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Steel Desulfurization Agent Selection: Calcium Carbide vs. Magnesium-Based vs. Lime – Which Offers the Lowest Overall Cost?
2026-01-12
The driving factors for hot metal desulfurization (HMD) of steel are environmental and material trends. The sustainability goal set by ecological agencies requires reducing CO2 emissions from steelmaking processes. It will result in reliance on scrap metal, which typically has higher levels of impurities such as sulphur and phosphorus.
There will be increased demand for desulfurization when scrap metal is used as a raw material, which brings us to the main question: Which desulfurization agent—calcium carbide, magnesium, or lime—offers the lowest overall cost? The analysis requires evaluating the reactions of calcium carbide, magnesium, and lime with sulfur and other impurities in steel. Simply comparing their cost price is not the right way of evaluating their economics.
This article explores mechanisms and processes for desulfurization—a comparison of the reagents available for improving steel. Moreover, we will mention the performance data of each material. At last, we will perform an overall cost analysis. Let's start with the basics.
Why Do We Remove Sulfur from Steel?
The presence of sulfur in steel changes its physical characteristics. It is an impurity in the motel steel that, upon removal, yields “clean steel”. Problems such as hot shortness, poor weldability, reduced corrosion resistance, and SO2 emissions arise from sulfur in steel. Therefore, we can utilize different mechanisms and reagents to remove the unwanted element.
Desulfurization Mechanisms and Process Configurations
Principal of Desulfurization
Our goal is to ensure that sulfur is efficiently removed from molten metal, which is typically at levels of 0.02% to 0.06% by weight. The addition of reagents will cause the impurities to collect at the top as slag, which can be conveniently removed, or leave the mixture as a gas.
The key parameters to consider in the desulfurization process are the percentage removed (efficiency), sulfide capacity, and mass transfer between the reagent and the metal. Each type of slag will have a different sulfide capacity, which is the ability of the slag to hold sulfur. The inherent speed of sulfur movement is its diffusion rate, which is about 1.2x10-8m2/s at 1350 °C.
Chemical Reactions
Lime (CaO)
CaO + [S] → CaS + [O]
The lime reacts with the lime to form calcium sulfide and release oxygen. However, the process is slow because an immediate layer (for example, 2CaO.SiO2) of dense material forms, blocking further reaction. There aren't any side benefits of adding lime to the molten metal.
Calcium Carbide (CaC2)
CaC2 + [S] → CaS + 2[C]
When calcium carbide reacts with sulfur, it forms calcium sulfide, similar to lime. However, it produces carbon, which forms a graphite layer around the particle. The process limits diffusion. However, this is controlled through managing particle size. The side benefit of calcium carbide is the heat it releases, which helps maintain the molten metal's temperature.
Magnesium (Mg)
Mg + [S] → MgS (solid)
The reaction between magnesium and sulfur is much faster than the other two reactions. Magnesium vaporizes upon reaction at 1090 °C. The sulfur compounds nucleate in the gas phase. It adds heat to the molten metal and minimizes slag production.
Performance and Efficiency Data
● Magnesium (Mg): It offers the highest efficiency, removing 85% to 95% of sulfur in less than 5 minutes.
● Calcium Carbide (CaC2): Calcium carbide particles can achieve 65-90% removal. However, its outcome is sensitive to particle size. Using 11.8µm particles can push the removal to 90%.
● Lime (KR): Lowest efficiency, removing 50-70% over 10-20 minutes.
The reagent particles remain in contact with the metal for a very short time —about 0.4 seconds—when injected as dust into molten metal using a submerged lance. In the other case of adding calcium carbide in 2-10mm size, the time increases to 20-40 seconds. For comparison, we will consider dust form for all. The penetration ratio (β), which relates to how deep the reagent is injected, is typically 23-29%.
Desulfurization Processes
● KR (Kanbara Reactor)
Uses lime with a spinning impeller at 100rpm for mixing (10-20 min). It results in high slag, but has a low reagent cost. The process is controlled to ensure the mixture's basicity and to limit iron loss from the solids loss.
● MMI (Magnesium Mono-Injection)
Magnesium granules were injected (under 5 min). The reaction is fast due to 1090 °C (vapor). The whole process produces low slag. The main disadvantage of MMI is revulcanization, the reabsorption of sulfur into the hot metal.
● Co-Injection
The process uses blends of Mg-Lime. The blend is in powdered form and is injected into the molten metal using an inert gas, such as nitrogen, to enhance mixing. The gas improves mixing by forming bubbles.
● Torpedo Ladle Co-Injection
The torpedo ladle is the transport ladle that carries hot metal from the blast furnace to the steel shop. It uses a calcium carbide and lime blend to co-inject, using an inert gas, into the molten metal for mixing. It removes sulfur from the metal. The exothermic reaction cuts the temperature drop.
Detailed Reagent Characteristics and Handling
Here are the profiles for the three desulfurization reagents converted into bullet points:
1. Lime (CaO) Profile
● Cost & Use: Cheapest reagent ($150/ton) and also the leading agent in the KR process.
● Drawbacks: Causes a significant 0.5-2.5% iron loss due to making thick slag.
● Kinetics: Slow reaction, limited by layers like 2CaO.SiO2.
● Performance: While 50-70% is a baseline for simple CaO processes, modern, optimized ladle metallurgy like the KR process with strong stirring and fluxing routinely achieves high desulfurization rates, often over 90% from initial hot metal sulfur levels.
2. Calcium Carbide (CaC2) Profile
● Cost & Use: Used in cost-effective co-injection mixes ($380/ton).
● Kinetics: Removal is limited by a graphite shell forming around the particles. It is highly efficient with proper particle size selection. The most favorable and cost-effective particle size is 2-10mm, which settles to the bottom of the ladle.
● Safety: The Main risk is reacting violently with water (forms acetylene).
3. Magnesium (Mg) Profile
● Cost & Use: Most expensive reagent ($2270/ton). Used for ultra-low sulfur goals (under 10ppm) in the MMI process.
● Kinetics: Fastest agent, achieving higher removal rates.
● Losses: Causes minimal slag/iron loss but is highly susceptible to reagent loss due to boiling.
● Limitation: Efficiency drops in high-carbon metal (e.g., HIsarna) because graphite blocks the reaction.
|
Metric |
Lime |
Calcium Carbide |
Magnesium |
|
Removal % |
50-70 |
65-90 (90 fine) |
85-95 |
|
Time minutes |
10-20 |
5-12 |
under 5 |
|
Slag kg per ton |
10-15 |
8-12 |
under 5 |
|
Iron % lost |
2-3 |
under 1 |
under 1 |
|
Temp drop °C |
25-40 |
15-25 |
adds heat |
|
Final sulfur parts per million (from 400) |
100-200 |
10-50 |
under 10 |
Cost Analysis
As we mentioned earlier, analyzing the reagents requires comparing prices, consumption rates, and process penalties like iron loss+energy loss for each method. Simply comparing their initial cost can be misleading. Here, we will conduct a cost analysis of lime, magnesium, and calcium carbide across different processes. We will use the cost analysis used by Schrama, F. N. H. (2021) in “Desulphurisation in 21st century iron- and steelmaking” and use the latest pricing as of Q3 2025. Before proceeding please view the following note:
Note on Cost Model and Data Sources:
The consumption figures, iron-loss values, temperature penalties, and wear/N₂ costs are taken directly from Schrama, F.N.H. (2021) – Desulphurisation in 21st century iron- and steelmaking, TU Delft. Most industrial data in the thesis originates from Tata Steel IJmuiden (2017–2020 operating conditions).
Actual costs at other plants will vary depending on local hot-metal composition, equipment design, reagent quality, labour rates, and energy prices. The relative ranking (Mg cheapest → Co-injection → CaC₂+lime → KR-lime most expensive) and the magnitude of penalties have been confirmed at multiple European and Asian integrated steel mills, but absolute $/tHM figures should be considered indicative rather than universally applicable.
Prices (IMARC Group only):
● Lime: $150/MT (Quicklime Report, Q3 2025)
● Calcium Carbide: $380/MT (Calcium Carbide Report, Oct 2025)
● Magnesium: $2,270/MT (Magnesium Report, Q3 2025)
Reagent consumption from Schrama (2021), Chapter 8.4.2, 8.5.1:
|
Process |
Lime (kg/tHM) |
CaC2 (kg/tHM) |
Mg (kg/tHM) |
|
KR-Lime |
12–15 |
— |
— |
|
MMI-Mg |
— |
— |
0.6–0.8 |
|
Co-Injection (Mg+Lime) |
4–5 |
— |
0.3–0.4 |
|
CaC2+Lime Blend |
4–6 |
6–8 |
— |
Penalty factors from Schrama (2021):
|
Factor |
Value |
Source |
|
Iron loss (KR-Lime) |
25 kg/tHM |
Ch. 3, p. 61 |
|
Iron loss (others) |
8 kg/tHM |
Ch. 3, p. 62 |
|
Temp drop (Lime) |
30°C |
Ch. 2, p. 30 |
|
Temp drop (CaC2) |
15°C |
Ch. 2, p. 30 |
|
Temp drop (Mg) |
0°C net |
Ch. 2, p. 30 |
|
Iron price |
$420/MT |
Ch. 8, p. 164 |
|
Temp cost |
$0.045/°C |
Ch. 8, p. 165 |
|
N2 + wear (KR) |
$1.25/tHM |
Ch. 8, p. 165 |
|
N2 + wear (MMI/Co-inj) |
$0.55–0.80/tHM |
Ch. 8, p. 166 |
Step-by-Step Cost Calculation (per tHM)
|
Process |
Reagent Cost |
Iron Loss |
Temp |
Wear/N2 |
Env |
TOTAL |
|
KR-Lime |
13.5 kg x $150/1000 = $2.04 |
25 kg x $0.42 = $10.50 |
$30°C x $0.045 = $1.35 |
$1.25 |
$0.25 |
$15.39 |
|
MMI-Mg |
0.7 kg x $2,270/1000 = $1.59 |
8 kg x $0.42 = $3.36 |
$0.00 |
$0.55 |
$0.15 |
$5.65 |
|
Co-Inj (Mg+Lime) |
(4.5 kg x $150.67 + 0.35 kg x $2,270)/1000 = $1.47 |
$3.36 |
$10°C x $0.045 = $0.45 |
$0.80 |
$0.15 |
$6.23 |
|
CaC2+Lime Blend |
(5 kg x $150.67 + 7 kg x $380)/1000 = $3.41 |
$3.36 |
$15°C x $0.045 = $0.68 |
$1.00 |
$0.30 |
$8.75 |
2025 Cost Summary Table (IMARC + Schrama Only)
|
Process / Agent |
Reagent |
Iron Loss |
Temp |
Wear/N2 |
Env |
Total ($/tHM) |
|
KR-Lime |
$2.04 |
$10.50 |
$1.35 |
$1.25 |
$0.25 |
$15.39 |
|
MMI-Mg |
$1.59 |
$3.36 |
$0.00 |
$0.55 |
$0.15 |
$5.65 |
|
Co-Inj (Mg+Lime) |
$1.47 |
$3.36 |
$0.45 |
$0.80 |
$0.15 |
$6.23 |
|
CaC2+Lime Blend (Torpedo) |
$3.41 |
$3.36 |
$0.68 |
$1.00 |
$0.30 |
$8.75 |
CHMD (Continuous) Savings
Schrama (2021), Chapter 8, p. 167:
“Continuous desulfurization reduces reagent by 10–15%, iron loss by 50%, wear by 20%.”
|
Process |
Batch Cost |
CHMD Cost |
Savings |
|
CaC2+Lime (Torpedo → CHMD) |
$8.75 |
$7.44 |
−15% |
|
Mg+Lime Co-Inj |
$6.23 |
$5.30 |
−15% |
Final Verdict — IMARC + Schrama Only
|
Agent |
Cost Rank |
Total ($/tHM) |
Best For |
|
MMI-Mg |
1st |
$5.65 |
Ultra-low S, speed |
|
Co-Inj (Mg+Lime) |
2nd |
$6.23 |
Balanced cost + performance |
|
CaC2+Lime (CHMD) |
3rd |
$7.44 |
P-removal, HIsarna, heat, continuous flow |
|
CaC2+Lime (Torpedo) |
4th |
$8.75 |
High-P hot metal in a batch torpedo |
|
KR-Lime |
5th |
$15.39 |
Only if no injection lance |
The co-injection process using CaC2+Lime (CHMD), with an initial cost of $380/MT, offers a competitive price to magnesium.
Conclusion: Decision for Cost-Optimized Choice
After thorough analysis of all three reagents, we conclude that Calcium Carbide and Magnesium are the most cost-effective. However, the total cost of the MMI-Magnesium agent is estimated at $5.65 per ton of steel. The lower initial cost makes calcium carbide a great choice, and it only costs $1.8-3 per tHM more than the MMI-Mg process.
Using magnesium comes with challenges, such as its low boiling point (1090 °C), which can cause vaporization and fuming, posing safety hazards. In comparison, the use of calcium carbide offers the added advantage further strengthening the steel and preventing brittleness. Calcium carbide is a dense material. It is safer and easier to control. Moreover, it has a lower slag volume than that of pure Mg used as a reagent.
Using calcium carbide (CaC2) is the ideal choice for industrialists. It comes with lower risks and offers a low initial cost. Continuous HMD (CHMD) using series reactors is the way forward. It is projected to cut overall operating costs by 10-15% compared to batch processes due to lower reagent consumption and minimized iron loss (<1%).
If you are looking for high-quality calcium carbide particles, then consider visiting the TYWH website. They offer excellent industrial-grade calcium carbide with impurities controlled under Si≤2%, Fe≤0.2%, P≤0.02%, and S≤0.2%. These are ideal for the co-injection process.
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