Metallurgy is a !eld ofscience that I love –incredibly diverse andelegantly simple.

Scientists are searching for cheaper,cleaner and more thorough ways ofextracting, recovering or recycling thevital metals that underpin advancedcivilisation. One company at thiscutting edge is Direct Nickel Limited.

A reluctant resourceUntil recently, most of the world’snickel supply came from sul!deresources. However, economicallyexploitable sul!dic nickel resourcesare dwindling, so we are moving to themore metallurgically complex laterite

ores, which constitute over 70% ofknown land-based resources.

Unlike sul!des, most lateritescannot be readily upgraded to high-grade concentrates (10–25% Ni) viafroth "otation or other simplebene!ciation techniques. So theef!cient extraction and recovery of thenickel is necessarily more complex,and costs more per tonne of metalproduced.

As with many mineral resources,nickel laterite deposits are usuallylayered, with an iron-rich limonite layerdominated by goethite (FeOOH), andan underlying saprolite layer that ismagnesium rich. And a major problemis that the existing processes are

Chemistry in Australia24 | November 2013

A new direction

for nickelA small Australian technology company isworking to solve a looming problem in theworld’s nickel supply.

BY DAVE SAMMUT

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usually much better at treating onelayer or the other, but not both.

The dominant pyrometallurgicalprocess (smelting) works best forsaprolites, usually by drying,calcining/reduction and electricfurnace smelting. These processesusually produce either ferro-nickel(Fe–Ni metal for stainless steelproduction) or nickel sul!de matte,which is further processed and re!nedto produce pure metal. However,smelting requires high-grade ores andhas substantial energy requirements.

Hydrometallurgy and the DNiprocessHydrometallurgy feels to me like trulyclassic chemistry, and I savour theingenuity inherent to this !eld. Take asan example the brilliant deception ofthe Nazis by Hungarian chemistGeorge de Hevesy. To prevent theNazis stealing the gold Nobel Prizes ofMax von Laue and James Franck, deHevesy dissolved the gold medals inaqua regia, preserving the solution in abottle left on his shelf at the Neils BohrInstitute in Denmark throughout theSecond World War, and afterwardsrecovering the gold for re-smelting ofthe medals.

The principles in hydrometallurgyhave a wonderful simplicity.Atmospheric leaching starts withequipment as straightforward as a tankwith an agitator. Toss in the electrolyte,the ore or concentrate and some acid,and wait for the witch’s brew to stew.

In nickel hydrometallurgy, the acidis the key – both for performance andeconomics. Previous attempts atcommercial laterite processing havefailed because of uneconomicconsumption of acid, particularly asthe sulfuric acid used by mosttechnologies is not regenerated orrecycled. The high magnesium contentin saprolite laterites results in highsulfuric acid consumption – up to500 kilograms per tonne of ore.

The elegance of Direct Nickel’s DNiprocess is the use of nitric acid – it ismuch more aggressive than sulfuric, so

it eliminates long leach times or hightemperatures and pressures. And it isalmost wholly recyclable – net nitricacid consumption rates are as low as40 kilograms per tonne of ore (albeit atthree times the price of sulfuric).Based on its current "owsheet, DirectNickel’s early estimates of capital andoperating costs suggest !gures in thebottom quartile of the nickel lateriteprocessing industry.

Using nitric acid, the DNi processcan leach both the saprolite andlimonite, and the feedstocks can beeither separate or mixed. The nickel(and cobalt) having been extractedinto solution, the waste residue is then!ltered, washed and disposed. Co-dissolved iron is then directlyhydrolysed to hematite, which is anadvantage over jarosite-producingprocesses, because hematite is pretty

much as environmentally stable as anyiron residue can get.

The pH of the ‘pregnant’ electrolyteis then raised using recycled MgO, !rstto precipitate contaminant aluminiumthat has co-leached with the iron andnickel, and then to recover a nickel–cobalt mixed hydroxide precipitate asan industry-standard intermediateproduct for sale.

The barren magnesium nitratesolution is evaporated to amonohydrate solid, which is thenthermally decomposed from moltensalt to produce MgO (mostly for sale,with some being recycled) and nitricacid/NOx vapours are sent to a seriesof absorbers and scrubbers forrecovery of nitric acid.

The devil is in the detailOf course, simple schematics areusually quite a long way from thereality of a plant as built. One of thekey challenges in commercialisingnew hydrometallurgical technologiesover the last few decades has been thecomplexity of the various systems thatneed to be applied around the corechemical process.

Put simply, leaching is often theeasy part. But the stronger the lixiviant(liquid used to extract the desiredmetal), the less selective the leachingprocess, and the larger and morecomplex the systems required forhandling co-leached contaminants.

Stronger lixiviants, highertemperatures and higher pressuresalso require more advanced materialsof construction. For the DNi process,the atmospheric leaching and

comparatively low temperature (about100°C) mean that 304 and 316stainless steel should be suf!cient.However, nitric acid is more corrosivethan sulfuric. While the steel should bepassivated (made less vulnerable toenvironmental factors) by nitric acid,the long-term performance ofmaterials is not as well proven as forthe more ubiquitous sulfuricprocesses.

As an aside, chloridehydrometallurgical systems are moreaggressive still, and it is sometimesjoked that 316 stainless is so namedbecause that is how many seconds itwould last in a chloride leach.

While !ltering and washing solid–liquid slurries is easy enough in the

Chemistry in Australia 25|November 2013

The elegance of Direct Nickel’s DNiprocess is the use of nitric acid – it ismuch more aggressive than sulfuric, soit eliminates long leach times or hightemperatures and pressures.

lab, the loss of entrained electrolytewith waste residues can be a big-ticketitem in minerals processing, from bothan economic and an environmentalperspective. As it scales up its process,Direct Nickel has been paying dueattention to the potential loss of nitrateswith its residues at the end of theleach.

On top of that, the DNi Processrequires high temperature and gassystems for the MgNO3 decompositionand conversion of NOx back to nitricacid. This will increase complexityagainst simpler atmospheric leachingprocesses and introduce speci!csafety issues that need to beaddressed. None of these problems isby any means intractable, but they allrequire speci!c engineering focus,and they all add to the cost of adeveloping project.

The production of an intermediatemixed hydroxide generatesappreciably less value per tonne ofnickel in product than metal, but hasthe advantage of limiting thecomplexity in the system. Perceived

technical risk is a major factor whentrying to secure !nance for a newtechnology project, so this is probablya good choice until the DNi Process ismore thoroughly proven.

Beyond the technologyThese complexities are at least part ofthe reason why the road tocommercialisation for new mineralsprocesses is so very long, and why somany concepts that look great onpaper fail to make it through tocommercial application.

Implementing a new mineralsproject takes four major factors: areally good technology, the simpler toexecute the better; secure access to aspeci!c feedstock over the full courseof time to implement the critical !rstproject (the minerals industry has atendency to ‘rush to be second’);enough !nance to develop thetechnology (DNi has already spent$40 million to get this far) and then toimplement a project running into thehundreds of millions of dollars incapital costs; and perhaps just asimportantly, the dogged tenacity tohang on through every setback alongthe way.

Although having started bylicensing partially developedtechnology from Drinkard Metallox inlate 2006, and having put in placecritical new patents for the nitric acidrecycling technology around the sametime, Direct Nickel is only now runningits !rst major pilot plant. This is prettynormal for developinghydrometallurgical processes.

Direct Nickel has been intelligent inits approach. It has achieved buy-infrom key experts in the !eld ofhydrometallurgy to collaborate in thedif!cult process of commercialisingtechnology – most notably CSIROMinerals and Teck Resources, butmore recently also PT Antam,Indonesia’s largest nickel producer.

The company’s one tonne per daypilot plant at CSIRO’s Perth facilitykicked off over the !rst quarter of2013. Direct Nickel announcedmilestone success in mid-July, with theproduction of its !rst marketablenickel–cobalt concentrate from a ten-day continuous campaign treatingIndonesian laterite feed containing25% limonite and 75% saprolite.

Dr Dave Robinson of CSIROexpanded upon this to speak of thesuccess in solid–liquid separation andresidue washing results, which helpmaximise acid recycling ef!ciency,noting that these results have actuallyimproved on the scale-up from the labto the pilot plant. Operations at the

Chemistry in Australia26 | November 2013

Nickel laterites usually occur in regions where prolonged weathering of ultramafic rocks has occurred;many of the known deposits occur within or close to the tropics. Iron oxides are responsible for the rustred colour typical of most laterites, as seen around this river in New Caledonia. Nickel mining forms asignificant sector of New Caledonia’s economy.

These complexitiesare at least part ofthe reason why theroad tocommercialisationfor new mineralsprocesses is sovery long ...

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plant are scheduled to continue to theend of 2013.

As noted by Richard Carlton, chiefoperating of!cer of Direct Nickel,‘nickel and particularly laterites have astigma to them so anyone claiming tohave a solution is viewed withscepticism. This extends to making itdif!cult to raise funds, made worse bythe tough state of global !nancialmarkets over the last few years.Partnering with reputable strategicpartners including Teck ResourcesLimited, PT Antam and CSIRO hasbeen an important boost to thecredibility of the DNi efforts tointroduce this new process.’

Carlton indicated the company’saim to be constructing an associated!rst plant during 2015, for operation by2018.

This timing to commercialise newtechnology points to a major "aw ininternational intellectual property

systems. Development andimplementation of any new mineralstechnology can easily take 20 years,and almost never less than ten. Even ifa company has the commitment andresources to bring its new technologyto market, by the time it has done sothe 20-year protection of its ideas isalready nearing its expiry, except tothe extent that the company can‘evergreen’ the developments in itstechnology over the course ofdevelopment.

There is no question that DirectNickel has a great technology, and thatits collaboration with CSIROsigni!cantly enhances its chances ofsuccess. But the inertia of industry, thechallenge of competing against sunkcapital, and the conservatism of!nance in the face of huge investmentrequirements all remain huge hurdlesto taking promising technology overthe line. I wish the team every success.

Robinson emphasises the widerange of opportunities forhydrometallurgy based on recyclednitric acid, and the additionalopportunities for value-adding byupgrading those processes to produce!nished products rather thanintermediates.

As hydrometallurgists, we share avision of clean, ef!cient metalsproduction. And as eternal optimists,for us the bucket is always half full.

Dave Sammut MRACI CChem is Principal at DCSTechnical Pty Ltd. DCS Technical has no affiliationwith Direct Nickel.

Chemistry in Australia 27|November 2013

The DNi process pilot plant at CSIRO’s Perth facility is scheduled to continue operations through to the end of 2013.

Direct Nickel