IMC’s proprietary RapidSX solvent-extraction (SX) process was developed for the low-cost separation of rare-earth elements (REEs), nickel, cobalt and other technology metals.

Pr-Nd oxide is in increasing demand for the production of high-performance permanent magnets, used in a wide variety of industrial, automotive, defence and clean-tech applications.

SX is a liquid-liquid process and a standard method used for separation and purification of elements and compounds in concentrates.

Some metals, such as REEs, are more difficult to separate. In such cases, the extract, scrub and strip unit operations of an SX circuit will contain multiple individual processing steps – typically mixer-settler units in conventional SX circuits. The associated low separation factors (the ability to separate elements with high yields and purities) in such systems, means that the process has to be repeated over and over again within each unit operation. Such systems are therefore highly complex, expensive and the process is time consuming.

A conventional SX circuit for the separation of the light REEs La-Ce-Pr-Nd into La-Ce and Pr-Nd, for example, may contain as many as 90 mixer-settler units. More than a dozen SX circuits would be required to produce a suite of individual, high-purity REE products – over 1,000 mixer-settler units in total.

The RapidSX process combines the proven chemistry of SX with a new approach to allowing the organic and aqueous phases to interact during processing, using proprietary column reactors. The columns are designed to increase the process kinetics within each unit operation, while minimising the settling times required after each process step occurs.

It reduces the number of process steps required in each SX circuit by up to 85-90%, significantly reducing the physical footprint of operations. The time to reach process equilibrium is also significantly reduced, from weeks in some conventional SX circuits, to a few days. The process also reduces the quantities of organic reagents required and the power requirements for equipment operation, as well as the amount of inventory required to be loaded into the system at any one time.

“We were pleased to work with MSV to demonstrate the effectiveness of the RapidSX process on Serra Verde REE concentrates," commented Gareth Hatch, president of IMC.

“Combining the time-proven chemistry of SX with IMC’s proprietary column-based approach, avoids the risks associated with novelty separation approaches that require expensive resins and other complex methods, not yet demonstrated at scale."

The demonstration project was conducted at IMC’s pilot-plant facility in Mississauga, Canada, capable of producing 2t/mth of REEs. The RapidSX process was developed as a result of funding from the US Army Research Laboratory, part of the US Department of Defense.

The high-value Pr-Nd oxide was separated to 99.5% total REE purity using the RapidSX process; lanthanum oxide was also produced as a byproduct of the demonstration programme, with 99.97% total REE purity.

IMC said that although the process needs to be further demonstrated at a larger scale, these initial results indicate average separation costs of below US$2/kg for a suite of high-value separated REEs. Capital costs for a 2,500t/y REE RapidSX-based facility are in the region of US$10-15 million.

“The future production of commercial-grade REE products is going to require the application of new, cost-effective approaches to the separation and purification of concentrates,” said Hatch. “IMC’s RapidSX process is one such approach, applicable not only to REEs, but to concentrates containing nickel, cobalt, copper, zirconium, scandium and other critical metals.”

Luciano Borges, Serra Verde’s CEO, said: “The positive results obtained through IMC’s innovative technology are an important confirmation of the commercial potential and versatility of the product we intend to offer the market’s separation segment in the late 2018.

“For Serra Verde, any technology that can amplify the market for our REE concentrates will always be welcome.”