## 2 Scanning Electron Microscopy and Mineral Characterization
### SEM-Based Automated Mineralogy (SEM-AM)  
SEM-AM is a tool that was initially designed to characterize mineral processing products and ones. The measurement process starts with collecting backscattered electron (BSE) images, which are analyzed using image analysis software procedures. Based on BSE image adjustments, the energy-dispersive X-ray spectra (EDS) are obtained at selected points. The EDS spectra of the sample are then classified based on the list of approved reference EDS spectra. Relevant software providers offer services such as particle analysis, EDS spectral mapping, sparse phase search, and point counting modal analysis using four principal SEM-AM measurement routines and different classification algorithms, which can be used based on the analysis requirements. The main challenges associated with the process are materials with very different hardnesses, polishing relief surfaces of particles, electron beam stability, and appropriate nonevaporating epoxy resin mixtures [84]. SEM-based automated mineralogy (SEM-AM) is still underutilized, although SEM instruments are widely distributed in industry, geosciences, and materials research. SEM-AM can produce valuable results for a variety of major applications by characterizing the primary ores and optimizing mineral concentration, flotation, comminution, and metallurgical processes in the mining industry through the generation of quantified reliable data [107; 108; 109; 110; 111]. Beyond the classical fields, the potential of SEM-AM has gained further interest on scientific and economic grounds. Some closely related topics are ore fingerprinting, metallurgy, and applications in petrology [112; 113; 114]. SEM-AM systems are a combination of hardware platforms, processing software, and specific image analysis. Any SEM with minor adjustments can be used as a hardware tool for SEM-AM. These adjustments include a high vacuum operation mode and additional internal mainboards. A vacuum pressure of 10\({}^{-5}\) to 10\({}^{-7}\) Pa is needed for its operation. Electron sources of tungsten cathodes and field emission guns can be employed. Tungsten cathodes can be used for economical operation; however, field emission guns are recommended for the long-term stability of electron beams for automated measurements. The speed of analysis and X-ray count rate are increased in SEM-AM by employing two or more EDS spectrometers in the SEM hardware. Multiple samples can be accommodated in a large sample chamber for simultaneous analysis in a single measurement session. A very accurate stage movement of SEM allows precise positioning using small intervals. For valuable analysis results, a fine-quality backscattered electron (BSE) detector is needed. In SEM-AM analysis, BSE image quality and stability are important factors, as the resultant image (in combination with the EDS spectrum) is used for phase or mineral discrimination. Prior to measurement, fixed working distances must be set to keep the BSE image gray levels constant [84]. Keeping the image calibration constant ensures that a specific phase or mineral always possesses the same BSE image gray level. The calibration process can be conducted with various BSE image gray levels of reference materials such as quartz (dark gray), copper  
Figure 5: Schematic diagram of an energy-dispersive spectrometer. (intermediate), and gold (very bright) [84]. The choice of calibration reference material should be made based on the sample material to be investigated. For example, many slags, industrial ash, or particulate materials are investigated using SEM-AM, and quartz or copper are used for calibration with dark gray to intermediate BSE image gray levels. This results in SEM images with better resolution and quality. For SEM-AM technology, four principal measurement routines can be outlined, which starts with collecting BSE gray-level images with respect to the calibrated gray level, as shown in Figure 6. The upper row represents the BSE images, while the bottom row indicates the EDS images of SEM-AM of one measurement frame.