THE VALUE OF MINERALOGICAL MONITORING FOR THE ALUMINUM INDUSTRY – PART 2

In the previous blog about mineralogical monitoring for the aluminum industry, we discussed the added value of accurate on-line and at-line mineralogical monitoring for bauxite ore. The advantages of X-ray diffraction (XRD) and near-infrared spectroscopy (NIR) that provide information about the mineralogical composition and important process parameters of bauxite were discussed. This information is not only important for bauxite mining but also for efficient downstream processing in the alumina refinery.

Step II. Alumina refining

Process

Alumina refineries process bauxite ore to produce alumina, which is then used to extract aluminium metal. Alumina (aluminium oxide) is a white granular material.

Figure 1. Alumina refining process (image courtesy of Australian Aluminium Council Ltd)

The process to produce alumina from bauxite ore is called the “Bayer process”, developed by Carl Josef Bayer in 1888 (figure 1). It consists of four steps: digestion, clarification, precipitation and calcination.

After milling, bauxite is mixed with caustic soda (sodium hydroxide) under high temperature and pressure. Alumina dissolves from the aluminium bearing phases (excluding clays). Undissolved impurities settle down as a fine red mud, which after few recycling steps, is discarded as waste.

The solution of alumina in caustic soda (liquor) goes through further clarification, filtration and precipitation steps. Alumina crystals are recovered from the caustic solution by mechanically stirring the solution in open-top tanks. The precipitated material (called hydrate) is washed and dried at temperatures exceeding 1000°C. The dry white anhydrous aluminium oxide powder (alumina) is cooled and conveyed to storage. Alumina powder is further used to extract metallic aluminium using electrolytic baths. Caustic soda is recovered and returned to the start of the process and used again.

Let’s discuss the effect of mineralogy on the above process. Temperature required for the digestion of diaspore α-AlO(OH) and boehmite γ-AlO(OH) (both called monohydrate alumina phases, MHA) is higher than for gibbsite γ-Al(OH)3 (called trihydrate alumina, THA). Therefore, the temperature for effective digestion of bauxite depends on the ratio between the different aluminium containing mineral phases.

In addition, the consumption of caustic soda per ton of bauxite depends on the amount of silica impurities: clays and quartz. Under certain conditions, these minerals react with caustic soda and consume part of the reagents from the process. Low-temperature digestion suffers from the reagent loss to clays only, but during high-temperature digestion, both quartz and clay minerals react with caustic soda, increasing reagent consumption and costs.

Therefore, the knowledge about the mineralogical composition of bauxite is an important factor that defines the efficiency of the Bayer process.

Analysis of alumina for quality control (QC) and quality assurance (QA)

Mineralogical monitoring not only adds value for the analysis of the raw material bauxite but also for the quality control of the final product from the Bayer process, alumina. XRD is the only suitable tool to distinguish between the different modifications of alumina (eg. α-Al2O3, γ-Al2O3) which defines the quality of dry alumina powder, as well as particle size and impurities.

The knowledge of the different modifications is important to predict and optimize the behavior during the smelting process. γ-Al2O3 is desired for the electrolysis since it dissolves more easily during the smelting process than α-Al2O3. For that reason, the ratio of the different sub-α and α-Al2O3 modifications of alumina must be monitored. The analysis of α-Al2O3 can be done with a classical straight-line calibration of the α-Al2O3 peaks or using full pattern fitting methods. The advantage of using the full information of the XRD pattern is the simultaneous quantification of all sub-α-Al2O3 modifications. Even a small fraction of 0.5 wt.% α-Al2O3 can be detected and quantified. Figure 2 shows a measurement of dry alumina powder using X-ray diffraction. The majority of the sample consists of g-alumina, with only 0.5% of a-alumina.

Figure 2. Automatic γ-Al2O3 and α-Al2O3 quantification of dry alumina using Aeris Minerals, measurement time is 10 minutes.

Impact of particle size

Particle size impacts directly on the rate of dissolution of the alumina in the cryolite bath and is therefore another important variable. Furthermore, fines are an issue from both health and safety as well as a product transport point of view, so particle size distribution needs to be carefully controlled. The ideal particle size distribution is defined between 45μm and 150μm to prevent problems with dissolution in the cryolite bath and the accumulation of fines during processing that cause conveying and process instabilities and health issues.

Figure 3 Typical display of on-line alumina process data

The application of on-line particle size analysis allows aluminium processors to operate more efficiently and to produce a more consistent product for downstream unit operations. Economic benefits in the form of reduced waste, reduced energy consumption, reduced manpower and increased throughput are achieved. The availability of industrially relevant systems, at a cost that can be recovered in a relatively short time, makes on-line analysis an increasingly attractive option.

Red mud – monitoring of waste products using XRD

Red mud is the bauxite residue generated during the refinement of bauxite into alumina using the Bayer process. It is composed of various oxide compounds, including iron oxides which give its red color.

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Depending on the bauxite grade about 1.3 to 2.2. tons of red mud are produced per ton of alumina. The treatment, long-term storage and re-use of the red mud is one of the challenges of alumina refining. The adequate analytical tools for the control of mineralogy, chemistry and physical properties of red mud are essential for the correct, environmentally friendly management of the waste product.

The complete mineralogical composition of the red mud sample determined by XRD is shown in Figure 4. The main part of the sample consists of the insoluble impurities of bauxite (titanium and iron oxides) and products of chemical reactions, which occur during the digestion steps. However, in this example, valuable aluminium bearing phases such as gibbsite, boehmite and diaspore still comprise about 25% of the red mud sample. This indicates that the processing, in particular the digestion, was not executed to the maximum level of efficiency.

Figure 4. Automatic quantitative mineralogical analyses of red mud using Aeris Minerals. Measurement time is 15 minutes.

Comprehensive analysis of bauxite and red mud mineralogy along with the analysis of digestion conditions should be performed to understand the root cause for the lost efficiency.

Value of analytical monitoring of mineralogy and particle size for the Bayer process

Alumina refining is a complex process the efficiency of which is directly related to the mineralogy of the bauxite ore. Fast and accurate mineralogical information throughout the entire process, speed of the XRD analyses, increased safety for the operators and the possibility to automate makes XRD a reliable and economic alternative compared to the traditional analytical methods such as wet chemistry and does justify the initial investment.

In our next blog, we will discuss the added value of mineralogical analyses for the next step in the bauxite-to-aluminum process: the conversion of refined alumina to aluminum metal.

 

Written by: Uwe König, Posted by: Malvern Panalytical – (www,materials-talks.com)

ISO CERTIFICATION: THE NEXT CHAPTER IN THE WROXI SUCCESS STORY

Hello, my name is Mark Ingham and I’m an expert on XRF. In my first blog, I’ll describe the history of WROXI reference materials and the benefits stemming from the new ISO 17034 accreditation.

Let’s take a look at why the WROXI reference materials for XRF have proved so popular over the last 15 years, and the benefits stemming from the new ISO 17034 certification.

The beginnings of WROXI

Do you ever find that inspiration only strikes when you’re faced with the same problem, day-in, day-out? It was certainly true for me when I came up with the idea for WROXI – our ready-to-use kits for making XRF calibration standards.

At the time – the early 1990s – I was working in the Analytical Geochemistry Group at the British Geological Survey (BGS) in Keyworth, near Nottingham, UK. We mostly used single-oxide standards for calibration, which was very time-consuming, and also difficult because the powders did not always fuse very easily.

As XRF is fundamentally  a comparative technique, it relies heavily on the accuracy of the sampling, preparation, calibration and measurement processes

A wide range of oxides

As a result of these difficulties, I began to think – why not mix the oxides of the commonest rock-forming elements together into a single set of standards? That would reduce the number of calibration samples needed, and also make it easier to fuse the powders to get clear, high-quality beads.

So that’s exactly what I did, and the ‘WROXI’ product (short for Wide-Range OXIdes) was born.

These WROXI standards were designed for our clients PANalytical. As time went by, the focus of BGS shifted away from analytical work, and in 2011 BGS decided to sell the facility to PANalytical, which I joined as a staff member.

For a while, BGS leased the laboratories to PANalytical, but when that arrangement came to an end, I moved (literally) just a mile or so down the road, from Keyworth to Tollerton. There, I helped set up a laboratory in The Coach House, which remains the ‘headquarters’ of our WROXI and other standards products today.

Our laboratories in The Coach House in Tollerton are where we make all our WROXI standards… and they’re the first in the world to produce synthetic CRMs for XRF certified to ISO 17034.

Why is WROXI so popular?

Through all these business changes, our WROXI standards have remained pretty much the same. (The only significant change was the introduction of a ‘Base’ set with ‘Cement’ and ‘Pro’ extensions in 2020, so customers in certain industries don’t have to measure more elements than necessary.)

So what’s the reason for WROXI’s enduring appeal? I think it comes down to four key points:

  • Using WROXI standards is quick and cost-effective. Just imagine having to set up an application for (let’s say) the 11 common oxides. Buying the reference materials, working out the fusion parameters, building the application, calibration, and would take months of effort. But with WROXI most of this work is already done, meaning your Epsilon 4 or Zetium spectrometer can be ready to run your samples within a week.
  • WROXI standards are totally synthetic. Unlike conventional reference materials made from stocks of geological samples, soils, fly ash or cement clinker, WROXI standards are made from high-purity, commercially available chemicals, so they’ll never run out.
  • Because WROXI standards are synthetic, we can avoid measurement uncertainties caused by peak overlap between different elements (such as titanium and vanadium), by not including them in the same standard. And of course, mineralogical effects and particle-size effects are eliminated during the fusion process, giving an order-of-magnitude increase in accuracy over pressed powder pellets.
  • The two extension sets make WROXI standards flexible – and we are always happy to develop custom standards containing uncommon elements or different concentration ranges. I recall an industrial recycling company a few years ago who needed to measure tungsten in their samples… as well as 20 other elements! At the time, there were only three reference materials available, none of which supported quantitation of tungsten, so we created a set of custom standards for them containing the entire suite of elements. This then allowed them to use the existing reference materials for validation.
The ‘Base’ WROXI kit contains pre-mixed powders containing the oxides of the 11 common rock-forming elements, ready for fusion into beads using your own equipment. The ‘Cement’ and ‘Pro’ extension kits offer additional elements that are useful in certain industries.

Certification of XRF reference materials: A ‘world first’

There’s also another advantage resulting from the synthetic nature of WROXI standards – we’re able to make them gravimetrically. This opens up the possibility of certifying them to the international standard for reference materials (ISO 17034), which is what we’ve now done with the launch of our WROXI Certified Reference Materials (CRMs).

It’s not been a quick job though – it’s taken two years to go through the ISO 17034 certification process. This is partly because we were the first laboratory in the world to request this for synthetic XRF Certified Reference Materials.

What does this mean for our customers? Essentially an additional confidence boost in the WROXI product. Our laboratories at Tollerton were already accredited by UKAS to ISO/IEC 17025 (the general laboratory standard for testing), but we’ve now had to go much further, by demonstrating that all the processes we use to make our WROXI CRMs meet strict requirements, that all our measurements are traceable, and that every single bottle of the finished product has a certificate and documentation trail associated with it.

The powders now come with the major endorsement of ISO 17034 certification. After 40 years in the XRF business, achieving this is a great milestone for me personally… and of course it further strengthens the ‘analytical chain’ of XRF instrumentation, supplies and expertise from Malvern Panalytical!

 

Written by : Mark Ingham Posted by: Malvern Panalytical (www.materials-talk.com)

16 TIPS TO PROLONG YOUR X-RAY TUBE’S LIFESPAN

X-ray tubes are generally designed to function properly under the most demanding conditions. Where X-ray tubes for benchtop systems would not have to be replaced during the entire system lifetime, the lifespan of an X-ray tube for floor standing systems is typically between 3 and 7 years. This is mainly determined by the way of use and maintenance. So, here is an overview of the main recommendations for optimal X-ray tube usage.

General tips

  1. Keep using your spectrometer and X-ray tube. X-ray tubes should not be left unused for too long, in any case not for more than 6 months. X-ray tubes like to be warm and this keeps the vacuum stable.
  2. Use the Iso-Watt switching feature. This forces the spectrometer to operate at a constant power during the switching between the different measuring conditions. A constant power helps the lifespan of the X-ray tube.
  3. Use the standby setting. In standby setting, the power -and especially the emission current- should not be too high, as this costs lifetime. A high kV setting during standby is no problem, since it helps the tube to remain stable against possible flashes.
  4. Keep the window of the X-ray tube clean. Make sure that no substance spills on the window, and never touch the windows under any circumstance. Not even for cleaning.
  5. Clean samples. When analyzing pressed powders make sure that they are prepared well and don’t crumble inside the spectrometer. Tidy sample preparation is an essential processing step for good analysis. This helps to retain your tube’s lifespan.

Tips for X-ray tube cooling maintenance

  1. Regularly check the condition of the chiller. Cooling water is critical (chemical and physical composition, temperature, flow), as the X-ray tube heats up, especially when operating at full power.
  2. The ideal water temperature. Cold water does not cool better than lukewarm water. The ideal water-in temperature for X-ray tubes is 20-25 °C. In very warm and humid conditions, 25-30 °C is recommended. It is best to always be above the dew point (dew point can be lowered by e.g. climate control in the surroundings).
  3. Clean and uninterrupted flow of cooling water is as important as the cooling water itself. Therefore, the tube’s cooling circuit must be checked and cleaned regularly. If you experience an unusually fast intensity degradation, it is almost certain that the X-ray tube is not properly cooled.
  4. Never us pure de-ionized water for cooling, as this is acid and chemically aggressive.
  5. Place the slit cooler in the correct way.

Tips for the X-ray tube settings

  1. Put the spectrometer on standby setting when the spectrometer will not be used for more than a few hours. This saves lifetime.
  2. Switch off the X-ray tube completely when the spectrometer will not be used for more than 24 hours.
  3. Switch off the water flow within 1-2 minutes when the X-ray tube is switched off completely. NEVER let the water flow for more than 2 minutes after the power is switched off. Otherwise, condensation of water inside the X-ray tube shield can occur.
  4. NEVER switch off the water flow first (inducing an automatic power off), as this can kill the X-ray tube instantly.

Tips to enhance the stability and lifetime of the X-ray tube

Every X-ray tube is designed to be operated at its maximum power. Applying maximum power is absolutely no problem. There is, however, no denying that every X-ray tube will undergo physical and chemical ageing. These ageing processes are driven mainly by high temperatures and high-temperature gradients inside the X-ray tube.

  1. Avoid maximum power if your application does not require it. At maximum power, the physical and chemical ageing processes inside the X-ray tube go faster than at lower power.
  2. Operating at 80-90% of the maximum power already has a significant positive effect on the stability and lifetime of the X-ray tube.

If you unexpectedly need a new X-ray tube, please contact us

 

Written by: Kimberly Oberholz, Posted by: Malvern Panalytical (www.materials-talks.com)

THE VALUE OF MINERALOGICAL MONITORING FOR THE ALUMINUM INDUSTRY

Bauxite is the primary source of aluminum worldwide. Without Bauxite, we could not cover up our leftover food with tin foil, have ladders to climb on or be able to cool our food in a refrigerator or cool our houses in the summer. A major part of the bauxite is the metallurgical grade, which after primary screening and washing, is processed in a refinery. The alumina (Al2O3) is extracted via chemical digestion using caustic soda, following the Bayer process. The waste product of this process is called red mud. The refined alumina is finally converted into metallic aluminum. This process takes place in smelters with a large number of electrolytic baths following the so-called “Hall-Heroult” process.

The efficiency and economics of every step in this process, as for any other ore-to-metal process, is defined by both the chemical and the mineralogical properties and composition of bauxite and alumina.

In the series: “The value of mineralogical monitoring for the aluminum industry” we will showcase the added value of adequate mineralogy control at every step on the way from bauxite ore to the aluminum metal.

Step I. Bauxite mining: Bauxite Ore Grades

Over 70% of the mined bauxite deposits are lateritic in nature (Australia, Brazil, South East Asia). The major constituent is gibbsite, Al(OH)3, with smaller amounts of boehmite, γ-AlO(OH), and diaspore, α-AlO(OH). Apart from the major Al-bearing phases, bauxite contain impurities, like iron oxides (hematite Fe2O3, goethite FeOOH), silica (quartz SiO2, clays such as kaolinite Al2Si2O5(OH)4 ) and titania (rutile TiO2, anatase TiO2).

The ratio between Al-bearing phases and impurities will define the maximum alumina yield (total available alumina) and digestion parameters such as temperature or caustic soda consumption

The digestion temperature is determined by the ratio between gibbsite, boehmite and diaspore. Whereas about 140-150 °C is sufficient to extract alumina from gibbsite, boehmite and diaspore digestion requires 240-260 °C.

The caustic soda consumption per ton of bauxite ore is directly proportional to the amount of reactive silica present (silica, which will react with caustic soda). At lower temperatures, only the silica of the clay minerals is reactive during the digestion. If higher temperatures are applied, quartz will also react and increase the caustic soda consumption.

Bauxite ore high in gibbsite and low in boehmite and silica content has the highest grade as it can be digested at the lower temperature with the lowest caustic soda consumption. Ore high in silica and iron oxides is considered as low grade or waste. Intermediate grade ore, high in gibbsite and boehmite and diaspore, can be refined, but at higher temperature.

To summarize, the most important parameter for bauxite mining and processing are:

  • Available alumina
  • Reactive silica
  • Ratio between Al-bearing phases

These parameters define the overall economics and efficiency of further downstream processing.

How is ore grade defined?

During exploration and mining, bauxite ore bodies are divided into grade blocks. Traditionally this was done using chemical analyses (X-ray fluorescence and wet chemistry) and geological prospecting. However, neither of these methods are comprehensive as accurate mineralogical probs. Wrong determination of one grade block is a loss of about 0.5-1 million USD downstream. Therefore, today more accurate tools, like X-ray diffraction (XRD) and near-infrared spectroscopy (NIR) are used for ore grading.

How accurate is bauxite ore grading using X-ray diffraction (XRD)?

Figure 1. Typical result of XRD analyses of bauxite using an Aeris Minerals benchtop diffractometer. 10 minutes measurement time allows accurate identification and quantification of all mineralogical phases present.

Before going to the real bauxite mine case study, let’s check the accuracy of XRD for bauxite analyses by measuring a set of bauxite certified reference materials from ALCAN.

Figure 1 shows a typical result of XRD analyses of bauxite. Any XRD pattern is a set of diffraction peaks of different intensities, located at certain diffraction angles (2θ), specific to a certain mineralogical phase. The peak positions allow the identification of the mineral phases. The relative intensities of each mineral contribution to the XRD pattern allow quantifying the relative amount of each mineral using the full-pattern Rietveld method [1].

In the example shown in  Figure 1, one of the ALCAN CRMs, BXT-02, was analyzed. This sample consists of nearly 60% of gibbsite and nearly 40% of impurities, including iron and titanium oxides, clays and quartz.

Figure 2. Comparison of total and available alumina as obtained by XRD with the certified values for ALCAN bauxite CRMs

How accurate are these numbers?

Unfortunately, phase composition is not yet being reported for bauxite CRMs; however, using our XRD results, we can calculate the chemical composition and compare it with the certified values.  We get very good agreement (Figure 2) between the certified values and XRD results, including the total alumina (total present Al2O3) and total available alumina values (total extractable Al2O3).

Actual bauxite mine case study using XRD

The results of the measurements with the bauxite CRMs show that XRD is an accurate and fast technique to monitor bauxite mineralogy, providing not only the complete mineralogy of a bauxite ore but also the important process parameters. The following case study trials the method on a set of samples collected from an operating bauxite mine.

Figure 3. Comparison of total available alumina and reactive silica as obtained by XRD with the reference values (wet chemistry)

20 samples from a Northern Brazil bauxite mine were analyzed. The mineralogical composition was quantified and used for the calculation of the total available alumina and reactive silica. The comparison of the XRD results with the reference values (wet chemistry) is plotted in Figure 3, showing a good correlation between wet chemistry and XRD results.

The graphs show that both methods are capable techniques for this application. However, each XRD measurement in Figure 3 took on average 15 minutes, including automatic sample preparation, scanning and quantification; while each wet chemistry data point was manually obtained, took hours and required use of hazardous substances.

Apart from reactive silica, total alumina and available alumina, XRD analyzed the complete mineralogical composition, including the ratio between gibbsite, diaspore and boehmite. All parameters together are available after a single sample test of 10-15 minutes.

The ability to get a comprehensive set of process parameters, speed of the analyses, increased safety for the operators, and the possibility to automate, makes XRD a much more economically attractive alternative to wet chemistry [2].

Bauxite ore grading using NIR

Figure 4. NIR spectra of main bauxite phases and associated minerals

Almost all bauxite minerals (quartz excluding) are spectrally active, therefore they can be identified and quantified using near-infrared spectroscopy (NIR). Figure 4 gives an example of NIR spectra of main bauxite phases as well as common accompanying and alteration phases. All bauxite phases have distinct spectral features and can be easily be distinguished from one another.

Quantitative mineralogical analyses using NIR is different than using XRD. NIR quantification requires a statistical model built using over 100 reference samples, mineralogical quantification of which was done using another primary technique, like XRD. Therefore, NIR can never be more accurate than a primary technique. The creation and modification of a quantification model is a more labor-intensive process compared to XRD.

Although NIR lacks the accuracy and flexibility of XRD, it has a great advantage – design simplicity. On one hand, this makes NIR devices very portable, on the other hand, NIR technology can be easily implemented as an on-line sensor over a conveyor belt. Both portability and on-line implementation are translated into extremely short feedback loops and fast decision making.

Portability makes NIR an ideal tool for the initial exploration of bauxite deposits as well as on the spot troubleshooting during ongoing mine operation. On-line NIR sensor will enable 24/7 bulk monitoring of bauxite run-of-mine. And it can also be used for the calculation of total alumina, reactive silica and total available alumina for low temperature digestive process.

In our next blog, we will discuss the added value of mineralogical analyses for the next step in the bauxite-to-aluminium process: the extraction of alumina from bauxite at a refinery.

 

Written by: Uwe König, Posted by: Malvern Panalytical – (www,materials-talks.com)

THE VALUE OF MINERALOGICAL ANALYSES FOR BASE METAL MINING AND BENEFICIATION – LITHIUM ORES

Increasing demand for effective energy storage used in personal devices, electrical cars, renewable energy storage facilities, boosted the global demand for lithium.

Lithium-ion batteries are not the only industrial use of lithium (e.g. catalysts, lubricants, heat-resistant glass and ceramics, alloys for aerospace), but undoubtedly, the most rapidly growing one.

Two main lithium production sources are hard-rock lithium deposits and lithium brines.

The later are lithium salts-enriched salines in the underground, which accumulate under the surface of dried lakebeds. A great advantage of lithium extraction from brines is lower production cost, which is a natural evaporation process, followed by further processing in a chemical plant. A natural evaporation assumes a low cost, but at the same time it is climate and weather dependent. The evaporation step can take up to a year and even longer, depending on the conditions. Only few regions in the world have economically valuably brine deposits (Chile, Argentina, Bolivia and China).

Lithium hard-rock deposits occur across the globe. The recovery process, although more costly, is not climate-dependent, which makes such deposits a more stable source of lithium. The three main countries producing lithium from hard-rock deposits are Canada, China and Australia. The latter is the leading producer with 18.7 million tons produced in 2018.

Lithium production from hard-rock deposits

Economically valuable lithium containing minerals that occur in hard-rock granite pegmatites deposits are spodumene, apatite, lepidolite, tourmaline and amblygonite of which spodumene is the most common lithium-bearing mineral.

Lithium ore is extracted either using open-pit or underground mining. The further processing can be broken down into the following key steps:

  1. crushing of the ore,
  2. concentration by froth floatation,
  3. thermal treatment in a rotary calcining kiln to convert α-spodumene into its β-modification.

Flotation and calcination efficiency are directly determined by the ore mineralogy. Therefore, frequent, fast and accurate mineralogy monitoring is essential for the optimized recovery rate and stable product quality.

In the introduction blog, we established that X-ray diffraction (XRD) is a fast, versatile and accurate mineralogy probe, which can be easily implemented in the process flow at mine operation and processing plant. In the following case study, we discuss the added value of XRD for the beneficiation of hard-rock lithium ore using samples from an operating lithium mine.

Monitoring of lithium ore feed, concentrates and tales by XRD

In the case study we used 14 samples from a lithium mine, representing the key steps in the lithium ore recovery: ten raw ore samples, one αspodumen concentrate and one tailing after the froth flotation step, one β-spodumene concentrate and one residue of the thermal treatment process.

All samples were prepared as pressed pellets and measured on an Aeris Minerals benchtop diffractometer with a scan time of 10 minutes, followed by an automatic quantification of the mineral phases.

Figure 1. Quantitative phase analysis of lithium ore sample #1 using Aeris Minerals tabletop diffractometer. Measurement time is 10 minutes

Figure 1 shows an example of a full-pattern XRD analysis of a hard-rock lithium ore.

Any XRD pattern is a set of diffraction peaks of different intensities, located at certain diffraction angles (2θ), specific to a certain mineralogical phase. Peak positions enable identification of present phases. The relative intensities of the peaks in the XRD pattern allow the determination of the relative amount of each present mineral. The method is called Rietveld refinement[1].

In the example shown in Figure 1, the main minerals present are spodumene LiAl(SiO3)2, quartz SiO2, albite NaAlSi3O8, anorthite CaAl2Si2O8, minor amounts of lepidolite K(Li,Al)3(Al,Si,Rb)4O10(F,OH)2 and traces of orthoclase KAlSi3Oand beryl Be3Al2(SiO3)6. The rest of the raw ore samples show similar mineralogy, some samples contain additionally traces of tourmaline (elbaite) Na(Li1.5Al1.5)Al6Si6O18(BO3)3(OH)4 and analcime NaAlSi2O6·H2O.

Figure 2. Mineralogical composition of 14 raw and processed lithium samples

The mineral quantification of the whole sample set is shown in Figure 2. Even though the mineralogy of the ore samples is consistent, the relative mineral quantities differ from sample to sample.

This information is extremely important for blending the optimal mixture for consistent input towards the beneficiation plant for further froth flotation.

Samples 11 and 12 in Figure 2 represent spodumene concentrate and tailings after the flotation step. 90% of the concentrate sample (sample 11) is spodumene with the minor amounts of quartz, albite, anorthite and traces of lepidolite, beryl, orthoclase and analcime. The main fraction of the gangue minerals went to the corresponding tailing sample (sample 12), which primarily consists of albite, quartz and anorthite. The mineralogical composition of concentrate and tailing after the flotation step indicates a high efficiency of the flotation process.

The remaining samples in Figure 2, sample 13 and 14, represent β-spodumene and corresponding residue from the calcination of α-spodumene concentrate (sample 11). The mineralogical composition of both, concentrate (sample 13) and residue (sample14), shows a reasonable efficiency of the calcination step. Over 92% of concentrate is the desired β-spodumene phase with minor amounts of anorthite and quartz. The corresponding tailing mainly consists of analcime, however, there are over 7% remaining β-spodumene.

The mineralogical analyses showed that the conversion of α- to β-spodumene during calcination was effective, however, the separation process should be further optimized to increase the yield of β-spodumene in the final concentrate.

Additional XRD-tools for process monitoring

In the above section we analyzed the mineralogy of 14 lithium ore samples, concentrates and tailings and residues. The results identified the weak spot in the process, which can be further improved. However, accurate full mineralogical analysis is not the only process monitoring tool, which XRD can offer.

Any deviation from a normal data spread within a cluster immediately a signals possible issues in the production process.

To summarize, hard-rock lithium recovery is a complex process, heavily dependent on the ore mineralogy. A flexible, fast and accurate mineralogical probe, like X-ray diffraction, greatly improves the efficiency throughout the whole process, provides tools for quick and easy monitoring of the process stability and gives necessary insights for counteractive measures when production issues arise.

 

Written by: Dr. Olga Narygina, Posted by: Malvern Panaltyical (www.materials-talks.com)

WITHOUT A DOUBT: THE FUTURE IS ADDITIVE

The role of material characterization in the next manufacturing revolution

Ever heard of the term ‘prosumer’? If you haven’t yet, chances are you will soon – perhaps you even already are one. Through customization, design involvement, or even manufacturing entire products, prosumerism blurs the lines between production and consumption. Think of personalized sports kits or print-to-order planners – these are prosumerism in action. And now, with the rise of 3D printing, consumers can create whole objects from the comfort of their own homes.

In fact, 3D printing is part of a wider process called additive manufacturing (AM). By connecting materials additively, usually layer-on-layer, AM can deliver greater sustainability, flexibility, and process efficiency. To start with, as an additive process, it generates less waste than its subtractive counterparts. It can also produce more complex parts than traditional manufacturing methods, while its potential for small-batch production enables greater customization and shorter product cycles.

The next manufacturing revolution?

But there’s more. As well as being advantageous to manufacturers, AM could be about to spark a revolution in our entire approach to manufacturing. For instance, by enabling the production of highly complex parts in just a single piece, AM opens up a whole new world of design possibilities. As it becomes more widely adopted, designing with these possibilities in mind will become the norm.

Even more excitingly, AM could democratize the design process. As tools like 3D printers and CAD software become less expensive, design and manufacturing will become more accessible to a greater range of consumers and businesses. This shift can already be seen in the ‘maker movement’ and prosumerism. And with technological developments, the quality and scalability of these products will only increase.

One crucial component

Nevertheless, for this AM revolution to become a reality, we’ll need one important thing: strong materials characterization. Because AM processes normally have fixed parameters, inconsistent material properties result in inconsistent finished component properties. And for AM to become the new manufacturing standard, it needs to deliver goods of consistently high quality. Indeed, lack of standardization, limited material selection, and weak mechanical properties are currently some of the biggest barriers to wider adoption of AM.

Material characterization helps solve these issues. How? By using it to analyze their raw materials, manufacturers can then optimize these materials for the specific AM process used. In this way, material characterization helps prevent common issues such as cracking, distortion, weakness, and poor surface finishes. This is especially important for metal powder bed AM, where a particularly large number of factors affect final component quality.

Solutions for the future

To support manufacturers with material characterization, we offer several solutions. For instance, to enable accurate particle size and shape analysis, we provide a range of laser diffraction and automated imaging systems. These support manufacturers to ensure a spherical shape and good size distribution in their metal powder particles. In turn, this helps them achieve strong flowability, powder bed density, melt energy, and surface finishes in the final component.

We also offer X-ray fluorescence (XRF) solutions to facilitate chemical composition analysis. With this floor-standing and benchtop XRF systems, manufacturers can analyze the elemental composition of their alloys and check for impurities. Several manufacturers are already using our solutions for this, helping them to avoid issues such as cracking.

Last but not least, our X-ray diffraction (XRD) solutions enable accurate analysis of microstructure: the crystalline phases and grain structures within powder particles. Our XRD systems support manufacturers in analyzing and optimizing the microstructure of their powder. In turn, this lets them deliver strong mechanical properties in their final manufactured components – such as strength, fatigue response, and surface finish.

In short, with these solutions, manufacturers can ensure that their AM-manufactured parts perform as effectively as possible. In this way, we’re helping drive the wider adoption of AM across numerous industries, applications, and regions. A new world of prosumerism, efficient design, and high-performance AM products is just around the corner!

Written by: John Duffy, Posted by: Malvern Panalytical (www.materials-talks.com)

EFFICIENT IRON SINTERING PROCESS CONTROL

In this blog we will discuss the added value of mineralogy monitoring at the next step of the ore-to-metal process, iron ore sintering.

Sintering is one of the iron ore post-processing steps to prepare iron ore fines for a blast furnace

Feed for a sinter plant consists of iron fines, coke, and flux (eg limestone). The feed is placed on a sintering bed, where thermal agglomeration (1300-1480 °C) takes place to produce clustered lumps, aka iron sinter (5-20 mm in size).

At a common sinter plant, the following sinter quality parameters need to be controlled:

  • Basicity, CaO/SiO2 – FeO (Fe2+)
  • Sinter strength index, SSI
  • Tumbler index, TI
  • Reducibility index, RI
  • Reduction degradation index, RDI
  • Low-temperature degradation, LTD

All the above parameters are linked to the properties of the mineral phases, comprising iron sinter. The main sinter phases can be divided into iron oxides and silicates, which are gluing the iron oxides together:

Iron oxides: Silicates of SFCAs:
Hematite: Fe3+2O3 Larnite: Ca2SiO4
Magnetite: Fe3+2+3O4 SFCA-a: Silica-ferrites of calcium aluminium, Fe2+ only
Wuestite: Fe2+O SFCA-b: Silica-ferrites of calcium aluminium, Fe3+, some Fe2+

X-ray diffraction (XRD) is a fast, versatile, and accurate mineralogy probe, which can be easily implemented in the process flow at mine operation and processing plant. Since all sinter quality parameters are linked to its mineralogy, XRD is a unique tool, providing in a minimum of time a comprehensive assessment of the sinter quality parameters. In the following case study, we discuss the added value of XRD for the process control at a sinter plant.

Accurate analysis of sinter mineralogy using XRD

For this case study, we used 49 sinter samples from a producing sinter plant. All samples were prepared as pressed pellets and were measured on Aeris Metals benchtop diffractometer with a scan time of 5 minutes, followed by an automatic quantitative phase analysis.

Figure 1 shows an example of full-pattern XRD analysis of one of the sinter samples, used in the study.

Figure 1. Typical result of XRD analyses of iron sinter using Aeris Metals. 5 minutes scans followed by the automatic phase quantification.

Any XRD pattern is a set of diffraction peaks of different intensities, located at certain diffraction angles (2q), specific to a certain mineralogical phase. Peak positions enable identification of present phases. The relative intensities of each mineral contribution to the XRD pattern allows us to quantify the relative amount of each present mineral using full-pattern Rietveld refinement [1].

In the example in Figure 1, the sinter sample primarily consists of hematite and magnetite with 23% of crystalline calcio-silicates (so-called SFCA phases) and 21% of the amorphous phase.

Comparing the XRD result of the sample in Figure 1 with the rest of the samples in the set (Figure 2), we see that mineralogy doesn’t change; however, the relative phase amounts differ from sample to sample.

Figure 2. Combined result of quantitative phase analysis of the entire iron sinter sample set.

Using the stoichiometry of the present mineral phases, the sinter FeO content, the most important sinter property since it is connected to the energy consumption in the blast furnace, can directly be extracted from the mineralogical composition (Figure 1, 2).

FeO quantification is done simultaneously with the quantitative phase analysis and is reported along with the phase composition.

A comparison of FeO values, as extracted from the XRD data, with the reference values, obtained by wet chemistry, is shown in Figure 3. We see a very good agreement between the XRD results and the given reference values. Every red data point on this graph takes 10 minutes on average, including automatic sample preparation, 5 minutes scan using Aeris Metals followed by an automatic quantitative analysis. Compared to a few hours of manual sample analyses using hazardous chemicals, the XRD is a fast and safe alternative. Would you still want to use wet chemistry for routine assessment of sinter FeO content?

Figure 3. Comparison of sinter FeO content as obtained from XRD (red circles) with reference values, obtained by wet chemistry (black diamonds).

Getting more from the same XRD data set

In the previous section we established that XRD is a fast and accurate tool for quantitative analysis of sinter mineralogy and determination of sinter FeO content. However, there are other sinter process parameters, which are dependent on the sinter mineralogy (e.g. strength, degradation index, etc.). Can we extract them from the same XRD data set?

The answer is “Yes”, we can by using a modern statistical method, Partial Least Square Regression, (PLSR) [2]. In short, a statistical model is built using a set of reference samples, for which the value of a process parameter (e.g. RDI, SSI, LTD) is known. Afterward, this model is used to predict the process parameter(s) directly from an XRD pattern. This eliminates the need for additional time-intense physical tests and increases the frequency of monitoring.

We applied the PLSR approach to the sinter sample set used in the case study. Part of the set, for which we had reference values of process parameters, was used to build (calibrate) the corresponding PLSR models. Afterward, the obtained PLSR models were used to predict the process parameters directly from the XRD data. Figure 4 summarizes the results for the studied sinter sample set.

Figure 4. results for the studied sinter sample set

Using PLSR approach we obtained sinter strength index SSI, reduction degradation index, RDI, and basicity. The rest of the sinter process parameters, e.g. low-temperature degradation index, tumbler index, reducibility index) can be obtained using the same approach.

Note that both, automatic full-pattern mineral quantification using the Rietveld method and PLSR analysis, can be simultaneously performed on the same XRD pattern. Thus, a single, 5-minute XRD measurement on the Aeris Metals benchtop diffractometer provides the full sinter phase composition along with all-important process parameters.

To summarize, most of the iron sinter quality parameters (aka process parameters) are determined by the properties of the mineral phases. XRD is an indispensable tool for fast, accurate, and tailored mineralogical analysis, which can be easily implemented into the process flow. XRD can be used not only for the fast-quantitative assessment of the full mineralogical composition of iron sinter and its FeO content. New statistical methods (e.g. partial least square regression) opened up new possibilities and enabled the extraction of relevant process parameters directly from the same diffraction data set, eliminating the need for additional time-consuming, costly tests.

 

Written by: Dr. Olga Narygina, Posted by: Malvern Panalytical (www.materials-talk.com)

OPTIMIZING THE PERFORMANCE OF TITANIUM DIOXIDE AND OTHER PIGMENTS FOR YOUR PAINTS, PIGMENTS, PLASTICS – Q&A

Characterization of TiO2 within the paint and pigment industry is a critical component of paint development. X-ray diffraction and DLS are important techniques as they identify the material and various features like particle size, shape, and size distribution. The physical properties of the final product depend on these features.

Our specialists from Malvern Panalytical shared tips that manufacturers can engage to fully optimize the use of their pigments for high-performance products.

Can we identify the surface treatment of TiO2 pigments with XRD?

If the surface capping entities are crystalline then they can be observed in X-ray diffraction (XRD) pattern. Moreover capping changes the size, size distribution and shape of particles which can be observed in Small Angle X-ray Scattering (SAXS) experiments which can now be done on a multipurpose Empyrean diffractometer.

Why the peaks in XRD become broader with decrease in particle size?

A diffraction peak originates from volume which is exposed to X-rays. The broadness of a diffraction peak is governed by two properties: size and strain of crystallites within this diffraction volume. When crystal grow to smaller sizes and the effect of defects in producing strained crystals is pronounced which results in producing broad peak in a diffraction pattern. But broadness is only partly due to strain. Size effects originates since distribution of coherently scattering domain (which produces diffraction intensity) increases with smaller sizes. For amorphous material it is almost truly randomly oriented, hence the peak is broadest.

TiO2 is UV light active ……How could we use in paints and it may damage the paints?

The UV active TiO2 produces radicals which break down the adjoining chemicals especially polymers. This leads to weathering of paint.

For agglomeration tendencies of pigments in actual paint products, how can we use DLS and XRD to assess this?

One can study agglomeration by taking successive SAXS scans which will show change in shape, size and size distribution of particles within the sample.

How can we distinguish nanoparticles and amorphous using SAXS

SAXS is sensitive to “particle” size, shape and size distribution only, it is not sensitive to crystalline nature of material. XRD on other hand is sensitive to crystalline nature, hence one must perform XRD scan of sample to distinguish between crystalline nanoparticles and amorphous particles.

How about the hematite based pigment. what is the advantage and disadvantage comparing with TiO2?

Hematite pigment is a non-white colored pigment that can be identified and quantified using XRD. With Cu K-alpha radiation, it produces fluorescence. This makes an higher background within an XRD scan and thus make it difficult for phase quantification. Usage of multi-core optics in combination with 1Der detector solves the problem of fluorescence and hence makes it possible to identify and quantify hematite in extremely low quantities.

Written by: Tamal Mukherjee, Postes by: Malvern Panalytical (www.materials-talk.com)

NEW Ferroalloy CRMs

Our partner ARMI | MBH team is continuing their work to develop more new products to ensure that they can provide the products you need for your analytical testing.

Ferroalloys are binary or ternary alloys containing iron alloyed with one or two additional elements. While often produced as an intermediate product for iron and steel manufacturing, some ferroalloys are used as final products; for instance, ferrosilicon is used as a heavy media in gravity separation of diamonds during kimberlite mining.

Ferroalloys are typically produced in furnaces by reducing oxides using carbon while being mixed with iron. The chunky material produced in the furnace is then crushed and milled into a powder and homogenized. The powdered ferroalloy can then be used as is, or mixed into a melt to alter or control the alloy composition.

In addition to the primary alloying elements, ferroalloys may contain additional elements at minor or trace levels, depending on purity and specifications. Careful monitoring of major elements is necessary to control the final ratio of alloying elements, monitoring of other elements is necessary to maintain the desired purity threshold and to ensure the final product meets specifications. In addition to being certified for the major elements, these four ferroalloys are certified for more minor and trace element values than any comparable CRMs available.

ARMI MBH has released four new ARMI ferroalloy CRMs in powder form in approximately 100g bottles to their portfolio.

One of the most common ferroalloys is, high-carbon ferrochrome which is used almost exclusively in the production of stainless steel and high chromium steels. We recently released high-carbon ferrochrome, IARM-FCrP-20, with Cr certified at 68.8 wt%, Fe at 20.6 %, and C at 8.6%. It is also certified for Co, Cu, Mg, Mn, N, Ni, O, P, S, and Si, with informational values for 20 other elements.

Ferrosilicon is utilized for many uses including the manufacture of cast iron, other ferroalloys and silicon for corrosion-resistant and high-temperature ferrous silicon alloys. Our newly released ferrosilicon, IARM-FSiP-20, includes Si certified at 77.0 wt% and Fe at 21.8%. It is also certified for Al, C, Ca, Co, Cr, Cu, Mg, Mn, Mo, Nb, Ni, P, Ti, W, Zn, and Zr with informational values provided for 21 other elements.

To deoxidize steel, ferromanganese is often used which helps to reduce issues with tensile strength, ductility and toughness caused during the production process. Ferromanganese, IARM-FMn-20, was recently added to our portfolio as a powder with Mn certified at 79.7 wt%., Fe at 16.6%, and C at 1.13%. It also has certified values for B, Co, Cr, Cu, Mn, N, Ni, P, S, and Si. Informational values are provided for 22 more elements.

Lastly, ARMI MBH also added ferroboron powder, IARM-FBP-20, to our portfolio with B certified at 18.4 wt% and Fe at 77.0%. It also has certified values for Al, C, Ca, Cr, Cu, Mn, Mo, N, Ni, S, Si, Sn, Ti, V, W, and Zr. Informational values are provided for 18 other elements, including Fe.

 

Written by: James Haddad PhD – Posted by: ARMI MBH (www.armi.com)

THE USE OF XRD FOR ADDITIVE MANUFACTURING OF METALS

Many manufacturers are now looking at metal powder-based additive manufacturing (AM) as a realistic alternative to more traditional manufacturing processes such as casting, forging, and machining. While AM can be expensive it can deliver huge advantages in sustainability, efficiency, and flexibility and requires less raw material consumption than subtractive processes. Parts produced through AM can also be made lighter and more complex, delivering efficiency during use.

A major difference in traditional metal fabrication processes compared with AM processes is the heating-cooling regimes involved. For AM processes, such as selective laser melting (SLM) and electron-beam melting (EBM), the heating-cooling regimes are very fast and location-specific, which can lead to different microstructures than those obtained with conventional processes, even with the same alloy composition. This is important as many engineers are looking to achieve similar microstructures to those achieved with conventional routes.

Consistent metal powder does not necessarily mean consistent properties

Metals can crystalize in different phases (ie. atomic arrangements) that have very different properties. As an example, the different phases of steel are illustrated in Figure 1. The pathways to phase formation in traditional processing are well-known, but in AM a different heating-cooling regime or different atomizing gases can produce products with a different phase composition and, therefore, different mechanical properties. When this powder is melted and rapidly recrystallized during an EBM or SLM process, there is further potential for phase transformation to occur. Grain microstructure can also be affected by processing conditions. It is more difficult to control grain structure in an AM manufactured part and this often results in large grain sizes compared with other methods.

Most engineers and metallurgists are looking for a fine grain structure since this improves material strength. This is why post-treatment is still commonplace for many metal AM processes. Grain orientation (also known as texture) is also important because a textured grain orientation can substantially change mechanical properties such as chemical reactivity, strength, and deformation response. This may lead to improved component strength or weakness, and premature failure.

Residual stress is another important characteristic of AM parts. Residual stresses are stresses that are retained in a component after manufacture and act in addition to any externally applied stress, increasing the risk of mechanical failure. AM components are more prone to residual stress due to highly localized cooling and rapid phase transformations that give insufficient time for stresses to relax to their equilibrium crystal structure. Residual stresses can occur anywhere in a material, but those located near a crack, pore, or at the surface of a component are of greatest concern since this is where stresses become most concentrated.

Why XRD is an important analytical tool

X-ray diffraction is a non-destructive analytical technique used to identify and quantify phases in a material. Every crystalline phase produces a characteristic diffraction pattern (e.g. fingerprint) as illustrated for steel in Figure 1.

Illustrations of the crystal structures of Austenite, Ferrite and Martensite and their corresponding diffractionpatterns
Figure 1: Crystal structures of Austenite, Ferrite and Martensite and their corresponding diffraction patterns

In addition to phase analysis, X-ray diffraction can also be used to analyze microstructural features such as texture, residual stress and grain size. Texture produces systematic deviations of peak intensity from the characteristic diffraction pattern of a phase. The intensity deviation can be used to quantify the fraction of grains in a certain orientation by tilting and rotating the sample in the diffractometer

A tensile or compressive residual stress will change the atomic spacing of a phase, which will produce a shift in the diffraction peak position. This can be measured with high sensitivity by X-ray diffraction. A series of measurements determine how peak position varies with sample orientation relative to the incident X-ray beam, which can then be used to precisely determine the atomic strain. If the elastic constant of the material is known, then the stress can be calculated.

X-ray diffraction can also be used to analyze grain size. Small grain sizes produce a broadening effect in the diffraction peak width that can be used to quantify crystallite sizes <200 nm. This makes X-ray diffraction a powerful technique to quantify the size of nanocrystalline materials. Peak broadening may also be produced by defects, such as dislocations or stacking faults, that are created during processing. Analysis of multiple diffraction peaks can be used to separate and quantify both size and defect concentration. In addition, area (2D) detectors can be used to image the Debye diffraction cone, which can reveal large grain sizes. New image analysis techniques can calibrate and quantify grain sizes larger than 10 µm.