Rapid dehydroxylation of nickeliferous goethite in lateritic nickel ore: X-ray diffraction and TEM investigation

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Abstract:

A method for extracting Ni and other metals from lateritic ores by means of shock heating has been investigated. Shock heating releases some of the metal from its goethitic host. Even though the transformation of pure goethite to hematite is known to occur via intermediate hydroxylated phases, the effect of other metals such as Ni substituting for Fe in goethites on this thermal transformation to hematite is unknown. The purpose of this study was to fill this gap, with the hope that the results will lead to more energy-efficient extraction methods and/or a better understanding of Fe geochemistry in thermally activated soils. X-ray diffraction, transmission electron microscopy with EDS, and thermal analysis were used to investigate mineralogical changes in nickeliferous goethites from five oxide-type lateritic nickel ore deposits that had been subjected to shock heating at temperatures in the range 220–800°C. Acicular, nano-sized goethite was the main constituent of the samples with minor to trace amounts of quartz, talc, kaolinite, chromite, maghemite, and Mn oxides. Goethite was partially dehydroxylated to OH-hematite at 340–400°C and had completely altered to well ordered hematite at 800°C. The OH-hematite was characterized by broad XRD peaks for reflections associated with the Fe sublattice. The goethite unit-cell a and b lengths remained almost constant with increasing preheating temperature up to 300°C, while the size of the c axis dimension contracted. The neoformed hematite crystals were larger than the precursor goethite crystals due to development, by sintering and surface diffusion, of regularly ordered hematite domains. The increase (1.5–2.6 fold) in surface area with increasing heating temperature (up to 340–400°C) reflected the development of slit-shaped micropores (∼300°C), which further developed into elliptically shaped micropores (∼400°C) in OH-hematite. With increased heating temperature, well ordered hematite formed with only a few micropores remaining. Such results may contribute to the development of more efficient procedures for extracting Ni from lateritic nickel ores, as the rate of dissolution of goethite in acid in 'heap and pressure' leach facilities will be enhanced by the increases in surface area and microporosity. The results may also provide valuable information on the probable effects of natural heating on pedogenic Fe oxides.

Keywords: DEHYDROXYLATION; GOETHITE; LATERITIC; NI ORE; SHOCK HEATING; TEM; XRD

Document Type: Research Article

DOI: http://dx.doi.org/10.1346/CCMN.2009.0570608

Publication date: December 1, 2009

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  • The JOURNAL publishes articles of interest to the international community of clay scientists, including but not limited to areas in mineralogy, crystallography, geology, geochemistry, sedimentology, soil science, agronomy, physical chemistry, colloid chemistry, ceramics, petroleum engineering, foundry engineering, and soil mechanics. Clays and Clay Minerals exists to disseminate to its worldwide readership the most recent developments in all of these aspects of clay materials. Manuscripts are welcome from all countries.

    Clays and Clay Minerals is the official publication of The Clay Minerals Society.

    The Editor-in-Chief is Professor Joseph W. Stucki jstucki@illinois.edu

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