Research Progress on Sample Preparation Methods and Analytical Techniques for Nickel Laterite

With the depletion of common sulphide nickel resources, nickel laterite is becoming more attractive as nickel oxide, nickel matte and nickel-iron, amongst others, can be produced directly. For the determination of major, minor and trace elements in laterite nickel ore, many kinds of measurement methods for a given element and many differences of details between detection methods based on the same principle are available, making it difficult to select the appropriate method. Recent research in the pretreatment method and technology of the detection of a number of elements (Al, As, Bi, C, Ca, Cd, Cl, Co, Cr, Cu, F, Fe, Hg, Mg, Mn, Ni, P, Pb, S, Sb, Sc, Si, Ti, Zn) in laterite nickel is reviewed in this paper. The proper pretreatment methods were selected according to the target elements and detection method. Acid dissolution and alkali fusion as the pretreatment methods are most widely used now. Although acid dissolution introduces less salt and operates more simply, the volatile elements such as As, Sb, Bi and Hg are often lost in the decomposition process, while Cr is frequently lost by smoking with perchloric acid. Alkali fusion has better decomposition ability for Cr, Si and total iron, while the subsequent analysis is difficult, because impurities as well as many other salts are introduced due to the loss of crucible material and the melting process. The determination techniques of nickel laterite are chosen on the basis of character and concentration of target elements and the equipment in the laboratory. Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES), which is suitable for the determination of elements content from 10-5 to 30%, is the main analysis method of major, minor and trace elements. X-ray Fluorescence Spectrometry (XRF) is used to analysis elements content of 10-3-1 in samples, especially for the detection of Al, Si, Ti, V and P. This method whose accuracy relies on a set of high quality standard sample is suitable for spot detection and determination of the large numbers of laterite nickel ore samples. Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) is appropriate for determining heavy elements with the content of less than 10-4 in samples, especially for the rare earth and noble metal elements. Atomic Absorption Spectrometry (AAS) is adopted in the determination of the low boiling point elements with the content level ranging from 10-4 to 10-2 which are liable to atomization, such as Ca, Mg, Ni, Co, Zn, Cr and Mn. Spectrophotometry is mainly used for detecting the Ni and P, while Atomic Fluorescence Spectrometry (AFS) for the measurement of elements which were easily to form gaseous hydride such as As, Bi and Sb. Some main content elements, like Al, Fe, Mg and SiO2, are analyzed by Volumetry. Although the detection period is a little longer, AAS, Spectrophotometry, AFS and Volumetry which just need common equipment meet the daily determination in the laboratory which lacks large scale equipment. In order to solve the applicability and other existing problems, it is necessary to study the microwave digestion method, direct mercury analysis method, ICP-MS method, and rapid determination of Cr and other elements. The progress in establishing appropriate detection methods is certain to serve the trade, analysis and comprehensive utilization of laterite nickel ore.