Sensor-based sorting

Sensor-based sorting, is an umbrella term for all applications in which particles are detected using a sensor technique and rejected by an amplified mechanical, hydraulic or pneumatic process.

If the amount of sub-economic material in the above-mentioned fraction is roughly 25% or more, there is good potential that sensor-based ore sorting is a technically and financially viable option.

The functional principle does not limit the technology to any kind of segment or mineral application but makes the technical viability mainly depend on the liberation characteristics at the size range 25–100 mm (0.98–3.94 in), which is usually sorted.

If physical liberation is present there is a good potential that one of the sensors available on industrial scale sorting machines can differentiate between valuable and non-valuable particles.

Sensor-based sorting has been introduced by Wotruba and Harbeck as an umbrella term for all applications where particles are singularly detected by a sensor technique and then rejected by an amplified mechanical, hydraulic or pneumatic process.

Liberation characteristics are well known and relatively easy to study for particulate lots in smaller size ranges, e.g. flotation feed and products.

The analysis is essential for understanding the possible results of physical separation and relatively easy to conduct in laboratory on a couple of dozens of grams of sample which can be studied using optical methods or such as the QEMSCAN.

In 2002, Cutmore and Eberhard stated that the relatively small installed base of sensor-based sorters in mining is more a result of insufficient industry interest than any technical barriers to their effective use [8] Nowadays sensor-based sorting is beginning to reveal its potential in various applications in basically all segments of mineral production (industrial minerals, gemstones, base-metals, precious metals, ferrous metals, fuel).

If liberation is present, there is good potential that one of available detection technologies on today's sensor-based sorters can positively or negatively identify one of the two desired fractions.

[11] The selection of a machine-type for an application depends various case-dependent factors, including the detection system applied, particle size, moisture, yield amongst others.

The applicable top size of the chute-type machine is bigger, as material handling of particles up to 300 mm (12 in) is only technically viable on this setup.

This sub-process has the function to pass single particles of the material stream in a stable and predictable manner, thus in a unidirectional movement orthogonal to the detection line with uniform speed profile.

In the detection sub-process location and property vectors are recorded to allow particle localization for ejection and material classification for discrimination purposes.

Spectroscopic methods such as near-infrared spectroscopy known from remote sensing in exploration in mining for decades, have found their way into industrial scale sensor-based sorters.

[13] To cope with high volume mass flows and for application, where a changing physical location of the sensor-based sorting process is of no benefit for the financial feasibility of the operation, stationary installations are applied.

Within stationary installations, sorters are usually located in parallel, which allows transport of the discharge fractions with one product and one waste belt respectively, which decreases plant footprint and amount of conveyors.

For higher grade applications such as ferrous metals, coal and industrial minerals, sensor-based ore sorting can be applied to create a final product.

The latter option has the disadvantage that the planned production time, the loading, of the sensor-based ore sorter is low, unless a significant intermediate stockpile or bunker is installed.

In addition, the tonnage is significantly lower in comparison to the total run-of-mine stream, the size range is applicable and usually uniform and the particles' surfaces are clean.

Prejudice against waste rejection with sensor-based sorting widely spread, that the loss of valuables, thus the recovery penalty of this process, supersedes the potential downstream cost savings and is therefore economically not viable.

Before entering into sensor-based ore sorting testing procedures there is the possibility to assess the degree of liberation through the inspection of drill cores, hand-counting and washability analysis.

The quantification of liberation does not include any process efficiencies, but gives an estimate of the possible sorting result and can thus be applied for desktop financial feasibility analysis.

Hand-counting is a cheap and easy to conduct method to estimate the liberation characteristics of a bulk sample wither originating from run-of-mine material, a waste dump or for example exploration trenching.

Outo of a sample set of multiple hundreds of fragments in the size range 30-60mm are measured individually on each of the available detection technologies.

Since the tests are conducted on industrial scale equipment, there is no scale-up factor involved when designing a flow-sheet and installation of sensor-based ore sorting.

Containerised units in conjunction with Diesel-powered crushing and screening equipment are often applied and used for production test runs under full scale operating conditions.

Tomra's sensor-based sorting equipment and services for the precious metals and base metals segment are marketed through a cooperation agreement with Outotec from Finland, which brings the extensive comminution, processing and application experience of Outotec together with Tomra's sensor-based ore sorting technology and application expertise.

Each machine can separate good products from wastes, foreign bodies and defects and guarantees high levels of food safety for the final consumer.

The expert conference “Sensor-Based Sorting” is addressing new developments and applications in the field of automatic sensor separation techniques for primary and secondary raw materials.

Up to 500,000 tons of raw tungsten ore are mined each year by Wolfram Bergbau und Hütten AG (WHB)in Felbertal, Austria, which is the largest scheelite deposit in Europe.