IM March 2024 March 24 | Page 26

Sykes Group recently launched the Sykes / Primax XH250
way it moves , we ’ ve got to get in and remove the water as quick as we can so they can recover the coal .”
BQE Water and a disruptive approach to selenium removal
BQE Water made a major announcement in February 2024 when it advised that it had completed the commissioning phase and transitioned to the operating phase of the agreement for a water treatment plant at a base metal mine in the southwestern US . Utilising its award winning Selen-IX™ process technology , BQE Water treats mine impacted waters , removing selenium to below 2 ppb ( parts per billion ), as well as dissolved metals , in compliance with applicable effluent quality regulations .
Under the agreement , BQE Water is responsible for clean water production for
environmental discharge . Compensation for operations services consists of a base monthly fee and a supplemental fee for additional water treated over and above the base . The base monthly fee is payable regardless of the volume of water reporting to treatment but is subject to the plant being available for treatment . Both fees are paid subject to the plant effluent meeting the target effluent water quality .
Since the completion of commissioning , BQE Water says the plant has been operating 24 / 7 with an overall plant availability more than 95 %. It is expected to run year-round and treat up to 4,500 gallons of water per minute , making it the largest Selen-IX plant currently in operation . The plant first removes a host of dissolved metals , followed by selenium removal . The key aspects of the plant design that led to the selection of Selen-IX technology for selenium removal included the stringent selenium effluent limit , the requirement for a rapid ramp-up in selenium removal capacity depending on flow and selenium concentrations , and the need to produce a stable non-hazardous residue .
David Kratochvil , President & CEO at BQE Water told IM : “ This project is a major development for us but it is important to emphasise that addressing selenium in waters is not all we do – today it probably represents about a quarter of our active projects . It includes a broad range of water treatment for environmental compliance including : achievement of ultralow discharge limits for a host of metals and cyanide ; the recycling of cyanide using SART , and ion exchange based technologies to selectively remove sulphate , ammonia , and thiosalts which are regulated directly or through effluent toxicity . The common denominator for all our projects is reduction of waste and generation of residues that are suitable for re-use ."
But undoubtedly , selenium is a big problem in mining – and BQE Water ’ s journey in that respect began way back in 2012 with a reaction to two things . Kratochvil : “ One – we started to get a lot of specific enquiries from mining companies around the world about dealing with selenium so there was a tangible market interest uptick . And at the same time , a major consultancy released a report stating that the best available technology to treat selenium in mining was biological treatment . But this was based on two installations of selenium removal technology at FGD plants in coal fired power plants , an application that could not be more different from mine waters with an entirely different setting and criteria including the flow , stability of the flow , the temperature of the water , what ’ s in the water , the discharge limit and receiving environment – everything is different . The reality is while consultancies have a role to play , fundamentally they tend not to be the technology innovators themselves with the associated in-house R & D – they usually apply what has been done before and tend to be conservative in terms of not wanting to take a risk with a new solution , even if it has a clear potential to address the problem in a more effective way .”
BQE Water started from the basis that every mine and every deposit is different therefore the water quality is different . “ We thought , why not be contrarian and look at something nonbiological , as we believed the mining industry needs a technology that to be able to adapt to changes in flow and water quality , that will still 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
24 International Mining | MARCH 2024