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Atmospheric heap-leaching to solve nickel laterite processing problems

Final Report Summary - NICAL (Atmospheric heap-leaching to solve nickel laterite processing problems)

The NICAL project had the two primary scientific and technical objectives of i) developing criteria for the identification of oxide-rich nickel (+cobalt) laterite resources suitable for the industrial application of new low-cost atmospheric heap-leach (AHL) technologies and ii) modify the existing AHL process already under development to cope with the processing of the variable mineralogical features of known, but currently metallurgically problematic lateritic resources.
The project further deepened the close technical understanding and transfer of knowledge between researchers at The Natural History Museum (NHM) and technical professional staff in Sardes Nikel Madencilik TiC. A.S. (SN) through the secondments between NHM and SN. It should be noted here that during the second reporting period, Sardes Nikel changed their name to Çaldağ Nikel (CN) although this had no effect on the running of the project.
The partnership used integrated geological and mineralogical studies to investigate lateritic nickel resources at the 'fossil' laterite deposits of Çaldağ in Turkey and Devolli in Albania which had been formed by deep weathering of a serpentinite protolith during the Mesozoic and Tertiary periods. Several scientific papers were published from this work and this is ongoing. During the second reporting period, a further ore type was studied from the active tropical laterite deposit of Acoje in the Philippines where a more complex range of silicate and oxide minerals was found to be present. Mineralogical investigation has employed a range of geochemical, XRD, SEM and EPMA techniques. At Çaldağ, nickel is found to be largely present in the mineral goethite. At Devolli, nickel also resides in goethite but is also found in a range of silicate minerals. At the Acoje deposit, nickel silicate minerals are more common.
The investigated ore types were tested using AHL experiments at a range of scales from bottle-roll lab scale, through 1m column tests to 4m large-scale columns. Proposed large-scale crib tests were abandoned after preliminary testing and replaced by more extensive large-column tests on the final chosen ore-type from Çaldağ. Products from the experiments were sampled regularly to investigate the leaching process at both the large bulk scale and at a mineralogical level. This new mineralogical data was planned to be fed back into a metallurgical modelling programme 'Metsim' in order to develop it as a more predictive tool for reaction modelling; this work is still in progress. The leach testwork was carried out on the three deposits chosen in Turkey, Albania and the Philippines, testing processes on a range of mineralogical ore types. Small-scale testwork successfully captured the initial breakdown of nickel-bearing mineral phases and the formation of transient mineral phases in the leach columns, previously not recognised by simple bulk testwork alone. This important information has been valuable in optimising the process of nickel extraction and retention of soluble nickel in the leachate during large scale testing.
The project was also able to develop and test a first-generation combined XRF-XRD analysis for mineralogical evaluation developed by InXitu Inc. of the USA. Initial testwork has yielded high-quality XRD data, fully comparable with large-scale lab-facilities, running the instrument both the laboratory at the minesite and in a field situation. Qualitative XRF data has also been successfully generated and results downloaded in a form suitable for further processing which is being developed with the manufacturer and associated researchers.
Further details of the project are available at www.nical.co.uk.