History of the Development of the Aachen Reactor

 The Aachen Reactor, a highly efficient mass transfer device, is now firmly established as a key processing step in many gold operations with many millions of ounces of gold recovered annually via the reactor.  It is the key technology to a number of innovative processes including the Leachox refractory gold process.

The development of the Maelgwyn Mineral Services (MMS) Aachen Reactor can be traced back to 1987. Interestingly and separately to completely opposite parts of the world.  In 1987 Michael Battersby, Co-founder of MMS with Dr Rainer Imhof, had emigrated from the UK to Australia and was working as metallurgical manager of a mine management company in the historic mining centre of Kalgoorlie.  A part of his work was to provide metallurgical consultancy to a number of operating gold mines in the area.  One of which was the Broad Arrow Gold Mine, about 40km north of Kalgoorlie. Mike had recruited a young metallurgist – Ivan Mullany – to be the plant metallurgist at Broad Arrow. A decade later Ivan was going to be very influential to the success of MMS.

The Broad Arrow Gold Mine was a small Carbon in Pulp operation that ran for a number of years and then, as reserves were depleted, it was eventually closed down and the plant dismantled.  The process plant was a few hundred metres from the famous Broad Arrow Tavern. An outback tavern made of corrugated sheets.  Mike and Ivan, with many other mine workers in the area, used to regularly stop off in the pub after work on the way back to town for a pie and some refreshment.  Mike still has the T-shirt! A bit worn now.

Broad Arrow Tavern T-shirt!

 In the pub, like all good metallurgists, the talk was about how to improve the gold recoveries on the plant.  The Broad Arrow ore was free milling and generally gave good overall gold recoveries – in the 90% - 95% range. But improvements could be made. Although free milling, the ore did have appreciable amounts of clay which made the pulp quite viscous. To add to this, the bore water in this region is renowned for having high levels of total dissolved salts (TDS). In the case of Broad Arrow up to 200,000 mg/L. This high TDS buffered the water making it quite difficult and costly to raise the pH to the high levels wanted for correct and safe operation.

To briefly recap the gold leaching process. To dissolve the gold, you need cyanide in the presence of oxygen with a high alkaline pH for safety to avoid the formation of hydrogen cyanide (HCN) poisonous gas. At Broad Arrow the oxygen came from a supply of compressed air that was blown into the tanks. The combination of the pulp viscosity and buffering made this quite inefficient. The dissolved oxygen (DO) levels required in the pulp were only barely reached and you go visually see the inefficiencies with large air bubbles rising to the surface and escaping to the atmosphere. So, the talk in the pub between Mike and Ivan was, occasionally, how could the oxygen utilisation be improved. It was actually an issue on most gold plants world-wide.

Around the same time in 1987 in Germany Dr Rainer Imhof was inventing and developing various pneumatic flotation systems.  He had come up with a gas dispersion and pressure hold-up concept and on the 10^th of December 1987 had duly applied for a German patent on the invention.

 

Dr Imhof’s gas dispersion and pressure hold up patent.

 Moving on to 1992 and Mike had joined the same company as Dr Imhof, although as Technical Sales Manager in Australia whist Dr Imhof was based in Germany.  Mike was now marketing the flotation technology developed by Dr Imhof.  Ivan Mullany had moved on to plant superintendent at the Emperor gold mine in Fiji. The mine had decided to test one of Dr Imhof’s pilot flotation cells at the mine. The tests were proceeding nicely but Ivan, who was having similar low dissolved oxygen levels at Emperor that were encountered at Broad Arrow, asked Mike if he could test the aerator that came with the pilot pneumatic flotation cell to see if it could increase the DO levels.  The answer that came back for the head office in Germany was a firm no.  Mike suggested to Ivan that he just run such a test over a weekend period when the German engineer, who was operating the pilot plant, was having his well-earned weekend break at the lovely beaches that Fiji has to offer.  This Ivan duly did and ran over the weekend, dismantling things and putting it back on the pilot plant before the German engineer arrived back at the mine. He didn’t notice a thing. On the plant the DO levels in the tanks doubled during the test and, as far as could be measured, it was thought that the gold recoveries had increased a few percentage points in that weekend period. A few percentage points increase in recovery is a considerable amount of extra revenue for a gold mine.

Mike and Rainer finally met when Rainer came out to Australia to attend the International Mineral Processing Congress in Sydney in 1993. They got on well and Mike explained what he had been doing and thinking about with Rainer’s aerators, for gold leaching.  Rainer went back to Germany and thought about the idea. In the meantime, Mike had been in discussions with various industry leaders in Australia about the concept. One of whom was Rob Dunne. He had arranged for trials of the flotation aerator to be undertaken at the New Celebration gold mine and the large Boddington gold mine in Western Australia.  Technically the trials were a success indicating an increase in DO levels, and increase in gold recovery and a decrease in cyanide consumption. Some of the work was actually reported in a technical paper.  However, the flotation aerators used were designed for low wear, batch flotation tests and not designed for continuous operation and the high wear rigours of gold ore slurries. A major redesign was required.

Some of the original designed pneumatic flotation aerators.

In 1994 Mike was then asked to move to Germany to head up the High Pressure Grinding Rolls division of the company. Here he worked a lot closer with Dr Imhof who was perfecting his new designs of an aerator that could be used in the gold industry.  Mike had quick success with the HPGR’s, essentially breaking their entry and use into mainstream metalliferous mining. He then went to the managers of the company with Dr Imhof’s new designs and a new business concept for the company in gold processing.  However, the company was not interested. There was a lot of internal company politics going on at that time and they also could not grasp that the industry was moving away for turn-key mineral processing plants, that had been their lifeblood for decades, to EPCM style contracts where engineering companies picked and chose what and whose equipment would be installed, mainly based on price.

In 1997 Mike decided that the had enough of working for a large multinational.  With Rainer’s new designs he believed he could develop a business concept that would support a new company.  He resigned, moved to Wales and on 21^st October 1997 registered Maelgwyn Mineral Services Ltd. The move and start up was a little bit more planned than random.  By this time Ivan Mullany was now manager at the Mines d'Or de Salsigne gold mine in the south of France.  Low and behold Salsigne was having the same old trouble with low dissolved oxygen levels.  Only at Salsigne it was amplified by the presence of sulphides in the ore that chewed up the various reagents used in gold leaching. As is seen later, this is a recurring theme globally.  Ivan had been asking for a while for Mike’s previous company to supply an aerator, as has been said, without success.  On the date of MMS’s registration, it received its first order for an Aachen Reactor REA200 from Ivan at Salsigne. Ivan Mullany has had a very successful career with two of the biggest gold mining companies – Barrick Gold Corp and currently Newmont Gold Corp, where he is Senior Vice-President – Projects.

 

Mark I Aachen Reactor Assembly

Dissolved Oxygen levels being measured in the tank after the Aachen Reactor in Salsigne, France

 

The order from Mines d'Or de Salsigne was quickly followed by and order from old friends at the Emperor gold mine in Fiji and then from Kanowna Belle gold mine in Australia.

 Development of the reactor at this time went into overdrive with Dr Imhof working on designs and concepts that would both increase the efficiency of the reactor and decrease wear to extend the units life.  Initially it was called an aerator but it was quickly realised that it was more of a reactor than an aerator.  It’s called the Aachen Reactor.  Most people think, with Mike and Rainer being based in Germany at the start of its concept, that is has something to do with the historic city of Aachen in Germany, close to the Belgium and Dutch borders.  In fact, it has nothing to do with the place Aachen.  At that time in the 1990’s the internet was not the thing it is now. Most information was still supplied “hard copy” such as product directories. It was simply that MMS wanted the aerator to appear first in any product listing and “Aa” Aachen got you that spot.  The “Aardvark Aerator” was seriously considered!

In the year 2000 Dr Imhof acquired the ownership rights of his own patents, where he was the inventor, from his previous company. He then vended them into MMS and joined Mike full-time. This was the catalyst for the expansion of the use of the reactors.  MMS had set up a subsidiary in South Africa. This company was close to the market and uses of the reactor, so could get immediate feedback on various issues. This assisted Dr Imhof to design ever larger units with more efficient gas dispersion and, crucially, much improved wear characteristics.  Some of these developments and inventions were novel enough to obtain world-wide patent protection for the new designs and then the various processes developed around the reactor.

There are currently (2020) over eighty Aachen Reactors in operation world-wide in various processing applications and many more in the pipe-line, both literally and figuratively so to speak!

 

 A Current Aachen Reactor Installation