After the most intellectually grueling 4 hours of my life, Dr Will Mayes and Prof. David Manning invited me back into the meeting room and were both standing with smiles on their faces.  I had passed my PhD viva – with one month’s minor corrections!

My time at Newcastle has been an absolute delight and it was sad to say goodbye last Friday.  There are many people who have helped me along the way, some of which have been acknowledged in my PhD thesis but also some which hadn’t – not least my examiners for taking the considerable time and effort out of their busy schedules to read and interrogate my thesis.  But also the friends from the Devonshire Building who, at the drop of a hat, helped me celebrate such a memorable occasion – you know who you are.

Formal thesis acknowledgements:

Firstly, I must thank my first supervisor Dr Adam Jarvis for his generous support and patience during my time at Newcastle.  Thanks are also extended to my secondary supervisors, all of whom have provided valuable assistance: Prof. Paul Younger, Dr Simon Reed, Dr Ian Watson and especially Dr Catherine Gandy.  This PhD was largely funded by The Coal Authority, and I am indebted to the efforts of Tracey Davis, without which I would not have had the fortune of indulging in this research degree.  My appreciation also extends to friends and colleagues at The Coal Authority for their assistance when faced with continued requests for information.

Over the last three years, I have spent many enjoyable hours both in the beautiful Lake District and in the immaculate laboratories of the Devonshire Building with Jane Davis and Patrick Orme.  Their help and shared experience was invaluable to successful completion of this research.  Additional assistance has been provided by other staff across the School of Civil Engineering and Geosciences, in particular Dr Angie Sherry for her help with the microbes.  Thanks are also extended to Leon Kirk of Acumen Waste Ltd. and Hein Schade of Helix Projects Ltd. who provided insider knowledge of the waste and minerals industry.  The information they provided was crucial in forming some of the economical calculations presented in this thesis.

Behind the scenes, my wonderful wife Claire has been a continued source of reassurance, inspiration, and above all, a fantastic companion.  Thanks also for proof reading my Thesis, along with my old man.  Dad, one day I’ll know where to put those punctuation marks!

Here is the abstract to my paper presented at the 2015 ICARD conference:

Treatment of mine drainage, during operation and following abandonment, can represent a substantial cost to mine operators and governing authorities. Recovery of valuable metals from mine drainage as part of the treatment process may offset costs, yet this is rarely seen in practice. Industrial-scale metal recovery from mine waters are the preserve of active treatment systems, where reactor conditions are carefully controlled to ensure consistent quality of product. In many circumstances passive treatment is the preferred approach, but close process control is not feasible in these systems. Analysis of substrate from a pilot-scale compost-based passive treatment system, which operated for two years, has been conducted. The treatment system, which harnessed bacterial sulfate reduction to remove metals as their sulfides, showed that under UK regulations used substrate was within the worst-case ‘hazardous’ category due to accumulated zinc, and required pre-treatment due to high total organic carbon. Typical costs for disposal are estimated at 1104 US$/tonne, excluding removal and transport. The majority of zinc accumulates in the upper substrate layer. Greatest zinc concentration of 14,050mg/kg (1.4%w/w) was observed in the 0– 230mm depth layer; whereas in the corresponding lower layer, 230–460mm, zinc was 808mg/kg (0.08%w/w). This suggests that selective ‘harvesting’ of upper substrate layers may reduce waste volumes generated, and higher zinc concentrations may be more amenable to metal recovery. Batch-scale leaching tests have also been undertaken, demonstrating recovery in excess of 83 – 96% of zinc from the upper-layer substrate, depending on acid strength used (20; 100; 500mol/m3 sulfuric acid), within a 100 hour leach test. The results are discussed in the context of the possible economic benefits of metal recovery for passive treatment systems at larger scale.

the full paper can be accessed here 

Might it be possible to de-contaminate mine water treatment system substrates using mine water? A mad idea, perhaps, although there is some method behind it…
The use of iron and sulphur oxidising bacteria is a well-established practice for metal leaching in the mining industry, harnessing a process which is responsible for causing acid mine drainage: bio-oxidisation of iron-sulphides within mine workings.
I’m currently attempting to apply this approach to the Nenthead treatment system substrate which is contaminated with zinc – probably as a sulphide. However, where microbes are concerned things are never straightforward, so many thanks to the Geosciences research team at Newcastle University for their ongoing advice and assistance in the lab.

Having undertaken leach-testing of metal mine water treatment substrate, and precipitation of dissolved solids from pregnant leach solutions, what is left is this grey-green sludge. Further analysis will show if this contains economic levels of metals!

Commodity?