analytical techniques in exploration

1. Analytical techniques to identify trace elements AMALA ANIE JACOB

2. Introduction • Elements in a deposit occur in a variety of concentration • Low level elements are undetectable • 19th Century – instrumental analytical methods introduced • “Trace elements” – (elements)very low level • Any element – having an average concentration of <100ppm

3. analytical techniques improved, become more sophisticated • New techniques – ultra trace analysis – more detection capabilities • detect elements of mass fractions ie, <1ppm and 10ppb

4. X- RAY METHODS • Widely used technique • Useful application in analysis of : • Geological materials, steels, cements, archeological samples, forensic samples and environmental samples • XRF technique – most widely used

5. X – RAY FLOURESCENCE • Analyze almost any element in periodic table from Fluorine( Z=9) upwards • New technology determine ultra low atomic no: elements ( B,C,O,N) • Advantages: • Less time consuming • Requires less amount of test sample • Multi element capability with wide dynamic range

6. Analyze both major and trace components in solid, liquid, thin film samples • Drawback: • Poorer accuracy and precision compared to AAS techniques

7. Mechanism • XRF working principle- External energy source EXCITE atoms in sample. EMIT X-ray photons of definite wavelength/energy. COUNTING no: of photons of specific energy emitted from sample; elements present are identified and quantified

8. XRF mechanism

9. Application • X-Ray fluorescence is used in a wide range of applications, including research in igneous, sedimentary, and metamorphic petrology • soil surveys • mining (e.g., measuring the grade of ore) • cement industry • ceramic and glass manufacturing

10. environmental studies (e.g., analyses of particulate matter on air filters) • petroleum industry (e.g., sulfur content of crude oils and petroleum products) • field analysis in geological and environmental studies (using portable, hand-held XRF spectrometers) • analyses of trace elements (in abundances >1 ppm - Ba, Ce, Co, Cr, Cu, Ga, La, Nb, Ni, Rb, Sc, Sr, Rh, Zr, Zn) in rock and sediment

11. Energy Dispersive X-ray Fluorescence ( EDXRF) • Analytical tool to monitor urban air pollutants like lead • Semiconductor type detectors • Receive entire emitted spectrum and decode it into a histogram • Require sophisticated electronics and computer software in order to decode the detector output

12. Wavelength Dispersive X-ray Fluorescence (WDXRF) • Use an analyzing crystal to disperse the emitted photons from the sample based on their wavelength and detector receive X-rays of a given energy • Detectors are assembled at fixed angular locations to analyze a few selected elements over and over • Not require heavy use of electronics and computer software

13. X- RAY DIFFRACTION (XRD) • Used to identify clay minerals, mineral analysis and mineral abundance measurements • Modern XRD’s identify solid specimens, compacted powder pellets

14. Mechanism • Powdered sample PACKED in an aluminum holder. PLACED in a diffractometer. BOMBARDED with X-rays. Diffracted rays COLLECTED by a detector. Using computer information collected are shown graphically in the form of diffraction patterns called DIFFRACTOGRAMS.

15. Patterns from an unknown sample is matched with a database of known minerals • Rapid recognition of the minerals of sample in minutes using a computer

16. Electron and ion probe microanalyzers • Beam of high energy electrons focused on about 1-2µm square of the surface of a polished section • Some electrons are refleced back – provide photographic image of surface • Others penetrate to depths of 1-2µm EXCITE atoms of sample GIVE OFF X-rays of specific wavelength. ANALYSED to identify and measure the elements

17.  concentrations of elements from beryllium to plutonium - at low level-100 ppm • Recent models of EPMAs can accurately measure elemental concentrations of approximately 10 ppm.

18. Ion microprobe analyzer • Uses a beam of high energy ions rather than electron source • Analyze a mass of secondary ions that give off from the sample • Measures heavy elements of much lower concentrations compared with electron microprobe technique • Widely used in search of gold and PGM in metallurgical testing

19. Applications • Material science & engineering - used for analyzing the chemical composition of metals, alloys, ceramics, and glasses • Mineralogy and petrology • Study of extraterrestrial rocks (meteorites) - analyze chemical data – study the evolution of the planets, asteroids, and comets

20. AUTORADIOGRAPHY • Alpha and beta particles emitted by radioactive minerals are recorded on photographic films or emulsions thus reveals their location in rock/ore • Identify ultra fine grained radioactive materials in ores • Simple and cheap • Analyze both hand specimen , thin and polished sections

21. CATHODULUMINESCENCE • Luminescence minerals contain fluorescence and phosphorescence • Using ultraviolet fluorescence microscopy – excited beam of electrons are analyzed • Minerals with closely similar optical properties/ which are very fine grained- identified by their different luminescence colors • Eg : calcite v dolomite, feldspar v quartz

22. Using this method – identify features like thin veins, fractures, authigenic overgrowths, growth zones in grains etc.

23. Neutron Activation Analysis • Analyze trace elements using radio nuclides emitted from the element • Here neutrons are used to irradiate and activate the sample • Nuclear reaction between neutrons and isotope of the element PRODUCE radio nuclides with characteristic half lives. EMITS radiation of varying energies MEASURED detectors and analyzed

24. Determine 35 or more elements including Au • Analysis of rare earths (La, Ce, Nd etc), incompatible elements(Hf, Nb, Ta) some trace (As, Co, Sb), minor (Ba, Rb) and major (Fe, Mg, Na) elements • NAA technique application: • Analysis of pure silicon • Trace elements in biological samples, drinking water and analyse cancerous tissues

25. NAA

26. Atomic spectroscopy techniques • Atomic Absorption Spectrometry (AAS) • AAS very sensitive – measure ppb of a gram in a sample • EMR of a particular wavelength – selectively absorbed – atoms of different elements • Selective absorption based on energies needed to excite electrons from one energy to higher energy level

27. Using detector- distinct pattern of wavelengths of any atom- compared with a known quantity • Concentration of target atom in sample increases, absorption rate will also increases proportionally Figure:  Elements detectable by atomic absorption are highlighted in pink in this periodic table

28. AAS

29. Flame Atomic Absorption Spectrometer (FAAS) • FAAS introduces sample into a flame –dissociated into constituent atoms • EMR in the UV/visible part of spectrum, DIRECTED flame, partially ABSORBED atoms • Inexpensive and simple to operate • Some refractory elements not determined – flame temp not hot enough

30. Analyze liquid samples only and relatively large samples required • Slow technique • Analyze single elements / a few elements within a sample • Measurement of large no: of elements – other techniques

31. FAAS

32. Graphite Furnace Atomic Absorption Spectroscopy (GF-AAS) • Sample DIRECTED graphite tube HEATED atomize the sample • EMR PASSED atoms within the tube ABSORB specific wavelength , which is detected and measured • GF-AAS differs from FAAS – higher atomisation temperature (3000K) • 100 to 1000 times better than FAAS • Both solid and liquid samples

33. GF-AAS

34. Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) • Rapid and precise monitoring of upto 50 elements • Principle • Sample solution spectrometer, atomized into a mist like cloud. Argon plasma with a stream of argon gas. ionized argon produces a temp – 7000°C – thermally excites the electrons of the elements in the sample.

35. Excited electrons emitt energy of specific wavelength. • Since the sample contain different elements a spectrum of light wavelengths are emitted simultaneously • Using a detector identifies which wavelength are emitted and intensity is measured • Analyst quantify elemental composition of sample relative to a standard reference

36. Excellent determination of refractory elements with high sensitivity • Much expensive • Detect many elements simultaneously, has much large dynamic range

37. ICP-AES

38. Inductively Coupled Plasma- Mass Spectrometry (ICP-MS) • Both ICP with mass spectrometry technologies are used for elemental analysis by generation of ions • Argon plasma of high temperature, about 10000°C is used to ionize the elements in the sample MS • MS sorts the ions according to their mass/charge ratio electron multiplier tube detector( identifies and quantifies)

39. Advantage : • Analyse about all elements in the periodic table • Detects both metals and non metals at concentration of about ppq • Compared to AAS – high speed prceision and sensitivity • Disadvantage: • Very expensive

40. ICP-MS

41. USES OF TRACE ELEMENTS • indium is a trace element that has been in commercial use  -In flat-panel devices such as LCDs and touch-screen mobiles, indium tin oxide (ITO) is used as a thin coat around the screen.  • Pure silicon is used in making chips in computer • Tantalum is another element that has been increasingly mined for its usefulness in modern technology. It is used as a capacitor for mobile phones.

42. lithium - Rechargeable lithium-iron batteries -widely used in batteries for wireless devices • gallium (a byproduct of bauxite and zinc) - used for solar cells and LED lights • Trace elements are very important for cell functions at biological, chemical and molecular levels - pharmaceutical industry

43. APPLICATION • Biological Materials : forensic analysis (Hair samples, Nails, Blood samples) - Nutrition studies( food, drinking water) • Environmental Materials : River, Lake, Beach sediments, Atmospheric Dust, terrestrial and extra terrestrial matters, pollution studies • Geological Materials :Ocean floor cores, Volcanic lava rocks, Mountain Rocks, Lunar rocks, Mars soils

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