Modeling of realistic microstructures on the basis of quantitative mineralogical analyses

In your dissertation, you look at how to make comminution technology more efficient. What exactly is comminution, and what is it used for?

Comminution is the generic technical term used when materials are intentionally crushed, ground or milled in a technical process. In my thesis, I use the concept in the context of mineral processing. Put simply, it means a lump of ore is broken up. However, the term also describes what happens to an old battery that is shredded for recycling or the milling of active pharmaceutical ingredients for making an ointment. Since it is essential to so many production and recycling processes, almost all man-made things are somehow comminuted before we can buy them as end users.

Your research aims to improve computer simulations of comminution systems based on the discrete element method. Can you explain this method and how it works?

It is an approach in which the motion of different objects can be simulated mechanistically. It is based on the evaluation of Newton’s laws of motion. The basic principle is to take the current state of each object (e.g. position and velocity) as the basis for calculating where these objects have moved to after a certain period of time. Interactions between the objects, like collisions, can be implemented as additional models so that they affect the states of those objects interacting with each other. We can use this approach to simulate how billiard balls move and collide, for example. With more complex interaction models, however, it is also possible to simulate the interactions between almost any objects—ranging from molecules to galaxies. Furthermore, these discrete elements can also be bonded together, creating arbitrary solid structures. By making such bonds fragile, it is possible to model breakable materials like rock.

You have developed a procedure for creating synthetic microstructures that can be used in effective mineral-processing simulations. To work, it is necessary to characterize real mineral microstructures. Would you shed some light on this procedure known as quantitative microstructure analysis?

In order to explicitly simulate the fracturing of mineral materials, for example by using the discrete element method with fragile bonds, it is necessary to provide such simulations with the proper information about the mineral materials’ microstructure. To do so, thin or polished sections of the real mineral material are analyzed with polarized light microscopy, which makes it possible to differentiate between the various minerals and grains.
Based on this, you can characterize the real microstructure in question with stereological methods. Specifically, you measure the sections by counting intersection points between the different grains or planimetry. This allows you to calculate parameters that describe the entire microstructure. In contrast to the typical qualitative verbal description of microstructures, which has historically often been used in mineralogy, this procedure is called quantitative microstructural analysis.

In your view, what are some of the most relevant real-world impacts or applications of your research?

Creating realistic microstructures on the computer, which are then used for further simulations, is far removed from our everyday activities. It is basic research. However, it’s a field of research with a huge impact on our life, since almost all man-made things undergo some kind of comminution in production or recycling. For example, it is estimated that around 3% of all energy consumption in the world is due just to grinding and crushing minerals. Making these processes more efficient can reduce that energy footprint significantly. What’s more, there are some applications where correctly understanding the influence of the microstructure is relevant to us. This can include the concrete in the pylons of bridges we have to cross every day to get to work or the liberation of rare earth elements, which are essential to countless technologies, ranging from light-emitting diodes to permanent magnets in the motors of electric cars.