Dr Paul F. Schofield is leading the part of the CoG3 project that focuses on describing and characterising new ore types, with an aim of developing new ways of extracting cobalt (Co). He reports back on a visit to Diamond Light Source.
In early September the Museum CoG3 team met with Prof Fred Mosselmans, a fellow member of the CoG3 consortium from Diamond Light Source. The team hoped to use Diamond’s facilities to study how cobalt is incorporated into the minerals of the Nkamouna cobalt-nickel laterite deposit in Cameroon.
The Diamond Light Source facility provides very intense, high-brightness beams of X-rays that are focused to produce powerful microscopes. Not only do these microscopes allow us to image the distribution of cobalt in natural materials with nanometre scale resolution, but they also enable us to measure how the cobalt atoms are actually bound into the atomic structure of their hosting minerals.
This information can be used to understand cobalt cycling within the Earth’s crust and to work out how this metal became so concentrated at Nkamouna. We also use this information to interpret results from the bioprocessing experiments being performed by other CoG3 partners (Bangor University and the Universities of Manchester and Dundee) and to produce models of the atomic scale behaviour of cobalt during bioprocessing.
The microscope facility we used is called the microfocus spectroscopy beamline (I18). It has a beam with a diameter of about a micron (one thousandth of a millimetre), so can analyse individual mineral grains that are finely intergrown with other phases.
This is vital for this study as the laterite deposits we are studying are mixtures of oxide minerals that are intermixed with each other at the micron scale. A few of these minerals contain cobalt, some contain nickel, others contain both cobalt and nickel while the majority are barren.
Another benefit of using the beamline is that it is not destructive to the sample, which means that the exact same samples remain available for further study and can also be returned intact to the collections at the Museum.
The samples are polished slices of rocks from the Nkamouna ore-zone fixed to microscope slides. These are carefully positioned within the X-ray microscope before acquiring chemical maps from a range of mineral textures, and then a set of X-ray spectra from selected areas within these maps.
Diamond Light Source runs 24 hours a day and at the time it may have seemed a gruelling four days and nights collecting data continuously, but that was just the beginning and it is likely to take several months of processing and computer modelling before we complete the data analysis phase of this study.
Paul Schofield