Searching for the elusive Gold and Silver metals

Searching for the elusive Gold and Silver metals

What happens when it is not readily visible and in free gold form?

You have to “see” where it is hidden – Handheld XRF can do that  either directly or indirectly

Multiple Readings for Multiple Elements allow you to discriminate and isolate the elements that follow the Gold and Silver.

Using Geo Statistical software it is possible to map the data collected by Handheld XRF from a specified location and plot the main elements vs the precious metal content measured to discern which mineralizations are richest in precious metals  and will allow quicker screening of large quarry areas.

Let us discuss the advantages and limitations of Handheld XRF analysis in situ for gold and silver analysis vs results you get from say ICP and Fire Assay in the lab.

In both ICP and Fire Assay you destroy the matrix of the sample which liberates the Gold and Silver from the matrix and allows a chemical process of collecting the precious metals using collectors like Bi or Pb, which alloy with the gold. A second step which takes the metal slug off the bottom of the fused flux from the fire assay and cupels it on a magnesium refractory which allows the collector and other base metals to permeate the cupel and leave the gold/silver behind, The resulting alloy can then be treated in nitric acid to dissolve the silver and leave the Gold. That gives you a mass of gold per gram of ore and allows you to ascertain the gold content of the ore. Using ICP we chemically dissolve the matrix into a solution of strong acid, very often we use a complexing agent like an amine to concentrate the Gold and or Silver before reading the resulting solutions on the ICP. In XRF we are analyzing whatever volume of sample is being excited by the XRF beam. Then we generate secondary X-rays in the ore based upon its elemental profile. The larger concentrations of elements will have the strongest x-ray response and that translates into higher counts. Unfortunately, the process is not linear in response as elements with higher atomic numbers will absorb radiation emitted by lower atomic number elements giving erroneous responses unless you correct for this absorption and enhancement effect. Fig 1. Schematic of a Handheld XRF showing the locaion of the x-rayt ube and detector and the barriers between the x-ray source and detector and the sample. The close proximty allows for relatively low powered instruments to produce reasonable x-ray flux volumes  Fig 2 -Results are typically available in a few seconds . Counting for longer improves the precision of the analysis and reduces the uncertainty (+/-) figure. A result is deemed to be significant at 3x the uncertainty value Fig 3        The volume of sample penetrated that produces secondary x-rays that can be measured by the detector and the escape depth for x-rays from different matrices gives a good indication of whether your measurement parameters are meeting x-ray physics constraints especially for Gold and Silver analysis For most ores Au can occur in several forms – free gold (not chemically bound) – Gold associated with other complex chemical formations like Arsenopyrites and thus not readily accessible to be measured. The limitation of XRF is we are measuring a very small sub sample of the ore and the Au distribution may not be homogeneous throughout the ore which means XRF results may be meaningless even if they are positive because of the disparity of gold distribution. If you hit a gold vein – really high results, if you measure ore with 400micron distribution of Au we may not see it, depending upon what other elements are present that could mask the Au x-rays – (elements like Fe, Cu, Zn, As, Pb and Bi may make it impossible for the Au x-rays to escape from the sample to the detector). Using a handheld XRF is only going to work well with prior knowledge of the gold distribution in the samples and the possibility of measuring placer elements which are easier to detect thereby allowing you to create an elemental map of the physical area you are quarrying. The chemistry/geology must be understood to interpret the results obtained meaningfully. Multiple readings of samples and using averaging may give a more meaningful idea of distribution in a defined area. The good news is that programs exist to feed multiple data points into for a long list of elements to be able to do discriminant analysis in which one can easily isolate the areas of greatest mineralization  and thus economic promise.

 Measuring Placer Elements

XRF comes into its own by reliably measuring placer elements – Cu, Zn S as indicators for Ag. As, Fe S for possible Au mineralization. Quartz veins with Carbon inserts can have Au in it. You obviously are crushing the ore that you are feeding into your air tubes to a certain mesh size to get consistent separation based on gravity.  On your gravity air table – your ability to selectively drop out the Au either in free form or in simple mineralization can easily be measured by XRF and give positive indications of amount for optimization purposes. The more concentrated the treated material is in Gold / Silver / PGMs the more reliable the XRF results are. The method is powerful but it’s not a magic wand and must be used with a good understanding of the physics involved. It is largely a surface measurement with x-rays penetrating the top few mm of material ( depending on the kV applied to the Xray tube – the higher the kV the heavier the atomic umber element that can be excited , the deeper the penetration into the sample). By regulating the kV, we can optimize which elements are excited and selectively measure elements of interest. The intensity of the x-rays generated will depend upon the amount of primary x-rays ( from the tube) you pump into the system – the mA setting. In XRF it’s a balance between exciting the sample and being able to read all of the secondary x-rays generated since the detector has a finite counting capacity. We optimize excitation by balancing the count rate into the detector by the count rate output. The higher number of counts you can process the better the sensitivity of the analysis  (ability to discern concentration differences within a sample)and the lower your limits of detection are ( the smallest amount you can reliably detect). This is where the Prospector 3 comes into its own. Dynamic adaptive electronic manipulation of the detector output allows it to process much higher count rates than competitive instruments out there. (3 to 5 times) – this translates into increased speed of analysis and lower limits of detectability for certain crucial elements of interest. Learn more about the Prospector 3 here – https://xrfsco.com/handheld-xrf

 Using Fundamental Parameter Processes to measure ores

XRF is the only analytical technique that will allow us to simulate theoretical Xray intensities once we know the complete matrix constitution. All other techniques are purely comparative requiring reference materials. Modeling the x-ray response and matching it to the measured sample allows meaningful iterative processes to estimate the actual concentration in the measured sample. The accuracy of the Fundamental Parameters approach is based on how close the sample is modelled (all elements present in the sample). As you can imagine the mathematical computation behind our Fundamental Parameter approach is very sophisticated and really comes into its own when we can match the actual measured sample spectrum against the theoretically generated spectrum. The closer the match the better the simulation works for unknown samples. Therefore, using a hybrid approach with some known reference materials allows one to create a regression calibration based on FP constants. The method is extremely versatile and quite robust. Having said that the FP method cannot compensate for the mineralization effect or the particle size disparity. Samples need to be ground to an 80 – 100 mesh size to give reasonable XRF results. Measurement of Ca element in mixtures of compounds like CaCO3 and CaSO4 will lead to erroneous results for Ca. With mixed oxides it is best to calcine or fuse the sample to convert the compounds to oxides. In conclusion while measuring samples in situ in a sample bag is very appealing and is often the driving force behind using Handheld XRF in the field , the accuracy of the analysis is highly dubious unless the samples have been reduced to a meaningful particle size and the mineralization is known, so that data produced can be interpreted correctly. XRF works well on homogenized samples of uniform particle size and known mineralization.

Method of Analysis

The majority of natural samples are heterogeneous. So, sample preparation before measurement is strongly recommended, especially for light element analysis. Samples must be crushed, ground, mixed and placed in 32mm XRF cups. Six different types of ores and concentrates were analyzed with ElvaX ProSpector LE: iron, copper, chrome, lead, tin, silver, and gold ores. ProSpector 3 has 2 main geology calibration modes: «Mining» mode and «Mining 2pass» mode. In «Mining» mode only one pass with one beam settings (35 kV voltage) is used. It allows to determine elements from Cl to U in low concentrations (until ~15%). This mode is best for geo exploration and analysis of low-grade ore. Advantage of this mode is absence of influence of LOI (loss of ignition) to measurement results. «Mining 2pass» mode consists from two passes (35 kV and 12 kV voltages) and allows to analyze light elements (Mg, Al, Si, P, S). Mining 2pass mode is used for analysis of high grade ores, minerals and silicate materials. It is assumed that LOI is low in this mode. For more deep analysis, LOI can be calculated using any other technique and then added to measurement result as undetectable element.  

Results of measurements of multiple ores showing correlation of Measured vs Certified Values

Examples of Measurements in different Ore types showing the versatility of the Handheld XRF especially for Gold and Silver ores From the above results it can be clealy seen that Handheld XRF is a huge advantage when measurements are made on samples that meet XRF constraints. For more information Contact Us

Find out how we can facilitate your exploration goals

The Rhodium Rodeo

The Rhodium Rodeo

Auto Catalysts are the new hot commodity in the metals recyling world

Rhodium prices have increased astronomically and Palladium and Platinum have followed suit.

This has driven the scrap metal business into a frenzy and the analysis of auto catalysts for the buying and selling of these commodities has never been more relevant.

The accurate analysis of the precious metal content embedded in a ceramic or metal monolith has become paramount as even a few ppm difference can amount to significant differences in the dollars paid and the dollars received.

Analysis parameters

The samples measured need to be representative of the whole monolith and will require grinding and size reduction for accurate XRF analysis. Although the elements of interest are generally Pd, Rh and Pt, many ancillary elements that make up the monolith will be included in the analysis protocol in order for the Fundamental Parameter methods to calculate the interdependence between elements accurately.

Families of Catalytic Converters

Auto manufacturers consider their converters  to be part of the secret sauce that separates their vehichles from the competition and they will have different typical amounts of Pd, Rh and Pt  on their specific choices of monolith. It is possible to create constrained Fundamental Parameter procedures that are specific to a certain auto make and model for ultimate accuracy.

Commodity-driven analysis at the speed of commerce

A versatile, reliable analyzer preferbly portable or able to be used as a standalone in a lab stand is a really elegant solution for this scenario

Enter the Prospector 3 – Elvatech Prospector 3

  • World’s fastest XRF analyzer (throughput 500 000 cps – more than three times as fast as any other handheld XRF) – highest accuracy within the shortest measurement time, excellent precision
  • World’s smallest (236 х 193 х 68 mm), and lightest (1.05 kg with a battery) handheld analyzer – easy to operate
  • Dustproof and waterproof instrument body, with IP-67 ingress protection rating
  • Automatic collimator changer for small spot analysis of jewelry, welds etc.
  • Folding display – for easy operation in the lab stand without connecting to a PC
  • Highest mobility – up to 16 hours of autonomous operation on a single battery charge, hot battery swap
  • Superior calibration stability, compensation of influence of ambient temperature and pressure variations – no need to spend time for calibration
  • Two CCD cameras for macro- and micro- view
  • Full compatibility with ElvaX PC software
  • Radiation safety: proximity sensor and low count rate detection
Data can be transferred from ProSpector 3 to a PC directly via USB, WiFi

Catalytic converters in cars are used for reduction of hazardous emissions, such as carbon monoxide (CO), hydrocarbons (HxCy) and nitrogen oxides (NOx). These harmful substances are converted into neutral carbon dioxide (CO2), water and nitrogen by catalytic chemical reactions, which are accelerated by three platinum group metals (PGM): platinum, palladium, and rhodium.

Catalyst analysis

Due to a great number of car catalyst types, an amount of PGM’s varies significantly. The fast and accurate testing method is required for the PGM’s content evaluation. XRF provides precise and fast catalytic converters analysis for simple sorting and price evaluation. Usually, a concentration of PGM’s in a car catalyst is much higher, than in ores.

With ElvaX spectrometers it takes just seconds to give the result as opposed to hours or days as in a laboratory. Together with simple operation training and easy sample preparation, they are ideal tools for the daily business for quality control and price evaluation during catalyst’s buying and selling.

Find out more about the Prospector 3

Contact us to setup an online demo – see reference https://elvatech.com/applications/car-catalyst/

Comparing XRD Geometries and a Case Study in using the Seeman-Bohlin Geometry in a portable diffractometer.

Comparing XRD Geometries and a Case Study in using the Seeman-Bohlin Geometry in a portable diffractometer.

X-ray diffraction

What is X-ray diffraction?

X-ray Diffraction (XRD) is a non-destructive technique that provides detailed information about the crystallographic structure, chemical composition, and physical properties of materials. A common analytical technique for the comprehensive examination of the structure of crystalline materials; in other words, scanning a material’s fingerprint. Often used for identifying and quantifying material phases and investigating crystallinity of materials

 

From EAG SMART Chart –

What are the applications of portable XRD?

  • Firstly, Identification/quantification of crystalline phase
  • Measurement of average crystallite size, strain, or micro-strain effects in bulk materials and thin film
  • Determination of the ratio of crystalline to amorphous material in bulk materials and thin films
  • Phase identification for a large variety of bulk and thin-film samples
  • Detecting minor crystalline phases (at concentrations greater than ~1%)
  • Determining crystallite size for polycrystalline films and materials
  • Determining percentage of material in crystalline form versus amorphous
  • Measuring sub-milligram loose powder or dried solution samples for phase identification

Different approaches to XRD Analysis

Bragg-Brentano geometry

 

The Bragg-Brentano geometry is the most used among diffractometers. In the diffractometer the relationship between θ (the angle between the direction of the incident beam and the specimen surface) and 2θ (the angle between the directions of incident beam and the diffracted beam) is maintained throughout the analysis.

 rs and rd are fixed and equal and define the diffractometer- or measuring circle in which the specimen is always at the center.

The geometry is called θ − 2θ geometry if the tube is fixed and the rotation of the specimen and receiving slit are coupled in a ratio θ : 2θ.

It is called θ − θ geometry if the specimen is fixed and both the tube and receiving slit rotate at an equal angle θ.

During rotation of the components the radius of the focusing circle changes.

 

 

Seeman-Bohlin geometry

The Seeman-Bohlin diffractometer can have a fixed tube and specimen. The radius, rd varies with 2θ to maintain the focusing geometry.

 Alternatively, the source and receiving slit rotate at an equal angle θ and both rs and rd vary to remain on the focusing circle. During rotation of the components the radius of the focusing circle remains the same.

For accurate measurement, the diffractometer components have to be aligned in such a fashion that the following conditions are satisfied:

  1. line source, specimen surface, and receiving slit are all parallel,
  2. the specimen surface coincides with the diffractometer axis for the Bragg-Brentano geometry or with the diffractometer circle for the Seeman-Bohlin geometry,
  3. the line source and receiving slit lie on the diffractometer circle

Seeman-Bohlin Geometry versus Bragg-Brentano Geometry

Though the Bragg-Brentano geometry is most used in diffractometers, the Seeman-Bohlin can be a serious alternative.

When it comes to capturing the diffraction pattern, the latter has some advantages.

With equal radius, the Seeman-Bohlin geometry provides double the resolving power of the Bragg-Brentano geometry.

The resolving power is defined as d/ ∆d and is obtained by differentiating Bragg’s law for n=1:

λ = 2d sin θ .

d θ /dd = 1/d tan θ                                   (1)

thus d /∆d = −1 /∆θ tan θ                        (2)

The variation in angle with respect to the specimen, ∆θ, in relation to the displacement along the circumference of diffractometer circle, ∆S, differs for both geometries:

∆θ = ∆S/ 2R for the Seeman-Bohlin (a) and

∆θ = ∆S/ R for the Bragg-Brentano geometry (b).

This is displayed in figure below. For the Seeman-Bohlin geometry the resolving power is:

d /∆d = −2R ∆S tan θ                                  (3)

whereas for the Bragg-Brentano geometry:

d /∆d = −R ∆S tan θ                                   (4)

where R is the radius of the diffractometer circle.

When a square box will be taken as outline of the occupied space the volume differs for both geometries.

For equal occupied space the radius of the Seeman-Bohlin geometry would be 1 /2 √ 2 times the radius of the Bragg-Brentano geometry In this case the difference in resolving power would be about 40%.

 

 

 

 

CASE STUDY OF RESOLUTION OF THE PLANET PORTABLE XRD

 

appnote3-Resolution_of_the_planet

Download our App Note on the Resolution of the Planet Portable XRD when compared to standard laboratory systems

Conclusion

The attainable resolution of the planet compares well to the attainable resolution of a standard laboratory-based instrument. The attainable resolution of the planet is best in class among currently available portable X-ray diffractometers.

References

  1. Design of an X-ray diffractometer (XRD) for a Mars-rover, Master’s thesis R.W.J. Melenhorst DCT 2006.14
  2. Report on Resolution of the Planet – XploreX EU
  3. EAG Smart Chart

 

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What makes Lubrication Oil Additive Analysis a challenge for X-ray Fluorescence Analysis?

What makes Lubrication Oil Additive Analysis a challenge for X-ray Fluorescence Analysis?

 What could be simpler than looking for a handful of elements in lubrication oil samples using your all powerful XRF?

On the surface, this is would appear to be a straight forward analysis, but in reality, the challenge of analyzing light matrix samples (low z elements of C and H with hetero atoms O, S , P, and N) by XRF is constrained by the wide variation in the mass absorbtion characteristics between sample types that you would want to analyze against calibration curves obtained from a set of mineral oil standards. 

The data reduction algorithms capability of your XRF software can accurately model the interelement influence coefficients and then apply the necessary corrections. However this requires the use of many calibration standards with independently varying concentrations for the elements of interest since the mathematical model is contrained by a series of linear equations which in theory should be N+1 the number N of elements .

The use of fundamental parameter analysis software improves the estimation of the influence coefficients for additive elements by modeling the entire elemental composition of the sample including the unmeasured elements ( not detectable by XRF)  in an acquisition or series of acquisitions conditions.

 

Two important TIPS

  • 1) Use standards whose elemental concentrations have been randomized and thus varying independently from each other
  • 2) Be sure to get standards that include the Oxygen content for each individual standard so that you can accurately model the Carbon, Hydrogen, and Oxygen contribution to the influence coefficients. or include them in the fundamental parameter calculation.

Given the physical nature of lubricating oil ranging from almost water like consistency to thick solid greases, the sample preparation requirements for XRF prove to be a good intersection for this type of material and the XRF analytical technique.

The lube oil product can almost always be measured on an “as received” basis and empirical calibrations for additives are readily created with a caveat. The added benefit of the fundamental parameter program in XRF allows for greater flexibility and a wider variety of lube oils with widely varying concentrations of elements used as additives to bestow a particular property to the lube oil product, are readily quantitatively characterized for the elemental concentrations of additive elements.

This is particularly important for new oil formulation to ensure the correct levels of additive are present in the oil and in wear metal detection in oil to be able to characterize wear debris with the view to estimating predictive maintenance scenarios

ASTM 7751 – attempts to address this and only a handful of vendors actually achieve accurate, precise analysis using their advanced software features.

 

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How elemental analysis has transformed with time to meet market demands -Laura Oelofse

How elemental analysis has transformed with time to meet market demands -Laura Oelofse

The ever-increasing need for speed that defines our competitive global landscape as enterprises vie to be first to market means supplementary technology needs to change to meet the needs of new processes.

The limitations of static locations, long analysis times with continuous often costly overheads needed to ensure functionality have become stumbling blocks to providing quick accurate answers for many of the questions raised by development engineers about the materials they work with and the products they are racing to put out to the marketplace

Increasing regulation to permeate marketplaces with reliable data and similar methods of comparative conclusions have also driven the need for quicker, high accuracy and reproducibility data to guide product improvement, ultimately inform business decisions and arbitrate buying and selling contracts.

The analytical instrument business has adjusted its product portfolios to meet the growing need of these innovative research, industrial and regulatory organizations and nowhere is this more apparent than the evolution of X-ray Fluorescence (XRF) as an elemental technique over the last 25 years.

From changes in form factors, power ratings, elemental ranges, and sensitivities to inclusion in hybrid technologies XRF and other atomic technologies like Laser Induced Breakdown Spectroscopy (LIBS), these technologies have escaped their surly bonds of laboratory relegation and have soared into history as untethered, portable, and infinitely useful tools. The changes brought about by the handheld, close-coupling lower powered geometries have transformed the XRF and LIBS usefulness and useability and powered their widespread adoption.

The transcendence of these technologies has been possible due to the concomitant miniaturization of strategic components like energy sources and power supplies, detectors, and computing capabilities. These coupled with communication and geo-positional advances like Wi-Fi, Blue Tooth transmission, GPS locators and the evolution of reliable, secure cloud-based storage have driven the XRF revolution. The advent of satellite communication has also improved the adoption of these technologies in remote locations.

What once filled an entire laboratory room has been reduced to bench tops and field portable equipment. The portability and “gun-like” form factor of handheld devices have been major advances in taking the analysis from the laboratory to the field, exploration site or production line. The transformation has also come with an increased complexity in data characterization and reduction to produce meaningful scientific measurements. The evolution of Fundamental Parameters techniques and the incorporation into these smaller XRF units have revolutionized the speed and accuracy of analysis while relaxing some of the more stringent mathematical requirements to satisfy linear equation models of conventional XRF technology.

What that means for you the process control engineer, exploration geologist, metallurgist, scrap metal dealer and mining superintendent is fast, on the spot analysis with defined precision and comparative accuracy to certified reference materials similar in composition to your materials.

Today’s XRF and LIBS analytical equipment offers

  • Increased portability and ruggedized form factors to withstand the rigors of field deployment allowing real time analysis at the site of production
  • Low power requirements allowing extended operation on battery packs with hot-swapping capabilities without loss of information.
  • Connectivity to transmit results to cloud based database applications via the internet
  • Fast analysis speeds based on major component recognition (especially useful for alloy sorting and grade differentiation in metals)
  • Ease of Use allowing accurate information to be produced by non-technical operators with a high degree of reliability
  • Depot style delivery and returns for serviceability and upgrades to enhance the desirability of ownership

All these features were brought about by industry needs driven by our global shifts in research into new materials, innovations in manufacturing, the increasing demands for raw materials from our mining sectors and the ever-present drive for economies of scale and process improvements.

Looking to the future we see innovation in the analytical instrument business being fueled by emerging technologies and the questions being generated by these pioneers of hybrid materials and engineering processes.

  1. The Internet-of-Things being incorporated into analytical platforms on a large scale to automate analysis to an on demand application for feedback to process control and to drive process variable adjustments in real time to maintain optimal process conditions and products.
  2. The emergence of 3D printing as a mainstream engineering methodology – printing of 3 D Wheel-Tire assemblies as being pioneered by Michelin – the opportunity for real time x-ray camera enabled computer tomography for fast renditions of 3 D process reliability
  3. The re-emergence of Space Exploration by Space-X and all the subsequent supportive technologies to address these new realities and materials
  4. Power technology and power generation of the future – the materials and the fuels and how X-ray Analytical technologies will be a part of the journey
  5. The ever evolving material science sector in its quest for materials with enhanced flexibility, versatility and reliability – analytical instruments designed to measure critical variables with increasing precision and increasing confidence in data produced exploring hybrid analytical techniques like thermal analysis, x-ray diffraction and x-ray fluorescence