Raw Material Consumption per Ton of FeSi75: Quartz, Coke & Iron

Quick Answer: Producing 1 ton of Ferrosilicon 75 (FeSi75) requires approximately 1.78 tons of dry silica when the calculation assumes 98% SiO2 purity, 92% silicon recovery and 75% silicon in the finished alloy. However, published industrial reference data for closed-furnace FeSi75Al production report approximately 1,930 kg of quartzite, 845 kg of coke, 250 kg of iron chips and 54 kg of electrode paste per ton of alloy, together with electricity consumption of approximately 8,800 kWh/t. These figures represent different calculation bases and should not be combined into one universal furnace recipe. Actual consumption depends on raw material assays, reductant quality, silicon recovery and furnace operating conditions.

For a FeSi75 producer, the main raw materials are quartzite, carbonaceous reductants and iron-bearing materials. Electrode paste is also consumed during furnace operation, while wood chips or other charge-conditioning materials may be used depending on furnace design. The correct charge must be calculated from the target alloy chemistry, the chemical composition of each raw material and the plant's actual material balance.
 

Key Raw Material Consumption for 1 Ton of FeSi75

The following table provides a published industrial reference for smelting one ton of FeSi75Al in a closed submerged arc furnace. It is useful for preliminary production planning and comparison, but it is not a guaranteed consumption specification for every FeSi75 plant.

Data source: Padhamnath, P., Migas, P. and Karbowniczek, M., "Theoretical Investigation of the Impact of Impurities in Recycled Silicon Used for the Production of Ferrosilicon," Proceedings, 2024, 108(1), 18. The published table reports typical material and energy demand for different ferrosilicon grades in closed furnaces.

Important: The reference table identifies the high-silicon product as FeSi75Al. Its figures are industrial reference values, not ZhenAn's measured production consumption. The exact quartzite assay, moisture basis and individual furnace operating conditions should be checked before using these figures for a plant-specific charge calculation.

What Raw Materials Are Used to Produce FeSi75?

Ferrosilicon 75 is produced through the carbothermic reduction of silica in a submerged arc furnace. The silicon released during reduction dissolves into the iron-bearing liquid phase to form the final Fe-Si alloy.

The main materials entering the production process are:

1. Quartzite: The Main Silicon Source

Quartzite supplies silicon through silicon dioxide (SiO2). Its chemical purity directly affects the amount of available silicon entering the furnace.

For FeSi75 production, the main purchasing and inspection parameters include:

• SiO2 content: Determines the theoretical silicon units supplied per ton of quartzite.
• Al2O3: Introduces aluminium-bearing impurities into the furnace system.
• Fe2O3: Contributes iron-bearing material and must be included in the material balance.
• CaO and MgO: Affect the oxide balance and slag formation.
• Moisture: Increases the as-received mass and adds a drying load.
• Particle size: Influences charge packing, gas permeability and furnace behavior.

Quartzite with a higher SiO2 content supplies more theoretical silicon per ton, but chemical purity alone does not determine its suitability. Thermal stability, particle strength and size distribution also affect furnace operation.

For a more detailed assessment, see our guide to quartz quality in ferrosilicon production.

2. Carbon Reductants: Coke, Coal and Semi-Coke

Carbonaceous materials provide the reducing carbon required to convert SiO2 into silicon. Depending on the furnace and raw material system, the reductant blend may include metallurgical coke, coal, semi-coke or charcoal.

When selecting a carbon reductant, evaluate more than its fixed carbon content:

• Fixed carbon: Determines the effective carbon available for reduction.
• Ash: Introduces mineral impurities and increases the oxide burden.
• Volatile matter: Influences gas generation and the thermal behavior of the charge.
• Moisture: Changes the as-charged weight and drying requirements.
• Electrical resistivity: Affects the electrical characteristics of the furnace burden.
• Reactivity: Influences the rate of carbon-related reduction reactions.
• Mechanical strength: Determines how much material breaks down into fines during handling and charging.
• Particle size: Affects packing, gas permeability and reaction contact.

The published closed-furnace reference lists approximately 845 kg of coke per ton of FeSi75Al. A plant using a different coke quality or a blended reductant system should calculate the required charge from the actual fixed-carbon analysis and its production records.

3. Iron-Bearing Materials: Iron Chips and Steel Scrap

Iron-bearing materials supply the iron component of ferrosilicon. Clean steel scrap, iron chips and other suitable iron-bearing feedstocks may be selected according to the plant's raw material system.

The quantity required depends on the target silicon content, the iron content of the selected feedstock and the recovery of iron into the finished alloy.

Before charging iron-bearing materials, check:

• Actual iron content.
• Phosphorus and sulphur levels.
• Chromium and other residual elements.
• Oxidation, rust and surface contamination.
• Moisture and physical size.

The reference consumption for FeSi75Al is approximately 250 kg of iron chips per ton of alloy. This figure should not be directly applied to every type of scrap or iron-bearing material because their iron contents and recovery conditions differ.

4. Electrode Paste and Charge-Conditioning Materials

Electrode paste is consumed during the operation of self-baking electrodes in submerged arc furnaces. Its consumption is separate from the carbon reductant charged for silica reduction.

The closed-furnace reference reports approximately 54 kg of electrode paste per ton of FeSi75Al. Actual consumption depends on electrode design, furnace operation and electrode management.

Some furnace systems also use wood chips or other charge-conditioning materials to adjust burden structure and gas permeability. Their quantities depend on the specific furnace and should not be treated as a universal FeSi75 input.

Calculation Basis: How Much Silica Is Needed for 1 Ton of FeSi75?

Before calculating the complete furnace charge, it is useful to establish the silicon material balance. Silica is the main silicon source, so its theoretical requirement can be calculated from the target silicon content, SiO2 purity and silicon recovery rate.

The following worked example uses:

The 92% silicon recovery rate is an assumption for this example. It is not a guaranteed recovery rate for every FeSi75 furnace.

Step 1: Calculate the Silicon Available from 100 kg of Silica

First, calculate the actual SiO2 content in 100 kg of silica:

100 kg × 98% = 98 kg SiO2

Silicon accounts for approximately 28/60 of the molecular mass of silicon dioxide.

98 × 28 / 60 = 45.73 kg theoretical silicon

Therefore, 100 kg of dry silica containing 98% SiO2 supplies approximately 45.73 kg of theoretical silicon before furnace losses.

Step 2: Apply the Silicon Recovery Rate

Not all silicon entering the furnace is recovered in the finished alloy. Some silicon can be lost through furnace gas, silica fume, dust and other process routes.

Using the assumed 92% recovery:

45.73 kg × 92% = 42.07 kg recovered silicon

Under these assumptions, 100 kg of 98% SiO2 silica contributes approximately 42.07 kg of silicon to the finished alloy.

Step 3: Calculate the FeSi75 Output Supported by 100 kg of Silica

The finished alloy contains 75% silicon. Therefore, the amount of FeSi75 supported by 42.07 kg of recovered silicon is:

42.07 ÷ 75% = 56.09 kg FeSi75

In other words, 100 kg of the specified silica theoretically supports approximately 56.09 kg of FeSi75 production under the assumed recovery conditions.

Step 4: Calculate Silica Consumption per Ton of FeSi75

Scale the calculation to 1,000 kg of finished alloy:

1,000 ÷ 56.09 × 100 = approximately 1,783 kg

Therefore, the theoretical dry silica requirement is:

Approximately 1.78 tons of 98% SiO2 silica per ton of FeSi75.

This is a theoretical silicon-balance result based on the stated assumptions. It should not be interpreted as the complete furnace charge or a guaranteed industrial consumption rate.

FeSi75 Silica Consumption Formula

The same calculation can be expressed using a general formula:

Silica Required (kg) = Required Silicon in Alloy ÷ (SiO2 Purity × Silicon Fraction in SiO2 × Silicon Recovery)

For one ton of FeSi75:

750 ÷ (0.98 × 28/60 × 0.92) ≈ 1,783 kg

For other grades, replace the 75% silicon content with the actual target silicon content. For an alloy with a variable silicon specification, use the target value agreed for the production batch.

Theoretical Silica Requirement vs Industrial Consumption

The theoretical calculation above gives approximately 1,783 kg of dry silica, while a published closed-furnace reference reports 1,930 kg of quartzite per ton of FeSi75Al.

These figures are not contradictory. They represent different calculation bases:

The industrial reference is approximately 147 kg higher than the theoretical calculation. The difference cannot be assigned to one specific cause without the original quartzite assay, moisture basis, furnace balance and operating data.

For engineering estimates, use the theoretical formula to evaluate the effect of silica purity and recovery. For preliminary production planning, compare it with relevant industrial consumption data. For an actual furnace charge sheet, use measured plant consumption and laboratory results.

How Much Coke Is Needed for 1 Ton of FeSi75?

Carbon is required to reduce silicon dioxide into silicon. The simplified overall reaction is:

SiO2 + 2C → Si + 2CO

According to the reaction stoichiometry, approximately 24 mass units of carbon are required for every 28 mass units of silicon produced.

For 750 kg of silicon in one ton of FeSi75, the theoretical carbon requirement is:

750 × 24 / 28 ≈ 643 kg of pure carbon

This is a chemical stoichiometry calculation, not the actual coke charge. Industrial reductant consumption is affected by fixed-carbon content, SiC formation, intermediate reactions, carbon losses and furnace operating conditions.

For example, if a reductant contains less than 100% fixed carbon, its total charged mass must be higher than the corresponding pure-carbon requirement. The plant must also establish the additional carbon allowance from its actual furnace balance.

The published closed-furnace FeSi75Al reference reports approximately 845 kg of coke per ton of alloy. This is a useful industrial comparison, but the figure should not be used as a fixed coke requirement for every furnace or reductant blend.

How to Calculate Coke Consumption from Fixed Carbon

A simplified calculation framework is:

Reductant Mass = Required Charged Carbon ÷ Fixed Carbon Fraction

For example, a coke specification showing 85% fixed carbon has a fixed-carbon fraction of 0.85. The coke mass must be calculated from the actual carbon charge requirement established by the furnace material balance, not by automatically treating the theoretical 643 kg as the complete industrial carbon demand.

When the furnace uses a blend of coke, coal, semi-coke or charcoal, calculate the carbon contribution of each component separately.

How Much Iron Is Needed for 1 Ton of FeSi75?

Iron-bearing materials supply the iron component of the finished Fe-Si alloy. The required input depends on the final alloy chemistry, the iron content of the feedstock and iron recovery.

The calculation framework is:

Iron-Bearing Material Required = Required Iron Units ÷ (Iron Fraction × Iron Recovery)

The required iron units should be calculated from the actual target alloy composition. The iron fraction should come from the chemical analysis of the selected scrap, iron chips or other iron-bearing feedstock.

The published closed-furnace FeSi75Al reference reports approximately 250 kg of iron chips per ton of alloy.

Do not automatically apply 250 kg to every iron source. Steel scrap, iron chips, mill scale and iron ore pellets have different iron contents and reduction behavior. Their actual consumption must be established from the selected feedstock and the furnace's material balance.

Other Materials Used in FeSi75 Smelting

In addition to quartzite, coke and iron-bearing materials, furnace operation may require other consumables and charge-conditioning materials.

Electrode paste and electricity should be included when calculating production costs, even though they are not part of the finished alloy's chemical composition.

How Does Silicon Recovery Change Silica Consumption?

Silicon recovery directly affects the amount of quartzite required for a given FeSi75 output. A lower recovery rate means that more silica must enter the furnace to supply the same quantity of silicon to the finished alloy.

Using 98% SiO2 silica and a finished alloy containing 75% silicon, the calculated dry silica requirement changes as follows:

The figures are calculated scenarios, not measured consumption data from individual furnaces.

Silicon recovery can be affected by:

• Quartzite purity and thermal properties.
• Carbon reductant quality and reactivity.
• Temperature distribution in the reduction zone.
• SiO formation, circulation and recovery.
• Charge permeability and particle-size distribution.
• Furnace operating stability and material losses.

A producer should calculate silicon recovery using actual silicon input and silicon recovered in the finished alloy, with a consistent material-balance boundary.

How Does Silica Purity Affect Raw Material Consumption?

The SiO2 content of quartzite determines how much theoretical silicon is available from each ton of dry material.

Using the same 92% silicon recovery assumption, reducing silica purity from 98% to 95% increases the calculated silica requirement:

98 ÷ 95 − 1 ≈ 3.2%

The corresponding theoretical requirement changes from approximately 1.783 tons to approximately 1.839 tons per ton of FeSi75.

Lower SiO2 purity also means a greater mass of non-silica material enters the furnace. Depending on the impurity composition, these oxides may contribute to slag and affect the chemical balance of the final alloy.

For this reason, quartz purchasing should consider both SiO2 content and the levels of Al2O3, Fe2O3, CaO and MgO.

Read our Quartz Quality in Ferrosilicon Production Guide for more information about chemical purity, particle size and furnace stability.

How Should Moisture Be Included in Silica Consumption?

The theoretical silica calculation above uses dry material. If delivered quartzite contains moisture, the actual quantity weighed into the furnace must be higher because part of the delivered mass is water.

Use the following conversion:

As-Received Silica = Dry Silica Required ÷ (1 − Moisture Fraction)

For example, if the dry silica requirement is 1.783 tons and the delivered quartzite contains 3% moisture:

1.783 ÷ (1 − 0.03) = approximately 1.838 tons

The moisture content should be measured on the delivered batch. Do not use an assumed moisture value when preparing an actual furnace charge sheet.

How Much Raw Material Is Needed for 10, 50 or 100 Tons of FeSi75?

For preliminary planning, the theoretical silica requirement can be scaled directly according to the target output, provided that the same assumptions are maintained: 98% SiO2, 92% silicon recovery and 75% silicon in the finished alloy.

This table covers silica only. Coke, iron-bearing materials, electrode paste and electricity must be calculated separately from the relevant raw material specifications and furnace consumption records.

How Does Raw Material Quality Affect Actual FeSi75 Consumption?

Two plants producing the same FeSi75 grade may have different raw material consumption because their raw material quality, charge design and furnace conditions are not identical.

How to Calculate FeSi75 Production Cost per Ton

Raw material consumption is one of the main factors determining FeSi75 production cost. However, the cost per ton cannot be calculated from quartz consumption alone.

A practical cost calculation should include the following components:

• Quartzite purchase cost.
• Coke and other carbon reductant costs.
• Iron-bearing material costs.
• Electrode paste consumption cost.
• Electricity consumption cost.
• Other plant-specific production and processing costs.

The raw material and electrode cost can be expressed as:

C_materials = (Q_quartz × P_quartz) + (Q_coke × P_coke) + (Q_iron × P_iron) + (Q_electrode × P_electrode)

Electricity cost is calculated separately:

C_electricity = Electricity Consumption (kWh/t) × Electricity Price (per kWh)

For example, the published closed-furnace reference of 8.8 MWh/t is equivalent to 8,800 kWh per ton. The actual electricity cost depends on the plant's electricity tariff.

For a reliable cost comparison, use actual consumption data from the same furnace and production period. Do not combine a theoretical silica calculation with an unrelated coke or electricity price and present the result as a verified manufacturing cost.

What Information Is Needed for an Accurate FeSi75 Charge Calculation?

A plant-specific charge calculation requires more information than the target FeSi75 grade alone. The following checklist can be used when preparing a production calculation or reviewing a supplier's raw material proposal.

What Does Raw Material Consumption Mean When Buying FeSi75?

Buyers purchasing finished FeSi75 do not normally need to calculate the producer's furnace charge. However, raw material consumption helps explain why quotations from different producers may vary.

Two FeSi75 offers should be compared using the same purchasing conditions:

• Chemical composition: Actual Si content and maximum limits for Al, Ca, P, S and C.
• Particle size: For example, 10–50 mm or 10–100 mm, together with agreed fines and oversize tolerances.
• Batch quality: COA and inspection requirements.
• Packaging: Jumbo bags and any specified moisture protection.
• Quantity: Total order tonnage.
• Delivery terms: FOB, CFR or CIF and the destination port.

For the actual product chemistry and purchasing requirements, read our Ferrosilicon 75 Specification Guide.

Our FeSi75 Supply

We supply FeSi75 according to agreed chemical composition, particle size, packing and inspection requirements.

Common lump sizes include 10–50 mm and 10–100 mm. Other screened ranges can be discussed according to your charging and handling requirements.

Batch COA can be provided, and third-party inspection by SGS, BV or Intertek can be arranged when required by the order.

You can review our Ferrosilicon 75 product page for available product specifications and supply information.

Frequently Asked Questions

Technical References

• Padhamnath, P., Migas, P. and Karbowniczek, M. (2024). Theoretical Investigation of the Impact of Impurities in Recycled Silicon Used for the Production of Ferrosilicon. Proceedings, 108(1), 18. – Published closed-furnace reference data for quartzite, iron chips, coke, electrode paste, electricity consumption and silicon yield.
• Ferrosilicon – ScienceDirect Topics. – Reference information on ferrosilicon production, material consumption and furnace reactions.
• U.S. EPA – Development Document for Ferroalloy Manufacturing. – Background on quartzite, carbon reductants, iron-bearing materials and electric furnace production.