Industrial Microwave Units
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Mineral

Recycling mineral sludge into lightweight aggregates

IDCO proposes recycling mineral sludge into lightweight aggregates with microwave.
This sludge comes from :

  • aggregates quarries wash (clayey or calcareous sludge)
  • mineral Industry (for example alumina manufacturing and red mud)
  • mining Industry

Lightweight aggregates are obtained either by expanding or by creating porosity in a fixed volume



Expansion (clay sludge - aggregates)

Clayet layey washing quarry sludge

Expanded aggregates


The expanded clay aggregates are completely natural and combine lightness, resistance, rot-proof, heat insulation, sound insulation, fire resistance and chemical resistance.

They are manufactured to date in rotary kilns with specific clay extracted from quarries operating especially for this purpose.

The use of the quarry washing sludge is IMPOSSIBLE in the current manufacturing processes (rotary kiln) because their expansion is impossible with the conventional heating (from the outside inwards).

General Features :

  • light : bulk density : 300 to 800 kg/m3
  • insulation: thermal conductivity : 0,08 to 0,13 W/mK (related to density)
  • resistance: crushing strenght : 1 to 3,5 N/mm2 or Mpa (NF 13055-1)
  • size : 3 to 20mm
  • Specific heat capacity : 1 kJ/kg°K

They are classified Euro A1 for fire resistance (NF 13501-1)

Market price : between 60 and 90 €/m3

The advantage : expanded clay has a value on an established and structured market

The beads uses are :

  • lightweight concrete
  • lightweight prefabricated products
  • hyproponic
  • gardening and decoration
  • earthworks and embankments
  • filtration


IDCO’s technology provides customized aggregates to the specifications of different applications:

high water retention balls for hydroponics (35% in 10 minutes) or sealed balls (less than 2% water), resistant and lightweight for lightweight concrete and lightweight prefabricated products.

Current French market estimation is 300.000m3 / year, but is steadily increasing and is expected to grow strongly with the entry into force of the RT2012 requiring the use of this type of material in buildings.

Expansion (clay sludge - process)

This type of recycling concerns clay sludge coantaining less than 15% limestone.

Their dryness should be about 24% (shovellable » or filter press output)

Sludge is mostly cycloning. Then they are either directly pouring directly into settling lagoon or flocculated, settled and then filtered before storage.


Quarry sludge recycling needs several milestones:

1 chemical analysis

Chemical composition knowledge is essential to evaluate the expansion feasibility and the necessity of additives : chemical element abalysis (SiO2, Al2O3, Fe2O3, CaCO3, CaO, Na2O, K2O ...) and mineralogical analysis (clay specifications)

2 – faisability : expert software

Expansion faisability is analyzed by an expert software (Riley diagram). This software computes percentages of additives so that silica, alumina and fluxes ratios are between determinated values.

 3 – Faisability: laboratory trials

The expansion occurs through the creation of gas from organic components while the clay is in a pyroplastic phase (about 1100 ° C).


IDCO laboratory tests validate formulations and the expansion temperature. They should be complemented by semi-industrial tests with 6kW/2450Mhz pilot.

4 – Industrial unit design

Only IDCO microwave technology make sludge recycling possible. The expansion level is very low and conventional processes with outside inward heating would stick the balls between them.

IDCO technology comprising heating from the inside outward and effective brewing allows an efficient and homogeneous heating.

  • Sludges are, if necessary, mixed to one or several additives (0 to 10% - by-products)
  • Mixture is shaped into pellets through an extruder
  • Pellets are preheated in an air heat exchanger
  • Pellets are heating again in a rotary kiln (prferably wood fuel) at 900°C
  • Preheated pellets are expanded into microwave oven (about 1100°C)
  • Expanded balls are cooled through an heat air exchanger
  • Cooled balls are screened and, if necessary, stored


Lightweight balls (calcareous sludge)

1 – Principle

Porosity is created by off-gases during heating at about 1000 ° C. Unlike the expansion, the volume of the ball stays the same.

  • The lightness of the grain is given by the final porosity (degassing of CaCO3 and organic matter)

  • The ball strength is given by structuring additives

Balls are lightweight (density 0.6 to 0.7), resistant and waterproof.


The beads uses are the same as those of expanded clay :

  • lightweight concrete
  • lightweight prefabricated products
  • hyproponic
  • gardening and decoration
  • earthworks and embankments
  • filtration


2 – Industrial unit

  • Sludges are, if necessary, mixed to additives (30% - by-products)
  • Mixture is shaped into pellets through an extruder
  • Pellets are preheated in an air heat exchanger
  • Pellets are heating again in a rotary kiln (prferably wood fuel) at 800°C
  • Preheated pellets are heated into microwave oven (about 1000°C)
  • Lightweight balls are cooled through an heat air exchanger
  • Cooled balls are screened and, if necessary, stored

Lightweight balls (aluminous sludge)

1 – Aluminous sludge in partnership with 

Aluminous red sludge (Red Mud or RM) is a by-product of the Bayer process, generated in the industrial production of aluminium from Bauxite.

They are composed of about 15% residual alumina, 50% iron oxide, 10% of titanium oxide, 6% of silica, 5% of limestone, and 5% of sodium and possess traces of heavy metals (chromium, vanadium, arsenic) and radioactivity from bauxite (4 to 5 times greater than that of a natural soil).


2–Geopolymer

Geopolymers are synthetic rocks formed from a "polymerization" of mineral molecular chains. The alumino-silicate-based geopolymer are designated by the term "poly(sialate)," which is an abbreviation of poly (silico-oxo-aluminate) or (-Si-O-Al-O-) n (where n is the degree of polymerization).

Poly (sialate) results from a "geosynthesis" of poly (silisique) acid (SiO2)n and sodium aluminosilicate, in alkali medium (sodium hydroxide). In this structure, the sialate group (Si-O-Al-O-) is a crosslinking agent.

This synthesis is particularly suited to aluminous sludge by adding active silica and soda and providing a specific heat treatment.

Geopolymerization is a polycondensation reaction which requires, for the aluminous sludge, a specific heating. The unique IDCO microwave process can realise this and reaction very quickly and on an industrial scale. The "crosslinking" operation takes place at a temperature of about 200 ° C

3 –Laboratory validation

The analysis of aluminous red sludge is essential to determine the precise rate of the additives (active silica and soda) and heating settings.

4– Industrial unit

  • Sludges are mixed to additives (active silica; soda)
  • Mixture is shaped in balls
  • Pellets are cold expanded
  • Lightweight balls are « reticuled» into microwaves oven at 200°C
  • Lightweight aggregates are stored