Mine of innovation

2 min read

UK engineers are to join forces with some of the biggest names in mining to develop technology that could slash the global energy bill.

The team, consisting of researchers from the University of Nottingham and power and sensing specialist e2v Technologies, is on the verge of commercialising a system that uses high-power microwave pulses to make rocks easier to grind.

Currently mining companies use giant tumble drier-like mills to break chunks of ore into smaller pieces that can then be crushed into powder, allowing copper or other valuable minerals to be recovered. According to Nottingham’s Dr Sam Kingman, this inefficient and time-consuming process is responsible for up to five per cent of the world’s total annual electrical energy consumption.

But Kingman claimed that microwave comminution, a concept first reported in The Engineer two years ago, has now reached the stage where it can offer

huge advantages over existing technology. By bombarding rocks with extremely high power, but very short pulses of microwave energy, massive thermal stresses are introduced into the rock, making it incredibly easy to break down.

Kingman said the group has received funding from companies including Rio Tinto, Kumba Resources (part of Anglo American), Placer Dome in Canada and BHP Billiton to build a pilot plant based on the technology. These organisations, some of the largest mining companies in the world, will invest up to £3m over the course of the three-year project.

The advanced technology is thanks largely to high-power microwave tubes and power supplies developed by e2v Technologies. This makes it possible to build systems that can apply microsecond 5–10MW pulses of microwave energy to cause a small, but extremely fast temperature rise. ‘You can put a rock in these machines, press the button, take it out and crumble it in your hands,’ said e2v’s technology director Trevor Cross.

Because the microwave energy required is pulsed, and the exposure time is so short, such an approach is extremely efficient. ‘It’s possible to create 5MW or 10MW pulses by storing up low power for a long time and discharging it over a short time. You can make pulses with 5kW or 10kW magnetrons,’ said Kingman. Indeed, laboratory tests indicate that microwave comminution will use 30–50 per cent less energy than traditional methods. ‘Microwave energy input with a pulsed sample is less than 1kWh per tonne.

The current typical energy consumption to process an ore is 5–20kWh,’ he added.

Kingman said the technology would have important environmental implications. ‘Annual world electrical energy consumption is around 14,000 million kWh. Each kWh of energy generated from fossil fuel releases about 1.5kg of CO2 into the atmosphere. If we can save even one per cent of the world’s energy usage, then that’s a lot of CO2.’

But the mining industry is not famed for its environmental credentials, and while it is under pressure to become more sustainable, a far bigger incentive is the need to process more ore more quickly. So a potentially more attractive advantage to the industry is the fact that using microwave comminution valuable mineral particles break away at a coarser size and are therefore easier to recover. ‘When you do an economic analysis, the benefit of getting more metal out of the ground is what’s really attractive to mining firms,’ said Kingman.

After the project Kingman hopes to demonstrate a pilot system capable of processing several hundred tonnes of rock per hour, which will fit inside a container and could be moved to different sponsor sites. If the project is successful, full-scale industrial applications could quickly follow, he said.