Article first published in Mexico Business News, October 2023. Reprinted with permission.
You can’t extract minerals from sulfide ores without creating tailings and without using water. However, you can do it with less water. Here’s how some of Mexico’s mining leaders are reducing their water consumption and making their mines safer at the same time.
Tailings are most often stored in tailing dams. If not designed, built, managed, and monitored properly, tailings dams can fail – bringing catastrophic consequences to communities and surrounding environments.
Yet tailings are an unavoidable byproduct of the mineral extraction process. Simply put, tailings are the fine material left behind after a valuable mineral has been extracted from a sulfide mineral-bearing ore. Tailings often take the form of a thick slurry which is traditionally pumped out into massive tailings dams where a portion of the water is recycled back to the process plant. In the impoundment dam, the sediment settles and the water at the surface slowly evaporates, requiring fresh water makeup to meet process plant water needs.
Finding a better way
Mexico has every reason to want to reduce the water intensity of mining operations. Water security is at the top of the agenda for government, businesses, and communities. The Federal Government is clearly dedicated to improving national water security and recently enacted a new mining law that – amongst other things – moves to tighten water extraction permitting.
At the same time, the potential risks related to traditional ‘wet’ tailings are mounting. Data suggests that the incidence rate of dam failures globally remains steady (at about 5 failures per year) yet the impact of these failures has become significantly more severe, largely because many of these are legacy tailings impoundments from an era when regulations were less stringent. Release volumes are increasing, fatalities are rising, and greater areas have the potential for environmental impact. Simply put, the more mines use ‘wet’ tailings, the greater the risk.
The leaders are already acting
Not surprisingly, many mine owners are asking how they might improve their water efficiency and enhance overall safety by reducing the amount of water in their tailings. Some – those working with dense clays, for example – have few alternatives. But a significant number are finding that there are a growing range of options for improving water use in tailings.
Ausenco recently completed a project in North Central Sonora. It’s a high-grade silver and gold project in a remote, mountainous location. Average temperatures are around 34 C. Average rainfall is less than 350 mm per year. Any water that is required for operations must be pumped more than 10 km over mountainous terrain.
After looking at various options, the Client team opted for a dry stack tailings solution. Dry stack tailings use a range of technologies to rapidly remove and reclaim as much water as possible from the slurry. The resulting material is then stable enough to be stacked with little to no risk of collapse or failure. This approach has allowed our client to reduce their overall water consumption by nearly 30 percent.
A world of opportunity
Dry stack tailings are a good way to improve the water efficiency of a mine. But it is not the only way. There are a wide range of technologies that can be applied at almost every step of the mining cycle.
At the mine face, we are seeing companies implement technologies like Minesense which measures the grade of the ore in every shovel as it is loaded into the trucks. This allows operators to quickly separate the low-grade waste from the higher-grade ore – before it goes into the processing cycle – thereby saving significant energy and water downstream in the process.
Similarly, there are several processing technologies that can help operators reject waste rock and material earlier in the process. Screening can help remove coarser material from the mill feed. Bulk sorting uses sensors to remove low-grade material from the primary crusher discharge. Coarse Particle Floatation (CPF) allows tailings to emerge in a sand-like state which is much easier to dry and much less difficult to manage.
All of these technologies are currently in operation in mines around the world. They are proven and measured. And early evidence suggests that – when these technologies are applied together – they can help cut energy and water use in half while virtually eliminating the need for traditional ‘wet’ tailings dams.
Put Mexico in the lead
I believe that Mexico could – and should – become a world leader in water-efficient mining technologies. Mexico certainly has the need, the opportunity, and the momentum to drive innovation and adoption in this area. Mexico’s mining companies have all shown interest in finding ways to reduce their water consumption. The new mining laws provide an additional catalyst to owners seeking to develop interests across the country.
Yet it will also take collaboration between the mining industry, the business community and government. The mining industry will need to be more willing to trade some margin in return for greater efficiency and reduced risk. The business community will need to help foster the new ecosystems that will need to grow in order to deliver on these new technologies. And governments will need to find ways to influence the cost/benefit ratio of investment for mining companies.
Reducing water usage in mining is good for everyone. And, with today’s technologies and approaches, the mining industry has the ways and means to really start slashing water consumption across the operational lifecycle. It is an opportunity they – and the people of Mexico – cannot afford to waste.
Contact Jim Norine to discuss further.