Welcome to Part 2 of Our Simulation Platform blog series.
In Part 1, we discussed how we have developed a suite of comminution, classification and concentration unit operations that complement SysCAD’s existing extractive metallurgical capability.
In this post, we discuss a particular key enhancement to the comminution and classification models; multi-component modelling.
Mineral processing flowsheet simulation packages like JKSimMet treat ore as a single solid component of a stream, possessing one set of comminution indices and a particle size distribution. For an equipment scale-up or mass balancing approach, as intended by JKSimMet, this is often sufficient.
However, operating plant streams are almost always more complex mixtures of many different ore lithologies, each having different processing properties as received from the mine and orebody. Active ore blending to control plant grades and throughput can further complicate matters.
In multi-component modelling, plant streams consist of multiple ore types, in varying quantities. Each ore type retains its own set of comminution and physical properties as well as its own particle size distribution.
Comminution and classification operations act on the ore types differently, yielding an overall stream product that is the sum of its components (and often the only thing that can be practically measured in a real plant).
Why multi-component modelling?
Understanding how ore mixtures are processed in a plant is becoming increasingly important for a range of tasks, such as:
- Quantifying the benefits of pre-concentration and ore sorting, especially energy efficiencies and metal recoveries;
- Mapping out plant performance over Life-Of-Mine as ore sources, compositions and grades change – essential for the planning of plant production, operations and capital expenditure;
- Reconciling plant performance with geometallurgical data sets;
- Best-utilising hard ore components as media in grinding operations;
- Debottlenecking plants where hard components recirculate and consume processing capacity – for little return;
- More accurate and flexible metallurgical models for diagnosis and optimisation.
To address such activities, we have modified our suite of unit operation models to handle streams with multiple solid components.
Modifying the models
The SysCAD software inherently has the capability to simulate mixed streams. This belies its more typical application to pyrometallurgy, hydrometallurgy, and alumina refining processes, where various chemical species and phases are the primary stream components.
So in order to simulate multi-component mineral processing circuits, we need only modify the existing unit operations to cope with the mixed streams that SysCAD presents them with.
Research in multi-component comminution has been ongoing for several decades. Greater focus has shifted to the area recently, as our clients begin to consider many of the opportunities outlined in the previous section.
Progress in the field can be hampered by difficulties in measuring the individual products of multi-component comminution. Typically, a particular property of one component must be exploited in order to measure its degree of comminution (such as magnetic susceptibility, acidic dissolution, XRF response etc). Naturally occurring orebodies are not always so generous in their provision of such properties!
Whilst this can limit some of the capabilities offered, our approach has been to take the path most reasonably rationalised by fundamental understandings, empirical experiences and/or published science.
Here is a cross-section of the approaches we have taken:
For jaw, gyratory, cone, impact and roller crushers an assumption of ‘single particle breakage’ is largely valid. That is, individual particles are exposed to crushing actions without interaction from other, adjacent particles.
In this case, multi-component modelling is fairly trivial, with ores being crushed independently of one another.
The situation becomes more complicated in the case of machines like AG/SAG mills, where internal multi-component loads combine to impart breakage energies to the constituent particles.
The JKMRC have been active in this area and our own previously theoretical modifications to the Leung/Morrell SAG mill model are strongly supported by their recent research results (Bueno et al, 2013).
Ball and rod mill models can similarly be modified to scale breakage rates/selection functions for ore types in mixtures.
High Pressure Grinding Rolls (HPGR)
HPGR comminution presents an interesting case. Breakage in these machines arises directly from the interaction of ore particles in a compressed bed.
Comminution is therefore affected by the composition of hard and soft materials in the feed mixture. Hard materials are known to act as a grinding agent, transferring the bulk of compressive forces (and hence comminution energy) to the softer components.
Research has shown the simulation of such mixtures in HPGR’s is quite possible (Abouzeid and Fuerstenau, 2009). However specialised test work is required to parameterise the split of energy between the components during comminution. The test work also requires the exploitation of a property that allows the comminuted products to be separated for analysis (acidic dissolution in Abouzeid and Fuerstenau’s case).
The multicomponent simulation of operating HPGR’s is therefore quite limited in a practical sense.
Current research in fundamental breakage processes, such as force chain modelling, Discrete Element Modelling etc., might provide a more useful solution in the future.
Classification is typically a size-based operation, although density can also play a role (e.g. hydrocyclones).
Multi-component classification models which consider the individual size or density properties of ore in mixtures can more accurately reflect the separation phenomena at work.
The energy implications of this are particularly relevant where hard, coarse or dense components are recirculated for additional (and often unnecessary) comminution.
Extending the multi-component concept
Integrating a multi-component framework into our comminution and classification model suite has opened up further opportunities for improving our simulation capabilities.
Utilising the same approach (and software modifications), we have also incorporated:
- Ore mineralogies (as distinct from lithologies; required to simulate downstream flotation and extractive metallurgy);
- Valuable metal grades, distributed by size, ore or mineral;
- Particle size-density distributions (essential for simulating gravity concentration);
- Flotation rates/classes;
- Liberation phenomena; and more.
Each of the examples above has been previously applied to our project work, providing genuine insight and helping us develop practical solutions.
Hopefully the above post has given you a view of the benefits of multi-component comminution modelling, our approach, and perhaps some of the limitations.
The framework we have described is ready to use, and we have successfully applied it to a range of projects over many years.
The multi-component framework is the means by which we have our comminution and classification models communicate directly with downstream concentration and extractive metallurgy processes, all within the same computational platform. This forms the basis for our consulting solutions such as Ore To Product.
In our next post, we will discuss how plant process control and operating philosophies not only have a role in process simulation, but are actually essential for capturing the true behaviour of complex minerals processing systems.
Bueno M P, Kojovic T, Powell M S, Shi F, 2013, Multi-component AG/SAG mill model, Minerals Engineering, 43-44 (2013) 12-21, http://dx.doi.org/10.1016/j.mineng.2012.06.011
Abouzeid A-Z M, Fuerstenau D W, 2009, Grinding of mineral mixtures in high-pressure grinding rolls, Int. J. Miner. Process. 93 (2009) 59-65, http://dx.doi.org/10.1016/j.minpro.2009.05.008