A 280-hour-long, small-scale pilot operation involving CSIRO researchers and Rio Tinto staff has “proved in practice” CSIRO’s direct solvent extraction (DSX) process to recover nickel and cobalt from laterite leach solutions.

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.”

When abrasive material is transported through steel pipe in mining applications, typically as pumped slurry, the pipe can quickly be eroded from the inside out, which in more extreme cases can result in pipe leaks and even failure, or significant maintenance costs and downtime for pipe replacement. 

Steel piping systems are widely used in mining to convey the product, ore, and tailing slurries to the processing plant, as well as to recycle the debris medium back to the mining area. Other mining applications include steel pipe for drop shafts for conveying product from high elevations, and for backfilling the mine excavation areas utilizing sand fill, classified tailings or paste fill. For these highly abrasive applications, mild steel pipe generally can’t stand up to the abuse for more than a year or two. As a result, mine operators constantly seek piping alternatives to reduce maintenance and prolong system life, at a price point that will not significantly impact the budget. 

At Mosaic’s mining operations in Florida, for example, phosphate is mined by draglines and then pumped as a slurry mixture of pebble-sized rock, sand, and clay through 20- to 22-in. steel pipelines to a beneficiation plant located anywhere from 1.5 to 14 miles from the mining site. “The slurry is so abrasive, standard grade carbon steel pipe just wears out too quickly,” said senior pipe technician John Pillard. “The slurry will wear the bottom right out if you don’t have good pipe.”

Today, there are a variety of “abrasion resistant” products and accessories that have entered the market to replace mild steel pipe in high wear areas. Most operate on the premise that when two objects meet, the harder object wins out. As such, products are available in a variety of increasing hardness, measured on the Brinell scale from A-R steel (200 BHN) through iron cast pipe (up to 800 BHN).

However, any product that is very hard throughout the wall thickness is also extremely brittle. Brittleness is unacceptable as piping systems are constantly flexing and moving as a result of pressure surges and spikes, and due to mechanical and physical contact at the facility. However, one type of pipe delivers the best of both worlds: an induction hardened pipe with an abrasion-resistant inner surface that tapers to a strong, yet ductile outer surface.

Manufactured by Port Washington, Wisconsin, USA-based Ultra Tech, this unique pipe is produced under the Ultra 600 brand. Ultra Tech begins with a steel pipe manufactured to a proprietary chemistry, followed by induction heating, and finally water-quenching the inner surface to create a single-wall pipe. 

At 600 BHN, the inner surface of this induction hardened pipe can withstand most common abrasives, and tapers to a 250 BHN outer surface that is ductile enough to accommodate normal handling during shipment, installation and maintenance. With this proprietary process, pipe can be created in various diameters up to 40 in., in varying lengths and wall thickness. 

Because the outer surface behaves like mild steel, the product can be cut and welded with proper procedure in the field, configured into a variety of fittings, and can accept the standard end options of flanges, weld rings and couplings. 

According to Pillard, Mosaic uses a combination of Abrasion Resistant (A-R) pipe rated at 230 BHN and the induction hardened Ultra 600. Ultra 600 is generally used for phosphate slurry transport, as well as for a waste discharge line that carries large particles such as limestone and even chunks of wood to a waste pit away from the plant. 

Much of the A-R pipe was initially installed prior to a merger in 2004, but since then “more of the induction hardened pipe is taking the place of the A-R pipe simply because it’s a better value,” said Pillard.

Pillard’s primary concern is to “get the most wear for your money.” He estimated in an extremely high wear application at the mine, A-R pipe could wear out in as little as a year and a half, while Ultra 600 could last twice as long in the same application. In a lower (yet still abrasive) wear application, Pillard has seen the induction hardened pipe last as long as six to eight years. 

“You don’t want a pipe that is three times better, but costs 10 times as much.  That’s not cost effective,” said Pillard. “The Ultra 600 induction hardened pipe lasts a lot longer than mild steel, with only a moderate price increase.” 

This article was provided by Ultra Tech (www.ultratechpipe.com).