The successful operation, as described in the February 2010 issue of CSIRO’s Process magazine, was stage five of a journey that Minerals Down Under Flagship researchers—working through the Parker CRC for Integrated Hydrometallurgy Solutions—and Rio Tinto Technology and Innovation staff have taken to further develop the technology to suit Rio Tinto’s leach solution and to test how well it works.

Lead scientist Dr. Chu Yong Cheng said stage five is the most important for any new solvent-extraction process. Called the “fully continuous” stage, it is essentially a small-scale pilot operation. “A lot of effort went into this operation: it was run continuously with extraction, scrubbing and stripping, over two shifts a day with hundreds of samples taken.”

However, that effort was justified because its success means the process has been proved “in practice and not just in principle,” he said.

Mark Godfrey, Rio Tinto principal adviser for hydrometallurgy, said DSX offers a simple and selective process for the full recovery of the nickel and cobalt from nickel leach solutions.

The core of the DSX process is the CSIRO-developed synergistic solvent extraction (SSX) technology, which Rio Tinto had earlier identified as a possible way of streamlining nickel processing. SSX uses organic solvent reagents to directly separate nickel and cobalt from impurities including magnesium, calcium and manganese without intermediate precipitation and re-leach steps, and does so with high selectivity, simple process flowsheets and potentially low capital and operating costs.

The latest stage in testing the SSX technology involved further optimizing operating conditions for extraction, scrubbing and stripping in a fully countercurrent operation mode and collecting data for plant design and operation. It followed on from previous work, including batch and semi-continuous stages, which helped the research team determine optimum conditions for the DSX circuit.

CSIRO’s Cheng said the latest results, now being evaluated by Rio Tinto, could be used for further larger-scale pilot work, plant design and operation. “More test work could be carried out to further improve the operation and accumulate more data for plant design and operation.”

Godfrey said the nickel and cobalt recovery results are very good. “Confirmation that there is no gypsum precipitation makes this an outstanding process and continued testing and development of DSX for nickel laterite processing is warranted.”