For successful mineral processing design it’s critical to evaluate the possibility of preconcentration or waste diversion before grinding. Mess up this step and you could be hit with avoidable downstream CAPEX and OPEX costs. 

At its core, preconcentration means exploiting particle differences as early as possible so that waste material isn’t unnecessarily fed to the mill and then deposited in tailings dams.  There are a few technologies that are well suited for preconcentration at the front of a mineral processing flowsheet. Below we’ve compared sensor-based ore sorting methods to dense medium separation to see how these popular mineral processes differ. 


The Basics Of Ore Sorting

Ore sorting can be broken down into two broad categories: particle sorting and bulk sorting. Both are dry processes and have the advantage of being able to sense a number of different mineral properties for separation. 

Particle sorting is for typically for particles larger than 30mm in size and capacity can be somewhat limited. This is due to the fact that each particle is sensed and sorted individually on a conveyor belt. Particles must be in a single layer for processing. As the particles move along the conveyor, they are scanned and material is selectively blown off course by air jets. 

Bulk sorting senses material on a conveyor belt and diverts large amounts based on average grade. Typically more than 10 tonnes will be diverted. There is no practical particle size limitation, but the large minimum quantities make it a fairly crude separation process. 


The Basics Of Dense Medium Separation

Dense medium separators separate particles based on their densities alone. The Condor Dense Medium Separator can be designed to separate particles into two (concentrate and tailings) or three products (concentrate, middlings, tailings). 

Here’s how it works. 

Using a feed hopper, ore is introduced into the head end of the Condor Dense Medium Separator with a small amount of the dense medium slurry. The slurry is made up of a suspension of ferrosilicon or magnetite in water and is introduced through the medium inlets at the bottom end of the separator, countercurrent to the ore feed. 

The densest ore particles are separated and transferred through the sinks outlets, while the less dense material is transferred to the second stage of separation where more sinks material can be recovered. 

The lowest density material reports to the floats discharge at the bottom end of the Condor DMS unit.  Each chamber of the Condor is equipped with an involute medium inlet and a sinks discharge, ensuring maximum separation efficiency during the multi-stage process.

Benefits Of Ore Sorting

Ore sorting can exploit a number of differences to sort particles including colour, density, hardness, radiation, and even electromagnetic properties. This means a wide range of mineral types can be separated using an ore sorting machine. Dense medium separation relies solely on particle density for sorting material, limiting the range of minerals that can be used with this process. 

Ore sorting is a completely dry process which requires no water. In fact, it’s necessary for the input material to be completely dry. This is great when resources are scarce, or conserving water is critical. However, this can also work against operations in parts of the world with heavy amounts of precipitation or groundwater. 

Ore sorting is also a simpler process with a small footprint. 


Benefits Of Dense Medium Separation

While dense medium separation can only rely on density to distinguish valuable materials from waste, it has the advantage of being able to sort a wider range of particle sizes. With ore sorting, the largest particle size should be no more than 3 times that of the smallest particle. This means all of the input material must be homogeneously sized for the chance of successful sorting. Dense medium separators, on the other hand, can have a wide range of input particle sizes and still be processed effectively. 

Dense medium separators can also accommodate smaller particle sizes. Ore sorting can run into capacity and efficiency issues if particles are below 30mm. In contrast, dense medium separators can sort particles down to 0.75mm in size. If you’re working with finer particles, dense medium separation is the way to go. 

Higher tonnages can also be accommodated with dense medium separation. Here’s a rule of thumb, for ore sorting using a 1 metre wide belt, tonnes per hour equals particle size in millimetres. So, for a 30mm input, you can process 30t/h, 40mm would allow 40t/h and so on.  

Dense medium separators do not have this limitation and can handle inputs of over 200t/h at fine particle sizes in a single unit. This also makes scaling up your operation easier with dense medium separation than ore sorting in a given  footprint and capital cost budget. 

Sepro’s Condor Dense Medium Separator is typically used in a pre-concentration duty to divert waste material away from grinding mills and tailings dams as well as to improve project economics. Removing waste from mineral processing at the beginning of the circuit directs downstream energy where it’s most useful, increasing operational efficiencies. 

Identifying and implementing the ideal preconcentration process is paramount to the best performance of any mineral processing application. To learn more about ore sorting, dense medium separation, or Sepro’s range of mineral processing equipment, give us a call today.