Multotec remains focused on new processes and technologies that result in improved efficiencies and reduced operational costs for its customers. With the advent of urban mining where recycled materials are reprocessed, the introduction of Clean-iX® technology could play a vital role in beneficiating rare earths components. The company’s partnership with Australian company Clean TeQ provides a technology that combines continuous and counter current ion exchange to produce a highly effective rare earth element (REE) process.
Carien van der Walt, Process Engineer for Environmental Products at Multotec Process Equipment, points out that the conventional REE process entails an initial beneficiation step, normally via gravity concentration. The concentrate produced is roasted with sulphuric acid to produce REE sulphate complexes. Thereafter the roasting discharge is mixed with water to produce a slurry which is atmospherically leached. The slurry from the leach circuit normally undergoes solid liquid separation to produce a liquid pregnant leach solution.
The pregnant leach solution is precipitated in two stages. The first precipitation stage involves precipitation with magnesia to produce a mixture of impurities such as thorium, uranium and iron. Stage II precipitation is normally conducted with the addition of ammonium oxalate to produce a mixed REE precipitate that is sold as the final product. “The main problem with this process is the production of radioactive elements such as thorium and uranium,” she explains.
“Clean TeQ looked at finding a way to reduce the potential hazards and environmental impact associated with this methodology, whilst realising capital and operating cost savings. The resultant Clean-iX technology has produced favourable results across the board in terms of increased rare earths yields, increased environmental stewardship and a very attractive and significant reduction in operational costs,” van der Walt says.
There are two options available for customers and in the first, rare earths can be recovered with far less thorium and uranium extracted reducing the amount of impurities sent to precipitation along with the final product. The second solution entails selective recovery of the uranium and thorium in two separate processes, resulting in the thorium, uranium and rare earths being produced as three separate streams.
Clean-iX® effectively replaces the leaching circuit and stage II precipitation in conventional REE recovery circuits with a resin-in-leach (cRIL) ion exchange process. This allows immediate extraction of the rare earths as it comes into solution and drives the leaching reaction, which reduces the leach time and leachate consumption.
“The end result is a better quality product and a significantly reduced radioactive waste factor. Clean-iX achieves recoveries of rare earth elements of up to 90% and higher and provides a substantial reduction in the amount of ammonium salt required to precipitate the rare earth elements downstream, as an additional bonus” van der Walt concludes.
The picture shows van der Walt training operators on the functionality of the Clean-iX pilot plant’s automation system.
