “We are moving to the point where companies invest in innovative solutions to do something that produces value at a lower cost.
“I also notice that more and more companies are seeing water as a value stream, rather than just something to treat and get rid of. I foresee that mines will look at how to use recycled or effluent water to produce revenue. Many mines have valuables in their water, which are currently discarded, in a sense,” says Van der Walt.
She concludes, “If a company has a technology that can recover the valuables in the water effectively, and which produces value from that, it is the type of innovation that the mining industry needs. This is where the CleanTeQ technology started. It didn’t start as a water treatment technology, but rather as metals recovery technology.”
She adds that water shouldn’t always be seen as a problem but rather as an opportunity. Also, water circuits on mines and in industry should be looked at holistically, rather than focusing on, or trying to address single aspects. She says this will result in water savings.
Published by Inside Mining