SAMPLING , ANALYSIS AND LAB ASSAY atomic number , with some exceptions , can be measured to varying precisions and detection levels .”
Moisture content is another critical property for mining companies to measure , especially in concentrates and products that normally go through further processing . Again , conventional moisture sampling is not always reflective of the conveyed flow of material here .
Microwave transmission has been successfully applied for moisture measurement of conveyed flows , achieving precisions of better than 0.5 % moisture , according to Scantech .
This process sees a microwave signal penetrate the full bed depth continuously using the differences in dielectric constant between water and mineral and organic matter . Free moisture molecules interact with the microwave field and disturbances are measured to determine how much moisture is present . The attenuation and group delay are measured and calibrated to known moisture content in that material over a customised range .
The technique is suitable for non-conductive and non-magnetic materials , according to Kurth
A Scantech customer in Western Australia recently abandoned conventional moisture sampling and moved to using the Scantech TBM210 microwave moisture analyser for its metallurgical accounting and reporting needs .
The reasons , or benefits , for such a shift were , according to the company , real-time continual representative measurement , which removes all the sampling errors associated with sample collection and analysis in the laboratory ; improved safety ( the client had concerns about isolation and lock-out procedures being followed during the night shift to collect manual samples ); and increased run time on the mill due to the lack of conveyor stoppages for sample collection .
At the same time as microwave transmission has proven effective in certain applications , fast neutron and gamma transmission also has a place when measuring moisture in coke , magnetite concentrate , lead sinter and other materials a microwave system may not be suited to .
Kurth explained : “ It ( fast neutron and gamma transmission ) measures hydrogen content directly and very accurately and this is correlated with water content in the conveyed material . Precisions of 0.1-0.3 % moisture have been consistently achieved in steel plants in Asia and Australia ( such as Dragon Steel , Nippon Steel , OneSteel and others ).”
Scantech still sees a role for sampling in the online analysis process , particularly when it comes to calibrating the instruments in question .
“ Calibration checks and any required adjustments are performed when sufficient laboratory results are available and may be undertaken every six months ,” Kurth said .
A new dimension
Late in 2021 , ZEISS took a major leap forward in the sector ’ s understanding of mineralogy with the release of ZEISS Mineralogic 3D software for automated quantitative mineralogy .
Billed to help achieve greater productivity and increased efficiency for the mining industry , the software leverages data from some of the world ’ s most advanced microscopes to understand composition , mineral relationships and fabric of the geological materials under scrutiny , including locked grains .
Such understanding means miners can respond faster to critical production questions , according to the company .
The scope of the software is vast , covering comminution improvements , through process enhancements , to assessing the quality of the final concentrate , and even analysing tailings .
Built on the ZEISS Xradia 3D X-ray microscope and microCT platforms using ZEISS DeepRecon Pro , ZEISS Mineralogic 3D software incorporates machine-learning protocols that recognise individual particles even when they are in contact with other particles . These particles are then automatically and individually analysed to provide a series of key outputs such as modal mineralogy , volume , porosity , feret dimensional measurements , associations and liberation . “ With ZEISS Mineralogic 3D , little to no sample preparation is required , stereological assumptions are eliminated as every grain is viewed in full in three dimensions and time to actionable data is significantly reduced ,” the company said .
Having previously been confined to 2D mineralogical data , the industry is set to reap benefits from such 3D analysis , according to Eddy Hill , Natural Resources and Metals , ZEISS Microscopy .
“ On a 2D sample / surface , you are always analysing a cross section of a particle ; you never really get a view of the entire particle ,” he told IM . “ With 3D analysis , you see the entirety of every single particle in the process .”
This “ ground truth ” allows mining companies to have an accurate assessment of the minerals in question – no longer having to rely on estimates – meaning the data outputs can be wholly relied on to make operational decisions much earlier in the mining process .
In fact , Hill believes the development of this solution could start to inform process flowsheet discussions as early as the prefeasibility stage , advising on potential mineral liberation .
“ We ’ re not just looking at the outside of the particles ( as we would with 2D analysis ), we are seeing the whole texture of our particles – the internal components , what ’ s locked , what the matrix looks like ,” he said . “ And we can start predicting how it is going to breakdown under different energies and find the sweet spot for grinding that much sooner .”
At the same time , when analysing a milled product , the 3D analysis can inform further down the flowsheet , for example in flotation .
The fact this mineralogical analysis is automated with the help of machine-learning algorithms also makes it more accessible for the industry , meaning on-site labs can rely on the smarts that ZEISS has embedded into its microscopes and software .
“ We have indexed the mineralogy , creating , if you like , a set of mineral libraries that recognise the minerals in our scans repeatedly and reliably every time ,” Hill said .
Analysis of a comminuted ore sample with ZEISS Mineralogic 3D reveals mineralogical , morphological and liberation details of the constituent mineralogy
“ Sampling campaigns need to reflect the appropriate ISO standard for that commodity , eg ISO 3082 for sampling of iron ores .”
He concluded : “ Online analysis technologies have become sufficiently developed to ensure representative , continuous measurement through the full bed depth of conveyed flows with results reported as frequently as every 30 seconds . Measurements are possible at precisions suitable
for process control and , in some cases , ore reconciliation and metal accounting .”
Assaying acceleration
One area where lab-based analysis will continue
to be a staple in the mining sector is assaying . This is also an area going through major disruption with the introduction of PhotonAssay technology .
FEBRUARY 2022 | International Mining 79