Minerals Processing
Cyber security considerations for Minerals Processing
As you read this post you likely have your fingers within eyesight. Are you perhaps wearing a ring? A watch? Unless you’ve printed out this post and are reading it on paper, you are likely making use of an aluminum-based electronic device. Have you ever considered how we get to these materials? If so, have you perhaps considered what the cyber security implications related to these processes maybe? If not, we are going to find out together in this post.
Security consideration: throughout this post you will find these security
considerations. These are used to highlight some of the important processes
that may be worth considering from a security perspective. This is not an
all-encompasing analysis, though, so try and keep the following questions
in mind when reading the post -
[1] Is this a critical process that may be worth protecting?
[2] What should we do to protect the system?
* Disclaimer: this information should not be used for nefarious or unauthorised
purposes but rather as an educational tool (see the Welcome post of this
blog).Introduction
At a high level, Minerals/materials processing refers to the extraction of valuable minerals from ore (naturally occurring material). By means of a simple example, diamonds are typically found within rock that needs to be extracted and processed in order to gain access to the diamonds. Variations of this process are employed to extract various minerals including coal, gold, silver, iron ore, manganese, and platinum, just to name a few. Figure 1 provides a better overview of the different types of minerals and how they are classified.
Security consideration: minerals processing forms an important aspect of our
larger industrial processes or industries as the raw products are used in many
of our daily products. A cyber attack on one of these processes is likely to
have significant impacts on the larger supply chain.Processing Methods
The various minerals highlighted in Figure 1, are not the same and they are each made up of individual properties that determine how the minerals are processed. Nevertheless, the same high-level process is typically followed, as shown in Figure 2, below.
We will consider each of these processes below:
Front Service
The front service is considered to be the starting point of the process. This begins with the extraction of material from the ground. This can take the form of a mine (open pit/underground) or a quarry. Whilst there exist various processes for extracting the initial material from the ground, one of the more intensive processes is that of drilling.
Various drilling methods are available. Auger drilling relates to a rotating helical screw that is inserted into the ground. When it reaches a certain depth, the auger will begin lifting pushing material up through the opening it is creating (think of a typical household drillbit).
Rotary air blasting is the most common shallow drilling method and essentially uses a piston action to break up the rock and compressed air to lift the material to the surface (note that different drilling actions may be used).
Aircore drilling makes use of a three-bladed drill bit and compressed air in order to drill holes. Figure 3, below, provides an overview of what such a drill bit looks like. Compressed air is pushed through the centre of the drill bit (hence the air core).
There are various other drilling methods including diamond core and blast drilling (the name is pretty self-explanatory — drill a hole and put explosives in it) that we are not going to cover in this post.
Size Reduction and Control
Once we have extracted the initial raw material, we need to break the material into smaller parts so that we can process it better. This is where crushing comes in. Crushing refers to the physical process of breaking the material down into smaller parts (literally crushing).
As with drilling, there are various types of crushers. Crushers are typically broken down into two groups, namely, compressive and impact crushers. The names are, again, relatively self-explanatory. Compressive forces result in the material being pushed together until it breaks. Impact crushers use the principle of high-force collisions to break the material apart. A simple example of a compressive crusher is a single toggle crusher as shown in Figure 4, below.
In this case, there are two plates (the one on the left is stationary). The plate on the right is connected to a rotating shaft that changes the position of the plate. As the material is crushed, it moves down the crusher becoming smaller and smaller.
Security consideration: the gap at the bottom of the crusher is an important
parameter to control for. If the gap is too large, the material that exits the
crusher is not the correct size and may impact the downstream process.Security consideration: dependant on the crusher design, V-Belts may be used to
connect the motor to the crusher shaft. If the motor spins too quickly, the
belts may start to slip. This could significantly damage the belts due to the
additional friction that this causes.A Vertical-Shaft Impactor (VSI), as shown below in Figure 5, releases material into a vertical shaft that is spinning at high speeds. A VSI is an example of an impact crusher. The material is propelled outwards and the collision with the walls of the impactor as well as the ‘rock-on-rock’ action cause the material to break down.
Side Note: Depending on the material, crushing is not necessarily a single-stage process. A larger process is typically comprised of three phases (namely, primary, secondary, and tertiary).
As discussed above, crushing is used to reduce the size of materials. However, crushing has limitations in the size to which material can be reduced. If a reduction in size below 5–20mm is required, grinding is employed. “Grinding is a powdering or pulverizing process using the rock mechanical forces of impaction and attrition.” Figure 6, below, shows the basic methods of grinding.
Grinding is typically performed in a mill. As with crushers, there are numerous different types of mills (outside of the scope of this post). Nevertheless, there are two basic mills that we can consider, namely Autogenous Grinding (AG) and Semi-Autogenous Grinding (SAG). AG mills only make use of the ore itself whereas SAG mills will add extra material such as steel balls to assist in the grinding process. SAG mills are typically larger and can, in turn, process more material. Figure 7, below, shows what a SAG mill may look like.
On the left-hand side is the feed chute, where material is placed into the mill. The ground material then exists the mill on the right-hand side. These mills are typically large in size, ranging from a cylinder diameter of 2.4m to 8.5m with the motor power output ranging from 55 kW to 4850 kW (obviously dependent on the exact product — bigger mills do exist).
Security consideration: if the mill moves too quickly, material may not have
been ground enough before exiting the mill (material is too large for downstream
processes). If the mill moves too slowly, it may be overloaded placing strain
on components such as motors. Security consideration: the startup speed of a mill, especially on very large
mills is important. If the material has been allowed to settle at the
bottom of the mill, and it is started too quickly, the material may move too
high up the drum and come crashing down. This can severly damage bearings and
other components. In addition, attempting to move a heavy weight very quickly
with electric motors may cause damage to the motors themselves. Side Note: a mill may be considered as one of the key components of a mine/processing plant. If the mill is not available, many other processes have to be shut down as well which may result in millions of dollars of lost production depending on the amount of time for which a mill is unavailable.
Whilst crushing and grinding significantly reduces the size of the material, we still need some way of controlling (measuring and sorting) the material.
Screening, as mentioned above, is used to separate material (typically based on size). The basic principle is relatively straightforward, as shown in Figure 8, below. The material is placed in a feedbox after which vibrations are used to move the material across the screening surface. Depending on the size of the material, it will either fall through or move across the screen.
Side Note: Stratification refers to the process of larger material moving to the top and smaller material moving to the bottom. This is an important characteristic of screens as it determines whether material will move through the screen or across it. Probability, in this case, relates to the likelihood that a particle will be rejected (move across the screen). Large particles will be easily rejected. However, as the size decreases it may take various iterations for the correct particles to pass through the screen.
Enrichment
Enrichment of the material is the improvement of the value of a mineral by removing impurities. Enrichment is typically performed through washing and separation. One of the simplest forms of washing is simply by using a wet screen which refers to water being sprayed onto the material in order to wash it.
Sometimes wet screens are not effective, though (e.g. clay). In this case, scrubbers can be used. Scrubbers work like a large washing machine, in which the material is rotated in a drum to break down the weaker material (in this case, clay). Figure 9 provides an overview of a scrubber.
Side Note: scrubbing is not the same as grinding in the sense that the primary material (the material we want to extract) is not broken down.
Security consideration: larger scrubbers (and ball / SAG mills) often make use
of specialised hydrodynamic bearings. These are control systems in themselves
that ensure that the bearings always contains a sufficient amount of oil. In the
event that the bearing does not receive the correct amount of oil, it may seize
which would result in the process having to stop and the bearings having to be
replaced.The other process that can be used is that of separation. Once again, there are various ways in which we can separate material with the first being gravity. In this case, water is added to the material, and due to different densities, the material can be separated. Another way to separate material is simply by means of water but without gravity as seen in the shaking table below.
The water is fed across the table with water as a medium. “Riffles” run perpendicular to the table and are used to catch heavier material whilst the lighter material flows over the “riffles”.
Security consideration: the frequency of vibration in a shaking table is an
important parameter. If it moves too slowly or too quickly, the concentration
of the tailings or concentrate may be affected (i.e. too much concentrate in
the tailings or too much by-product in the concentrate).The spiral concentrator in Figure 11 also makes use of gravity to separate material. As it moves down the chutes, lighter material will move to the outside of the chute whilst heavier material will remain on the inside.
Side Note: Tailings refers to the by-product of the mineral extraction process that we have covered. Tailings typically contains some amount of water and needs to be stored in a dam, aptly named a tailings dam. The product that has been extracted is referred to as concentrate.
Upgrading
Once the concentrate has been extracted, it is unlikely to be of much use due to the water content and other materials. Subsequently, the product needs to be upgraded.
Side Note: upgrading can also be performed on the tailings to ensure that it is as environmentally friendly as possible and that as much water has been extracted as possible.
One of the simplest ways to remove water is by means of gravity. The spiral dewaterer shown in Figure 12 is a fairly straightforward process.
The feed is placed in the dewaterer and the spiral slowly moves the material up an incline. As it moves up, the water is drained by means of gravity.
Security consideration: water does not immediately seperate from the material.
If the spiral moves too quickly, the water may not have enough time to seperate
from the material before reaching the end of the spiral. The process may have
to be repeated.As the material becomes finer, the ability to remove water by means of gravity decreases resulting in the inability to use gravity-based methods. One of the methods that can be employed is compression whereby the water is pushed out of the material similar to how pressure forces water out of a sponge. Various other methods can be used but do not form part of the scope of this post.
Conclusion
In this post, we considered, at a high level, what minerals processing entails. The typical lifecycle includes the extraction of the material, size reductions, and control, enrichment, and upgrading. Each of these processes and the components involved have failure modes that could perhaps be invoked from a control system / digital perspective. When designing minerals processing systems, it is important that we keep the cyber security considerations in mind.
Security consideration: we managed to identify several security
considerations throughout this post. Nevertheless, we may have missed
something. Feel free to leave a comment with additional considerations!
