Local researchers are using a unique method of nano-material imaging to more effectively determine the highly variable acid leaching values of Western Australian nickel laterite ores.
The study, a joint project involving the Curtin University Centre for Materials Research and CSIRO Division of Process Science and Engineering, could have a far reaching impact on hydrometallurgical processing for these ores which have previously been difficult to characterise.
Curtin PhD student and lead author Tony Wang applied his knowledge in materials science and applied material characterisation techniques on mineral analysis.
Mr Wang used energy-filtered transmission electron microscopy (TEM) imaging to analyse the ores, a method relatively unfamiliar to metallurgists or geologists.
"We know that TEM is an analysis tool for nano-materials and it has much better spatial resolution than normal scanning electron microscopy (SEM) based techniques," Mr Wang says.
"In TEM, electrons passing through [the] sample lose energy, different elements in samples grab characteristic amount of energy from the incident primary electron beam.
"By detecting electrons with the amount of energy loss we are able to map where these elements present in a nano-scale particles/sample features."
Mr Wang says the ores analysed by Inductively Coupled Plasma (ICP) mass spectrometry or X-ray fluorescence (XRF) methods tell the practitioners how much nickel is present in the ores but not how much nickel can be extracted.
"The difference can be surprisingly huge," he says.
"For example after same acid leaching time some ores can release 90 per cent of nickel while the other types can only give 10 per cent of nickel.
"Therefore mineral processing scientists in CSIRO use X-Ray Diffraction to examine the mineralogy of these ores, hopefully a better correlation between types of ores and the acid leaching rates can be derived.
"This is based on the fact that different minerals in the ore mixture have different chemical properties therefore different acid leaching rates.
"The point I am emphasising in my paper is in the third levels, with the nano scale elemental imaging techniques, we are able to examine how the minerals are linked."
Mr Wang also found the goethite-silica cementation structure in some WA laterite ores explained why some goethitic laterite ores did not leach and release the nickel.
"These goethite crystals are enveloped or covered by silica inside the cementation structures," he says.
"We found the cementation can be broken down by caustic digestion using potassium hydroxide liquors.
"On the contrary, all the fast leaching ores in my sample suit contains ubiquitous discrete acicular or needle shaped goethite.
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Xiaodong Wang, Robbie G. McDonald, Robert D. Hart, Jian Li, Arie van Riessen, Acid resistance of goethite in nickel laterite ore from Western Australia. Part I. The relationship between goethite morphologies and acid leaching performance. Hydrometallurgy, Volume 140, November 2013, Pages 48-58, ISSN 0304-386X, dx.doi.org/10.1016/j.hydromet.2013.09.005.