Water management for a greener future

The buzz words are out there – green, net-zero, ESG, decarbonization. But is our mining industry meeting the challenges? Canadian Mining Journal held its second Reimagine Mining virtual symposium on Oct. 12, 2022, to hear from experts on how far we have come and what lies in the future.

PANEL MEMBERS: DR. MONIQUE SIMAIR, CEO and principal scientist of Maven water and environment; AJ MACDONALD, VP of engineering with Integrated Sustainability; and DR. SYLVIE ST. JEAN, director for environment and reclamation with Osisko Development

The regulatory landscape is changing quickly, as public opinion demands sustainability and environmental accountability of all industries – none faster than mining. But without mining, there will be no green future because the change cannot happen without lithium, nickel, copper, graphite, uranium, and critical minerals; fortunately, the Canadian mineral industry is poised to supply them. The sector is among the leaders in digital, sustainable production.

Among the fastest changing aspects of water management is the regulatory framework. How are Canadian miners responding to the evolving requirements for water management?

Provincial regulations, in particular, have had a significant impact on the mining community. Luckily, responsible miners already treat water to drinking water quality – if not better.

What is new more recently is the restriction of the amount of fresh water that can be pumped or diverted for a project. Canada is lucky in having abundant fresh water, but not all countries are. Moreover, many jurisdictions have strict limits on when and how much treated water can be released.

Many profitable Canadian miners already made water management a big part of their planning in the engineering phase of development. At this point, proper water plans start to save money. Amounts of both fresh and recycled water are reduced. Treatment costs are down for smaller volumes. Piping and storage requirements are less. Smaller tailings facilities are needed, and it is the same for closure bonds. These add up to lower initial capital requirements.

Those savings continue throughout the life of the project with technologies such as ore sorting, paste backfilling, and dry tailings stacking. That adds up to lower operating expenses.

Other mining companies with less forward thinking executives, continue to plan water use around the needs of the mine and mill. They are of a mindset to retrofit water management to existing operations and finding it extremely expensive. Sometimes, a retrofit is not successful (meaning more expense).

The ultimate goal of water management is not to rely on mechanical or chemical treatment methods, but create natural filtration. Not every solution will suit every project.

Treatment methods can be loosely grouped in three types: active, semi-passive, and passive. Active treatment relies on the use of mechanical means and chemicals, and often a dedicated building. It is the most expensive of the three options. Semi-passive falls in the middle, and carries a middle-sized price tag. Passive treatment, which exists in nature, should be the goal of every water management plan, and it is the least expensive over the long-run.

No single technology will work in every operation. It may even be necessary to combine technologies to suit a specific site. Liming systems, bioreactors and treatment wetlands can all have their place. Combining these methods will probably be the way to go for at least the next decade.

Using multiple technologies can be quite difficult and requires very specific skill sets. This is where collaboration between the mine planners and specialized engineering firms is so useful. It may be necessary to start with an active system, add semi-passive treatment to various streams over time, and transition to a passive system at closure.

What new techniques are on the horizon to help miners reach the ultimate goal of passive treatment?

Both metal and organic materials may make up the toxic portion of effluent streams. Metals can be removed or reduced by reducing the solubility of the metal. They might be transformed into salts or the pH manipulated to reduce solubility.

Twenty years ago, the major technology involved using lime or other chemicals to precipitate solids then dealing with the sludge. Today, technologies have advanced to using bioreactors to create sulphides that form metal sulphides minerals that then precipitate. A new plant has recently been permitted in British Columbia that uses both high pH with lime and sulphide.

There are other precipitation technologies that are being adapted from other industries or sectors. For example, a biological nitrification-denitrification system adapted from a domestic wastewater treatment plant can be used to remove nutrients. B.C. is also home to one of the first ion exchange plants to remove selenium, and it uses an electro-reduction process for the sludge management.

Software, too, is being adapted from other sectors. The willingness to adapt is key. The goal in many other sectors is to discourage precipitation and the scaling that results. For mining, the software has to be adapted to encourage precipitation and the removal of metals.

When the environmental, governance and social (ESG) team is involved in planning, they often consider water management. Such teams are involved in sustainability, and part of that is reducing the carbon footprint of an operation. Treating wastewater with lime can generate significant amounts of carbon dioxide (CO₂), so other technologies are of interest. If even part of the water treatment can become semi-passive, total CO₂ is reduced.

Decarbonization ties into the Technology Readiness Assessment for emerging technology proposed to control or treat effluent discharges from major mines. This is a nine-level scale where levels 8 and 9 are considered acceptable; level 7 is considered as R&D and may meet regulatory requirements; but level 6 and below lack the site specific confirmation to support their use. British Columbia has already issued guidelines to assess the application of new methods in water treatment.

Many semi-passive water management technologies are adapted to a specific mine site, and therefore fall in level 6 or below. For example, there is much variation in gravel beds or wetlands developed for a site-specific effluent that they can only be assessed at a low level. The opportunity comes when they are created on a small scale, probably paired with active treatment. Later, when closure is imminent, the data will be in hand for the passive system and it could meet the higher level requirements for sole use.

The panel offered their thoughts on what water management is going to look like a decade from now. There will be an influx of remote control, big data, and artificial intelligence (AI). Management systems will be increasingly site-specific, including the use of biochemical reactors, depending on the amount of water that needs treatment.

Incorporating different types of technology in different orders will be a trend as systems are individualized. Such systems are already being called treatment trains. Maybe one unit will treat for cyanide, the next for nitrate, perhaps several for the removal of various metals. Expect off-the-shelf solutions to be less appropriate.

The challenge today is not to merely treat water, but create effective water management beginning with development and through post closure. Canadians can take the lead in into how we use water, how little we use, how much we recycle, and how well we treat it. We need to be building today the technologies that will be effective 10 or 20 years from now. 

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