Tag Archives: tailings storage

United thinking on mining, water solutions can save money and protect the environment, Worley says

Today, the need for extraction and refinement of copper and other transition materials is essential to world development, as we navigate a transition to more sustainable energy technologies, Saleem Varghese and Carola Sepulveda* write. But as its importance has grown, copper ore grades have decreased at a rate of approximately 25% over the last decade – increasing demand pressures on the commodity – meaning miners need to process more material to achieve the same output.

Today’s copper mines also need a lot of water. A 50,000 t/d ore copper mine will consume around 30,000 cu.m/d of fresh water. This isn’t a problem in some geographies, but it’s critical to the viability of operations in some of the most copper-rich regions on earth, such as the Americas.

Copper miners in the Americas are united by the need to secure their water supply, reduce water consumption and manage their environmental impacts. What can they do to overcome these interrelated challenges, while meeting their production targets?

Where are we now?

Mining and processing depend on vast amounts of water, and for South American miners this leads to complications. The copper mines of the Americas are frequently located in arid and mountainous regions where water is scarce. Indeed Chile, a leading copper mining nation, is currently enduring a ‘mega-drought’ of 13 years and counting. Here, water is a national security issue, leaving some rural communities reliant on tankers to supply fresh drinking water.

This importance is recognised by miners as well, with local community impact and water management being the industry’s top ESG risks, concerning 78% and 76% of respondents, respectively, according to research by EY.

Indeed, by 2040, all Chilean copper mines are expected to be in areas suffering from water stress. Likewise, water efficiency is increasingly becoming a serious problem, with the water-energy nexus shifting and water becoming more expensive. For water-intensive mining processes, lack of access and an increasing price per litre can be potentially difficult hurdles to overcome.

For modern copper miners, there is a historic separation between mining and water operations which must be reengineered to improve water access and use. As mines see their speed to market and output slowed due to water stress, there are three key challenges which, if solved, will help the industry as it extracts the materials to electrify the world. Only by managing water and mining operations together and bringing in collaborative expertise, can miners tackle the challenges before them and deliver at pace.

Understanding the three critical factors for mining success

Water management is the key ESG factor copper miners face today, and this manifests in three key issues: one historic, one present and one which poses a challenge now and will only get worse.

The first challenge is securing a reliable water supply.

The second challenge is reducing water consumption and increasing water efficiency, to ease pressure on water supply.

And the third challenge is minimising environmental risks.

Overall, water issues could affect the viability of mining projects in many regions around the world. Mining operations require significant amounts of water for processes including mineral extraction, ore processing, dust suppression and more. However, in many areas such as in Latin America water is becoming scarce due to drought, climate change and overuse.

Supplying modern mines

To supply mines and refining plants, mines have recently moved away from shared groundwater supplies to desalinated water. Desalination is more expensive but offers less impact on local communities and environment. Given that mines in the Americas are usually distant from the coast and at higher altitudes, desalination represents a difficult challenge for engineers to make feasible. Alternatively, to secure groundwater lifting licences, consumption needs to be effectively managed, and any water put back into the environment must be treated effectively.

Solving the supply challenge by altering water consumption

In effect, the first problem, supply, can be eased by tackling the second issue: water consumption. If supply is the historical issue, using water more efficiently to alter consumption is the issue of today. Whether it’s water use in particle flotation or lost in tailings slurries (for transportation and storage), making sure these processes are done as economically, efficiently and sustainably as possible is key. This is where new technologies and solutions come in.

An example of this is seen in the storage of tailings. Where water cost and procurement are not an issue in different locales and climates, the storage of tailings in a slurry form is common. In arid conditions where water resources are strained, the economic sense behind storage slurries evaporates. Slurries not only take water out of the operational system and into a closed storage system (which will need to be replaced), but it also allows the potential for water loss through evaporation and seepage.

Dry storage techniques – which have increased in scale in recent years – are the obvious solution with greater water reclamation from tailings and increased safety in storage. Moreover, high-altitude mines and liquid-based storage pose a potential risk to those downstream, making dry storage safer and more effective.

Copper tailings from an old mine that are deposited between rock berms that help contain the sediment

Another example of reducing consumption can be through greater efficiency when appraising the ores to be processed. This can be done with advanced ore sorting technologies such as those offered by NextOre, a cutting-edge technology able to provide real-time analysis of newly extracted ores. Rather than typical analysis methods which can detect mineral particles at or near the surface of ore, NextOre’s magnetic resonance technology can evaluate and sort much coarser ore with accuracy and speed. This allows miners to selectively remove the waste or lower grade material before it enters the processing plant – ultimately saving water, with only the best ore to be utilised.

A common misconception about water projects is that they are expensive and require significant resources to implement. While water projects can be costly, it is important to consider the long-term benefits that they bring, such as increased water availability, environmental impact mitigation, improved access to clean water for communities, and further growth for industry.

Saving water, and protecting the local environment

The third issue, which is increasing in importance by the day, is managing the risk of localised environmental issues, especially acid mine drainage that can contaminate the natural environment.

This is an issue that is only going to become harder to tackle as the ores we are required to mine become lower grade and the ability to avoid sulphur-forming ores is lost. In this respect, new technologies can help as more challenging ores are treated.

Overall, the challenges faced by the industry cannot be addressed by a single solution, or by siloed teams attacking from all angles. A unified, collaborative approach will be needed for the best results.

The design and implementation of a water management approach should be tailored to the specific mine site needs and context of the community and stakeholders involved. For projects to succeed in the future, they must integrate mining, water and environmental capability under one roof – from front-end studies to delivery, and operations through end-of-life. Miners will benefit from working with a collaborative partner to consider mining operations and water issues holistically, and how new mining technologies can operate synergistically to help tackle these water challenges.

Why internal and external collaboration is key for businesses

The mining industry will struggle to solve its water challenges alone. And it doesn’t need to. The complexity of modern mine operations – and need for diversified expertise – simply reflects the scale of the energy transition, and the need to continuously improve environmental outcomes to maintain the social licence to operate.

The answer is not straightforward and requires a deep understanding of operations, mining, water management and the surrounding community. Collaboration needs to be coordinated to develop and implement real solutions for the enduring issues facing miners.

If done right, copper mining will bring lasting value to communities through low-impact operations that share the benefits of water infrastructure and provide meaningful local economic contributions. This is the responsible way to ensure we deliver the copper our world desperately needs.

*Saleem Varghese is Copper Growth Lead at Worley, while Carola Sepulveda is Water for Mining Lead, Peru, at Worley

South Star’s filtered tailings plan for Santa Cruz graphite project stacks up

South Star Mining Corp’s aim of using a filter press and eliminating the requirement for a tailings storage facility at its Santa Cruz graphite project in Bahia, Brazil, has been given a boost following positive bench scale test results.

The Toronto-listed company said it had received positive results for the laboratory bench scale filtered tailings tests performed on two simulated tailings samples from Santa Cruz. Two tailings samples (+325 mesh and -325 mesh) were generated and tested in laboratory facilities in Belo Horizonte, Brazil, it said.

Five scenarios were completed for the leaf filter tests with various solids densities, feed rates, vacuum pressures, and cake thickness:

  • -325 mesh sample at 10% solids;
  • -325 mesh sample at 10% solids at higher feed rate and vacuum pressures;
  • -325 mesh sample at 20% solids;
  • -325 mesh sample at 20% solids with minimized cake thickness, and;
  • +325 mesh sample at 10% solids.

The tests resulted in cake with humidity varying between 23% to 35% and cycle times ranging from 19:23 to 49:47 minutes, according to the company. Based on the bench scale leaf tests, additional pilot tests are being performed to better quantify the range of possible solutions and also test a mixture of the +325 and -325 mesh materials to create a third sample type, the company said, adding that results of the pilot tests were expected shortly.

South Star said the goal of the testing programme was to examine the potential for altering the proposed flow sheet from the process circuit presented in the preliminary economic assessment (PEA) to include a filter press and eliminate the requirement for a tailings storage facility.

“By incorporating filtered tailings technology, the majority of the water from the tailings would be removed and recirculated and allow the dried tails to be placed together with waste rock in a co-disposal waste facility,” the company said.

South Star CEO, Eric Allison, said: “We are very pleased with these initial results from our filtered tailings test programme and their positive implications for utilising dry stack tailings at Santa Cruz for both our trial mining plant and the final full-scale facility. Co-disposal of the waste should not only reduce the project’s environmental impact, risk profile and physical footprint, but should streamline our permitting and licensing processes as well.”

The company plans to incorporate the results of the programme into the prefeasibility report scheduled for completion in the September quarter, it said.

The mid-2017 PEA on Santa Cruz outlined an indicated resource of 14.99 Mt at 2.70% Cg with 404,741 t Cg, and inferred resources of 3.57 Mt at 2.90% Cg with 103,591 t Cg. Graphite deposition at Santa Cruz is found at surface within oxidised material providing a very favourable strip ratio, and requiring no crushing or blasting, according to the company.

The PEA stated Santa Cruz has a post-tax internal rate of return of 78% and a payback period of two years. Mine planning for the existing graphite deposit outlined a 12 Mt mineable resource with a diluted grade of 2.63% Cg providing support for a 19-year open-pit mine. Life of mine average yearly production came in at 15,800 t alongside operating costs of $413/t.