WATER MANAGEMENT
Stantec on the future of mine water treatment
Daniel Dupon is Stantec Technical Leader – Mine Water Treatment , and gave IM some insights into how the industry has changed and is changing . “ Traditionally , the nature of mine influenced water ( MIW ) dictated that conventional technologies be the focus when developing process solutions . The conventional approaches rely on base neutralisation and chemical precipitation to eliminate acidity and dissolved metals concentrations . While these approaches have been very effective and comprehensive , the direction of regulatory trends ( such as permit limits always moving in a more stringent direction ) and the expanding array of MIW chemical characteristics and complexity is forcing the envelope of potential technologies to widen .”
Dupon says that today , when engineers consider the challenges that mining companies need to overcome , the arsenal of solutions that can be applied , and potential future operational limitations , ingenuity is essential . Much of this arsenal is improved by possible application of advanced treatment technologies , such as RO ( reverse osmosis ) and ion exchange .
“ At the beginning of my career , the idea of applying advanced technologies to MIW treatment projects was not understood , if not ludicrous . Just a couple of decades later , we are placing high reliance on the capability of these technologies , while studying ways to increase efficiency and improve operations and cost .”
But with many technology improvements come new challenges that need to be overcome , such as liquid waste ( versus solid waste with conventional processes ) and application sensitivity . “ These new challenges tend to be the ‘ tail wagging the dog ’ when recommending the best solutions for clients and their mining operations .”
Dupon adds : “ Accurate projections of future MIW trends for a particular mine site are essential to defining the best advanced technology approach due to the higher degree of application sensitivity . Understanding the
Daniel Dupon , Stantec Technical Leader – Mine Water Treatment application sensitivities to MIW is imperative because the typical water supply and other industrial applications do not address the complexity of MIW characteristics , such as low pH or treatment of metalloids ( ie As , Mo , Se ). In the realm of MIW treatment , these advanced technologies are great tools to work with , but success will ultimately depend on a greater understanding of effective application and optimised design .”
A combined conventional and advanced technology approach is becoming the norm , says Dupon . In many cases , the number , and chemical diversity , of constituents of concern in the MIW is driving the complexity of process flow sheet to require five or more specific treatment steps , many of which target a single constituent . Industrial treatment applications have typically involved ‘ package ’ systems that are combined to form a complete system . As vendor technologies become more specialised , Dupon sees the package approach becoming more and more prevalent in mining .
Finally , there is much to be learned from other industries . “ For decades , the standard in mine water treatment has been the high-density sludge ( HDS ) process because most mine waters had acidity and metals . Now , and recently , we also need to account for other constituents like arsenic , fluoride , and molybdenum . Thus , the degree of crossover from other treatment fields such as municipal to mining is becoming more pronounced and , in many respects , results in a challenge that the process engineer finds more rewarding than the standard solution .”
Desalination and decision making
IM caught up with Golder ’ s Director , Water Strategy and Sustainability , Dr Hu Fleming , who has extensive experience with major desalination projects working for consultancies and industry alike , including as former Global Head of Water at Anglo American . He told IM : “ In general desal , the cost per cubic metre delivered has come down significantly which is why we are seeing desal take a much larger role in the global water supply mix , not just in mining . The current delivered at desal plant price broke the $ 1 per cubic metre level about three years ago and there are commercial operations already running at $ 0.60 per cubic metre . This has been achieved mainly through various operational and technical improvements . But in mining it ’ s not that simple – this is probably the smallest part of the cost . First off , few mines are at the coast so the cost of a desal project in mining is the desalination plant itself , then the intakes and outfall structure , and the pipeline to the mine site , and the associated power / pumping stations to make conveyance happen . Taking Escondida as an example , the
View of the Alumbrera mine tailings area in Argentina
desal plant was , approximately $ 250 million but the pipeline was $ 300-400 million , and the power boost stations another $ 50 million plus . This is not unique to Escondida , it holds true for many mining desalination projects – it ’ s necessary to think about all in cost .”
Fleming added that the other major factor in mining desalination is the management of the brine . Municipal desalination plants may allow brine concentrate to return to the sea , but most governments will not allow miners to do this as there is no direct public benefit to the desalinated water . So , brine management can be another significant cost and has stopped a lot of mining desalination projects early on . You can spend $ 10- 12 per cubic metre just on brine issues alone .
Mines generally don ’ t need the quality of desalinated water – taking Chile as an example , everyone focuses on the big desal projects , but for every desal plant there have been 2 or 3 conventional seawater pipelines supplying mines as an alternative approach . Generally , it ’ s the smaller and medium sized miners that have gone down this route , which comes with its own issues such as corrosion of pipelines and potential cracking plus , depending on the commodity , losses in flotation recovery .
What about mines collaborating to share water from a single large plant ? Fleming said this is already happening . In Chile , Teck is building a large-scale desalination plant on the coast for mining in the Tarapacá Region where the desalinated water will be pumped by five booster stations up 4,300 m to the QB2 concentrator plant . But Collahuasi ( Glencore and Anglo ) have been considering teaming projects , including building an aqueduct to transport desalinated water left over from QB2 to its site as a back-up resource , or , to share in a desalination plant , for example . Similar deals have been and are being , considered elsewhere – such as potentially sharing of a desalination plant between Newmont ’ s El Morro and Teck ’ s Relincho copper / moly project in Chile . Several regional developers are planning building desalination plants for power stations , where miners are considering becoming off-takers to the water , as in the Santiago region with Codelco and Anglo American .
MARCH 2021 | International Mining 41