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More than two years ago, the team of the RICE research centre of the Faculty of Electrical Engineering (FEE) of the University of West Bohemia (UWB), led by František Mach, introduced an electrostatic plastic separator. The principle, in which a strong electric field sorts the individual parts of a mixture according to their electrical charge, has been tested by the scientists in other materials. The separator will also find its application in the management of electrical waste, mineral raw materials, and in agriculture.

"In the last year, our project has significantly shifted and transformed. Together with one of our application partners, we have fully explored the use of the separator in the cleaning of agricultural crops," says František Mach from FEE, describing the new use of the equipment initially intended for separating plastic waste from industrial production. Scientists have found that the separator can be used, for example, to clean crop seeds from weed seeds and inorganic impurities or to separate healthy grains from mechanically damaged grains.

The electrostatic separation process itself is almost identical to that of plastics: the polluted mixture of agricultural crops is sucked into the separator, travels through an air conveyor where different parts of the mixture acquire different electrical charges due to friction, and then enters a separation chamber with two electrodes to which a high voltage is applied. There, the different elements of the mixture are separated precisely according to whether they are attracted or repelled by the electrodes. The pure crop is left in the collection basket, and everything else is separated into other baskets.

The principle of separation remains the same for agricultural applications, but the technology needs to be adapted. The differences are mainly at the chemical level of the crop, for which the separator settings need to be changed. "We use mathematical models to predict the behaviour of the material in the electric field, but we also have a large amount of data and experience that helps us to adjust the electrode settings, collectors, and the voltage so that the results are as good as possible," explains František Mach, adding that while the separator can sort plastic grit with 99-percent purity; when working with agricultural crops the requirement is up to 99.9 percent purity.

"Our separator technology seems to be relatively unique in this respect. Thanks to it, we can separate weed seeds from the mixture, often as large and heavy as the seeds we need to clean," says František Mach.

In addition to its variability and high separation quality, the separator also has the advantage of being energy-efficient. The power consumption of the high-voltage part of the separator is only in units of watts.

The technology, the development of which was financially supported by the Ministry of Industry and Trade of the Czech Republic, and which was initially used for the separation of various types of plastics, is thus finding further application. It can be used for such mixtures of materials that are sufficiently distant from each other in the triboelectric series and for which it is, therefore, possible to perform separation based on their different charge. In addition to plastics and agricultural crops, this can also include minerals. "We are able to separate what is charged," adds František Mach with exaggeration.

Given the technology's broad applicability, the FEE team is currently working on creating a start-up company that will take over the technology and ensure its market launch.