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Recycling - Ash / Slag

What are incineration slags?

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

Process

Incineration of household waste takes place in moving grate incinerators or fluidized bed furnaces, after which the residue is cooled in a water bath. The resulting product is a slag mass, called IBA (incinerator bottom ashes). This consists mainly of two main parts: metal and mineral fractions. Incinerator slags are usually first buffered (aging) and then upgraded in what is called an SCF (slag cleaning furnace). The metal fraction consists of both ferrous and non-ferrous metals. It is important to recover as much metal as possible to ensure that the mineral fraction is as pure as possible for potential future use as a building material.
Goudsmit offers a complete range of products with which these valuable metals can be recovered optimally, and has developed a special conveyor belt feeder that increases the yield of eddy current separators.

 

Incineration slag processing with non-ferrous eddy current separators

For example, Goudsmit has a (38HI) high frequency eddy current separator that is suitable for separation of even the finest metal particles from these slag fractions. Through various real-world tests Goudsmit has determined that the 38HI technology performs best in the slag-reprocessing sector. This is due to the extremely high magnetic force and rotation speed. Particularly when it comes to the separation of heavy metals such as copper and brass, we achieve a significantly higher separation yield than other systems. There are currently several options for producing new raw materials from minerals. These include granulates suitable for use in the civil and hydraulic engineering sector and concrete and asphalt industry and, in the future, raw materials safe for use in fully-fledged building and construction products.

Product

Incinerator slags, also known as bottom ashes, contain on average: 8-12% ferrous metals, 3-5% non-ferrous metals and ±80-85% minerals. Ferrous metals are easy to separate through magnetic techniques, such as overband and magnetic drum separators. These relatively pure ferrous fractions can then be fed directly back to the metal manufacturing industry (iron smelters / iron producers / blast furnaces) as secondary raw materials. Non-ferrous metals are separated as metal mix by eddy current technology. This metal mix can consist of aluminium, copper, zinc, brass, stainless steel, lead, nickel, gold, silver, palladium, platinum, magnesium and titanium. The table below shows the relative permeability of these non-ferrous metals. This value gives an indication of the susceptibility of the material to separation based on the eddy current principle. Buffering the slags results in aging. This leads to adverse chemical reactions with the pieces of aluminium metal. They erode and are then more difficult to separate. Buffering eliminates much of the moisture in the slag. On average, the moisture percentage will then be between 10 and 20%. 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. For the fine fractions several eddy current separators are often placed in a cascade arrangement to achieve optimal separation yield. The first machine, for example, mainly removes the bulk metals and the aluminium (LNF, light non-ferrous metals). The second eddy current separator focuses on the heavy metals (HNF, heavy non-ferrous metals), including the copper parts and wires.

Sample/specimen of 0-16mm fraction bottom ash

Minerals consist of stones, ceramic, glass and slags. These granulates, referred to in the Netherlands by their Dutch initializations IBC (material that may only be used if isolation, control and monitoring measures are taken) and AEC (a product of waste-to-energy plants), can be used as building material for applications such as: dikes, sound barrier walls and road construction. Government authorities have decreed that in the future these mineral fractions must be suitable for use as normal building materials (i.e. not subject to regulatory requirements for isolation, control and monitoring measures). Such applications would include use as concrete blocks, pavement tiles and bricks.

Material

Electrical conductivity

Density

Conductivity/Density

 

σ = [1/Ω ⋅ m]

ρ = [kg/m3]

σ/ρ = [m2/kg ⋅ Ω]

 

x106

 

x103

Non-magnetizable metals

 

 

 

Aluminium

37.0

2700

13.7

Magnesium

21.7

1740

12.5

Copper

59.9

8960

6.7

Silver

62.1

10500

5.9

Zinc

16.9

7140

2.4

Gold

41.7

19320

2.2

Brass

15.2

8500

1.8

Cadmium

13.3

8650

1.54

Tin

8.7

7300

1.2

Chrome

7.7

7190

1.07

Bronze

7.1

8900

0.80

Solder 50-50

6.7

9000

0.74

Titanium

2.3

4510

0.52

Platinum

9.4

21450

0.44

Lead

4.8

11360

0.42

Stainless steel

1.4

7800

0.18

Magnetizable metals

 

 

 

Cobalt

17.2

8850

1.95

Nickel

14.3

8890

1.61

Steel

5.6

7800

0.71

Non-magnetizable metals

 

 

 

Carbon

0.00

3500

0.00

Glass

0.00

2600

0.00

PVC

0.00

1300

0.00

 

 

 

 

Sustainability

Green Deal

Green Deals are the way to a sustainable economy. Main objectives are to reduce CO2 emissions, promote renewable energy and reduce energy consumption. Reuse of the ever-scarcer and ever-more-expensive fossil fuels is also a priority. For bottom ashes this primary means quality improvement of the reprocessing. Specifically, this means:

Green deal logo
  • maximum separation of ferrous and non-ferrous metals;
  • reduction of leaching to achieve suitability for use as construction aggregate;
  • the reduction of non-mineral fractions with the intention of use as aggregate (in concrete, asphalt and other products) or production of an immobilized waste that meets the requirements for a formed building material.

In this Green Deal it has been agreed that in 2017 half and in 2020 all processed bottom ash must be usable as normal building materials (i.e. not subject to requirements for isolation, control and monitoring measures). In addition, a minimum of metals (75% from fractions > 6 mm) must be recovered and less than 15% residual material may remain. Market players are busy working to employ current and future techniques to this end. Goudsmit is also developing its machines for optimal performance in such treatment processes.

Sustainable economy

A sustainable economy is an economy that is growing with respect for people, the environment and society. This rising awareness is an important part of the way we in the West want to and should proceed in the future. Putting the environment first, followed by people and then profit would be an ideal transition for the future of the Western world.

Circular economy

The circular economy is an economic system that is intended to maximize reuse of products and raw materials and minimize value destruction. This is in contrast to the current ‘disposable’ system in which raw materials are turned into products that are destroyed at the end of their useful service life.

Urban Mining

Urban Mining is the mining of the valuable materials that have ended up in the municipal waste. Metals are an important part of this. Basically it is just the recycling of metals, but calling it Urban Mining creates new awareness. The 'mining' of these metals as valuable secondary products is an important future vision, because currently too much metal is ending up in our waste. One example of such an initiative would be the collection and processing of the many old mobile phones that are still somewhere in our homes. They are full of valuable metals and other materials that would otherwise simply vanish. 

Similar product flows:

  • bottom ash (IBA)
  • household waste incinerator slags
  • aluminium incinerator slags
  • copper incinerator slags
  • metal-rich sludge
  • steel incinerator slags
  • stainless steel incinerator slags
  • metal incinerator slags
Unprocessed aluminum incineration slag

Products

Ferrite overband magnets

Suitable for thin to thick layers and do not require a control box. Very reliable and available in many belt widths. Transverse or inline installation above your conveyor belt.

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Neodymium overband magnets

Suitable for fine fractions in thin layers; also separate weakly magnetic particles. No control box required. Transverse or inline installation above conveyor belt. Also for mobile applications.

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Electro overband magnets

Electromagnetic overband magnets have a deeply penetrating magnetic field and are therefore suitable for very thick layers. A control box is required. Installation perpendicular to or in line with conveyor belt.

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Add-on magnetic head pulleys

Magnetic head pulleys capture ferrous and weakly magnetic particles and continuously carry them away. Suitable for installation in existing belt conveyor systems, in the bulk transshipment or recycling industries for example.

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EddyXpert - Eddy current separator

All-rounder; robust eddy current separator. Many possible combinations for desired application.

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EddyFines - Eddy current separator

Advanced, robust eddy current separator. For separation of the smallest non-ferrous particles.

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Magnetic drum separators Recycling

For separation of magnetic and weakly magnetic ferrous particles from a flow of material.

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Permanent drum separators for scrap

Applications: recycling of scrap. High capacity and deeply penetrating magnetic field. For the separation of extra large and sharp ferrous particles.

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Electro drum separators for scrap

Applications: recycling of scrap. High capacity and very deeply penetrating magnetic field. For the separation of extra large and sharp ferrous particles.

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