Water treatment is one of the key tools that miners have at their disposal to address onsite water demands whilst reducing the impact on precious freshwater resources, thereby, enhancing sustainability.
At the onset, in examining water treatment initiatives at mines, it is important to take two scenarios into account. In the first case, where mines are water positive, they have too much water and must deal with the excess. In the second, where mines are water negative, they do not have enough water and need to ensure sufficient water to operate. To ensure the sustainability of operations mining companies are required to become proactive in maintaining their licence to operate through undertaking initiatives that are geared towards managing either water excess and/or shortfall
To manage water shortfall effectively, mining companies are looking at diversifying their water sources to reduce risk and enhance water resilience. For this reason, they are using performance and risk-based criteria to identify and prioritise opportunities which deliver best “bang for their buck”. Traditional water supply options including recycling, reuse, as well as an increased use of innovative treatment methods and desalination are broadening the portfolio of solutions.
Developing a water solution
Experienced Engineering Procurement and Construction Management (EPCM) firms have a bigger role to play in helping mines to address their particular water treatment needs, points out specialists from Black & Veatch, a global EPCM firm with a strong presence in Africa. “At the outset, it is important to recognise that every mine situation is different, and the solution may differ depending on various considerations,” says Dennis Gibson, Chief Technical Officer for Mining, Black & Veatch. “The optimal solution will entail identifying and assessing options from all potential opportunities, considering factors such as safety, technical feasibility, reputation, reliability, cost, environmental aspects, as well as the social impacts and benefits.”
According to Gibson, this stage may require working closely with regulators, and regional environmental and water planning groups, and also relies heavily on integrated water resources planning to develop sound contingency plans that factor in resilience and cost-effectiveness. This is paramount as mines have to be guided through the maze of permitting and environmental studies, as well as considering closure and remediation impacts. Noteworthy, water sustainability in mining operations can be achieved through effective and efficient usage and minimising negative impacts on the external environment.
Desalination as a possible solution
Desalination is one of the viable water treatment supply options for mines in Africa. The advantage of water desalination is that it takes water from a source that is uncorrelated with hydrologic cycle risk, notably from the sea.
The concept of desalination, which has been around for hundreds of years, continues to offer solutions to help improve the world’s supply of potable water. However, implementing it on a large, global scale poses a host of challenges. Current technology relies on reverse osmosis, which pumps water through semi-permeable membranes to remove impurities. While cost-effective, this technology is not ideal, as it uses large amounts of energy and can impact the environment in terms of greenhouse gas emissions and brine disposal.
Hearteningly, there is currently a lot of research and development going into the technology, from investigating new types of membranes to testing out vaporisation. Two new approaches – closed-circuit desalination and concentrated solar stills – are pushing the boundaries with valve technology.
But these solutions may only be available for commercial application in the next decade or more, while many mines need more immediate remedies. So, creativity and innovation will continue to play a critical role when developing water and wastewater treatment options.
Advanced technologies can be specific to the challenge. For example, the facility at BHP’s Escondida copper mine in Chile’s Atacama Desert, which is one of the driest regions on earth.
In the project brief, BHP wanted to deliver a sustainable solution which did not impact on the environmentally sensitive water sources that it previously used. BHP then consulted Black & Veatch to lead the engineering design, procurement, resident engineering and commissioning for the marine and desalination components of the Escondida Water Supply (EWS) project. The project scope was for the water conveyance and storage system, the high-voltage substations and transmission lines, and a new private communication network for the mining operation. The network included supervisory control and data acquisition (SCADA), voice over internet protocol (VoIP), security video, and fire protection circuits.
In the project, a remote-controlled micro-tunnel boring machine was used to carve a 530-metre-long tunnel to capture water from deep within the sea. This allowed getting a water quality and consistency that eliminated some pretreatment processes, making the desalination process even more efficient.
Ultimately, the desalination solution brought about improved water supply reliability, as well as preserving the area’s important fresh water resources. Presently, the EWS is the largest desalination facility in the Americas, delivering 2,500 litres per second of fresh water to the Escondida mine almost 170 km away to an elevation of 3000 m