WATER MANAGEMENT & TREATMENT
work when the water is very cold or stops flowing for a few months , and in general not as difficult to maintain as a biological set-up . We got funding from a couple of mining companies who at that time were going through stages of permitting and in their projects , selenium had been flagged as one of the major environmental issues . So they had a lot at stake and they did not like the biological approach so that ’ s why they helped us fund the tech development .”
But why is selenium a problem in mining and how did it become a problem ? Kratochvil says it has always been there but has not been measured and the detection limits were not where they are today . But more importantly , the aquatic toxicology of selenium is a relatively new science and one that is still fast evolving . “ The understanding of its impacts on the receiving environment is increasing – particularly that the nature of selenium toxicity is not acute rather it is chronic long term through genetic mutations in organisms and you need to have seen generations of organisms before you actually see an effect . So if you start a mine , and you have selenium in your discharge , you are unlikely to see effects for maybe ten years . But eventually you will see them and by then it is too late . The danger for the industry and something the regulators recognised , was that by the time you start seeing effects the bioaccumulation has already started and it is very difficult to turn the dial back – so the industry needed something proactive and that would catch it early using conservative regulation limits .”
In very low levels , selenium is a micro nutrient – the problem is that aquatic organisms are way more sensitive to it than humans . Drinking water standards are orders of magnitude greater than those for fish . It starts in micro algae and plankton then invertebrates and fish and so on . Another important piece is that the first step – the way selenium update happens between the water and the algae – depends on a lot of site specific factors such as water flow rate – in lakes and marshes bioaccumulation starts much more quickly than in a river . “ While the biological systems can remove 90 % or so of the inorganic selenium , a small portion of what is left is converted from the inorganic form which is not as bio-accumulative , as the organo forms that the biological approaches actually generate in small amounts . Those small amounts are orders or magnitude more bio-accumulative than the inorganic selenium that was in the water in the first place . So in some ways the biological treatment can , in some cases , make the effluent more toxic . This was not appreciated until people started building these plants and measuring different forms of selenium in effluent and the regulators said you not only have to sample the water but also take samples of fish tissue – where levels were actually going up faster than before the treatment plant was put in .”
What happens to selenium at the end of treatment ? Kratochvil : “ It goes into a residue and just by its nature , the biological residue is really unstable . If you put in into a conventional landfill , it will get into the leachate ; you can hope for the best and store it under anaerobic conditions . But with an inorganic approach like ours – you are not generating any of the organic selenium species , it just filters the selenium out in the first place plus you can treat on demand , and the water temperature does not matter . Plus you generate a solid inorganic residue that even has potential markets like steelmaking . And none of the biological approaches alone can reach the regulated limits in the receiving environment without relying on dilution downstream .”
How does Selen-IX actually work ? This process concentrates the selenium into a small volume of brine solution that is treated with electrochemical cells to precipitate the selenium as a stable iron-selenium solid . After the solids are separated from the liquid , the brine solution is recycled back to the ion exchange circuit , eliminating waste liquid brine . XRD and TCLP analysis have verified the solids to be non-toxic . Selen-IX units are compact modules with a small footprint and can be easily deployed in remote locations to treat multiple discharge points just as they can for one single big discharge point .
Selen-IX has US and Canadian patents in place as that is currently where the regulations are the toughest on selenium . BQE Water already sees potential elsewhere , however , for example there is a new project in Peru that has already flagged selenium . Plus there is no doubt that it is going to be present in many of the mined deposits worldwide . It also cuts across different commodities – copper , gold , coal , zinc and so on . It is just isn ’ t on the regulatory frameworks of other major mining countries – yet . It is also worth pointing out that many of the mines in the US and Canada are discharging water into relatively pristine natural habitats that are ecologically sensitive . That is also the case in many other regions but not necessarily at every site .
BQE Water has moved through concept , proving at lab and pilot scale plus numerous demos and is now building full scale treatment plants as outlined in the recent project announcement . This client cannot be revealed due to NDAs but is one of the major global base metal producers . However , other clients like Seabridge Gold , which used Selen-IX to secure regulatory approvals for the KSM project , have been public about their use of the technology and their support of it . “ They knew they had time before implementing selenium treatment , so they were able to look at emerging technologies and take advantages of innovation , and seek out the best possible solution for their project rather than just going with the biological approach that was the only commercially available technology at the time they began their search . Also the world is changing – many miners are not waiting until regulators tell them to do things – they want to be proactive where they can as they want to be sustainable and be upfront with local communities in what they are doing .”
Veolia Water Technologies and new developments in selenium removal
Further to the above discussion on biological versus inorganic approaches to selenium removal the biological methods themselves are also evolving , and IM also spoke to Veolia Water
International Mining | MARCH 2024