Title

Removal of Sn from iron melts by sulfide volatilisation: treatment of non C-saturated melts

Removal of Sn from iron melts by sulfide volatilisation: treatment of non C-saturated melts

Authorship

MORAES, CARLOS A. M.; CAMERON, A. M.; SALE, F. R.

MORAES, CARLOS A. M.

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CAMERON, A. M.

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SALE, F. R.

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DOI

10.5151/2594-5300-29Aciaria-205-224

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Abstract

The removal of tramp elements from steel scrap still presents difficulties despite the many studies of this problem over the past decade or so. Besides the economical, environmental protection and natural resource conservation factors, the recycling of tinplate scrap has become important because of the high quality of the base steel from which tinplate is made. The use of CO and SO₂ gas mixture to remove tin from iron-tin-carbon melts by volatilisation as SnS(g) was investigated. The influences of the initial C, S and Si contents in the melt, the level of SO₂ in gas mixture, the total flow rate of the gas mixture, and the temperature on the detinning process were investigated. For the detinning of non C-saturated melts, an increase of C in the melt increased the removal of Sn. As C raises the partial pressure of SnS by increasing the activity of Sn in the melt, the detinning reaction was pushed to the right-hand side to reach a new equilibrium. When the initial contents of Si and S increased in melts containing 0.6 to 3 wt%C, the removal of Sn also increased for a constant SO₂ level. However, the removal of tin worsened when the SO₂ level increased to 5% as a result of the formation of FeS phase. The increase of the total flow rate of the gas mixture and the working temperature were favourable to the detinning process. It is reasonable to consider based on the effect of the studied parameters on the rate of tin removal that the chemical reaction at the metal/gas interface is the rate-controlling step for the detinning process in the present work. The best detinning rate was achieved when tinplate samples with additions of 3 wt%C, 0.6 wt%S and 4 wt%Si were melted. 150 ml/min of gas mixture containing 2% of SO₂ was bubbled into the melt at 1600°C. Sn was essentially removed after 30 min of reaction.

The removal of tramp elements from steel scrap still presents difficulties despite the many studies of this problem over the past decade or so. Besides the economical, environmental protection and natural resource conservation factors, the recycling of tinplate scrap has become important because of the high quality of the base steel from which tinplate is made. The use of CO and SO₂ gas mixture to remove tin from iron-tin-carbon melts by volatilisation as SnS(g) was investigated. The influences of the initial C, S and Si contents in the melt, the level of SO₂ in gas mixture, the total flow rate of the gas mixture, and the temperature on the detinning process were investigated. For the detinning of non C-saturated melts, an increase of C in the melt increased the removal of Sn. As C raises the partial pressure of SnS by increasing the activity of Sn in the melt, the detinning reaction was pushed to the right-hand side to reach a new equilibrium. When the initial contents of Si and S increased in melts containing 0.6 to 3 wt%C, the removal of Sn also increased for a constant SO₂ level. However, the removal of tin worsened when the SO₂ level increased to 5% as a result of the formation of FeS phase. The increase of the total flow rate of the gas mixture and the working temperature were favourable to the detinning process. It is reasonable to consider based on the effect of the studied parameters on the rate of tin removal that the chemical reaction at the metal/gas interface is the rate-controlling step for the detinning process in the present work. The best detinning rate was achieved when tinplate samples with additions of 3 wt%C, 0.6 wt%S and 4 wt%Si were melted. 150 ml/min of gas mixture containing 2% of SO₂ was bubbled into the melt at 1600°C. Sn was essentially removed after 30 min of reaction.

Keywords

Detinning, iron melts, sulfide, volatilisation

Detinning, iron melts, sulfide, volatilisation