WO2020096462A1

WO2020096462A1 - Carbon based raw material

Info

Publication number: WO2020096462A1
Application number: PCT/NO2019/050239
Authority: WO
Inventors: Thorsteinn HANNESSON; Jón Viðar SIGURÐSSON
Original assignee: Elkem Asa
Priority date: 2018-11-06
Filing date: 2019-11-05
Publication date: 2020-05-14
Also published as: NO345717B1; NO20181425A1; AR116979A1

Abstract

The present invention relates to acarbon-basedraw material for the production of ferrosilicon alloy and silicon metal, wherein the composition is, in weight % based on the total weight, excluding added water: at least one fossil carbon reductant in the amount of 40 –80;at least one of silica source or iron oxide(s) sourcematerial in the total amount of 0.5–25;optionallyat least onematerial comprising bio-carbon,in the amount of 5–40;and a binder system comprising hydraulic cement in the amount of 4 –12, and micro silica in the amount of 3 –12.Further, the present invention relates to a method or producing such composite carbon-based raw material and the use thereof.

Description

CARBON BASED RAW MATERIAL

Technical Field:

The present invention relates to a carbon based raw material to produce ferrosilicon and silicon. The present invention also relates to a method for the production of said carbon based raw material and the use thereof.

Background Art:

Silicon and ferrosilicon are produced from silica (Si0₂) rich minerals such as quartzite and quartz, by carbothermic reduction. The carbonaceous reductants used in the production process are conventionally coal, coke, charcoal and wood chips. The silicon and ferrosilicon alloys are produced in three phase submerged electrical arc furnaces, to which is charged a raw material mix, comprising said silica rich minerals, carbonaceous reductant and, when ferrosilicon is produced, an iron source. A reaction model for the reduction of silica assumes two distinct reaction zones in the furnace charge. An upper reaction zone with a temperature below 1.500 °C and an inner reaction zone or crater zone in the lower part of the furnace, with temperatures over 1.800 °C. Carbon materials in the upper reaction zone react with silicon monoxide, which is generated in, and rises from the crater zone, to form silicon carbide, which is an important intermediate product in silicon and ferrosilicon production:

2 C(s) + SiO(g) SiC(s) + CO(g) (1)

This reaction (1) is a gas - solid reaction where the reaction takes place at the interface between the gas and the solid carbon material. The rate of reaction depends on the specific surface area and the porosity of the solid carbon. The specific surface area and the porosity , along with other factors, determine the reactivity of the reducing material towards SiO gas in the upper reaction zone, and thus the Si recovered in the metal with respect to the Si charged to the furnace. Some of the SiO gas escapes, however, from the charge and reacts immediately with oxygen in the ambient air above the furnace charge, to form solid Si0₂ particles or microsilica dust, also known as silica fume.

The solid silicon carbide, formed in the upper reaction zone, moves into the crater zone and reacts with molten silica to form silicon, and silicon monoxide:

Si0₂ (1) + SiC(s) Si(l) + SiO(g) + CO(g) (2) The silicon accumulates at the hearth of the furnace and is eventually tapped from the furnace into ladles for post taphole treatment and casting. In the traditional production of ferrosilicon alloy, an iron source is added to the raw material mix (charge). The iron source is mainly in the form of iron oxides, e.g. iron ore pellets or mill scale from steel mills. The iron oxides are mostly reduced by CO gas in the upper reaction zone. The reduced iron together with silicon accumulates at the hearth of the furnace to form molten ferrosilicon.

The traditional approach to procurement of reducing materials for the smelting industry is to search in the market for carbon materials that meet the requirements as set by the specifications of the alloy to be produced. This greatly limits the availability of raw materials available. Even with using traditional raw materials that meet specifications, there are normally operation instabilities related to variations, such as size and moisture. These variations need to be adjusted for but frequent variations can easily cause unwanted disturbance of furnace stability.

Thus, there is a need to provide a new carbon based raw material for the smelting industry to alleviate the disadvantages discussed above.

Further, there is a desire to provide a low cost reducing material that meets all chemical and physical specifications required for the production of different grades of ferrosilicon and silicon metal by the carbothermic smelting process.

There is also a desire to provide a carbon based raw material for the production of ferrosilicon and silicon metal by the carbothermic smelting process, providing a high silica yield. Summary of Invention:

The present invention alleviates at least some of the shortcomings of the traditional materials, by designing and manufacturing a low cost reducing material that meet chemical and physical specifications required for the production of different grades of ferrosilicon and silicon metal by the carbothermic smelting process.

In a first aspect, the present invention relates to a carbon-based raw material for the production of ferrosilicon alloy and/or silicon by a carbothermic reduction process, wherein the composition comprises, in weight % based on the total dry weight: at least one fossil carbon reductant in the amount of 40 - 80 wt %; at least one silica source and/or at least one iron oxide(s) source, in the total amount of 0.5 - 25 wt %; optionally at least one material comprising bio-carbon, in the amount of 5 - 40 wt %; and a binder system comprising hydraulic cement in the amount of 4 - 12 wt %, and microsilica in the amount of 3 - 12 wt %.

In an embodiment, the at least one fossil carbon reductant is petroleum coke particles, coke particles, coal particles or a mixture thereof.

In an embodiment, the at least one silica source is silica particles, microsilica particles, quartz particles, quartzite particles, or a mixture thereof.

In an embodiment, the at least one iron oxide(s) source is mill scale particles or iron ore concentrate particles, or a mixture thereof.

In an embodiment, the material comprising bio-carbon is one of milled wood, shredded rubber, charcoal, or a mixture of any combination of two or three thereof. In an embodiment, the carbon-based raw material is in the form of a briquette having a cross-section of about 30 - 100 mm.

In a second aspect, the present invention relates to a method for producing a carbon- based raw material according to the present invention, comprising the steps of:

- mixing fossil carbon reductant particles in the amount of 40 - 80 wt %, at least one silica source and/or at least one iron oxide(s) source in the total amount of 0.5 - 25 wt %, a binder system comprising hydraulic cement in the amount of 4 - 12 wt % and microsilica in the amount of 3 - 12 wt %, and optionally at least one material comprising bio-carbon, in the amount of 5 - 40 wt %, (wt % being based on total dry weight), and adding water to obtain a castable mixture;

- forming the obtained castable mixture into briquettes; and

- curing.

In an embodiment of the method, the amount of water is 5-15 wt %, based on the total weight of the mixture. In an embodiment of the method, the at least one fossil carbon reductant is petroleum coke particles, coke particles, coal particles or a mixture thereof.

In an embodiment of the method, the at least one silica source is silica particles, microsilica particles, quartz particles, quartzite particles, or a mixture thereof.

In an embodiment of the method, the at least one iron oxide(s) source is mill scale particles or iron ore concentrate particles, or a mixture thereof.

In an embodiment of the method, the material comprising bio-carbon is one of milled wood, shredded rubber, charcoal, or a mixture of any combination of two or three thereof.

In an embodiment of the method, the castable mixture is filled in moulds to form briquettes having a cross-section of about 30 - 100 mm.

In a third aspect, the present invention relates to the use of a carbon-based raw material according to the invention, as at least part of the feedstock material in the carbothermic reaction process for the production of ferrosilicon or silicon metal. The carbon-based raw material according to the present invention is used as a reducing agent in said carbothermic reaction process..

Detailed description of the invention

In the present context the terms“carbonaceous raw material”,“reducing agent”, “reducing material”,“carbon based briquette” may be used interchangeably for denoting the carbon-based raw material according to the present invention.

In the present context“silicon metal” is used for denoting silicon produced by the carbothermic reduction process. Although silicon is a metalloid, it is commonly also referred to as silicon metal. Silicon produced by the carbothermic reduction process is normally of metallurgical grade of 96-99 % purity, however, the purity may vary depending on the purity of raw materials used and furnace operation.

In the present context the term“briquette” should be understood as a block, brick, lump, agglomerate or corresponding type of body, typically comprising a binder.

In the present context silica and quartz may be used interchangeably, unless otherwise specified. Quartz is crystalline silica (SiCk), which traditionally is the main raw material for the carbothermic process for the production of silicon metal and ferrosilicon. Silica may also be amorphous silica (S1O2) such as microsilica and radiclone dust (waste silica fume). The carbon-based raw material according to the present invention is a new composite carbon-based material, generally in the form of a briquette, comprising at least one fossil carbon reductant, at least one silica source and/or at least one iron oxide(s) source, a binder system comprising hydraulic cement and microsilica, and optionally at least one material comprising bio-carbon. The new composite carbon-based raw material is suitable for use as a reducing agent in the carbothermic production of ferrosilicon and silicon metal. Due to chemical and/or physical properties and interactions in-between the constituents in the briquette, combined effects, which are further explained below, will enhance the SiO reactivity of the carbon-based briquettes, and thus improve Si recovery, reduce C0₂ emissions, lower the consumption of the electrodes and may also reduce the energy consumption in the production process.

Throughout the present description and the following claims all amounts of the constituents in the carbon-based raw material, according to the present invention, are weight percent (wt %) based on the total amount (sum) of the dry constituents present, thus excluding any added water, unless otherwise specified.

The at least one fossil carbon reductant particles are suitably petroleum coke particles, coke particles, coal particles, or a mixture thereof. The petroleum coke (also called petcoke) can be both green and calcined of different forms, e.g. green, delayed petcoke. The coal may be of different origin and composition, such as low ash, medium-high volatile coal. The fossil carbon particle size is up to about 5 mm, such as up to 2 mm, and including fines with a particle size down to micron size, such as about 1 pm.

Advantageously the particles have a size of between 0.1 mm to 3 mm. The fossil carbon particles may be fines recovered from the main process in production of coal, coke and petcoke. The said fossil carbon reductant particles are present in the amount of 40 - 80 wt % based on the total dry weight of the carbon-based raw material, e.g. 56 - 75 wt %.

The binder system comprises hydraulic cement in the amount of 4 - 12 wt %, e.g. 5 - 10 wt %, and microsilica in the amount of 3 - 12 wt %, e.g. 3 - 10 wt %, based on the total weight of said raw material, excluding added water. The hydraulic cement can for instance be common or general-purpose Portland cement (e.g. Type I, according to ASTM Cl 50). By addition of microsilica, it was found that less hydraulic binder was needed in order to gain the same strength compared to if microsilica was not added. At the same time the silica/silicon compounds in the cement and the microsilica are sources of silica for the carbothermic reduction process. Microsilica, also known as silica fume, is an amorphous form of silica. The term “microsilica” used in the description and claims of this application refers generally to particulate, amorphous S1O2 which may be obtained from a process in which silica (quartz) is reduced to SiO-gas and the reduction product is oxidized in the vapour phase to form amorphous silica particles. Microsilica typically has a specific gravity of 2.1 - 2.3 g/cm³ and a specific surface area of 5 - 50 m²/g (BET). The primary particles are substantially spherical and are of micron and submicron size. Microsilica is preferably obtained as a co-product in the production of silicon alloys in electric reduction furnaces, but may also be (co)-produced in other processes. The at least one silica source and/or at least one iron oxide(s) source should be present in a total amount of 0.5 - 25 wt %, e.g. 5-25 wt %, based on the total dry weight of said raw material, excluding added water. The silica and/or iron oxide(s) present in the carbon-based raw material enhances the SiO reactivity of the reducing agent, leading to an increased silica yield, and thus increased total silicon recovery. The iron oxide(s) and/or silica present in the carbon-based raw material also provides iron source and silica to the process. Thus the constituents contributing to the enhanced SiO reactivity are also reactants of the carbothermic reaction process.

The silica (Si0₂) source(s) in the carbon-based raw material can be a natural or synthetic crystalline type silica, e.g. natural high silica minerals, such as quartz and/or quartzite. The silica source particles may also be of amorphous type silica, such as microsilica, or a mixture of the crystalline silica mineral and the amorphous type silica. Suitably, the silica source(s) is present in an amount of 0.5-25 wt %, e.g. 5-25 wt %, based on the total dry weight of said raw material. The silica source particle size should be up to about 10 mm, e.g. from about 0.1 pm to 10 mm. The silica particles can also include quartz fines.

The at least one iron oxide(s) source is typically mill scale, and/or iron ore concentrate Mill scale consists of mixed iron oxides, iron(II) oxide (FeO), iron(III) oxide (Fe₂0₃) and iron(II,III) oxide (Fe₃0₄, magnetite), and some elemental iron. Mill scale is generally formed on outer surfaces of plates, sheets or profiles when they are being produced by rolling red hot iron or steel billets in rolling mills, and varies in compositions. All forms of mill scale can be used as the iron oxide(s) source in the present invention. Suitably, the iron oxide source(s) is present in an amount of 0.5-25 wt %, e.g. 5-25 wt %, or 10-25 wt %, based on the total dry weight of said raw material.

The particle size of the iron oxide(s) source should be up to about 5 mm, e.g. from 0.1 pm to 5 mm.

The carbon-based raw material may contain 5-25 wt % of the at least one silica source or 5-25 wt % of the at least one iron oxide(s) source, however, the at least one silica source and the at least one iron oxide(s) source may both be present in the carbon-based raw material, in a total amount of 5-25 wt % based on the total dry weight of the carbon-based raw material.

The effects of silica (added silica and Si compounds from cemenf) in the briquettes:

The reactions (1) and (2) above are the two stage reaction between silica and carbon taking place in the furnace, one taking place in the hearth of the furnace where silica smelt and reacts directly with SiC (reaction (2). The other (reaction (1)) is the reaction between SiO gas and solid carbon in the upper part of the charge of the furnace. If, however, fine grained C and S1O2 are in close proximity, such as within the briquettes according to the present invention, at sufficient temperatures (above about 1600 °C), both reactions can take place at the same site, i.e. in the briquettes:

Si0₂(s) + 3 C(s) SiC(s) + 2 CO(g) (3)

Reaction (3) is endothermic. The required energy for reaction (3) is predominantly thermal energy directly from the charge (i.e. heat from exothermic reactions and SiO (g) condensation), thus heat from electrical energy is not the main source of energy (heat). The endothermic reaction (3) may have the effect of cooling down the briquettes in the charge, thereby enhancing the condensation of SiO gas by the following reaction; 2 SiO (g) Si (1) + Si0₂ (s,l) (4)

The enhanced condensation of SiO gas will increase the energy efficiency of the smelting process and the Si yield in the production process. The effects of iron oxide(s) source in the briquettes

The iron oxide(s) source, e.g. mill scale and/or iron ore concentrate, reacts mainly in the upper reaction zone. The different forms of iron oxides are mostly reduced by CO gas to elemental iron. This reaction increases porosity inside the briquettes, as the iron oxide has higher volume than the elemental iron, giving greater access for SiO gas to the exposed carbon. The increased porosity may thus lead to enhanced SiO reactivity of the carbon-based raw material, due to the increased gas-solid interface area.

The said reduction reactions of the iron oxide(s) are endothermic, and have the effect of cooling down the charge. The cooling of the charge may shift the Boudouard equilibrium to the right: 2 CO(g) C0₂(g) + C(s) (5) thereby increasing the amount of solid carbon in the charge. It should also be noted that iron oxides and, in particular metallic iron, act as catalysts in the Boudouard reaction.

As stated above, cooling of the charge may also enhance condensation of SiO gas.

The effects of material comprising bio-carbon

The optional material comprising bio-carbon is a material consisting of or comprising a carbon neutral carbon source with respect to C0₂ emissions. The optional bio-carbon comprising material is one or more of the following: milled wood, shredded rubber or charcoal. The at least one bio-carbon comprising material, when present in the carbon- based raw material, is present in the amount of 5 - 40 wt %, e.g. up to 35 wt % or up to 30 wt %, e.g. 10-30 wt %, based on the total weight of said carbon based raw material, excluding added water. Said bio-carbon comprising material opens up porosity, and adds highly reactive carbon to the briquettes, thus enhances the SiO reactivity of the carbon-based raw material and increases the silica yield of the carbothermic production of silicon of ferrosilicon. The at least one bio-carbon comprising material also contributes to the total carbon content in the carbon-based raw material. The carbon- based raw material, according to the present invention may include all three types of bio-carbon comprising material, i.e. milled wood, shredded rubber and charcoal, a combination of two types of the of bio-carbon comprising material, or only one of the specified bio-carbon comprising material types.

In an embodiment, the material comprising bio-carbon, as an additional carbon source for the briquettes, is shredded rubber from tires, added in amounts as indicated for the bio-carbon comprising material above. The particle sizes of the shredded rubber should be up to about 10 mm, e.g. from about 0.1 mm to 10 mm. Old rubber tires are ready available waste material, partly made from bio-carbon. As the rubber is pyrolyzed within the briquettes it creates porosity, thus increasing the SiO reactivity of the carbon- based briquettes, due to the increased gas-solid interface area, as explained above. The rubber contains up to 30 % of solid carbon black, which acts as a carbon reductant in the carbothermic process. Additional carbon could also be deposited in the briquette from cracking of the rubber elastomer. As the briquettes are heated up in the furnace, the thus formed solid carbon particles will be retained within the matrix of the briquette. The carbon black deposited within the briquette is a very finely grained powder and is therefore quite reactive. The increased porosity, and the deposited solid carbon particles and carbon black particles, enhance the SiO gas reactivity of the carbon based raw material.

In an embodiment, the material comprising bio-carbon, as an additional carbon source for the briquettes, is milled wood. The amount of milled wood should be according to the ranges indicated for the bio-carbon comprising material above. The particle sizes of the milled wood should be up to about 10 mm, such as from about 0.1 mm to 10 mm.

As the milled wood is carbonized in the briquettes during heating in the furnace, it will leave pores and voids in the briquette. The formation of pores enhances the SiO reactivity, as explained above. The pyrolytic process will also leave some solid carbon deposited within the briquettes, which acts as a carbon reductant in the same way as explained for the shredded rubber.

In an embodiment, the material comprising bio-carbon, as an additional carbon source for the briquettes, is charcoal. Charcoal is a highly reactive form of carbon. The amount of charcoal should be according to the ranges indicated for the bio-carbon comprising material above. The particle size of the charcoal should be up to about 10 mm, e.g. from about 0.1 mm to 10 mm. Addition of charcoal in the carbon-based raw material opens up pores and voids into the briquette as charcoal is porous by nature and reacts fast, thereby enhancing reactivity, in the same manner as explained above for the rubber and the milled wood.

The carbon-based briquettes according to the present invention, withstand handling without disintegrating or generation of considerable amount of fines, e.g. during production, transport, storage and use. The carbon-based briquettes according to the present invention may be produced in a variety of shapes and sizes, however, as a raw material for the carbothermic reduction process such briquettes should in general have a size (cross-section) of about 30 - 100 mm. Advantageously, the cross-section of the briquettes is in the range of about 60 - 100 mm. The briquettes may have different shapes, e.g. cylindrical, rectangular, round, elliptic, pentagonal, hexagonal, octogonal, etc. A pentagonal or hexagonal shape, such as an elongated pentagonal or hexagonal shape, may be advantageous for the transport of the briquette through transportation systems, siloes and the furnace. It has been found that briquettes with a hexagonal shape or pentagonal shape, having a size (cross-section) of about 60 - 70 mm, are very suitable for use in a carbothermic reduction process.

Examples of compositions of the carbon-based briquettes according to the present invention may comprise petroleum coke, coke and/or coal in the amounts as specified above, binder, mill scale and at least one of rubber, milled wood and charcoal. In another examples, compositions of the briquettes according to the present invention may comprise petroleum coke, coke and/or coal in the amounts as specified above, binder, silica (quartz) and/or microsilica and at least one of rubber, milled wood and charcoal.

In a specific embodiment, the composition of the carbon-based raw material is, in weight % based on the dry materials:

petroleum coke fines, coke fines and/or coal fines: 56 - 75 wt %;

mill scale or silica: 15 - 25 wt %;

hydraulic cement: 6 - 10 wt %;

microsilica: 4 - 10 wt %;

and 6 - 15 wt % water (based on the total weight of the material).

The relevant constituents and the binders are mixed together in a suitable mixer, e.g. cement mixer or the like, water is added, generally in the amount of 5-15 wt %, based on the total weight of the composition, forming a castable mixture, and the mixture is formed into briquettes, and left to cure. The forming of briquettes may be done by filling, e.g. by pressing and/or vibrating, the castable mixture into moulds. After proper curing the briquettes are ready for use. By curing it is meant curing of the hydraulic cement binder. The curing and drying can be done at normal temperatures. It is, however, possible to reduce the curing and drying time by moderate heating, e.g. to about 40 to 50 °C, hence, the briquettes are produced with a well-known, low cost technology of the same type as for casting of e.g. concrete stones/briquettes. The use of the present carbon-based briquettes will reduce the CO2 emission from the smelting process, e.g. due to the shift in the Boudouard reaction which converts some of the CO2 gases into reactants in the form of solid carbon particles. In addition petroleum coke has a higher ratio of fixed carbon relative to volatiles, i.e. high Fix C / total C ratio, compared with coal and coke, which also results in lower CO2 emissions. Further, the milled wood, the shredded rubber and the charcoal provide a carbon neutral bio-carbon to the mix, thus lowering the carbon dioxide footprint.

The following Examples illustrate the present invention without limiting its scope.

Example 1: Laboratory scale tests

Test of briquettes were made in the laboratory to optimize the physical and chemical properties of the briquettes, thus aiming to find suitable proportions of water, cement, microsilica, mill scale, silica and carbon, with respect to strength and curing time. From the briquettes, two proto types were selected for SiO gas reactivity tests. The test used was the modified SiO reactivity test, developed at the SINTEF laboratories of NTMJ, the Norwegian ETniversity of Science and Technology in Trondheim, Norway (T.

Lindstad, S. Gaal, S. Hansen and S. Prytz: "Improved SINTEF SiO-reactivity test", INFACON XI, India 2007). The composition of the test briquettes is shown in Table 1 below. The amount of water is based on the total weight of the briquettes.

Table 1 Composition of test briquettes.

The SINTEF reactivity tests gave in general very good results. The reactivity measured was similar to that of reactive char and charcoal, which are the materials traditionally used, and considered to be the most suitable reduction materials, in the production of ferrosilicon and silicon metal. The results of the reactivity tests are given in table 2. Table 2. Results of the SINTEF reactivity tests.

Reactive char and charcoal have reactivity lower than 1.000 ml SiO. The lower this figure is the more reactive is the carbon. High reactivity improves silica yield in the process. It is seen from table 2 that the carbon based raw material briquettes according to the present invention have a reactivity of respectively 806 ml SiO and 793 ml SiO, which are very good results, indicating a very high reactivity.

Example 2: Furnace tests

Out of the samples in Example 1, sample A was selected for a full-scale test in a furnace. The sample A showed a SINTEF reactivity of 806 ml SiO (corrected R10 value). The method and equipment used for producing the briquettes were the same as used to produce precast concrete pavement stones and bricks. All components were weighed and charged into a concrete mixer. After thorough blending, the obtained mixture was pressed and vibrated into hexagonal moulds of 6 x 7 cm. The briquettes were then discharged from the moulds for drying and curing at ambient temperatures for 7 days. After curing the briquettes were ready for use.

The first test batch was 502 Mt. It was tested in a 37 MW ferrosilicon furnace, producing 75 % ferrosilicon. The briquettes comprised up to 10 % of the fixed carbon in the furnace charge, where the rest of the carbon in the charge were normal reductants; char, coal and wood chips. The test was successful with respect to good silica yield and specific energy consumption. The specific energy consumption improved by more than 3 % during the test as compared to the specific energy consumption prior to and after the test. In addition, the specific electrode consumption significantly reduced.

Having described different embodiments of the invention it will be apparent to those skilled in the art that other embodiments incorporating the concepts may be used. These and other examples of the invention illustrated above are intended by way of example only and the actual scope of the invention is to be determined from the following claims.

Claims

P a t e n t c l a i m s

1. A carbon-based raw material for the production of ferrosilicon alloy and/or silicon by a carbothermic reduction process, wherein the composition comprises, in weight % based on the total dry weight:

- at least one fossil carbon reductant in the amount of 40 - 80 wt %;

- at least one silica source and/or at least one iron oxide(s) source, in the total amount of 0.5 - 25 wt %;

- optionally at least one material comprising bio-carbon, in the amount of 5 - 40 wt %; and

- a binder system comprising hydraulic cement in the amount of 4 - 12 wt %, and microsilica in the amount of 3 - 12 wt %.

2. A carbon-based raw material according to claim 1, wherein the at least one fossil carbon reductant is petroleum coke particles, coke particles, coal particles or a mixture thereof.

3. A carbon-based raw material according to any one of claims 1 or 2, wherein the at least one silica source is silica particles, microsilica particles, quartz particles, quartzite particles, or a mixture thereof.

4. A carbon-based raw material according to any one of claims 1-3, wherein the at least one iron oxide(s) source is mill scale particles or iron ore concentrate particles, or a mixture thereof.

5. A carbon-based raw material according to any one of claims 1-4, wherein the material comprising bio-carbon is one of milled wood, shredded rubber, charcoal, or a mixture of any combination of two or three thereof.

6. A carbon-based raw material according to any one of the preceding claims 1-5, wherein the carbon-based raw material is in the form of a briquette having a cross- section of about 30 - 100 mm.

7. Method of producing a carbon-based raw material according to any one of claims 1-6, comprising the steps of:

- mixing fossil carbon reductant particles in the amount of 40 - 80 wt %, at least one silica source and/or at least one iron oxide(s) source in the total amount of 0.5 - 25 wt %, a binder system comprising hydraulic cement in the amount of 4 - 12 wt % and microsilica in the amount of 3 - 12 wt %, and optionally at least one material comprising bio-carbon, in the amount of 5 - 40 wt %, wt % being based on total dry weight,

- adding water to obtain a castable mixture;

- forming the obtained mixture into briquettes; and

- curing.

8. Method according to claim 7, wherein the amount of water is 5-15 wt %, based on the total weight of the mixture.

9. Method according to any one of claims 7 or 8, where the castable mixture is filled into moulds to form briquettes having a cross-section of about 30 - 100 mm.

10. Use of a carbon-based raw material according to any one of claims 1 - 6, as at least part of a feedstock material in a carbothermic reaction process for the production of ferrosilicon or silicon metal.