In conversation with Bill Johnson: Stirred Milling Pioneer

Although Dr. Bill Johnson has been for several years one of my most respected Minerals Engineering reviewers, I met him for the first time only three years ago, at the SME Annual Meeting in Denver, where he was inducted into the International Mining Hall of Fame.  Later in the year he was in Cape Town to present a keynote lecture at Flotation '17. 

Bill Johnson (right) with his long time colleague Joe Pease in Denver
for their induction into International Mining Hall of Fame

In over 45 years in minerals processing, Bill has made outstanding advances to the treatment of complex ores. He pioneered the use of the paradigm of size-by-size mineral liberation-class behaviour, and is a masterful user of this approach to drive major improvements to mineral processing plant design and performance. He was pivotal to the development of flowsheets and new processes for McArthur River, Mount Isa, Hilton and George Fisher, and has provided highly skilled technical support for a global array of operations.

Bill’s professional achievements have been recognised by the award of the President’s Medal from the Australasian Institute of Mining and Metallurgy for his work on advancing the processing of complex sulphide ores in 1993 and the CSIRO Medal for his contribution to the commercial development of the Jameson flotation cell in 1990. Recently, in 2008, he received the Mineral Industry Operating Technique Award, which was shared with Peter Woodall for the development of the IsaMill technology.

Dr. Johnson has had substantial careers in operations, research and education. He provided leadership of the Minerals Process Engineering program at the University of Queensland from 1998 to 2005 and in 2002 and 2003 leadership of the Division of Mining and Minerals Process Engineering was an additional responsibility. He continues to provide training and professional development on specialist topics for the minerals industry. He is presently an Adjunct Professor at the Julius Kruttschnitt Minerals Research Centre, a part of the Sustainable Minerals Institute, and a Principal Consultant with Mineralis. His educational and training experience includes teaching undergraduates and supervising postgraduate research together with running “in house” courses on advanced topics for technical staff. Bill is a respected mentor and widely known for his success in developing the professional skills of many minerals processing engineers during his time in the corporate sector and academia.

Bill Johnson was born in Stanthorpe, Queensland on 18 January, 1947.  When he was young, his grandparents told him many stories of the Cania Goldfield in Central Queensland.  Cania had an unusually long life as a goldfield and as a small town with some permanent residents. Gold was discovered just to the north of Cania Gorge in 1870 and the township known as 'Cania Goldfields' soon sprang up along Three Moon Creek. The township's population fluctuated over time until mining finally ended in the early 1920s. The waters of Lake Cania eventually covered the remains of the goldfields after Cania Dam was built on Three Moon Creek in the early 1980s.

Bill's grandparents had lived on or near the goldfield during the first 30 years of their lives, their involvement being mainly in the commerce in the town. Bill's mother was born in 1920 and started school in Cania. 

The background of Bill's family history in mining in Australia dates back to 1853, when his great-great grandparents left England with their two young sons, apparently attracted by the gold rush which commenced in Australia in 1851. They disembarked in Melbourne and travelled to southern New South Wales, where two further sons were born, the first of these, Noah Smith, being Bill's great-grandfather, born in 1855. 

The family followed the gold discoveries in a northerly direction, eventually reaching the major Gympie Goldfield in southern Queensland in 1867, the year of its discovery. This major field continued to be important until around the time of World War 1. The family largely remained in Gympie, but Noah did not. The Eidsvold Goldfield was proclaimed in November 1887 and Noah, now married with one daughter born in 1887, moved north from Gympie to Eidsvold in 1888. In 1893, he moved a little further north to the Monal Goldfield where he is shown in the photo below of a gold processing plant, holding two daughters, the one born in 1887 and another born in 1889. Bill’s grandmother, born in 1892 at Eidsvold, was too young to be in the picture. In 1896, Noah moved to the Cania Goldfield, a short distance away, for the rest of his life.

Monal stamp mill, 1890s

 

Top left: Bill with his sister Janette in the school playground in 1955,
where his father was the sole teacher. Bill was 8 and Janette 2.
Top right: Bill at school in 1957
Bottom: Bill and his younger brother gold panning at Ballarat in 1976

During his schooldays Bill developed a love of chemistry, and believed that the minerals industry was a way of applying chemistry and obtaining employment, given the range of possibilities in Australia at that time. He was awarded a Commonwealth Scholarship to attend university by the Federal Government. As part of the scholarship scheme, before attending the University of Queensland, it was necessary to be interviewed by an adviser employed by the Federal Government on possible suitable courses. Options included geology and geophysics. It seems that the adviser had a creative streak because he also provided an option which he called a Metal Chemist, which combined all the chemistry subjects with all the extractive metallurgy subjects and Bill was the only person to take this grouping of subjects at the university while he was there, and in 1967 he graduated, majoring in chemistry, with a minor in metallurgy. 

Final year photo 1967: Bill is 7th left on back row. 9th left is Don McKee who would be the JKMRC’s 2nd director, and 5th right front row is the 1st Director Alban Lynch

Then in 1968 Bill had the chance of undertaking an Honours Year Thesis with Alban Lynch (MEI Blog 11th August 2014). This was to be an investigation of the effect of various chemical variables in laboratory flotation of Mount Isa copper ore and Prof. Lynch planned to arrange for vacation work in the mineral processing laboratory at Mount Isa at the end of 1967/start of 1968. The research in 1968 would have to be in metallurgy. A problem was that Bill was not eligible for this option because he only had a minor in metallurgy, however the Dean of Science was very supportive of inter-disciplinary study and supported the plan strongly. The study under Alban Lynch occurred as planned and in 1968 Bill graduated with a first class honours degree in Metallurgy, after which he received a PhD in metallurgy in 1972 from the same university. His PhD work included a 5 and a half month spell at the Philex Mining Corporation in the Philippines for plant data collection, the most important outcome from the data being the relevance of the entrainment mechanism for hydrophilic minerals.

Bill says of Alban Lynch “Alban provided very clear lectures. He was very earnest but also approachable. It was clear from comments during lectures that he had well developed links to industry which were needed for his research group and the style of research he was employing – the use of industrial plants as the “laboratory” for data collection. He was entering the stage of research work on flotation in addition to grinding and classification."

After working for ASARCO in Arizona until 1976, he lectured at the University of Melbourne. He joined the CSIRO Division of Mineral Engineering in 1978 where research on the Lead/Zinc concentrator at Mount Isa Mines Limited was his main project and in 1982, he moved to Mount Isa where he continued applied research on the difficult ore treated in the Lead/Zinc Concentrator and other plants and ores of MIM Holdings, becoming the Minerals Processing Research Manager (1989-1997) of the laboratory and pilot plant facilities at the operating site in Mount Isa.

Several members of the Mount Isa Minerals Processing Research group with staff from
operations and engineering: Peter Williams, Lee Burton, Brett Gold, Bruce Mullan, Dave Fouhy,
Joe Pease, Kim Fisher, Bill Johnson, Ben Cronin, Brigitte Lacouture, Wally Onton and Mark Duffy

A major aspect of research at Mount Isa when Bill was Minerals Processing Research Manager was the development of the commercial viability of mining the McArthur River zinc-lead-silver deposit in the Northern Territory, 40 years after its discovery in 1955. It had long been recognised that the complexity of the McArthur River ore demanded a new approach to grinding and regrinding to produce commercial concentrates. Regrinding to a P80 of 7µm was required but there were no commercially available mills suitable for this task in the base metal industry.

Bill had been aware of the possibility of reopening work on the McArthur River ore for a couple of years before it happened. He had been reading and rereading papers from Prof. Klaus Schonert over a couple of years to try to ensure that he always had processing options if a project did commence on the difficult ore. A paradigm shift in mineral processing came about via Bill's attendance at the 7th European Symposium on Comminution in Ljubljana, Yugoslavia in 1990, where grinding methods in a wide range of industries were showcased. Bill saw the potential for large-scale adaptation and development of advanced stirred milling for the ultra-fine regrinding required by the McArthur River ores. This technology was unknown to the mining industry, being used only for small volumes of high value products, mainly in the food, chemicals and cosmetics industries. In the following months, Bill struck associations with a number of specialist firms, eventually settling with German manufacturer Netzsch for ongoing R&D.

A small laboratory sized Netzsch batch mill was purchased and installed at Mount Isa and after promising results work moved from the laboratory to the pilot plant in 1991. A continuous standard Netzsch mill (100 litres) was purchased for the pilot plant. This was the second largest mill in the Netzsch range at that time, the largest being a 500 litre mill. From the pilot plant experience, it was found that the regrinding technology could achieve the regrinding target of P80 of 7 microns but significant internal modifications were required for continuous operation in a real plant in the base metal mineral industry. Various options for the modifications were conceived and tested by the project staff at the Mount lsa site and the implementation of the findings into the design was facilitated by a partnership with Netzsch.

The next step involved trials of the modifications in the largest Netzsch mill (500 litres) which was tested in a small Lead/Zinc Concentrator at the Hilton operation close to Mount lsa. After further testing with a larger prototype in 1994, the go-ahead for the full-scale regrinding mills (3000 litres) at Mount lsa and McArthur River was given later in the year - the world's first application of the technology to base metal mining.

Bill conceived the idea for producing a viable concentrate and developed a pool of competent people to carry it forward. An expanded research team of 20 people, led by John Andreatidis and assisted by Michael Young (pictured below), worked under Dr. Johnson. Project Metallurgist John Andreatidis worked on the laboratory phase, the pilot plant phase, and the design modification phase and then moved to McArthur River Mining, a subsidiary responsible for the new operation. Mechanical Engineer Peter Woodall played a very important role in the pilot plant phase, the design modification phase and in numerous later activities with the mill. Kam Leung worked on data collection for the design of the primary grinding circuit and became the Metallurgical Manager for McArthur River Mining, with John Andreatidis in his team, when the new operation was approved and under development. The new operation commenced in May 1995 with four lsaMills in the regrinding duty.

John Andreatidis, Bill Johnson and Michael Young with McArthur River ore

The research also delivered increased metal recoveries at Mount Isa, the work being strongly supported by management and the Isamine R&D manager Jim Fewings. The Lead/Zinc Concentrator manager at that time was Joe Pease, who said that the team delivered the first significant breakthrough in fine grinding in 50 years, and the most significant development since SAG milling. The IsaMill technology which is marketed by Glencore Technology has spread into other duties in mineral processing and larger models have been developed, resulting in a large number operating in industry. 

IsaMill at Ernest Henry Mine, Australia

Bill left Mount Isa in December 1997 for the University of Queensland, but was available to the company for a specified number of days each year for the initial years at the university. From 1990-1997, he had visited the university each year to deliver a significant portion of one of the final year subjects in mineral processing. He gave undergraduate courses at the university until the middle of 2005 and was involved with the redesign and unitisation of the degree (1998-1999), AusIMM accreditation in 1999 and Institution of Engineers, Australia accreditation in 2002. He also organised “hands-on” field trips in the second and third years of the degree and the creation of two “hands-on” practicals at a coal washery near Brisbane. 

In conjunction with Mineralurgy (now Mineralis), Bill has delivered a large number of courses, usually at mine sites, on mineral recovery – size analysis, mineral recovery–size–liberation analysis and analysis of non-sized separation data. This 3 day course has been delivered 38 times with the vast majority being since 2005. Some of these were delivered overseas, in South Africa, New Zealand, Canada, USA, Mexico and Laos. He has also delivered a 2-day sulphide flotation chemistry course on 8 occasions, the largest number of courses being presented in 2015.

Consulting through Mineralurgy (now Mineralis) has provided Bill with projects on a wide range of topics and ores. During the consulting period, other highlights were the preparation of a flotation chapter in the SME Mineral Processing and Extractive Metallurgy Handbook (2019), three chapters in Process Mineralogy (2016) produced by SMI-JKMRC, a major portion of a chapter in History of Flotation (2010), and an updated version of a chapter (written and published in 2010) for the second edition of Flotation Plant Optimisation (2019), produced by the AusIMM.

A major highlight was being awarded the 2015 G.D. Delprat Distinguished Lecture for the Metallurgical Society of the AusIMM. This involved its preparation and delivery at eight locations in Australia. In 2017 MEI was honoured to have Bill as a keynote lecturer at Flotation '17 in Cape Town. 

Bill with MEI’s Jon Wills at Flotation ‘17

With such a busy professional life, it is good to see that Bill sets time for relaxation. He plays tennis weekly, exercises regularly and takes an interest in the results of various sports. He also has a keen interest in current affairs and history. He and his wife have travelled overseas as tourists six times from 2006 to 2017, with each trip lasting 4 to 5 weeks and taking particular interest in the many historical sites that were visited. In addition he regularly attends a small French conversation group, as his son has a French wife. Bill and his wife look after their 3 year old granddaughter each week.  

Bill and his wife Francyn and sons David and Alexander in 2005

Bill and Francyn with granddaughter Freya and son Alexander

Bill Johnson has played a huge part in the evolution of comminution, so my final question to him was how does he view the future of comminution, particularly with the increasing use of stirred mills?

He said "The impetus for the use of medium and high speed stirred mills was to obtain an economic means for reaching, in regrinding, product P80 values in the 5 to 10 µm range. However, at present, only a small minority of ores require regrinding into this region. To obtain substantial sale numbers, the technology has relied on its energy efficiency and its suitability for provision of a “clean” size reduction environment for the minerals, the latter being important for the flotation process. The application of the technology has spread into the normal regrinding range and into grinding stages along rougher banks and its use has been demonstrated in the final stage of primary grinding.

In general, the technology has the capability to regrind to product P80 values in the 1 to 5 µm range. This capability may be required for some future ores. The economic case for such regrinding will be made more readily if only a small portion of the ore requires such very fine regrinding. To achieve this outcome, it becomes necessary for the progressive liberation properties of the valuable mineral in the ore to be understood and for the design of the separation circuit to provide the necessary matching progressive recovery stages for the valuable mineral. There is also scope for the mills to become larger in volume and installed power, subject to the mechanical engineering constraints for each design.  

The chemical environment which can be created inside a stirred mill can be altered to suit the type of separation which is being sought in the following flotation process. However, the desirable chemical environment inside the mill, demonstrated at small scale, must be retained in any larger scale version of the process. In the future, the avoidance of process surprises because of unintended differences in the chemical environment in the stirred mill at various scales for the process (e.g. laboratory, pilot plant and industrial) will be important.

The connection between the ore texture and the most relevant size reduction mechanism requires better understanding. The attrition mechanism in stirred mills may be beneficial in achieving liberation with some ore textures but this may not be the case for other textures in achieving liberation of the key minerals".  

It has been a pleasure and a privilege to interview Bill Johnson for MEI. He is an inspiration to all mineral processors.

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