Bottom ash & incinerator slags

Powerful magnetic separation and sorting technology for recycling incinerator bottom ash.

Recycling industry | Goudsmit Magnetics

Domestic waste combustion process:

Burning household waste occurs in large ovens, after which it is cooled with water or air. The resulting product is a slag mass called IBA: Incineration Bottom Ashes. 

It consists mainly of two materials: metal and mineral fractions. Incinerator slags are usually first buffered (ageing) and then upgraded in what is called an SCF (slag cleaning furnace). 

The metal fraction consists of both ferrous and non-ferrous metals. 

Hereby it is important to recover as much metal as possible, creating a pure mineral fraction that is used as secondary building material.

What are incinerator slags?

Incinerator slags are a product of the waste-to-energy (WtE) process in which household waste is burned to generate warmth and electricity for households, for example. It is a grey, cement-like mass, coarse in texture.



  • minerals: 85 - 90%
  • ferrous / iron containing: 4 - 10%
  • non-ferrous: 2 - 5%


  • specific mass: 1,000 - 1,500 kg/m³
  • humidity: 0 - 30%
Separating ferrous metals

Ferrous metals are easy to separate with overband magnetic separators. The relatively pure separated ferrous fractions can then be fed directly back to the metal manufacturing industry (iron smelters / iron producers / blast furnaces) as secondary raw materials. 

The finer fractions contain so-called magnetic slag, these are nuggets consisting of mineral and metal. Magnetic slag can be best separated with a 1,800 or 3,000 gauss head roller magnet. 

Using the band speed and the position of the separation bulkhead, the grade of the material can be determined very accurately.

Ferrite overband magnet | Goudsmit Magnetics

Ferrite overband magnet | Goudsmit Magnetics

Eddy current separation

The eddy current technology separates non-ferrous metals as a metal mix. This metal mix can consist of aluminium, copper, zinc, brass, stainless steel, lead, nickel, gold, silver, palladium, platinum, magnesium and titanium. 

The drier the material, the more easily the metals can be separated. The finer the fractions are, the more difficult it is to separate the non-ferrous metals. Often, in the fine fractions, we place multiple eddy current separators in cascading order. 

This generates an optimal separation yield. The first machine, for example, focuses on the bulk metals and the aluminium (LNF, Light Non-Ferrous metals). The second eddy current focuses on the heavy metals (HNF, Heavy Non-Ferrous), including the copper parts and wires.

Eddy Current separator | Goudsmit Magnetics

Eddy Current separator | Goudsmit Magnetics


These products have been widely used in bottom ash application. The advanced technology ensures the best separation performance and easy operation.

Magnetic head pulley | Goudsmit Magnetics
Add-on magnetic head pulleys

Magnetic head roller separators for the efficient separation of iron parts and magnetic slag.

Overband magnet | Goudsmit Magnetics

Ferrite overband magnetic separators for separating the larger iron parts

Overband magnet electro

Electro overband magnets separate iron parts from thick layers, often applied at the beginning of the process

EddyXpert separator | Goudsmit Magnetics

EddyXpert 12 and 22HI-pole eddy current separators for the recovery of non-ferrous metals in the coarse and medium-small...

EddyFines Eddy current separator

EddyFines 38HI eddy current separator for the recovery of non-ferrous metals in the fine fraction with particles from 0-...

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