Microanalysis and Characterization
CANMET-MMSL uses a variety of equipment to provide microanalysis and characterization of mineral samples for the mining and related industries. For accurate determination of the elemental composition of mineral grains, such as for analysis of diamond indicator minerals, CANMET-MMSL uses electron microprobes. To analyze samples in their natural state, such as for the analysis of dust in samples of respirable air in underground mines and in emissions from smelters, CANMET-MMSL uses variable-pressure scanning electron microscopes. Listed here are some of our specialized equipment:
- The JEOL 8900 electron microprobe has five wavelength dispersive spectrometers, with a wide range of diffracting crystals, and a light element energy dispersive system. This equipment enables non-destructive elemental analysis of microscopic volumes. In general, an element in concentration of ~100 ppm can be analyzed in a sample volume of ~3 µm3. Electron microprobes provide an electron beam that is more stable than scanning electron microscopes, thereby providing higher accuracy microanalysis.
- The JEOL 733 electron microprobe has four wavelength dispersive spectrometers and a wide range of diffracting crystals plus a light element energy dispersive system.
- The HITACHI S3200N variable-pressure scanning electron miscroscope (VP-SEM) has a light element energy dispersive spectrometer. This equipment can be operated in either a high vacuum mode (~0.001 Pa) or a low vacuum mode (1 to 200 Pa) and enables magnifications typically higher and with better depth of focus than those obtained by conventional optical microscopy. The magnification range of SEM is ~20 to 300 000X, with a practical operational magnification of ~60 000X. For high vacuum SEM, the samples need to be dry and generally a very thin (~0.005 µm) layer of a conductive material needs to be applied. In the low vacuum mode, no special sample preparation is required to perform electron microscopy studies. Non-conductive and wet samples can be studied in the low vacuum mode. The system has a cooling stage that reduces the dehydration of wet samples. The VP-SEM is equipped with an energy dispersive detector to obtain information regarding the elements present in the samples. Quantitative elemental analysis is also possible.
- The JEOL 820 scanning electron microscope, equipped with a light energy dispersive spectrometer, backs up the HITACHI S3200 in its high vacuum mode;
- Cameca 4-F Secondary Ion Mass Spectrometer (SIMS or ion microprobe) equipped with high energy electron guns for analysis of insulating samples and complemented by a range of mineralogical standards;
- A proton microprobe (micro PIXE) analysis is available.
- X-ray diffraction facilities include a Rigaku automated rotating anode X-ray powder diffractomer (12 kW), Guinier, Gandolf and Debye-Scherrer cameras, microdiffractometer, and 4-circle automated single crystal diffractometer;
- Surface analysis X-ray is done using photoelectron spectrometer (XPS) with achromatic and monochromatic anodes, ion sputtering, imaging capability, and fracturing and reaction UHV chambers.
- Auger electron spectrometer (AES) with cylindrical mirror analyzer, ion etching and in-situ fracturing capability.
Image analysis is mainly used to determine mineral quantities and mineral liberation to assess the performance of mineral processing plants. The CANMET-MMSL system has a dedicated electron microprobe with a state-of-the-art image analyzer. The dedicated electron microprobe provides a very stable electron beam current using a beam stabilizer that checks and regulates the beam current every second. This allows CANMET-MMSL to perform image analysis based on backscattered electron images (BSE) which is applicable in some 90% of the cases. In this mode the CANMET-MMSL image analyzer is capable of studying ~30 000 particles per hour. This is several times faster than any other comparable modern system commercially available.
In addition, CANMET-MMSL uses a special algorithm for rapid liberation measurements. Analysis of many particles is required in order to have reliable information with respect to low grade samples such as the very few valuable mineral grains lost in tailings. For ~10% of mineral liberation cases, there is an overlap with some mineral of interest in the BSE image. For these cases, the system runs using a combination of BSE mode and X-ray information for elements of interest from the energy dispersive detector or from the wavelength dispersive detectors. Combining BSE and X-ray information makes it possible to analyze ~4 000 particles per hour.
The system is also used for automated gold mineral searches or for automated searches of platinum group minerals. The automated search runs overnight, analyzing literally several million particles. The system is used in this mode to further understand the behaviour of precious metal mineral grains during metallurgical processing.
Image input from optical microscopes allows us to use the image analyzer for other applications such as surface crack density measurement on rock and concrete samples, and particle size analysis of ion exchange resins.
CANMET-MMSL has been involved in image analysis and applied mineralogy for over 30 years.