Tailings and tailings dams are part and parcel of the gold mining industry since time immemorial. Tailings are the waste products from mining after the valuable minerals such as gold and copper have been extracted using mechanical and chemical processes to grind up the ores into fine sand.
Tailings are not environmentally friendly as they are acidic and contain high concentrations of mercury, arsenic and other toxic substancies. Another reason for concern is that mining companies store tailings behind earth-filled embankment dams.
These containment facilities are vulnerable to failure because:-
- Dyke construction with residual material from mining operations;
- Sequential dam raise along with an increase in effluents;
- Lack of regulations on design criteria especially in developing countries; and
- High maintenance cost after mine closure
Once it breaks, there is major impact on the economy, surrounding properties and people’s lives.
On a global scale, incidents of tailings dam failures have occurred often in the reported 18,000 mines around the world. The failure rate in the past 100 years is estimated at 1.2%.
Unfortunately, many toxic chemicals are used in mining. These include cyanide, sulfuric acid and solvents for separating the minerals from the ores.
Cyanide is used to separate gold from ore. It is often spilled into waterways during gold mining and when ponds filled with mine wastes burst and spill. Mining companies said that cyanide in water quickly become harmless. But this is true only when there are lots of sunlight and oxygen. Even then, it leaves behind other harmful chemicals. If cyanide is spilled underground, or if the weather is cloudy or rainy, it can remain harmful for a long time, killing fish and plants along rivers and making water unsafe for drinking and bathing. Cyanide is so dangerous that it has been banned in some countries.
But technology innovator Clean Mining, part of the Clean Earth Technologies group, is taking the solution one step further by eliminating the need for tailings dams altogether.
Cleaning Mining’s cyanide and mercury-free gold processing offers a clean, green and cost-effective retreatment option for tailings and an alternative to conventional tailings storage. It uses a benign reagent made from low-cost, plant-based organics, that has proven to be as effective and much safer for people and the environment.
Used in conjunction with a de-watering system, the process produces dry tailings that are safer and easier to store. Better still, the reagent itself can be recovered after processing and reused.
For years, cyanide heap leaching is the traditional method adopted to recover metal ores. This low-cost practice helped gold mines to extract gold deposits profitably. Cyanide is adopted in 90% of gold extracted worldwide. Of the 1.1 milllion tons of hydrogen cyanide (HCN) produced annually, only 6% is converted into sodium cyanide for use in the mining industry.
Because this chemical compound has, on occasions, caused environmental problems through mishandling or spills, mines have increasingly come under stricter regulations by governments and condemnation by environmental groups.
Cyanide is highly toxic and can result in substantial environmental impacts and public health risks if released into the environment. Cyanide spills have resulted in major fish kills, contaminated drinking water supplies and harmed agricultural lands.
In 2000, a tailings dam ruptured at a mine operated by Aural S.A. in Romania, spilt 3.5 million cubic metres of cyanide-contaminated waste into the Tisz and Danube Rivers killing fish and poisoning water supplies as far as 400 kilometres down the river in Hungary and Yugoslavia. In 2014, 500,000 gallons of cyanide solution used in heap-leach gold mining spilled from a retaining pond at the Proyecto Magistral mine in Mexico after heavy rain.
Industry claims cyanide is relatively safe because even if it spills, it breaks down rapidly in surface water. But, the compounds that cyanide breaks down into can be harmful. Cyanide spills into ground water can persist for long periods of time and can contaminate drinking water aquifers.
With so much inherent danger of using cyanide in gold mining, isn’t it time for the industry to search for sustainable alternatives?
Clean Mining, part of the Clean Earth Technologies Group, is one of the first companies in the world to develop an effective and commercially viable solution to get rid of toxic chemicals in gold ore processing. Mining companies can also do away with tailings by using a de-watering process in conjunction with Clean Earth Technologies’ solutions to generate dry tailings.