‘We stand today on the edge of a new frontier’ President John F. Kennedy
No, this Journal Comment is not about weapons of mass destruction. Nor is it an anglicized version of the names of folk heroes such as ‘Terreblanche’ and ‘de la Rey’ to bolster the latest pop tune to be sung at cricket matches. Rather, it relates to the analytical sciences and the physical methods of examination of materials. Analytical science was the subject of two papers in the last issue and a suite of papers on corrosion and physical metallurgy in this issue, which are particularly relevant to the Tera Ray topic. My first six months’ work in the mining and metallurgical industry as a chemical engineer was in an analytical section of the Government Metallurgical Laboratory.
This first assignment was to help to handle the crisis of hundreds of samples from the gold mines for uranium analysis. There was no other method for determining accurately the trace amounts of uranium in the gold mine residues other than that evolved at the GML. This involved ultraviolet spectrophotometry after a complex purification using diethyl ether and chromatographic separations on cellulose pulp substrates. It was demanding and accuracy was of the greatest importance as the results were of huge economic significance. All samples were done in triplicate with a standard reference sample in every batch and, if the triplicate results did not agree within certain limits, one was required to repeat the determination. This experience taught us chemical engineers the challenge and absolute necessity of accurate results in all research work of importance and how easy it was to obtain spurious results.
The availability of analytical standard samples were and still are of vital importance. The paper by S. Marsland was a revelation to me as to what is today available and essential to modern instrumental methods. We were handling techniques and equipment that we had not even dreamed about at university and it was a fascinating experience which remained an absorbing interest for the rest of my career. It has been an enduring fascination to witness the extent to which physical techniques have become vital not only in research but in plant control and performance data for the ubiquitous computer systems. The paper by J. de Villiers on the Rietvlei procedure using X-ray diffraction methods, which have evolved since my first experience with the early methods using photographic film to record the diffraction patterns, was particularly intriguing.
I have been fortunate to be able to observe how almost the complete spectrum of electromagnetic radiation has become applicable in the minerals industry. At the high energy end were the gamma ray spectrometers for determination of trace elements after neutron activation giving sensitivities of the order of 10 to the minus 10 parts per billion and the use of multidimensional statistical cluster analysis to identify the sources of diamonds stolen from fining operations. At the next energy level were the X-rays for crystal diffraction determination and for the X-ray fluorescence methods, which have been developed over the decades into online techniques for mineral composition analysis. Coupled with these were the evolution of the electron microprobes and positron probes for quantitative analysis of minute mineral particles.
Next in line were the ultraviolet portion of the spectrum for a host of elements and their complexes using differential spectrophotometry. And the parallel development of spectrometry in the visible light region, which included the atomic absorption methods that have revolutionized the rapid methods of solution analysis of almost all metals of economic importance. The ultimate development in atomic absorption are the induction coupled plasma spectrometers, which are now the standard tool for geochemical prospecting, gold and platinum metals and almost all of the metallic elements of the periodic table. After the visible spectrum are the infrared regions of the electromagnetic waves, with the well-known application of enabling one to obtain images in the dark, as well as multiple reflectance methods to determine layers on mineral surfaces, particularly of organic compounds.
At the other end of the electromagnetic sequence are the low frequency radio waves, which are of little value in analytical methods (unless you consider deep space astronomy, using the new square kilometre array telescopes, a branch of analytical methods). However, the higher frequency microwaves are becoming increasingly important in surveying complete ore deposits using multiple emitters and receptors in a computerized tomographic examination over the depth and circumference of the deposit. Then there are the micro radar survey methods in underground and open pit mining. If we look at the frequency of the complete electromagnetic spectrum, we get the following values (in Hz): Radio waves 105 to 109, microwaves 109 to 1011, Infrared 1013 to 1016, visible and ultraviolet light 1016 to 1017 and the X-rays and gamma rays 1017 to 1021. There is only one band in this spectrum that has not been explored and represents the new frontier in the analytical sciences.
This is the band between the microwaves and infrared lying between 1011 and 10 13 Hz, with the centre point at 1012 Hz. The reason for this gap is that it has not been possible to generate such waves reproducibly and at useful intensities. But now in Australia, methods have been developed to do this and in typical fashion they have dubbed them tera rays to follow on the mega and giga prefixes in common usage in the computer age. This is the new frontier in analytical science. And it is being explored in several major universities, and commercial rights have already been assigned. They are penetrative rays as far as the human body is concerned and there is much excitement in the medical field. As far as I know there has been no reference to mining and metallurgy. So let’s look a little further.
The wavelengths of these rays range from 10 microns, to 1000 microns which fortuitously is the same size range of many mineral particles in slurries in mineral processing. As with the longer microwave region, there will some interaction with water molecules and the hydroxonium ion. Thus the tera rays could be of interest in hydrated species on mineral surfaces. Both these properties make it a potentially useful tool in corrosion studies. The paper on galvanized coating on steel covered with paint layers suggest that the tera rays could be an interesting tool to look at the interfaces, particularly as corrosion is associated with water forming an electrolytic cell. The resolution of the tera rays are several orders of magnitude better than the microwaves used for distance measurement such as in the Tellurometer and perhaps could be of value in establishing rock structures in terms of rock mechanics; and it is not impossible that they could contribute to the holy grail in mining in getting to grips with the valuable metal content on the stope face.
It has been mentioned in the literature that the tera rays are being considered for detecting weapons, drugs and explosives on persons boarding aircraft. Maybe diamond miners could be interested in detecting secreted diamonds on or in persons on the mine. This is a truly new frontier for mineralogists, metallurgists and all those interested in physical methods in plant control, exploration and automated methods in mining. Maybe tera rays will reawaken an interest within the DME and DST and its Innovation Committee and the statutory bodies in longrange mineral and mining analytical frontiers. R.E. Robinson March 2007
- Written by R.E. Robinson
- Hits: 6324