The mining industry is a leader in innovation in water treatment

“Why mining?” This is a question people often ask when they learn that I am a water treatment expert and focus on this sector. My answer is often enthusiastically long, but the gist of my answer is this: the mining sector is as innovative as it gets. In fact, this sector is usually at the forefront of technological development. Mine water treatment takes many years – often ten or more – before municipal water treatment or treatment in sectors such as agriculture and food production. This is due in part to the ever-tightening regulatory regime for mine water quality in Canada. Regulatory requirements mean that the mining sector is always under pressure to develop and improve technology to ensure compliance and find new ways to reduce existing pollution to lower levels than currently possible. Moreover, as science progresses and knowledge about toxicology and bioaccumulation increases, new elements and compounds emerge that are analyzed for treatment. As such, we continually evaluate how existing technologies can help solve “new” problems they were not originally designed to solve. The complex challenges this sector faces, and the corresponding innovations that keep it always responsive to these challenges, make it a dynamic and enjoyable sector to be a part of.

So what are the key aspects of mine water treatment that are driving this innovation in terms of technological progress and development?

PROBLEM: Water pollution in mining

Mining activities inevitably interact with water in many ways, leading to potential contamination. Here are the main sources:

> Process water: Water is used in the grinding and extraction processes. This water typically ends up in a waste pond before it is treated and released. Mines often partially treat this water before it enters the tailings pond, removing contaminants such as cyanides and sulfides.

> Rock warehouses: Both ore storage and uneconomical rock storage can lead to contamination. Rain and snow leach minerals from these rocks, sometimes causing oxidation and acidification.

> Exposed mines and underground mine walls: Newly exposed rock surfaces in workings or underground mines may leach and oxidize, contributing to water pollution.

> Shooting activities: Explosives used in mining contain ammonia and nitrates, which can contaminate water when interacting with rock.

> Infrastructure outflow: Unlike municipalities, mines must treat all water runoff from roads, parking lots and rest areas.

> Mine camps and human resources infrastructure: Water used in the camps, including drinking water and sewage, also requires treatment.

SOLUTION: Advanced water treatment

Simply put, treatment needs are determined by comparing the target water quality for discharge with the actual water quality. If any component exceeds the target value, then it qualifies for treatment. In Canada, the Canadian Council of Ministers of the Environment (CCME) issues the Canadian Environmental Quality Guidelines (CEQG), which apply after a specific mixing zone. Additionally, guidelines such as the Metal and Diamond Mining Effluent Regulations (MDMER) and the Coal Mine Effluent Regulations (CMER) apply to end-of-pipe discharge. Provincial criteria may also apply.

Mining usually takes place in highly mineralized places. If the mineralized area is close to the surface, the water quality may sometimes be naturally elevated in terms of metals and other elements. It is common for water in mineralized areas to naturally exceed federal and provincial target guidelines. In such cases, we need to develop site-specific guidelines to protect the environment, taking natural concentrations into account.

Why mining stands out

In Canada, mining is subject to more stringent water quality regulations than most other sectors, including agriculture, forestry and municipalities. For example, mines must treat contact water to a much cleaner level than municipalities treat wastewater before discharging it. They also often have to collect, test and treat water from roads and parking lots, which municipalities typically do not do. This stringent regulatory environment is driving innovation, forcing mining companies to develop and implement advanced water treatment technologies.

How do you treat water?

Different jurisdictions have different guidelines for developing site-specific goals and identifying treatment candidates. For example, in British Columbia, if an ingredient is expected to exceed 80% of the target regulated concentration, it is flagged for control under the “Best Achievable Technology (BAT)” process. This process helps identify appropriate methods to treat or mitigate potential contamination.

There are two main methods of water treatment: transfers and transformations.

Ttransfers: Transfers move pollutants from one place to another without changing their form. Examples of commonly used transfers are membrane separation, ultrafiltration and reverse osmosis. Transfers are effective but require a plan to remove concentrated contaminants to prevent re-contamination. If you fail to combine this with transformation, you will have to manage disposal. The ingredients have not changed form, they have only changed their location, so a disposal plan is required to eliminate the risk of re-contamination. Not all components behave the same way and cannot be treated with the same transformations. You need to know the properties of the ingredient and the conditions necessary to undergo the transformation you are targeting.

Ttransformations: : Transformations change the basic properties of pollutants through chemical or biological reactions. Transformations can make pollutants more stable and easier to manage. An example of a commonly used transformation is the biological oxidation of cyanide to ammonia to nitrate or the reduction of nitrate to nitrogen (the most common gas in our atmosphere).

Transfers and transformations are often combined in water treatment. For example, microbes can reduce sulfates to sulfides, which then bond with metals such as copper and zinc to form stable, insoluble compounds that can be filtered.

A leader in water treatment innovation

Mining must meet stricter discharge criteria than other sectors, which is driving innovation in water treatment. You would think that the amount of selenium discharged from a sewage treatment plant into a river would be as stringently regulated as selenium released from a mine. That’s not the point. However, these pressures are driving innovation in mine water treatment at an unprecedented rate. In some cases, such as selenium, the mining sector is also improving analytical methods for detecting contaminants because available methods were not sensitive and accurate enough to reproducibly meet the guidelines. The need for high precision and effective purification has pushed mining to the forefront of water treatment technology.

How can we do better?

Mining already leads the way in water treatment technology, but there is always room for improvement. Here are some ideas:

> Celebrate your victories: Highlighting advanced practices and technologies to strengthen the sector’s leadership, strengthen public trust and enable other sectors to adopt and improve them to the standards applicable to mines in Canada.

> Share your learning: Continue to disseminate evidence-based information to the public.

> Improve source control: An ounce of prevention is worth a pound of cure. Treatment may seem more impressive because it “fixes the problem,” but prevention is even better. Mines continue to innovate in this area alongside water treatment.

> Decentralization of treatment: Co-management or triage should be used to enable more effective local treatment. This will also help mines close more easily.

> Decarbonization of water treatment: Reduce greenhouse gas (GHG) emissions by using newer technologies that replace traditional methods such as lime treatment.

> Rapid technology maturation: Technology readiness assessments and technology maturation plans streamline the development of new technologies. They facilitate communication and permitting, enabling faster and cheaper technology implementation.

The most important innovation: gravel bed bioreactors

Gravel bed bioreactors (GBBR) are a technology known by several different names. They are sometimes called gravel bed reactors (GBR), rock bed bioreactors (RBBR), or a similar variation. The author developed the first full-scale GBBR in North America to treat metals and nitrates from mine water at a mine in Ontario. There are currently two GBBRs in operation, as of 2019 and 2020 respectively. While many technologies are taking a backseat as a result of “interesting research” that is unrelated to bringing the technology to market, these systems have progressed from Technology Readiness Level (TRL) 6 to 8 in less than two years. Testing included bench and column scale trials (off-site and on-site climate control under real-world conditions). These tests were planned to eliminate threats and information gaps in order to improve the technology. This Technology Maturation Plan (TMP) focused on maturing technologies for implementation and permitting, which was critical to its rapid success. Each of these GBBRs treats approximately 20,000 m³per day of water from a tailings pond or neutralized water from a potentially acid-producing rock dump. Treated dissolved metals may contain as much as 3 mg/l copper or 4 mg/l zinc combined with 10 to 30 mg/l nitrates. The GBBR was operated in parallel with a conventional low-density sludge (LDS) system. Not only did GBBR outperform LDS for metalworking due to the metal-cyanide complexes that only GBBR could process, but it also performed nitrate treatment in the same step. These cost savings are significant, but can also result in greenhouse gas emissions reductions of approximately 2,000 tons per year compared to conventional LDS treatment. For many ingredients, such as nitrates, copper and zinc, mBio GBBR currently achieves levels of TRL-8. Maven Water & Environment is expanding the deployment of its mBio systems across Canada and for a broader range of ingredients.

Application

Water treatment is a complex and critical part of the mining industry. This requires site-specific consideration and there is no one-size-fits-all solution. This and the stringent guidelines imposed on the sector have made mining a leader in water treatment. Understanding the basics of pollution sources, needs, and cleanup methods can help us appreciate the innovations driving this sector. Through continuous advancements and an emphasis on continuous improvement, the mining industry has established water treatment standards that other sectors can emulate.

DR. Monika Simair is a globally recognized leader in passive and semi-passive water treatment for the mining sector, including bioreactors, artificial wetlands, in situ treatment and source control methods. She is the founder and CEO of Maven Water & Environment (www.mavenwe.com) and can be reached at [email protected].

---