Around the world of mine water treatment

Titanium mine discharge. Credit: Mykhailo Pavlenko via Shutterstock

Any open-cast mine requires good water monitoring, and the technologies behind this are only becoming cheaper and more effective. Drones offer a convenient, safe, effective and cheap way to aerially survey and monitor mine waste water and sediment flows, both on-site and in surrounding water courses. Better safety comes from better monitoring, and more frequent surveys give a clearer view of water movement over time. Cheaper surveys mean more frequent surveys, and modern monitoring has improved every step of this chain.

But one of the most difficult challenges for drones, or unmanned aerial vehicles, is the monitoring of effluent from legacy mining sites. This is, in large part, because the scale of the problem is so huge. A recent study published in the journal Science estimates that “23 million people live on floodplains affected by potentially dangerous concentrations of toxic waste derived from past and present metal mining activity.” In total, it added, the number of people exposed to contamination sourced from long-term discharge of mining waste into rivers, “is almost 50 times greater than the number directly affected by tailings dam failures.”

As an example, this problem is particularly acute in the UK. Two centuries ago, the country’s industrial revolution began on the back of coal mining and the steel industry. Today, the UK’s Environment Agency has to deal with the “thousands of abandoned mines left scattered across our landscape”. Many of these closed well over 100 years ago, but still pollute the UK’s rivers and ecosystems. In 2011, the Agency set up the Water and Abandoned Metal Mines programme with funding from the government. This has enabled the identification of various feasible remedial measures at a number of the most polluted sites, including liabilities from underground coal mines. WAMM now operates 44 mine water treatment plants in England, plus another 30 across Scotland and Wales.

But while pollution from coal mines is easy to see, pollution from abandoned metal mines is not always obvious. These are responsible for over half the metals found in the UK’s rivers such as cadmium, zinc, lead and copper.

Co-ordinated work on cleaning up pollution from abandoned metal mines across England only started in 2004. At the time, the Environment Agency and Newcastle University assessed the scale and nature of this type of pollution: “About half the cadmium, lead and zinc in our rivers comes from these mines, as much as from all industrial discharges, and more than 1,500km of rivers are polluted,” the study found. In Weardale, County Durham, more than 80km of rivers have been polluted by abandoned metal mines. This type of pollution can cause damage to the environment as well as risking human health.

Detection of these pollutants can even come from space, with ground assistance. Last year, Dublin-based Internet of Things (IoT) company Davra agreed a second contract with the European Space Agency (ESA) to further develop a system that can predict mine pollution. One of the company’s methods is to analyse Earth observations from ESA satellites and drone imagery to monitor mine tailings. After analysing the satellite imagery, Davra does a risk assessment of the site using drones.

Davra CTO Joe Quinn said: “There are sensors built into the dam walls, and we take the feed from those sensors. Every three to five days, ESA satellites fly over the dam wall and we receive a new set of imagery. Satellite imagery can give you millimetre-level precision on the vertical axis, so if a dam wall is moving plus or minus 10-20mm in height we can see that from space." The ESA is now funding trials of the technology in South America, Africa and Australia.

In China, researchers Mingzhe Lei and Ning Zhou at the CHN Shendong Coal Group, together with Yang Li and Yue Zhao at Summit Technologies, aim to create a universal mine water circulation performance evaluation index. The researchers say that the IoT, together with aerial monitoring, has enabled “substantial theoretical advancements” for mine water treatment. However, researchers hope to build this out into better use of mine water resources in China.

In an article, the researchers write that more mine water can be used for equipment cooling and dust removal. “Currently, the majority of registered mining enterprises nationwide, with the exception of a few water-free mines in the northwest region, have established and operated mine water treatment systems. Based on incomplete statistics and estimates, the total treatment capacity for various types of mine water in the country exceeds 5 billion cubic meters per year.”

US-based mining software company Strayos is also moving into the monitoring game, using advanced image processing and AI systems. The company has entered a partnership with aerial intelligence company Quantum-Systems GmbH, which manufactures electric vertical take-off and landing systems for drones that feature fully integrated cameras and a LiDAR scanners for precise data collection and aerial mapping.

Elsewhere in the country, wastewater treatment equipment manufacturer Ecologix Environmental Systems recently announced a solution to minimise the impact of large runoff streams and metals-laden wastewater on the local environment. The company’s plant removes solids and metals from groundwater, ahead of a deionisation process. Its design, installed at Dow Chemical in Mississippi, integrates a 200 gallon-per-minute incline plate clarifier, with chemical mixing tanks, flow equalization, clearwell tank and raised platform for a sludge dewatering filter press.

Ultimately, all US water discharges must satisfy the Environment Protection Authority. Following an investigation of wastewater discharges from the site in 2022, a real-time water monitoring system went live in October, at Camp Gully Creek near Metropolitan Collieries’ Helensburgh coal mine site. Under new EPA requirements, Metropolitan has installed a total of four water quality monitors, two in the creek itself. The others monitor the site’s wastewater treatment plant and its sediment dam spillway.

Executive Director Operations Jason Gordon said the new monitors provide continuous, real-time data on water quality. These have already significantly enhanced the EPA’s understanding of the potential impact of discharges from the site. “This is the latest step in our commitment to modernise the monitoring of water discharges from the mine. In addition to the installation of the monitoring system, the EPA required Metropolitan Collieries to complete a wastewater discharge impact assessment, which we are currently reviewing,” he said.

Growing environmental awareness and regulation means a greater need for groundwater monitoring than ever before. Drones, satellites, and small sensors all enable this, but their coverage is not as global as you might think. In the more remote mining areas of the world, such as in parts of Africa and Latin America, terrain and isolation make remote connectivity difficult. The use of drones and satellites at mine sites for water treatment, sediment and effluent management can be expected to increase in the coming years, even in those environments that are today technologically challenging, but the next evolution of the technology will enable wider use around the world.