In industrial automation, 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.
The technique is generally applied in mining, recycling and food processing and used in the particle size range between . Since sensor-based sorting is a single particle separation technology, the throughput is proportional to the average particle size and weight fed onto the machine.
Functional principle of sensor-based sorting The main subprocesses of sensor-based sorting are material conditioning, material presentation, detection, data processing and separation.Kleine, Christopher; Wotruba, Hermann and Robben, Mathilde: A new tool for mining engineers – The sensor-based sorter. Sustainable Development in the Minerals Industry (SDIMI) Conference 2011, Aachen, Germany,
Material conditioning includes all operations which prepare the particles for being detected by the sensor. All optical sensors need clean material to be able to detect optical characteristics. Conditioning includes screening and cleaning of the feed material. The aim of the material presentation is the isolation of the particles by creating a single particle layer with the densest surface cover possible without particles touching each other and enough distance to each other allowing for a selective detection and rejection of each single particle.Wotruba, Hermann: Sensor Sorting Technology – Is the Minerals Industry Missing a Chance?. Proceedings of XXIII International Minerals Processing Congress, IMPC 2006, Istanbul, Turkey
There are two types of sensor-based sorters: the chute type and the belt type. For both types the first step in acceleration is spreading out the particles by a vibrating feeder followed by either a fast belt or a chute. On the belt type the sensor usually detects the particles horizontally while they pass it on the belt. For the chute type the material detection is usually done vertically while the material passes the sensor in a free fall. The data processing is done in real time by a computer. The computer transfers the result of the data processing to an ultra fast ejection unit which, depending on the sorting decision, ejects a particle or lets it pass.Kleine, Christopher and Wotruba, Hermann: Added value to the mining industry by the integration of sensor based sorting. Aachen international mining symposia, Mineral Resources and Mine Development, Institute of Mining Engineering I, May 26th and 27th 2010, 411-434
Sensor-based ore sorting Sensor-based ore sorting is the terminology used in the mining industry. It is a coarse physical coarse particle separation technology usually applied in the size range for . Aim is either to create a lumpy product in ferrous metals, coal or industrial minerals applications or to reject waste before it enters production bottlenecks and more expensive comminution and concentration steps in the process.
In the majority of all mining processes, particles of sub-economic grade enter the traditional comminution, classification and concentration steps. 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. High added value can be achieved with relatively low capital expenditure, especially when increasing the productivity through downstream processing of higher grade feed and through increased overall recovery when rejecting deleterious waste.
Introduction Sensor-based sorting is a coarse particle separation technology applied in mining for the dry separation of bulk materials. 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 , 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.
The separation is based on features measured with a detection technology that are used to derive a yes/no decision for actuation of usually pneumatic impulses. Sensor-based sorting is a disruptive technology in the mining industry which is universally applicable for all commodities. A comprehensive study examines both the technology's potential and its limitations, whilst providing a framework for application development and evaluation. All relevant aspects, from sampling to plant design and integration into mining and mineral processing systems, are covered.Robben C, Characteristics of sensor-based sorting technology and implementation in mining [Book]. - Shaker Verlag GmbH, in der Schriftenreihe zur Aufbereitung und Veredlung, Other terminologies used in the industry include ore sorting, automated sorting, electronic sorting, and optical sorting.
Definition 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.Wotruba, Hermann, und Hartmut Harbeck. "Sensor-Based Sorting." In Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH Verlag GmbH & Co. KGaA, 2010.
Liberation characteristics As for any other physical separation process, liberation is pre-requisite for possible separation. 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.
For larger particles above it is widely known for applications that are treated using density separation methods, such as coal or iron ore. Here, the washability analysis can be conducted on sample masses up to 10 tonnes in equipped laboratories. For sensor-based sorting, where laboratory methods can only tell about the liberation characteristics where the describing feature is the density (e.g. iron ore, coal), hand counting, single-particle tests and bulk tests can reveal the liberation characteristics of a bulk material: Hereby, only single particle tests reveal the true liberation, while hand counting and bulk testing give a result which also incorporates the separation efficiency of the type of analysis. More information on the testing procedures used in technical feasibility evaluation can be found in the respective chapter.
Historical development
The oldest form of mineral processing practiced since the Stone Age is hand-picking. Georgius Agricola also describes hand-picking is his book De re metallica in 1556.Agricola G De Re Metallica Libri XII [Book]. - Wiebaden : Fourier Verlag GmbH 2003, 1556. Sensor-based sorting is the automation and extension to hand picking. In addition to sensors that measure visible differences like color (and the further interpretation of the data regarding texture and shape), other sensors are available on industrial scale sorters that are able to measure differences invisible for the human eye (EM, XRT, NIR).
The principles of the technology and the first machinery has been developed since the 1920s (.Sweet A T [Patent] : 1678884. - United States of America, 1928. Nevertheless, widely applied and standard technology it is only in the industrial minerals and gemstone segments. Mining is benefiting from the step change developments in sensing and computing technologies and from machine development in the recycling and food processing industries.
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 Cutmore, N. G. and Eberhardt, J. E. “The future of ore sorting in sustainable processing”. Cairns, Australia : s.n., 2002. Processing Conference 2002. 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). Precondition is physical liberation in coarse size ranges (~) to make physical separation possible. Either the product fraction, but more often the waste fraction needs to be liberated. 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.
Feed preparation A size range coefficient of approximately three is advisable. A minimum amount of undersized fine material must enter the machines to optimize availability. Moisture of the feed is not important, if the material is sufficiently dewatered and the undersize fraction is efficiently removed. For surface detection technologies sometimes spray water on the classifying screen is required to clean the surfaces. Surface detection technologies would otherwise measure the reflectance of the adhesions on the surface and a correlation to the particle's content is not given.
Main machine types During the more than 80 years of technical development of sensor-based ore sorting equipment, various types of machines have been developed. This includes the channel-type, bucket-wheel type and cone type sorters.Clayton C G and Spackman R Gold ore sorting Nr. 4830193 [Patent]. - United States of America, Dec 29 1987.Blagden T and Verboomen J Clean coal at the speed of light [Report]. - Caboolture, Australia : Australian Coal Industry's Research Program (ACARP) Project No C13052, 2009. The main machine types being installed in the mining industry today are belt-type and chute-type machines. Harbeck made a good comparison of both disadvantages and advantages of the systems for different sorting applications.Harbeck H and Kroog H New developments in sensor-based sorting [Journal] // Aufbereitungs Teechnik 49. - 2008. - pp. 4-11. 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.
Chute-type machine The chute-type machine has a lower footprint and fewer moving parts which results in lower investment and operating costs. In general, it is more applicable to well liberated material and surface detection, because a double sided scanning is possible on a more reliable on the system. The applicable top size of the chute-type machine is bigger, as material handling of particles up to is only technically viable on this setup.
The cost for most average farmers and industry workers is around $500 for the study and ergonomic design of the sensor. The sensor itself is still a prototype not yet built but looking to be approved by FDA around 2003
Belt-type machine The belt-type machine is generally more applicable to smaller and to adhesive feed. In addition, the feed presentation is more stable which makes it more applicable for more difficult and heterogeneous applications.
Sub-processes The separation in both machine types comprises the following sub-processes:
Feed distribution