Processing of slags and ores with screening machines

Slag screening

Waste is incinerated in a waste incineration plant. What remains is slag and scrap. Waste incineration ash can contain a significant amount of ferrous and non-ferrous metals. The recycling of non-ferrous metals (NF metals) is of special interest due to their further use as secondary raw materials. The processing and use of recycled metals requires less energy input than the extraction of metal from raw materials and at the same time saves carbon dioxide (CO2).

But it is important that the recovered metals have few impurities from mineral slag residues, since low purity of the metal concentrates reduces the market value or even prevents material recycling altogether.

Screening machines for processing slags

Most slag processing methods are similar in their approach. Coarse components are first sorted out, and the remainder is divided into a fine and coarse fraction by a screening plant. The iron content is removed from the fine fraction by a magnetic separator. In a further step, the coarse fraction is crushed and then screened a second time. Subsequently, an eddy current plant recovers usable non-ferrous metals from the material stream. The resulting fine fraction is combined with the fine fraction from the first processing step. The outcome after the processing is a usable product similar to fine crushed stone as well as recyclable metal fractions.

For pre-classification, which usually requires separating cuts between 40 and 100 mm, we recommend the RHEox linear motion screen with its extremely robust design. It requires very little maintenance and is well suited for high capacities with medium as well as coarse separations. Pre-classification is useful because processing aggregates only function properly when the ratio of maximum to minimum particle size does not exceed a certain value. Another reason for pre-classification of metal concentrates is that the mass ratio between metal particles and adhering mineral impurity becomes worse the smaller the metal particle becomes, due to the increasing specific surface area of small particles. This highly impurified fraction therefore requires more complex processing than the coarser particles.

Due to the extremely random grain shapes of the non-ferrous metal concentrates consisting of flat, curved and elongated pieces, continuous classification of the finer material is very difficult. To solve this difficult screening task, a RHEsonox® screening machine is used upstream of the eddy current plant. The advantage of this type of screen lies in the combination of two vibration mechanisms. The first vibration excitation is a linear vibration generated by two counter-rotating unbalance motors and used to transport the screening material. The second type of vibration is a direct excitation of the screen cloth by using electromagnetically excited beater bars, which leads to accelerations of the screen cloth up to 15 g in standard operation. During the cleaning intervals, accelerations of up to 50 g can be achieved. These high accelerations keep the screen mesh free and knock off adhering mineral components from the coarse particles.

Ore screening

Ores are minerals of economic importance which are mined for their yield of metals. They are not suitable for direct processing. Therefore, it is often necessary to process them in several steps. With the help of efficient sorting and classifying equipment with high throughput rates, we are able to guarantee particularly economical production..

Screening machines for processing ores

The purpose of ore processing is to increase the metal content by removing the dead rock or to separate ores of different metals. Accordingly, it is an enrichment (concentration) or separation (separation). Screening machines are used after the crushing process that is when it is necessary to separate the resulting grains into specific size fractions, the so-called classifying.

Due to its robust and low-maintenance design, the linear vibrating screen RHEflex® is used for capacities from 10 t/h and separations from 2 to 10 mm in the field of prescreening or classification of ores. It is extremely uncomplicated and tolerant to material fluctuations.

For finer separations down to 10 µm and lower feed rates, the RHEstack® precision screening machine is used. It offers a large screening area at a compact design size. The applied micro-throwing principle not only achieves extremely pure screening results due to the large number of contacts of the material with the screen cloth, but also prevents wear on machine parts.

Recommended screening machines for ores & slags



Flexible and low-maintenance linear vibrating screen for pre-screening or uncomplicated classification.

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Combination of vibrating mechanisms reliably screens even fine material with irregular grain shapes.

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Ideal choice for numerous sharp separations in the fine- to medium-grain range.

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Product examples

  • Black metallic ores (chrome, nickel, cobalt, ...)
  • Non-ferrous metal ores (copper, zinc,...)
  • Light metal ores (bauxite, lithium,...)
  • Precious metal ores (silver,...)
  • Blast furnace, steelworks & metallurgical slag
  • Aluminium slag

Your benefits

  • High purity of recovered metal concentrates
  • Simple pre-classification on low-maintenance and robust linear vibrating screens
  • Finer fractions can be reliably classified despite irregular grain shapes