Use of Sodium Sulfate for Copper Removal from Molten Iron
This paper describes the results of studies to improve the effectiveness of Na2SO4 for removing copper from molten iron. These studies included the use of sulfate mixtures, recycling of used slags, and additions of Na2SO4 in lump form versus powder. The results can be summarized as follows
Sulfate Mixtures. Tests with two types of mixtures were described. One consisted of CaSO4, Na2SO4, and K2SO4 and the other consisted of K2SO4 and MgSO4. Certain variations within both types of mixtures showed substantial copper removal, but none were as effective as Na2SO4 alone. The natural occurring mixture of K2SO4 and MgSO4 showed particular promise and warrants further study, along with other natural-occurring salts. A systematic study of such sulfates with and without Na2SO4 would be worthwhile in determining whether more effective, low-cost mixtures can be developed.
Recycling Used Slags. Used-slags were almost as effective as fresh Na2SO4 when used on higher copper irons than those from which the slags were obtained. A detailed study of slag chemistry should be performed to determine the significance of certain factors on slag reuse, such as sodium oxidation, side reactions with silicon and other elements, and relative copper concentratons in slag and molten iron. Such a study should reveal optimum conditions for slag recycling, with and without fresh Na2SO4. This approach appears promising for achieving direct reduction in the costs of using Na2SO4.
Lump Versus Powder Na 2 SO 4 . Copper removal with lump additions was distinctly better than with powder additions. One advantage of the lump material is that it provides a more complete reaction with the molten iron and reduces the loss of unreacted Na2SO4 from the crucible that occurs with powder additions.
Based on the literature and private discussion, other possible approaches for improving efficiency of the Na2SO4 process are suggested for further study.
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