From Ore to Metal
Mon 14 Nov, 2022
From Ore to Metal: Efficient Ways for Elemental Analysis
Metals are indispensable for modern technologies and daily life. Often, they need to be extracted from ores using sophisticated processes and must satisfy the highest purity requirements. The changing awareness of the finite reserves of raw materials gives increasing significance to a sustainable circular economy that incorporates metal recycling.
In terms of elemental analysis, the mining and metal industry value chain involves vastly different requirements. During early exploration and exploitation of potential mining sites, it is mostly major contents of elements in raw materials that need to be determined. In later process stages – for example during the production of high-purity metals and alloys – trace and ultra-trace elements play a more significant role in areas such as quality control, for instance. Different solutions are available depending on the task at hand and the various analytical challenges, which will be discussed in this article.
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The importance of metal
Technological progress was, and is only, possible due to the special and versatile properties of metals. Almost every naturally occurring metal is now required for our daily lives. Examples of these include: the use of iron in steel; lithium when producing lithium-ion batteries and recently in the field of e-mobility; and copper and precious metals as vital components in electronics and the semi-conductor industry. Even rare earth elements (REE) are now essential for many products in the field of sustainable energy – including wind turbines, catalysts, energy-saving bulbs and electric cars.
Metals, with the exception of precious metals, are not found in their pure form but are bound in minerals and ores – some are widespread, some only occur in limited quantities in just a few regions of the world. Due to their hugely valuable nature, even small concentrations in ore make mining worthwhile in some circumstances.
Nevertheless, it is not only metal extraction but also the recycling of metals in all forms that has now become critically important. In times of resource scarcity, uncertainty regarding material availability, a changed consumer awareness and rising demand from emerging economies as they become industrialized nations, a sustainable circular economy is becoming increasingly vital.
For this reason, used metals must be collected and recycled. Its consistent quality makes metal a sustainable material which, generally, can oscillate between raw material and waste for generations. For instance, 80 percent of all the iron ever brought into circulation is still present today.
Analysis of metals, minerals and ores
Mining a pure metal requires technically sophisticated processes. High-tech applications also demand high-purity materials. Consequently, their analysis along the mining and metal value chain is extremely important to ensure the commercial viability of mining and the quality of the end product. This presents various analytical challenges, which include the evaluation of possible mining sites, process control in facilities like smelters or foundries, quality control of unrefined products and purity testing for trace impurities as part of the quality control, to name just a few. To master these routine analytical tasks in the most efficient way requires highly robust, accurate and flexible instrumentation.Early on, a considerable number of raw materials need to be analyzed to create detailed specifications. This means major contents and concentrations of elements must be determined. AAS (atomic absorption spectrometry) with flame atomization is often employed for these tasks.
In later stages of the process, different analytical challenges arise. Trace and ultra-trace elements can influence the quality of high-purity metals or alloys significantly. However, the detection of these traces and ultra-traces requires instruments with higher accuracy and precision. Here, methods like ICP-OES (mg/kg to % range) or ICP-MS (ng/kg to mg/kg) offer the sensitivity required for these analyses.
Metals and alloys need to be solubilized before analysis using AAS, ICP-OES and ICP-MS, to obtain a measurable solution. These samples have a challenging matrix, which can impact the quality of the results. High contents of base metals such as copper, cobalt, chromium, nickel, iron and zinc, and trace elements (additives or impurities) can interfere with the correct quantification. Contents of SiO2, Al2O3, carbon (graphite, carbides) as well as refractory elements can have negative effects as well.
Sample preparation introduces another source of analytical challenges. Open vessel sample preparation on a hot plate with mixtures of HNO3, HCl, HF, as well as HClO4 and NaHSO4, can result in incomplete sample digestion. However, this can be avoided by using proper sample preparation methods like melt digestion and microwave pressure digestion.
Which analytical techniques are ideal for which application?
- More robust to harsh environmental conditions at the site of operation
- Flame-AAS: ppm to % values for individual or a few elements
- Graphite furnace AAS: Trace and ultra-trace elemental analysis
- Offer wider working range compared to flame-AAS as well as advantages in throughput, particularly for multi-elemental analysis
- ICP-OES: Increased number of elements or samples
- ICP-MS: Trace and ultra-trace elemental analysis
Especially during exploration and exploitation, equipment often needs to operate in harsh environmental conditions and very remote places. There are mining sites that are several thousand meters above zero. Air pressure and oxygen levels are much lower in these environments and can tremendously influence the measurements. Proper laboratory facilities are also rare in these places.
Therefore, instruments should ideally be user-friendly, easy to set up and if necessary, be operated by personnel without in-depth specialist training. Consumable availability is another big issue. Rare or specialist chemicals are not readily available at many mining sites because of their remote location. The instruments must operate with as few additional operating materials as possible. For example, the routine AAS novAA 800 of Analytik Jena can be operated with LPG gas, which is available even in the most remote places on earth.
Besides those general characteristics, analytical qualities such as accuracy, precision and method robustness are still key. Analytik Jena’s solutions provides suitable analytical methods to determine the content of metals in ores, impurities in pure metals, and to monitor the preparation process.
Nowadays, automation also plays a significant role since the number of samples for these routine applications is constantly increasing. Increased sample throughput – through automation and/or innovative analysis techniques – can decrease the overall costs of analysis and free up workforce resources.
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