WATER MANAGEMENT
As the mining industry focuses on improving productivity , reducing operating costs , and venturing into ever more challenging and remote locations for new projects , there is an increased need to look upon water as a wholeproject issue , argue SRK ’ s Tony Rex , Corporate Consultant ( Hydrogeology ) and Tom Sharp , Principal Environmental Engineer in a recent article on the water management big picture in mining . “ Add broader perspectives such as stakeholder considerations and effects of a changing climate and water can present a significant risk to a mining project if not fully understood and managed .”
The authors point to a changing climate meaning that many mines and projects are located in regions where climate patterns are already changing . The way water is managed on mine sites needs to adapt accordingly ; from effective flood risk mitigation through to ensuring operational continuity under drought conditions .
There is also a need for integrated water management : “ whole-operation water management begins with effective mine site water balances but also requires a joined-up approach between the various functional teams running the mine . Interactive dashboards are just one example of how diverse water management activities at an operation can be more effectively managed .”
Clients often want specific issues investigated , or solutions developed for a particular problem . Groundwater management is one area where very specialised , niche studies are required to fully understand the conditions at a particular project site before appropriate solutions can be
CleanTeQ Water DESALX ® plant at Fosterville Gold Mine
Finding a water balance
The management & treatment of water in mining is evolving , linked to new technologies , more modular and mobile solutions , plus the industry step change in the wake of wet tailings dam failures , reports Paul Moore
evaluated and designed . Tailings facility management is another focus area for targeted studies . “ In both cases , the combination of targeted field investigations and testwork , careful data analysis and appropriate modelling are essential in delivering a successful outcome .”
Then comes water care and good governance : employing water re-use and minimisation methods in mining operations not only reduces costs but also reduces risks and improves corporate governance indicators . Mine operations are becoming increasingly aware of their water ‘ footprint ’ and the benefits this approach delivers .
Mines also need to be good neighbours . “ The increasing recognition of water as a finite resource to be safeguarded , managed and shared with the wider community is driving mining companies more and more to improved mine water management throughout the design , operational management and closure lifecycle of projects . The other way of looking at this is conflict-mitigation ; working alongside and with local communities and being recognised as good neighbours .”
SRK says it helps identify , manage and mitigate risks in mine water management while also highlighting opportunities through innovative thinking and embracing a whole project approach .
Saline water treatment
In some regions , mines also need to take heed of the waters they are encountering during operations . Taking one specific example , SRK ’ s Sharp says mining
operations frequently hit saline groundwater below permafrost on the Canadian Shield . Saline groundwater on the shield is primarily a calcium chloride brine . Management options need to meet compliance limits for total dissolved solids ( TDS ) and chloride in receiving waters .
“ TDS concentrations in groundwater increase with depth below the permafrost and can exceed 50,000 mg / L . The Canadian Council of Ministers of the Environment long term chloride limit for protection of aquatic life is 120 mg / L . A TDS limit of 1,000 mg / L has also been set for some mines in the north . Treatment options are limited , expensive , and energy intensive . Conventional treatment involves a concentration step ( typically a membrane process ). At TDS concentrations over 30,000 mg / L , most membrane processes are not feasible . Evaporation and crystallisation is cost prohibitive for mine operations . This leaves two feasible options for managing saline groundwater : discharge to the environment or storage in completed pits or underground workings .”
Discharge to the environment requires enough assimilative capacity ( dilution ) in the receiving water to meet compliance limits . The assimilative capacity varies seasonally in the north , which may require mine water storage during low flow periods of the year . Discharge to a lake may initially meet compliance limits but if the loading to the lake exceeds the rate at which TDS is flushed from the lake , concentrations may eventually exceed the compliance limit . Discharge to the marine environment is a viable option but depends on proximity .
“ Saline water can also be disposed of in completed underground workings and pits . This requires integrating water management and mine planning . Disposal in underground workings isolates the saline water from the environment but sufficient volume needs to be available when saline inflows begin . Saline water can be stored in a pit by forming density stratified lakes where the saline water is deposited first and overlain with less dense freshwater . Creating this type of lake in a pit is challenging , but has the potential for the long-term storage of saline water without impacting the environment .”
SRK says there is an increased need to look upon water in mining as a whole-project issue
MARCH 2021 | International Mining 39