Raw materials

About Raw materials

As Ferro Duo, we can accept and process by-products from the iron and steel, cement, and chemical industries and return valuable products to the corresponding industries as part of the circular economy. The same applies to the recycling of corresponding waste. With years of experience, a corresponding authorisation basis and patented processes, we can accept numerous materials and subject them to sustainable processing.

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Ferrous sulphates

Ferrous-(II)-sulphate is produced as a by-product or waste in various industries, for example in the iron and steel industry and the titanium dioxide industry. Monohydrates as well as heptahydrates are produced in different qualities. Ferro Duo trades and processes these qualities as a certified waste management company and offers its customers individual solutions.

Iron chloride

Ferrous chloride is a by-product of steel pickling and the production of titanium dioxide. Besides its use in the chemical industry, e.g. for the production of iron oxide pigments, it is also used in other areas such as water treatment or biogas plants. The versatile use of iron-(II)-chloride reduces the amount of waste and contributes to the efficient use of resources in industry.

Iron oxides

Iron oxides are an important by-product or waste of the chemical and steel industries. They are produced in metallurgical plants, e.g. during the rolling of steel and the refining of pig iron. Iron oxide is also produced in the chemical industry, e.g. when roasting sulphur gravel.

Oil mill scale is produced as an aqueous, oil-containing iron oxide residue during the steel production process. The formation of mill scale is based on the interaction between the hot steel and the surrounding air. As soon as the steel leaves the furnace and enters the rolling mill, it comes into contact with the oxygen in the air. The high temperature promotes oxidation of the steel, causing a thin layer of iron oxide to form on its surface. This oxide layer is called mill scale. During rolling, parts of this oxide layer come off together with lubricant (e.g. oil) and must be disposed of.

Oxygen steel mill dust is generated as a by-product during the production of steel in an oxygen steel mill. The generation of oxygen steel mill dust begins when pig iron and scrap are fed into the steelmaking process. The process consists of blowing pure oxygen through the molten iron bath to reduce the carbon content and remove other unwanted impurities. During this process, fine dust particles are produced, which are called oxygen steel mill dust. The dust is composed of various compounds, including iron oxide, metal alloys and heavy metals.

Abrasive sludge is produced as a by-product or waste during the grinding process in various industrial applications such as metalworking and surface finishing. The generation of grinding sludge occurs when abrasive materials such as grinding wheels or abrasives come into contact with a workpiece surface to finish or polish it. During the grinding process, fine particles are produced which, together with the coolant or lubricant, are removed as a sludgy mixture called grinding sludge. This mixture can have different compositions depending on the type of grinding process and the materials used.

Sulphur gravel burn-off occurs during the process of sulphuric acid production by roasting sulphur gravel. Sulphur gravel is a mineral raw material that contains sulphur and various metal sulphides, especially iron-(II)-disulphide. Roasting is an important step in sulphuric acid production, in which the sulphur gravel is heated to release sulphur dioxide (SO2). The sulphur gravel is placed in so-called roasting furnaces and heated at high temperatures. The heating causes the sulphur gravel to react with oxygen and produce sulphur dioxide, while the metal sulphides are converted into oxides. The released sulphur dioxide is then further processed in sulphuric acid production. The remaining residue after roasting, the sulphur pyrites burn-off, mainly contains metal oxides of different compositions and can be utilised via different routes.


Various types of slag are produced in the iron and steel industry, including blast furnace slag, pig iron ladle slag, converter slag and pouring ladle slag.

Blast furnace slag   is a by-product of iron and steel production that is produced during the blast furnace process. When iron ore is smelted in a blast furnace, various materials are used to aid the process and remove impurities. The slag is formed by the melting and reaction of these materials and separates from the actual molten metal. The slag consists mainly of silicates, oxides and other mineral compounds. Depending on the cooling rate of the liquid slag, a distinction is made between two products with different properties. A small cooling rate produces mainly crystalline blast furnace slag, whereas rapid cooling produces glassy granulated blast furnace slag. The exact composition of the slag varies depending on the materials used and the specific production conditions.

Pig iron ladle slag is produced during the transformation of pig iron into steel in a pig iron ladle. Here, too, a slag is produced that consists of various mineral components.

Converter slag is produced during the manufacture of steel in a converter. The slag forms when the molten pig iron is injected into the converter, where it reacts with oxygen.

Ladle slag is produced when liquid steel is poured into a ladle. Here, too, a slag is formed that consists of various mineral components.

Steel mill dusts and sludges

Blast furnace gas sludge is produced during the dedusting of blast furnace gas during the production of pig iron in the blast furnace process. Blast furnace gas is the term used for the process gas that leaves the blast furnace at the upper end. The rising flow entrains particles that have to be separated from the gas flow before it can be used further. As a rule, solids separation is carried out in a two-stage process with wet separation of fine dust. This wet separation produces the so-called blast furnace gas sludge. Besides carbon and iron, this contains heavy metals such as zinc, lead and cadmium. Due to the high heavy metal content, this sludge cannot be recycled without prior treatment. Ferro Duo offers you customised solutions for this and will be happy to advise you on how to solve your individual problem.

Electric steel mill dust is generated as a by-product or waste during the production of steel in electric furnace plants. Electric furnace dust is generated during the melting process in the electric furnace. During this process, scrap, alloying materials and other metal additives are added to the furnace. Electric current is passed through the molten metal to heat it to high temperatures. The electrical resistance causes the material to heat up, melt and chemically react with each other. During this process, electric furnace dust is formed. The resulting dust particles are composed of metallic compounds, oxides, slag and other substances.

Fly ashes

Fly ash is a material produced during the combustion of coal or biomass in power plants. It is fine particles that are transported out of the combustion chamber via the flue gas flow during the combustion process. The dust-like ash is carried along in the flue gases and settles in the filters of the flue gas cleaning systems. Fly ash consists mainly of mineral components such as silicon dioxide, aluminium oxide, iron oxide and calcium oxide. Depending on the type of fuel used and the combustion technology, the composition of fly ash can vary.

Paper ashes

Paper ash is produced as a by-product or waste during the combustion of paper or paper-based materials. During combustion, the organic components of the paper are broken down, while mineral components such as inorganic fillers remain as ash. Paper ash can contain different components depending on the composition of the paper burnt. Typically, it consists of inorganic compounds such as calcium carbonate, clay minerals or titanium dioxide. The exact composition depends on the paper materials used and the manufacturing process.

Boiler sand

Boiler sand is produced as a residue during the combustion of coal or other solid fuels. The residue consists mainly of unburnt fuel residues, ash and mineral compounds that were not completely burnt during the combustion process. The formation of boiler sand can depend on various factors, such as the quality of the fuel, the combustion temperature and the design of the boiler system. Efficient combustion technology and optimal control of the combustion process can help to reduce the amount of boiler sand. Depending on its composition, boiler sand can be considered for different applications.

Bypass dust

Large quantities of different dusts are produced during the manufacture of cement. These differ significantly in composition, particle size distribution and place of origin. Based on this, they can be classified as raw material dust, raw meal dust, cement kiln dust, clinker dust, coal dust, and cement dust. With the exception of cement kiln dust, all other dusts have the same chemical composition as the corresponding raw material and can usually be traced back to the manufacturing process. Cement kiln dust, on the other hand, contains varying proportions of raw meal constituents, clinker compounds and newly formed salts (especially chlorides), which are specifically removed from the cycles via the cement kiln dust. Due to this use of a bypass to remove part of the kiln gas and the salts it contains, this dust is also referred to as bypass dust. Ferro Duo offers innovative processes to maximise the proportion of recycled bypass dust and make processes as efficient as possible.


Gypsum is produced as a by-product or waste in various industries, such as flue gas desulphurisation in power plants or in the production of titanium dioxide using the sulphate process.

Flue gas desulphurisation uses limestone or quicklime as an absorbent to reduce the sulphur dioxide (SO2) content in the flue gases. In this process, flue gases from incinerators are passed through a solution containing calcium hydroxide (milk of lime), whereby the sulphur dioxide in the flue gas reacts with the calcium hydroxide to form calcium sulphate (also known as gypsum). The gypsum is separated from the solution and then further processed.

Gypsum also plays an important role in titanium dioxide production. In the production of titanium dioxide, ilmenite, a mineral ore, is treated with sulphuric acid to obtain titanium dioxide. In the process, gypsum is produced as a by-product or waste during the neutralisation of the so-called dilute acid from ore digestion.

Gypsum has various areas of application. In the construction industry, it is often used as a building material to make plasterboard or as an aggregate in plasters and mortars. Furthermore, gypsum is used in agriculture, for example as a fertiliser or to improve soil structure.

Aluminium oxide

Aluminium oxide is a chemical compound consisting of aluminium and oxygen. It is obtained in both primary and secondary aluminium production. In both production processes, a molten aluminium is produced. This melt produces so-called drosses, which consist mainly of smelting salt, aluminium and aluminium oxide, and ammonia. This mixture is rich in aluminium oxide and can be utilised as a raw material.

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John doe

Department Manager Mill Scale

  • Ferrous sulphates
  • Iron chloride
  • Iron oxides
  • Slags
  • Steel mill dusts and sludges
  • Fly ashes
  • Paper ashes
  • Boiler sand
  • Bypass dust
  • Gypsum
  • Aluminium oxide
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