A Pierce-Smith converter (often spelled Peirce-Smith) is a large, rotating cylindrical furnace used in metallurgy, primarily for refining copper [1]. It is the most common method used to convert molten copper matte (a mixture of copper and iron sulfides) into blister copper (which is about 98-99% pure).
This type of converter remains the dominant technology in copper smelting, accounting for about 90% of the world’s copper matte refining.
How it works?
The converter is a large, horizontal steel drum lined with basic refractory bricks (like magnesia), which can withstand high temperatures and the corrosive molten materials [2]. The process works by blowing air or oxygen-enriched air through the molten matte to cause chemical reactions that remove impurities
The process happens in two main stages:
The slag-forming stage (Slag Blow)
The main goal of this stage is to remove iron.
- Charging: molten copper matte (typically 40-70% copper) is poured into the converter from a ladle. A silica-based material called flux is also added [3].
- Blowing: Air is blown into the molten bath through pipes called tuyeres [4].
- Reaction: The oxygen in the air reacts with the iron sulfide (FeS) in the matte, converting it to iron oxide (FeO) and sulfur dioxide (SO2) gas [5].
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- Reaction: 2FeS + 3O2 → 2FeO + 2SO2
- Slag Formation: The iron oxide (FeO) immediately combines with the silica (SiO2) flux to form a liquid slag (iron silicate) [6].
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- Reaction: 2FeO + SiO2 → 2FeO. SiO2 (Slag)
- Skimming: This slag is lighter than the matte and floats on top. The converter is rotated to pour off, or “skim,” the slag, leaving the iron-depleted matte behind. This matte is now much richer in copper and is called “white metal” (mostly copper sulfide, (Cu2S) [7].
The copper-making stage (Copper Blow)
The goal of this final stage is to remove the remaining sulfur [8].
- Blowing: air is again blown through the molten white metal.
- Reaction: the oxygen reacts with the copper sulfide (Cu2S), converting it directly into metallic copper. The sulfur is released as sulfur dioxide gas.
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- Reaction: Cu2S + O2 → 2Cu + SO2
- Product: the resulting product is molten blister copper. It gets its name because as it cools, the dissolved sulfur dioxide gas escapes, leaving a “blistered” surface. This copper is then sent for further refining (anode refining) to reach over 99.9% purity.
Why is it important?
The Pierce-Smith converter was a revolutionary invention when it was introduced by William H. Peirce and Elias Anton Cappelen Smith around 1908 [2].
Its key innovation was the use of a basic (magnesia) refractory lining instead of the acidic (silica) lining used in the older Manhès-David converters [2]. The old acidic lining was rapidly consumed by the basic iron oxide (FeO) slag, often lasting only a few batches.
The basic lining of the Pierce-Smith converter is not consumed by the slag, allowing it to last for months. This drastically reduced operating costs, increased efficiency, and quickly made it the industry standard worldwide.
Reference
[1] H. Ahmed, L. Ricardez-Sandoval, and M. Vilkko, “Optimal Scheduling of the Peirce-Smith Converter in the Copper Smelting Process,” Processes, vol. 9, no. 11, p. 2004, Nov. 2021, doi: 10.3390/pr9112004.
[2] “William H. Peirce,” Wikipedia. Oct. 03, 2020. Accessed: Oct. 23, 2025. [Online]. Available: https://en.wikipedia.org/w/index.php?title=William_H._Peirce&oldid=981699766
[3] N. Cardona, P. J. Mackey, P. Coursol, R. Parada, and R. Parra, “Optimizing Peirce–Smith Converters Using Thermodynamic Modeling and Plant Sampling,” JOM, vol. 64, no. 5, pp. 546–550, May 2012, doi: 10.1007/s11837-012-0329-x.
[4] “Peirce-Smith converter | metallurgy | Britannica.” Accessed: Oct. 23, 2025. [Online]. Available: https://www.britannica.com/technology/Peirce-Smith-converter
[5] H. Ahmed, L. Ricardez-Sandoval, and M. Vilkko, “Optimal Scheduling of the Peirce-Smith Converter in the Copper Smelting Process,” Processes, vol. 9, no. 11, p. 2004, Nov. 2021, doi: 10.3390/pr9112004.
[6] “Peirce-Smith Converter – Kumera – Creating Efficiency | Kumera Corporation.” Accessed: Oct. 23, 2025. [Online]. Available: https://kumera.com/engineering-technology/peirce-smith-converter/
[7] N. Aminizadeh and S. H. Mansouri, “Thermo-chemical model of the Pierce-Smith copper converter,” Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering, 2007, Accessed: Oct. 23, 2025. [Online]. Available: https://www.semanticscholar.org/paper/Thermo-chemical-model-of-the-Pierce-Smith-copper-Aminizadeh-Mansouri/2335e5dd16e31fbc26dba462b43933869e10ef32
[8] H. Ahmed, L. Ricardez-Sandoval, and M. Vilkko, “Optimal Scheduling of the Peirce-Smith Converter in the Copper Smelting Process,” Processes, vol. 9, no. 11, p. 2004, Nov. 2021, doi: 10.3390/pr9112004.
