A Selective Fragmentation (SELFRAG) device for liberating minerals, microfossils from rocks: more efficient, effective and safer for the UK community.

Lead Research Organisation: NERC British Geological Survey
Department Name: NERC Isotope Geosciences Laboratory

Abstract

High voltage material fragmentation device (commercially known as a SELFRAG lab) for effectively dust free sample fragmentation along grain boundaries, for UK researchers.

A significant portion of NERC Science require the analyses of materials (minerals, fossils) that are extracted from solid rocks. The quality of the minerals or fossils extracted from the rocks directly impacts the data derived from their analyses. For example, for U-Th/He thermochronology, to interpret the 'cooling age' of a mineral requires knowledge of the crystals geometry, for other processes (cosmogenic nuclide dating) the puriting of the mineral separate that is dissolved to derive an exposure age, impacts the age uncertainty. Thus, for nearly all research applications, complete objects (as opposed to fragments) are highly preferable and often required.

Increasingly, researchers are getting samples from difficult to access places and the amount of material is limited. This applies to expeditions to remote locations where physical limits and logistics limit sample size, and in scientific drilling where the volume of material is limited by the width of the drill core. In these cases, ensuring maximum recovery of high-quality minerals or microfossils from smaller volumes of rock sample is really important. Often the cost of obtaining samples can be many thousands of pounds (considering a single drill core can cost hundreds of thousands of pounds to drill, and recover).

Commercial high-voltage fragmentation devices are now commercially available (SELFRAG). Such devices present three major advantages over conventional crushing and milling processes:

(1) IMPROVED QUALITY OF MATERIALS liberated from rocks, whole crystals (as opposed to fragments) and microfossils can be routinely recovered enhancing subsequent analyses and derived science (see below). Experience in the community is that some rocks that SELFRAG separation can make the samples viable compared to non-viable with conventional crushing/milling;

(2) FASTER PROCESSING TIMES - processing via SELFRAG vs. conventional crushing and milling is ~6x faster (30 minutes vs. 3 hours, including cleaning time) resulting in significant improvements in process efficiencies;

(3) SMALLER SAMPLE VOLUMES REQUIRED - for regular rocks estimated that sample size can be reduced 2 to 3x due to the higher yields of high-quality mineral/micro-fossils. This is becoming increasingly important studies where sample size is limited, i.e., fieldwork in remote regions, or when working with samples from scientific drilling (e.g., International Ocean Discovery Program based research).;

(4) 'Dust-free' fragmentation of rock effectively eliminating user exposure to dust and harmful substances (e.g., asbestos, naturally occurring radioactive materials (NORM)). Processing of samples is carried out in water - a much reduced need for personal protection equipment and/or extraction related to dust.

A high-voltage selective fragmentation device (SELFRAG) for the UK would provide the broad benefits outlined above to an entire research community, providing safer and more efficient ways of working, and improved quality of materials liberated from rocks that will directly improve subsequent analyses.

Finally, this is a relatively new technology and new innovations are still be explored and developed, for example using high-voltage to study the energy required for rock failure, or using high-voltage fragmentation to experiment with materials recycling (i.e., what is the most effective way to fragment an iPhone and recover the rare elements for re-use).

Planned Impact

The SELFRAG Lab Facility will represent innovation in:

Process Efficiencies - Higher yield from smaller samples e.g. drill core (ICDP, IODP, UKGEOS, industry). Process is 2-3x quicker compared to conventional crushing and milling methods, therefore more time for research. Process efficiencies are a major UKRI drive.

Science application area broadening. Materials science and resource management e.g. extracting critical metals from recycling of mobile phones, are relevant to NERC's investment in Resource Recovery and Waste. Material purification currently uses microwave technology but could use SELFRAG (see University of Nottingham PP letter). SELFRAG can be used as a testbed for a novel communition process (see PP letter from Leicester) within the mineral extraction process to enhance the liberation of complex minerals from ore, reducing the environmental impact of e-tech resource extraction.

Health and Safety. Occurring in water, the SELFRAG process produces essentially zero dust offering a safer process for operators (e.g. from silicosis, asbestosis). Naturally occurring radioactive materials (NORM) may also be handleable. Containing and constraining the preparation of such materials, if this represents a practical way of working with them, will allow a wider variety of materials to be researched.

Impact will be measured through an annual survey to users (and potential users), monitoring user satisfaction and recording outputs (i.e., publications) that have resulted from the use of the UK SELFRAG Lab system.

Health and Safety is a major concern for many UK HEI and Research Centres involved with crushing and milling of rocks. Whilst measures are put in place to minimise the exposure to dust using extraction systems and personal protection equipment, the most effective way to minimise risk is to eliminate the source of the hazard. SELFRAG operates with the sample in water, effectively making it dust free. Eliminating the risk will prevent any future dust-based injury or sickness claims on the public purse.

Electro-fragmentation significantly reduces the amount of energy required for rock comminution. Research into the development of lower impact ore exploration and extraction (Leicester PP) could generate more cost effective, efficient and lower energy processes for natural resource exploration for UK industry, directly benefiting the UK economy and contributing towards energy-use reduction targets for the UK.

The NERC Services & Facilities work with the research community including NERC Research Centres (see PP letter Murton NOC) to solve scientific problems and generate publishable peer-reviewed output. As a NERC Facility, the NEIF user-community will benefit directly from this instrumentation with >30 papers/a likely benefiting. A significant proportion of these will derive from the network of geochronology researchers within the UK who will benefit additionally from the unique science opportunities a SELFRAG Lab will bring. Access to this instrumentation at a free-at-the-point-of-access Facility (and through pay-as-you-go) will significantly strengthen the geochronology-based collaborations already occurring within the UK. Potential beneficiaries will be the materials science, recycling and radioactive waste communities where electro-fragmentation offers clear possibilities as well as the civil engineering community whom fundamental investigations of rock mechanics would benefit. This will broaden the reach of this NERC Facility to other science funding bodies (STFC, EPSRC) where there are mutual synergies in the science. Another key output will be the increased interfacing with industry where this technology offers distinct advantages and where a SELFRAG Lab Facility at the BGS could be used as a testbed for capability development. For example, critical damage threshold analysis and the energy required for disaggregation, mining and tunnelling could be investigated using SELFRAG.

Publications

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