Thanks for highlighting what is, and will increasingly be, an important issue for the industry.
Your idea of BSE images of the powder will work but is perhaps not the best route to getting a representative and quantitative size analysis. Preparing a representative sample for quantitative size analysis by SEM is challenging.....as it is difficult to ensure that you have a representative sample from the bulk powder, that the big particles don't fall off, that the fine particles are not shadowed by larger particles, that you do not have agglomerated cakes of finer particles, it is hard to image nanosized particles etc etc....you get the idea.
As an alternative, I would suggest using a laser based particle size analyser. With our system in the lab we have had our best success with the "wet" analysis, which analyses the powder in a water carrier through the system. This will immediately give you the statistics of your size distribution for a large number of particles, and can measure from 10s of nanometers up to 1-2mm. This system has its limitations as well....the biggest challenge I have found is that the amount of material analysed is very small and so it is important to ensure that you have a representative sample. Also, important to make sure that your sample does not dissolve or react with water! You could get an XRD analysis done to confirm the average composition of the powder, which the environmental report would also appreciate knowing.
Hope this helps and best of luck.
Steven Matthews, PhD
Department of Chemical and Materials Engineering
The University of Auckland, Auckland, New Zealand
Phone: +64 9 9236373 or +64 9 3737599 ext 86373
University Profile Page: University Profile/Research Summary Link
Associate Investigator - The MacDiarmid Institute for Advanced Materials and Nanotechnology www.macdiarmid.ac.nz
Associate Investigator - "Surface Engineering for Advanced Materials" www.arcseam.com.au