Analytical Tools in Mineral Processing

The modern mining process covers discovery of an ore body, extraction of minerals and finally returning the land to its natural state. Syensqo is the leading solutions provider to the mining industry focusing on the extraction process of minerals. Syensqo's specialty mining reagents help customers improve their productivity and reduce operating costs while meeting complex metallurgical challenges. Within Syensqo, many analytical techniques, which are related to the characterization of value and undesired minerals, are adopted to understand the mineral deposits of customers and to support new reagent development. These are the same techniques that are widely utilized in the mining industry, so that scientists can use the data to help customers troubleshoot their operation issues. This document will focus on the analytical techniques and applications in the Mineral Processing industry, although some of them can be also applied to Alumina Processing and Solvent Extraction. 

 Elemental composition and mineralogical information are two major analytical needs in the characterisation of an ore body, as well as samples of crushed-, ground ores and flotation products. Mining industry laboratories typically analyse large numbers of samples for both exploration and mine production purposes on a regular basis, utilizing a variety of analytical techniques. 

There is a high demand from the mining industry to use elemental analysis in order to analyze the quality and extent of metals in an ore body as well as the samples taken from the processing operations. This is crucial to qualify the commercial feasibility of a mine during exploration, to reduce operation costs, to improve the recovery rate and to optimize product quality during production. There are many different types of qualitative and quantitative analyses available. Broadly speaking, the elemental analysis methods can be categorized into 1) wet chemical analysis and 2) spectroscopy. 

In general, wet chemistry procedures for mining applications involve dissolving the mineral samples in an acid and analyzing the solutions using colorimetric, volumetric or gravimetric methods. Wet chemistry methods work better with samples that are relatively “pure”, and not as well with samples exhibiting complex composition. Spectroscopy techniques provide better selectivity and can measure multiple elements at the same time. This will be illustrated in more detail below.

Flame Atomic absorption spectroscopy (AA), Inductively coupled plasma optical emission spectrometry (ICP-OES) and X-ray fluorescence (XRF) are widely used spectroscopy techniques for elemental analysis in the mining industry. Each technique has its own benefits/disadvantages and is chosen specifically for the characterization needs (Table 1). It should be noted that there are two main types of XRF instruments, wavelength dispersive (WD-XRF) and energy dispersive (ED-XRF), which differ in sensitivity and price. There is also portable XRF which sacrifices some functionalities for portability, which is extremely helpful for field studies. Only WD-XRF is listed below for comparison.

Please check the following link for more information on the techniques.

ICP-OES (currently not available)

XRF (currently not available)

Mineralogy analysis involves the identification and the mode of occurrence of minerals as they relate to the beneficiation of ores. It plays a primary role in optimizing the treatment of any particular ore, maintaining optimum metallurgy, or trouble-shooting effectively in an operating plant. Some examples that show the importance of detailed mineral information are:

• Occurrence of the desired element in more than one mineral, particularly if the minerals have different responses to chemical reagents. Examples: gold as native gold vs. gold in solid solution in pyrite; copper in chrysocolla vs. chalcopyrite; copper in chalcopyrite, malachite vs. Cu-bearing goethite; tin in cassiterite vs. frankeite.
• Variability in mineral composition (substitution, isomorphism). Examples: variability of Ag in solution in gold grains, high-Fe versus low-Fe content in sphalerite.
• The presence of gangue minerals that can have an adverse effect on beneficiation; eg. montmorillonite and talc.
• The presence of rare or unexpected minerals.

Mineral identification can be accomplished using microscopy, physical, chemical and instrumental methods. This document will focus on vibrational spectroscopy (Near IR, Raman), optical microscopy, Scanning Electron Microscopy with Energy Dispersive X-Ray Analysis (SEM-EDX), Automated SEM / EDX (Mineral Liberation Analysis) and X-ray diffraction (XRD). Please check the following link for more information on the techniques.

While the above sections emphasize the laboratory techniques, it should be noted that online analyzers for process control are becoming increasingly recognized as the next generation technologies. Online monitoring enables a continuous input of chemical and mineralogy information about the operation process. It greatly reduces the time gap between the data collection and the decision making on operation adjustment, therefore improving the real-time process control for the customers. In fact, there are some online elemental analyzers that are commercially available for conveyor belt ore sorting, e.g online XRF, online laser-induced breakdown spectroscopy (LIBS), etc. Significant efforts are being made to bring more potential online monitoring techniques to the industry, e.g. online timegate Raman, online XRD, etc. 

Another direction for future technologies is portability. The lightweight handheld instruments with simple infrastructure are highlighted for their capabilities to deliver rapid results in any location close to the field. For example, portable XRF (pXRF) and portable LIBS are exciting tools with many applications in mineral exploration and mining. It can provide elemental information much faster than traditional lab analysis in the field for faster decision making. There are more portable analytical instruments currently available or being developed (FTIR, NIR, etc).