Background

Nickel is one of the most important base metals for modern infrastructure. Over 60 percent of world nickel production (nickel metal based) is used for the making of stainless steel. There are mainly two types of resources for nickel mining – sulfide and laterite (oxide) ores. More than 70 percent of world nickel resources on land are found in laterite ores. Nickel laterite ore deposits are formed by weathering of ultramafic rocks in tropical to subtropical regions. Stratigraphic rock facies of nickel laterite deposit are typically layered upward as follows: serpentinized peridotite – saprolite – transitional rock – limonite – ferricrete. These rock facies are also gradually changed in mineral assemblages and chemical compositions. Nickel is extracted from ores mined from saprolite to limonite layers. X-ray fluorescence spectrometry (XRF) is a well-known analytical method to determine chemical composition in materials with high accuracy and simple sample preparation. Therefore, XRF technique is used for process and quality control in many industries. Sample preparation by fusion bead method allows high accuracy analysis of geological samples, because the method completely eliminates sample heterogeneity such as grain size and mineralogical effects, caused by various rock-forming minerals in geological samples. For the analysis of nickel laterites by XRF, high spectral resolution is required to detect trace amount of cobalt, since the wavelength are very close between iron and cobalt so that a large iron peak overlaps to the small cobalt peak in the spectrum. In addition, high sensitivity is required for the analysis of light elements such as magnesium. Wavelength dispersive XRF (WDXRF) can meet both of these requirements. This note demonstrates advanced methods to determine wide range chemical composition of rocks in nickel laterite deposits by fusion method.