Artisanal mining continues to threaten water quality

While regulated mines have greatly improved their environmental performance over the years, specifically with regard to water management, the use of liquid mercury in artisanal and small-scale mining (ASM) continues to pose a serious threat to water quality in certain African regions, says Canada-based water purification and metal recovery specialist NanoStruck.

ASM produces about 20% to 30% of the world’s gold every year, contributing about 500 t to 800 t.

NanoStruck says about 650 t to 1000 t of mercury is released through ASM into the environment every year, owing to poor environmental management practices. ASM also accounts for about a third of all human-released mercury.

Other environmental problems associated with ASM include the direct dumping of tailings and effluent into rivers, improperly constructed tailings dams, acid rock drainage from mining areas and absent or improper mine closure procedures.

NanoStruck Technologies CEO Bundeep Singh Rangar acknowledges, however, that monitoring environmental violations and enforcing the rules that combat those violations remain difficult, owing to a lack of resources and the scattered and inaccessible nature of ASM.

He adds that water pollution from mines is often cited as a major concern among all mining industry stakeholders. In the past, mines operated without the environmental management strategies and control technologies that are standard practice among larger mining companies today, contributing to the current environmental concerns about proposed mines.

The company points out that if protective measures are not taken, mining operations can have adverse effects on the groundwater and surrounding surface water, including unnaturally high concentrations of arsenic, sulphuric acid and mercury, among other chemicals, being present over a significant area of a surface or subsurface.

Among the challenges faced by the mining industry and at mine sites is the need to reduce water losses during processing while increasing water recycling.

“It is unusual for a mine not to have the ability to recycle process water, which is commonly retained within the mine’s closed cycle and stored either in a tailings facility or a dedicated water storage facility,” says Rangar.

NanoStruck outlines five principal technologies used to monitor and control water flow at mine sites – diversion systems, contaminant ponds, groundwater pumping systems, subsurface drainage systems and subsurface barriers. In the case of acid mine drainage, contaminated water is commonly pumped to a treatment facility that neutralises the contaminants.

Sources of Contamination

Rangar highlights that the potential for water contamination at a mine site depends on several factors and that there are instances where the extraction of some types of ore impact on the quality of water in the surrounding area more than the extraction of other types of ore.

Ores, such as sulphides, are more chemically reactive than others and have a greater tendency to dissolve in and contaminate water, explains the company, adding that common contaminants that are naturally present in metal ores include metals, metalloids and salts.

Chemicals used in mineral preparation and metal extraction processes can also increase water contamination. Chemicals used to process metal ores include cyanide, sulphuric acid and organic chemicals. A mine can use a combination of physical and chemical processes to separate metals from ore.

Rangar further mentions that climate also plays a significant role in water contamination at mine sites, depending on the amount of water around the site. For instance, mines in permafrost regions, where the groundwater could be frozen, would not have the same concerns for groundwater contamination as mines operating in warmer regions.

The company also highlights that a mine’s operating status, such as whether it is under construction, operating, or closed, can also affect its potential to contaminate water.

For example, the potential for water contamination from process chemicals is minimal, following the closure of a mine, but if the mine workings were to be subjected to natural flooding, minerals could dissolve and mix with the surrounding groundwater.

The company also highlights that modern water management practices and improved mine designs greatly reduce the potential of water contamination at mine sites. In general, old abandoned mine sites have a higher potential to pollute nearby waterways, as the current water-control techniques required by modern environmental regulations were not in place when the mine was in operation.

“Knowledge about water management and impact reduction has greatly increased over time, and the prevention of water contamination is currently an important component of mine operation and closure plans,” says Rangar.

Moreover, the company highlights that water management and water-level monitoring are important components of mine design, used to avoid tailings dam failures.

Tailings comprise finely ground rock and mineral-waste products from mineral processing operations. These are usually deposited in the form of a water-based slurry into tailings ponds, which are sedimentation lagoons enclosed by dams built to capture and store the tailings.

Tailings ponds were first introduced to prevent the direct discharge of mine water into surface water.

In more tropical climates, mines may be permitted to discharge water that meets water quality guidelines into surface waters. There are several cases in drier climates where no water is directly discharged from tailings ponds because evaporation is the major water removal process. 

Meanwhile, mining companies use heap-leach piles for environmental and economic reasons. Heap-leach piles comprise crushed ore, sprayed with a dilute solution containing process chemicals, such as cyanide, to dissolve or leach valuable metals out of the rock.

The metal-bearing solution, or leachate, is captured by liners and drains, and processed to remove the metals. The solution is often reused and recycled.

Negative Impacts of Water Contamination

Water contaminated with high concentrations of metals, sulphide minerals, dissolved solids or salts can negatively affect the quality of groundwater, surface water and aquatic ecosystems. Impacts on aquatic life can include increased mortality, health or reproductive problems and a reduction in the number of species present in the ecosystem.

Impacts on human health can also occur when the quality of water used for irrigation, drinking, and/or industrial applications is affected.

Water contamination can result in the need for water treatment or the adoption of a different water source for human consumption. NanoStruck notes that large and medium-sized mining companies worldwide are implementing environmental-monitoring programmes and water-management strategies to reduce the impact of water contamination.

Product Overview

NanoStruck, which develops technologies that remove molecular-sized particles from water for purification purposes, has developed a green sanitation system called the Nanosan unit.
This unit was designed based on nanotechnology for rural and informal areas under severe water stress, where the construction of basic infrastructure for water and wastewater treatment is not economically feasible.

The key criteria that were taken into consideration when constructing the Nanosan unit were the need to reduce household water consumption by up to 70%, improve the health and hygiene of users and prevent water contamination, which impacts on the environment, groundwater resources and river systems, owing to raw sewage spills.

The environment-friendly unit – which processes raw sewage into usable grey water, with a minimal risk of groundwater contamination – contains no harmful chemicals and requires a limited amount of external water to operate.

“The Nanosan unit is user friendly, cost effective and easy to maintain, transport and install anywhere in the world. It is also 100% green, as it doesn’t depend on outside power sources,” says Rangar.

It can collect rainwater and is also hygienic, safe, odourless and fully water-borne, with no connection to the municipal water supply or sewer infrastructure required.

Moving Forward

“Population growth, continued rapid economic development and climate change will drive the increase of water stress in some parts of the world,” says Rangar.

This means the heightened demand for water will eventually exceed availability and may further impact on the quality of existing resources. Global awareness of this trend has resulted in increased attention to this issue among governments worldwide, international organisations and civil society.

NanoStruck says leading companies in the mining sector have also anticipated this trend and a large body of research is informing their pragmatic responses.

These responses include improved water management processes through increased efficiency, technological innovation and sharing best practice among industry stakeholders.

“It is vital that the mining industry continues to engage effectively with water specialists about sustainable water management and that it properly understands the value of water to all users and the environment,” says Rangar.
 

Rangar further notes that the monetary value of water will continue to rise and will become a growing consideration in financial planning and feasibility studies for mining operations.

Innovators like NanoStruck will continue to develop technology to find innovative solutions to the world’s water challenges, including the need to obtain alternative water sources, reduce the mining industry’s water demand and design more efficient and effective means of water management and treatment.