Monday, 2 February 2015

In Conversation with Philip Gray- mineral processing visionary

I first met Philip Gray in the mid-1980s when he presented an interesting lecture to the final year mineral processors at Camborne School of Mines on the limitations of comminution and flotation in the processing of complex sulphide ores. At that time he was President of the Institution of Mining and Metallurgy (IMM) and was an independent consultant, working, amongst other things, with Prof. Noel Warner of the University of Birmingham on the Warner Process for smelting zinc and lead from low-grade ores.  Following on this theme some 20 years later, he presented a keynote lecture at Pyrometallurgy ’07 in Falmouth, highlighting the natural advantages of pyrometallurgy in the processing of ores. He argued that reactions are much faster at high temperatures than they are in slurries or aqueous solutions, and mineral characteristics are lost in melts, making the reactions controllable by known universal thermodynamic and kinetic laws. Separation by differential melt solubility or volatilisation permit recoveries that are impossible by mineral processing methods. Since that time he has remained a strong advocate of the Warner Process and although now, at 88 years of age, he is retired, he still has a keen interest in the minerals industry, so it was a privilege to discuss with him his career and thoughts on mineral processing.

Philip Gray graduated in 1947 with an ARSM and BSc in Metallurgy from the Royal School of Mines, London, and has been engaged in the extractive metallurgical industry ever since. His distinguished career has covered all the disciplines in his chosen field, including research and development, engineering and design, business development and consulting.

Following his first role as a Research Officer at the Atomic Energy Research Establishment, he continued his R&D activities at the Commonwealth Science and Research Organisation in Melbourne, Australia from 1951 to 1955 where he worked on hydrometallurgical methods of extracting uranium from Australian mineral deposits. In 1955 Philip returned to the UK and joined the Research and Development section of the Imperial Smelting Corporation at Avonmouth, and became Technical Manager in 1971.

From 1978, he became an independent metallurgical consultant engaged by many mining companies worldwide. Apart from working with Professor Warner he was involved with Research and Development into extracting rare earths. He was elected President of the IMM in 1984, and in the same year was made a Fellow of the Royal Academy of Engineers. In 2013 he was awarded The Institute of Materials, Mining and Minerals Futers Gold Medal, for outstanding services to the international minerals industry, an accolade he shares with another of my interviewees, Tim Napier-Munn.

He has been a great advocate of the Warner Process and I asked him what it is about the Warner Process that he finds so attractive? Did he think it will ever be seriously adopted by the industry? When Noel Warner first came up with this process for recovering zinc and lead from mixed sulphide concentrates, Philip hailed it as novel and feels that it still is. Using the sphalerite mineral to be desulphurised by metallic copper and then recycling the copper mattes for desulphurisation by air to generate heat is “a neat idea” as it vaporises zinc to be condensed using the Imperial Smelting Furnace technology. It also recovers lead and copper if present. Operating at around 1000C the processing dynamics are very fast compared with flotation and electrowinning.

He remembers how Noel got a pilot plant built and operated in the University of Birmingham, but not greatly to the University’s pleasure! However it demonstrated that the closed circuit could be worked on a big scale, and a number of people were attracted to come and see it, but enthusiasm was not overwhelming. Philip feels that this response was to a considerable degree based on long established industry opposition to all things new, and also due to there being some  defects in the process -  it cannot reduce zinc oxide to metal and therefore take feed that is part oxidic; the design and running of a plant with a recycling matte flow in the circuit would be  most difficult since the matte circuit must have some means of raising it to maintain continuous circulation - this has still not been suggested. Although he still admires the novelty of the Warner Process he now accepts that it “probably won't fly” and believes that Noel has arrived at that conclusion too.

During his long career, Philip must have seen great changes in the minerals industry. He says that when he thinks back over his 60 years or so to his student days the fundamentals of recovery of concentrates from ore feed has not changed at all!  “The ore is crushed, ground to get as much liberation as possible and then sulphide minerals collected by froth flotation and sent to the smelter for metal recovery. The presumption in this is that the information from chemical analyses with some identification of main minerals under optical microscopy is sufficient information to decide the flow sheet”.

He sometimes feels regret that the ore-body on which flotation was first developed and used was Broken Hill where much of the zinc mineralisation is marmatite  with a high iron content and many of the crystals are “as large as peas”. Liberation is not difficult but smelters are not best pleased with the iron. He acknowledges that during his time in the industry there have been big advances in the size and sophistication of grinding and flotation equipment, but this has not stopped the cost and energy consumption of liberation and flotation soaring for many productive plants for recovery from ore.

Philip recently had a short article published in Materials World with some interesting and radical ideas on refining the extraction process. He discussed how materials research has delved into the depths of rearranging atoms and molecules to generate materials with extraordinary physical properties. “If we can rearrange a material’s atoms to find new associations that are different to its better known properties, then should we not look to rearrange desirable and undesirable elements to extract them more efficiently?” 

I asked him if he could elaborate on this. “We now have in the UK a monthly publication, Materials World, from IOM3, providing side by side articles on minerals and ore processing with articles about materials made using new knowledge which has been applied by reconstructing atoms to produce quite remarkable properties; e.g. graphene.  This seems to me how the atomic structure of minerals might be changed to make recovery of wanted elements selected for recovery. Research, please!”

He says “I imagine that ore be brought to the surface or, perhaps, attacked in situ, so that mineral surfaces are exposed (quite a different requirement from separating a whole clean mineral particle for collecting by  flotation or gravity and processing for element recovery).  I would imagine that this might need application of energy to 'shuffle the atoms up a bit'. This is where there should be a substantial reduction in energy requirement and cost for very fine grinding and flotation compared with the present with, hopefully, higher recovery of specified elements. One should thereby be able to justify an ore treatment using energy in quite large quantities; note that energy is now cheaper. It seems to me that selecting specific elements for recovery is likely to be more economic than selecting impure minerals for poor recovery in the next step.” He said that we are provided today with nearly everything which is capable of doing for us much more useful services than only a few years back. “This has generally been possible from fundamental research work in the laboratory carried out only for the purpose of establishing new knowledge, not for the purpose of improving technology - but this can follow by using the new knowledge”.

“The general guideline is that basic research has in the last relatively few years taken almost every practical technology a large step forward.  As examples of such we can list medical and pharmacological practices (the recent news that the incident of new Ebola cases in W Africa has taken a steep fall); all uses of IT for transmission, computers ( a really staggering advance over the past ten years- note what nearly all of us have in our pockets); the provision of energy for industrial and  domestic use; the utilisation of more efficient farming methods and crop and stock nutrients; the use of minor elements (e.g. the rare earths) for  gaining greater sensitivity in information projection in all forms of IT; all aspects of aircraft design and use. We can go on citing many more technologies which have leapt forward from the foundation of research to add knowledge. I would cite ore processing as one (I hope not the only one) that has still to start.”

It is apparent that, although having been retired for some time, Philip still has a great interest in the minerals industry, and he told me that he keeps in touch as best he can by reading journals and occasional email chats with me and others in our profession. It was a pleasure, as always, to talk to him, and I wish him and his wife Joan a very peaceful 2015.

It would also be interesting to have the views of blog readers on Philip's comments on research. Do we need more blue-sky research to develop mineral processing?

More Conversations



  1. Blue sky research is important, and often for the serendipitous results that can come out of it. Unfortunately it is also very difficult to justify, and many will tell you why it won't work or why you shouldn't bother.
    Mike Albrecht, Manager Mining Projects at Roberts Companies, USA

  2. It seems that Philip Gray and Noel Warner are unaware of Sherritt’s process for zinc that went into operation in the 1980s. In this process zinc sulfide concentrate is treated in an autoclave at 150oC in presence of oxygen to get zinc into solution, lead and elemental sulfur in the residue. After purification of solution, the acid generated during electowinning of ZnSO4 solution is used in the leaching step. No vacuum, no SO2 emission which must be collected to make sulfuric acid, no complex reactor, no high temperature (1200oC), no slag, no circulation of molten material on two level hearths, no abrasion of refractories, no recycling, and no complex operating conditions like Warner process.

    Fathi Habashi, Quebec City, Canada

    1. I think you may have missed the point, Fathi. I am no extractive metallurgist, but as you say the Sherritt process treats concentrates, while the Warner Process was intended to direct smelt the ore, obviating the need to concentrate

  3. Yes Barry totally agree. However there is little appetite for it these days, with reduced research departments on most operating sites and in head offices of major companies. Of course a rich or very large deposit with difficult mineralogy and thus not readily amenable to or sufficiently economic with conventional processing techniques will drive research. It is interesting what industry finds and develops when there is a pressing need - cf. the 'sulphide' problem at Broken Hill towards the end of the 19th century. Note that while experimental findings can be original often the real skill and novelty is converting testwork findings into a practical flowsheet with all the other steps and stages glossed over by testing. This can include discovering new equipment used in other industries (cf. ultra-fine milling), developing new techniques/procedures, engineering aspects, etc. The hydrometallurgical flowsheet developed by DoeRun a few years ago for producing final products from lead and zinc concentrates, which included pilot plants as well as demonstration plants, is an excellent example of what focused blue sky research can produce. But not for the faint hearted - expensive, time consuming and resource heavy.
    Andrew Newell RungePincockMinarco, Australia

    1. Hi Dr. Barry
      Yeh of course I agree with you and Andrew's view. Most of the universities and research institutes world wide are carrying out high quality research work,are they fall under "blue Sky" research??
      Like me, I shifted from fundamental research to real plant, the research required here is quite different. There is a huge paradigm shift.

      The link or marriage between these two i.e., lab scale exploration and implementation is much essential and required. The real plant don't wait for long term research to make changes and bring some improvements. Though one has to develop the expertise in the same scale and implement it and make a bench mark.
      Dr. Rama Murthy Yanamandra
      Principal Researcher at Tata Steel


  4. Important we define the term ""Blue Sky"rerranging what we already know in different configurations is not blue sky to me. Rather something we havn't thought of, most of these discoveries are stumbled on (as the broken hill sulphide problem. So where do you start? how can you think of something that hasn't been thought of?
    Enzo Artone
    Principal Consultant at METOPS

    1. 'Stumbled on' because they were trying to find a solution I would suggest Enzo, however not 'Blue Sky' as such.
      You make a good point concerning 'Blue Sky" - a term used widely for exploration companies for unknown 'potential'.
      Mike uses the word serendipitous which is an excellent description of what can happen when one explores with an open mind possible technical solutions.
      As Gary Player once said "The more I practice, the luckier I get!"
      Andrew Newell

  5. Ore processing as practised traditionally is selected on the mineral differences of specific gravity, surface contact to collecting bubbles, or reaction to leachants for separation in solution by precipitation or electro deposition. Selection is by test work and optical surface observation. No heed is taken of the long prehistory of the section of the Earth' s crust that may have been subjected to many influences of temperature, contacts, pressures, etc over millions, if not billions, of years. It would be amazing if the best ore processing procedure for all ores could be simply found from the principle that all fit current processes.

    Early in my career I was a member of a team in Australia trying to find an efficient means of extracting uranium from ore in which the uranium was contained in a mineral called davidite which had no crystalline characteristics because radio activity had destroyed them. The significance of ore prehistory was not realised.

    Over recent times the access to equipment that enables the atomic and sub atomic structures of materials to be revealed which has enabled many technologies to be devised from the building of new lightweight high strength materials, to the specification of antidotes to E Bola. Numerous other technologies have made great steps forward following research revealing new knowledge about the basic structures of materials.

    I suggest that it is time that we applied these research tools to know the in-depth characteristics of ores that have taken many years to form. I believe that this knowledge may lead to pre-treatments designed to activate the element metals that are sought without wasting vast amounts of energy ( e.g. very fine grinding). Research projects to establish new scientific facts carried out in academic institutions is not nearly as expensive as the development programmes that may follow from the knowledge.

    I propose that it is time that we knew much more of the various structures of ores and from there to devise means of processing directly to extract desired elements rather than their residual crystals.

    Philip Gray


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