Nonferrous metals include aluminum, copper, magnesium, lead, nickel, tin, titanium, zinc, and their alloys. Each of the nonferrous metals has specific and unique advantages like, e.g., electrical conductivity (copper), low weight (aluminum) and corrosive resistance (zinc). Therefore, they are constituent part of many products in the automotive, aerospace, mechanical engineering and construction sector. Furthermore, many nonferrous metals belong to the group of materials that do not degrade and lose their properties in the recycling process. They are integral element of modern recycling processes, which are characterized by high energy and resource efficiency.
STEPS OF SAMPLE PREPARATION
The primary and secondary production of nonferrous metals requires highly accurate analysis of the chemical composition of the metal, its raw materials and intermediate products. In modern industrial production processes, analytical measures for quality control are x-ray fluorescence, x-ray diffraction and optical emission spectroscopy. The accuracy and reproducibility of these analytical procedures depend from perfect sample preparation. HERZOG provides the optimal equipment and procedures for preparation of solid and powder samples without contamination and material loss.
CRUSHING
Herzog crushers are designed for the coarse crushing and pre-crushing of sample material. The analytical fineness required for a subsequent spectroscopic examination is normally achieved with the aid of a disk vibration mill.
Herzog jaw crushers are designed as jaw crushers equipped with one movable and one fixed breaking jaw. This involves pressing the material to be crushed through the moving jaw and against the fixed jaw and crushing it through the application of pressure and impacts. The moving jaw is moved by an eccentric shaft and is thereby forced into an elliptical movement pattern that crushes the material and moves it downwards. If the grain size is smaller than the width of the bottom gap, the crushed material drops into the collecting container. Using no-rebound funnels prevents material from escaping out of the crushing chamber. IN some automatic machines we also integrate double rocker crushers.
Depending on the material being crushed, the jaw crushers can be supplied with crushing jaws made of different materials. One characteristic of jaws made of manganese steel is that they harden further over time with increased use. Stainless steel is recommended when the formation of rust can be expected due to feed material. Tungsten carbide jaws are particularly hard resistant to wear. Their service life is long even when used on hard materials.
With the cone crusher, the crushing occurs in the gap between the crusher jacket and the crusher cone. This gap opens and closes circumferentially as a result of the eccentric tumbling motion of the crusher cone. The advantage of the cone crusher is that the material is crushed continuously by pressure and friction. There is no alternating working stroke and no-load stroke as occurs with the jaw crusher. The HP-CM/AUT is a crusher especially designed for automotive catalyst. Entire monoliths can be crushed down to a particle size suitable for fine grinding. The crushed material is captured in a special container (3 l), which can be easily removed by the operator. The material loss is reduced to a minimum and cleaning of the crusher is achieved by compressed air.
PULVERIZING
Grinding and pressing is a time-saving and cost-saving sample preparation procedure that is used in the analysis of many inorganic and organic materials. Using powdered samples not only allows the chemical composition to be determined, it also permits the use of X-ray diffraction methods (e.g. cement, salts) for some applications in order to determine the mineral content.
Prior to pressing, the material must be finely ground in order to guarantee sufficient homogeneity. HERZOG offers a wide variety of disk vibration mills in different sizes and configurations for the grinding of sample material. Very hard materials (e.g. silicon carbide) can also be ground down to a grain size that is sufficiently fine to guarantee a high-quality analysis. Along with the program parameters, the attainable fineness is also dependent on the following factors:
- Material
- Input quantity
- Grinfing aids used
- Grain size when out in
Generally, a grain size that permits an analysis is obtained after about 60 seconds in the case of most materials. If milling is performed for longer, agglomerations and material accumulations occur in the grinding vessel in the case of specific materials.
To perform the analysis by means of RFA, it is often necessary for the sample material to be ground to a grain size of < 75 µm. The grinding vessels must be made from wear-resistant materials in order to guarantee sufficient abrasion resistance. This applies particularly when the sample contains very hard mineral phases and has abrasive properties (e.g. clinker, silicon carbide, etc.).
This means that during grinding, there is inevitably abrasion of the used grinding stones and of the grinding vessel. Depending on the application, the grinding vessel should be suitably hard and should have a chemical composition that does not contain any elements that are of analytical interest. Different grinding vessels are available in order to prevent the entry of elements that are relevant to the analysis.
The automatic mills are especially suitable for preparing precious metal bearing materials because the machine offers various cleaning options to avoid cross contamination. Three cleaning features namely compressed air, sand cleaning and wet cleaning allow a sufficient material removal. Using the different cleaning functions, cross contamination can be reduced to a low ppm-level. Furthermore, spoon sampling during the material input provides the possibility to pre-contaminate the grinding with the following sample. The final particle size after ± 30 seconds of milling is commonly 90% below 50µm. Grinding vessel, ring and puck have to be made from chrome steel in order to avoid line overlapping by elements introduced by the grinding stones.
PELLETIZING
Grinding and pelletizing of sample material for XRF and XRD spectroscopy is an established procedure not only within the primary extractive industry but many industrial processes. HERZOG offers a wide range of different equipment from manual machines to fully automatic laboratory solutions. For sample pelletizing HERZOG provides manual and automatic machines. For manual applications with small or medium sample loads following models are available: TP20, TP20E, TP40, TP 40/2d, TP60, TP60/2d, HTP40, HTP60. All standard pelletizing procedures can be completed using manual pellet presses. The sample material is filled in manually. Dependending on the used model the pressure is generated manually or by an electrical hydraulic unit.
The automatic pellet presses HP-MP, HP-P, HP-PA, HP-PD6 are automatically dosing the ground material into the press tool. After pressing excess material and dust is removed from the steel ring. In the HP-P a second press tool can be used as option to avoid cross contamination between two divergent material types. The ready pellet can be automatically transported to the analyzer. Following analysis the ring is automatically cleaned and stored in a ring magazine. The HP- PD6 is a special pellet press for pelletizing of samples for diffractometry analysis. Few grams of sample material is pelletized into a ring using very low pressure. For stabilizing the material within the ring an aluminium button is inserted using a special backloading procedure.
Depending on the analytical requirements, it is possible to choose between four standard pressing methods:
FREE PRESSING
Free pressing is the lowest-cost pressing method because no consumables are required. Precise dosing of the sample material is also not required.
TWO COMPONENTS PRESSING
2-component pressing: Pressing of 2 components requires an additional work step, but also offers the possibility of preparing small sample quantities for analysis. The refill magazine (e.g. boric acid, Boreox) is dosed and pre-pressed in an initial work step. A special pressing tool cover is used for this. The actual sample material is then pressed into the prepared matrix in a second pressing step.
PRESSING IN AN ALUMINIUM TRAY
Pressing in aluminium cups: For pressing in aluminium cups, the plunger should have a suitable venting groove in order to prevent compression of gases in the plunger. Aluminium cups are available in various diameters. Aluminium cups have the advantage that no significant costs are incurred if the samples are to be archived. Nevertheless, aluminium cups offer no guarantee with regard to eruptions occurring on the edges.
PRESSING IN STEEL RINGS
Pressing in steel rings: Using steel rings offers far-reaching advantages over the other pressing methods with regard to use in automated sample preparation systems. Using steel rings reduces the risk of contamination in the spectrometer by preventing eruptions on the sample edge. However, high costs are incurred if the re-useable rings must be archived. Two rings types are available for pressing in steel rings (Ø 40 mm & Ø 51 mm).
A three-stage brush system can be used to clean used steel rings after the analysis. This can be used with both manual and automatic presses. On manual presses, it is placed manually into the ring and is then removed manually. In automated pressing, the cleaning runs entirely without the operator’s intervention. The empty rings are then automatically stored in the internal magazine.
Almost no additional binding agents for, e.g., catalyst material are necessary to achieve a high quality pressed pellet with a smooth surface. Cleaning of the automatic press is commonly done by means of compressed air. If cleaning by air is not sufficient, a Mylar foil can be used to cover the pressing tool. The pressed pellets can be prepared by using the automatic pelletizing press HP-PA, which can be connected with the pulverizer HP-MA in a linear automation. This allows batch processing of up to 100 samples with a minimum work load.
REPRESENTATIVE SPLITTING
Representative sampling of secondary raw materials is an important prerequisite to ensure a reliable physical and chemical analysis and in the end lot value determination. After the primary sampling, size-reduction has to be undertaken in such a way that the final aliquot presented to the analytical laboratory displays the lot as much as possible 100 %. The relative sampling variation (RSV) of the sub-sampling to realize the size reduction should be less than 5 %. The prospective RSV has to be determine for each new application with an at least 5-folded simple replication experiment to ensure a full conformity to a representative operation. Representative splitting is of particular importance in PGM recycling but also many other material and commodities sectors like, e.g., mining, food, pharma, secondary raw materials, and agricultural products.
FUSION PROCESS
Fusion is an extremely efficient method of sample preparation for various analysis methods such as X-ray fluorescence, ICP and AA. The term fusion normally covers the mixing of a sample with a fusion agent, fusing the mixture and pouring in the form of a glass bead or dissolving in an acid solution.
Fusion is the best method when standards or sample material do not have a consistent matrix. This is normally the case with exploration, environmental and geological samples including mining material, minerals, clay, ores, dusts and waste materials. It is also often used with mixing materials such as cement, catalysts and electronic materials.
IMPROVING THE ANALYSIS RESULTS
Preparation with the aid of the fusion process results in a significant improvement in analytical accuracy. There are various reasons for this. Firstly, samples that have an identical chemical composition can differ from each other in terms of mineralogy and particle size. This alone can result in different counting rates in the analysis instrument. The fusion process eliminates these factors and thereby increases measuring accuracy. Secondly, dilution occurs in fusion through the addition of a fusion agent. This leads to a reduction in the interaction between the elements being analysed and a reduction in the so-called matrix effect. Thirdly, fusion makes it significantly easier to perform a calibration. On the one hand it is possible to produce perfect matrix-matched standards for a large number of materials. On the other hand, synthetic standards can be used if no referenced standards are available. Accordingly, synthetic standards can be produced for almost any material without the complex regression analyses for creating calibration curves.
AVOIDING ERRORS
Fusion is an extremely important part of material analysis by way of X-ray fluorescence, ICP and AA. Fusion is an excellent method for avoiding errors that can have a negative influence on the accuracy of the corresponding measuring method. Fusion is also the simplest and most reliable method for preventing errors arising from inhomogeneous particle distribution, mineralogical effects and insufficient surface quality.
IMPROVING THE SAMPLE SOLUTION
Fusion can easily dissolve oxidic samples that are difficult to prepare with the aid of acidulation. Conventional acidulation of resistant material such as silicates aluminium, zirconium etc. takes a long time and often only results in incomplete dissolving. However, complete sample dissolving is an extremely important factor for improving the accuracy and reliability of analysis results.
PERFECTLY SUITED TO FLUORESCENCE ANALYSIS
The fusion process produces a glass bead that is perfect for X-ray fluorescence instruments. The glass bead has the optimum dimensions, displays excellent homogeneity and has a flat surface.
TIME SAVING
A typical fusion process seldom takes longer than ten minutes. In contrast, acidulation takes hours before a satisfactory result can be obtained.
SAFETY
Fusion is a reliable sample preparation process that requires no harmful acids and reagents. Special safety measures are therefore not necessary. The fusion process is especially safe when it is done with apparatus that has automatic sample handling, fusing and pouring of the melt.
THE FUSION PROCESS
The most common method is borate fusion. This involves fusing a sample with an excess of lithium borate and in the form of a glass bead with a flat surface. During the fusion process, the sample’s material phases are converted into glass-like borate, which results in a homogeneous fusion bead that is perfectly suited to X-ray fluorescence analysis.
The finely ground sample material is first mixed in a crucible with a borate fusion agent (usually lithium), consisting of 95% platinum and 5% gold. The crucible is then heated to temperatures in excess of 1000°C until the sample is dissolved in the fusion agent. Movement of the melt during the fusion process improves the homogenisation of the material still further. A wetting agent (bromide, iodide, fluorine) can be added in order to support the separation of the melted material from the wall of the platinum material.
