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The dangers of tailing dams

Perched alongside thousands of mining operations around the world are tailing dams – vast reservoirs that store a toxic sludge of mining by-products, including water, rock particles and chemicals like cyanide and mercury. There are an estimated 3,500 active tailings dams currently in existence globally and some of these dams represent the largest engineered structures on the planet.

Depending on who you talk to, tailing dams are considered an engineering marvel and mining necessity, while others declare them as an unnecessary hazard and major environment threat.

Statistics are equally divergent.

In the decade between 2007 and 2018, some 27 serious tailing dam failures were reported. While these represented a small proportion of the total number of active dams in existence, the failures were significant and resulted in the displacement of communities, loss of lives and significant ecological damage.

No matter what your position on tailing dams, awareness of the risks and costs associated with them are mounting. Clean Mining Managing Director Jeff McCulloch says, armed with this information, it’s time for the mining sector to move on, clean up and avoid the unnecessary social and economic dangers of tailing dams.

Dam failure

One might assume, given the hazardous contents of tailing dams, that there are regulations dictating the use of reinforced concrete or stone to ensure long-term structural stability of tailing dams. But this is not the case.

Most mines opt for the cheaper ‘upstream method’ where the tailings themselves are piled up, with more tailings added to increase the height of the dam as mining operations continue.

Dams built using the upstream method are more likely to collapse because, once dried, the tailings used to create the barrier become less dense and more sand-like, increasing the likelihood that it will erode and become unstable.

The negative environmental impacts of this are obvious and wide reaching. If the dam breaks it releases hazardous materials into the water, soil and air, and can destroy communities and the environment.

The January 2019 failure of Brazil’s Brumadinho Dam, which claimed more than 130 lives, saw about 12 million cubic metres of waste expelled into the environment, engulfing homes and roads in its path.

Another Brazilian dam failure in 2015, the Mariana Dam disaster, caused the release of a 60 million cubic metres of iron waste into the environment, displacing numerous communities and claiming the lives of 19 people.

And, the long-term social and environmental effects of both collapses are expected to be felt for decades to come.

Chemical leaching

Traditionally, around 90% of gold is processed using the hazardous chemicals like cyanide or mercury. Using these toxic chemicals to release fine gold ores from rock is a process that has existed for over 100 years.

Mr McCulloch explains that, beyond the risk of chemical exposure facing workers directly involved in mining operations, these toxic chemicals are often also expelled into tailing dams with waste water from the extraction process.

Even if the dam does not collapse, these highly poisonous substances can still leach into the local surrounds, contaminating the soil and water supply.

For a person, just a grain-sized dose of cyanide or 1.5 grams of mercury is deadly. For fish, trace amounts cyanide would prove fatal. The potential risks are great.

Rising costs

Tailing dams require regular inspections and ongoing monitoring, and these costs appear to be mounting.

In June 2019, South32 Chief Executive Officer Graham Kerr^ reported the company would spend $55 million on 37 tailing dam storage facilities in FY19, up from $35 million the previous year. On top of this, miners face a major capital cost associated with constructing the structures and then monitoring and remediating sites once they are no longer used.

Of the 37 tailing dam storage facilities managed by South32, just under half (17) are inactive or closed. That’s millions of dollars spent after mining operations cease or are suspended.

Once a mine is closed, inspections should continue. However, they may not always be conducted as thoroughly, even though they still present a serious chemical, heavy metal, radiation or physical risk.

Clean alternative

Clean Mining’s gold recovery process eliminates the need for tailing dams and replaces toxic chemicals like cyanide and mercury with a safer, less hazardous and more environmentally-friendly chemical reagent containing thiosulphate.

The non-flammable and water-soluble inorganic compound dissolves fine gold out of ores into a solution, this alternative reagent can also be recovered after processing and reused.

 

“This enables miners of all sizes, from small-scale and artisanal miners through to larger-scale miners, to tap the Earth’s riches in a more sustainable way,” says Mr McCulloch.

 

“In instances where tailings dams are either too risky or are not possible – for example in areas of high rainfall, with high seismic activity or in close proximity to dense populations, or in highly sensitive environmental areas with low water resources or mountainous terrain – our solution comes into its own.

“We offer the option of producing dry stack tailings (DST) by including a dewatering and chemical recovery processes.

“Our leaching reagent chemicals are also reusable, so there is an immediate operating cost benefit if miners choose to recover the chemicals and water used. In addition, the dewatering process produces DST that can be repatriated or stored.”

As a result, a mine that uses Clean Mining’s technology has a smaller footprint, lower environmental risk, reduced water use and chemical recycling options.

Surrounding communities are safer and the mining operation has a lower risk profile too, which may lower insurances and create a positive sentiment among shareholders who are keen to invest in a clean, responsible mining operation.

To learn more about Clean Mining’s technology, visit cleanmining.co.

 

^ Mining Weekly Article South 32. Read More >

Image: Expelled waste from Brazil’s Brumadinho Dam 2019

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